МИНИСТЕРСТВО ОБРАЗОВАНИЯ И НАУКИ ХАБАРОВСКОГО КРАЯ
Краевое государственное автономное
профессиональное образовательное учреждение
«Губернаторский авиастроительный колледж г. Комсомольска-на-Амуре (Межрегиональный центр компетенций)»
Сборник спец. текстов для студентов III-IV курсов специальностей
22.02.05 - «Обработка металлов давлением»
ОГСЭ.03 «Иностранный язык»
Разработчик: Тургенева Наталья Константиновна
преподаватель КГА ПОУ
«Губернаторский авиастроительный колледж
(Межрегиональный центр компетенций)»
John B. Tytus12
Sheet metal embossing16
Plate roll bending27
History of steelworks’ plant and equipment28
Workpiece materials and power requirements47
Types of presses59
Etymology of smith80
Hardening and tempering (quenching and tempering)85
In chemistry, a metal (Greek: Metallo, Μέταλλο) is a chemical element whose atoms readily lose electrons to form positive ions (cations), and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms.
Periodic table showing the various types of metals and nonmetals.
Metals are sometimes described as a lattice of positive ions surrounded by a cloud of delocalized electrons. They are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. On the periodic table, a diagonal line drawn from boron (B) to polonium (Po) separates the metals from the nonmetals. Most elements on this line are metalloids, sometimes called semi-metals; elements to the lower left are metals; elements to the upper right are nonmetals (see the periodic table showing the metals).
An alternative definition of metals is that they have overlapping conduction bands and valence bands in their electronic structure. This definition opens up the category for metallic polymers and other organic metals, which have been made by researchers and employed in high-tech devices. These synthetic materials often have the characteristic silvery-grey reflectiveness (luster) of elemental metals.
Metals are usually inclined to form cations through electron loss, reacting with oxygen in the air to form oxides over changing timescales (iron rusts over years, while potassium burns in seconds). Examples:
4Na + O2 → 2Na2O (sodium oxide)
2Ca + O2 → 2CaO (calcium oxide)
4Al + 3O2 → 2Al2O3 (aluminium oxide)
The transition metals (such as iron, copper, zinc, and nickel) take much longer to oxidize. Others, like palladium, platinum and gold, do not react with the atmosphere at all. Some metals form a barrier layer of oxide on their surface which cannot be penetrated by further oxygen molecules and thus retain their shiny appearance and good conductivity for many decades (like aluminium, some steels, and titanium). The oxides of metals are basic (as opposed to those of nonmetals, which are acidic), although this may be considered a rule of thumb, rather than a fact.
Painting, anodising or plating metals are good ways to prevent their corrosion. However, a more reactive metal in the electrochemical series must be chosen for coating, especially when chipping of the coating is expected. Water and the two metals form an electrochemical cell, and if the coating is less reactive than the coatee, the coating actually promotes corrosion.
Metals in general have superior electric and thermal conductivity, high luster and density, and the ability to be deformed under stress without cleaving. While there are several metals that have low density, hardness, and melting points, these (the alkali and alkaline earth metals) are extremely reactive, and are rarely encountered in their elemental, metallic form.
The majority of metals have higher densities than the majority of nonmetals. Nonetheless, there is wide variation in the densities of metals; lithium is the least dense solid element and osmium is the densest. The metals of groups I A and II A are referred to as the light metals because they are exceptions to this generalization. The high density of most metals is due to the tightly-packed crystal lattice of the metallic structure. The strength of metallic bonds for different metals reaches a maximum around the center of the transition series, as those elements have large amounts of delocalized electrons in a metallic bond. However, other factors (such as atomic radius, nuclear charge, number of bonding orbitals, overlap of orbital energies, and crystal form) are involved as well.
The nondirectional nature of metallic bonding is thought to be the primary reason for the malleability of metal. Planes of atoms in a metal are able to slide across one another under stress, accounting for the ability of a crystal to deform without shattering.
Hot metal work from a blacksmith.
When the planes of an ionic bond are slid past one another, the resultant change in location shifts ions of the same charge into close proximity, resulting in the cleavage of the crystal. Covalently bonded crystals can only be deformed by breaking the bonds between atoms, thereby resulting in fragmentation of the crystal.
The electrical and thermal conductivity of metals originate from the fact that in the metallic bond, the outer electrons of the metal atoms form a gas of nearly free electrons, moving as an electron gas in a background of positive charge formed by the ion cores. Good mathematical predictions for electrical conductivity, as well as the electrons' contribution to the heat capacity and heat conductivity of metals can be calculated from the free electron model, which does not take the detailed structure of the ion lattice into account.
When considering the exact band structure and binding energy of a metal, it is necessary to take into account the positive potential caused by the specific arrangement of the ion cores - which is periodic in crystals. The most important consequence of the periodic potential is the formation of a small band gap at the boundary of the brillouin zone. Mathematically, the potential of the ion cores is treated in the nearly-free electron model.
An alloy is a mixture of two or more elements in solid solution in which the major component is a metal. Most pure metals are either too soft, brittle or chemically reactive for practical use. Combining different ratios of metals as alloys modifies the properties of pure metals to produce desirable characteristics. The aim of making alloys is generally to make them less brittle, harder, resistant to corrosion, or have a more desirable color and luster. Examples of alloys are steel (iron and carbon), brass (copper and zinc), bronze (copper and tin), and duralumin (aluminium and copper). Alloys specially designed for highly demanding applications, such as jet engines, may contain more than ten elements.
In chemistry, the term 'base metal' is used informally to refer to a metal that oxidizes or corrodes relatively easily, and reacts variably with dilute hydrochloric acid (HCl) to form hydrogen. Examples include iron, nickel, lead and zinc. Copper is considered a base metal as it oxidizes relatively easily, although it does not react with HCl. It is commonly used in opposition to noble metal.
In alchemy, a base metal was a common and inexpensive metal, as opposed to precious metals, mainly gold and silver. A longtime goal of the alchemists was the transmutation of base metals into precious metals.
In numismatics, coins used to derive their value primarily from the precious metal content. Most modern currencies are fiat currency, allowing the coins to be made of base metal.
The term "ferrous" is derived from the latin word meaning "containing iron". This can include pure iron, such as wrought iron, or an alloy such as steel. Ferrous metals are often magnetic, but not exclusively.
Noble metals are metals that are resistant to corrosion or oxidation, unlike most base metals. They tend to be precious metals, often due to perceived rarity. Examples include tantalum, gold, platinum, and rhodium.
A gold nugget
A precious metal is a rare metallic chemical element of high economic value.
Chemically, the precious metals are less reactive than most elements, have high luster and high electrical conductivity. Historically, precious metals were important as currency, but are now regarded mainly as investment and industrial commodities. Gold, silver, platinum and palladium each have an ISO 4217 currency code. The best-known precious metals are gold and silver. While both have industrial uses, they are better known for their uses in art, jewelry, and coinage. Other precious metals include the platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum, of which platinum is the most widely traded. Plutonium and uranium could also be considered precious metals.
The demand for precious metals is driven not only by their practical use, but also by their role as investments and a store of value. Palladium was, as of summer 2006, valued at a little under half the price of gold, and platinum at around twice that of gold. Silver is substantially less expensive than these metals, but is often traditionally considered a precious metal for its role in coinage and jewelry.
Metals are often extracted from the Earth by means of mining, resulting in ores that are relatively rich sources of the requisite elements. Ore is located by prospecting techniques, followed by the exploration and examination of deposits. Mineral sources are generally divided into surface mines, which are mined by excavation using heavy equipment, and subsurface mines.
Once the ore is mined, the metals must be extracted, usually by chemical or electrolytic reduction. Pyrometallurgy uses high temperatures to convert ore into raw metals, while hydrometallurgy employs aqueous chemistry for the same purpose. The methods used depend on the metal and their contaminants.
Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys.
Some metals and metal alloys possess high structural strength per unit mass, making them useful materials for carrying large loads or resisting impact damage. Metal alloys can be engineered to have high resistance to shear, torque and deformation. However the same metal can also be vulnerable to fatigue damage through repeated use, or from sudden stress failure when a load capacity is exceeded. The strength and resilience of metals has led to their frequent use in high-rise building and bridge construction, as well as most vehicles, many appliances, tools, pipes, non-illuminated signs and railroad tracks.
The two most commonly used structural metals, iron and aluminium, are also the most abundant metals in the Earth's crust.
Metals are good conductors, making them valuable in electrical appliances and for carrying an electric current over a distance with little energy lost. Electrical power grids rely on metal cables to distribute electricity. Home electrical systems, for the most part, are wired with copper wire for its good conducting properties.
The thermal conductivity of metal is useful for containers to heat materials over a flame. Metal is also used for heat sinks to protect sensitive equipment from overheating.
The high reflectivity of some metals is important in the construction of mirrors, including precision astronomical instruments. This last property can also make metallic jewelry aesthetically appealing.
Some metals have specialized uses; radioactive metals such as uranium and plutonium are used in nuclear power plants to produce energy via nuclear fission. Mercury is a liquid at room temperature and is used in switches to complete a circuit when it flows over the switch contacts. Shape memory alloy is used for applications such as pipes, fasteners and vascular stents.
Bending is a common metalworking technique to process sheet metal. It is usually done by hand on a box and pan brake, or industrially on a brake press or machine brake. Typical products that are made like this are boxes such as electrical enclosures, rectangular ductwork, and some firearm parts such as the receiver of the AKM AK-47 variant.
Usually bending has to overcome both tensile stresses as well as compressive stresses. When bending is done, the residual stresses make it spring back towards its original position, so we have to over bend the sheet metal keeping in mind the residual stresses.
Rolling mill for plates and wires (goldsmith tool).
Rolling mill for cold rolling metal sheet like this piece of brass sheet.
A rolling mill is a machine or factory for shaping metal by passing it between a pair of work rolls.
Rolling mills are often incorporated into integrated steelworks, but also exist as separate plants and can be used for other metals, and other materials.
Rolling mills historically have been of several kinds:
Depending on the temperature of the metal being rolled, rolling mills are typically hot or cold rolling mills.
A slitting mill was used to cut flat bar iron into rods for nail-making.
A tinplate works normally contained at least two rolling mills, one for hot rolling and the other for cold rolling single plates, prior to tinning.
From the Industrial Revolution, puddled iron, after consolidation with a powered hammer (shingling), was rolled into bar iron using a rolling mill with grooved rolls. The grooves provided were progressively smaller, so that on successive passes through the rolls, the cross-section of the bar became smaller and the bar itself longer. By designing the rolls appropriately, it is possible to obtain iron or steel with various cross-sections, including I-shaped girders and railway rails.
For silversmithing mainly two types are used, a flat one (with two cylindrical rolls) for rolling sheet and one with grooved rolls for rolling octagonal wire. The rolls are made of hardened steel.
John B. Tytus
John B. Tytus (1875-1944) was the inventor of the first practical wide-strip continuous rolling process for manufacturing steel. This process greatly reduced the cost of manufacturing steel, and was first implemented in a new Armco plant in 1924. By 1940, twenty-six plants had been built. He was a Yale University graduate but learned the steel business from the ground up. His home in Middletown, Ohio, the John B. Tytus House, was declared a National Historic Landmark in 1976.
John B. Tytus was born in Middletown, Ohio on December 6, 1875. His father owned a paper mill, which Tytus found fascinating as child. He attended the common schools until age fourteen. He then attended Westminister prep school at Dobb's Ferry, New York, which prepared him for admission to Yale University. He graduated from Yale in 1897 with a bachelor's degree in English literature and returned to Middletown to work in the family Paper Mill. Soon afterward, his father died and his family sold the mill. He went to work with a bridge builder at Dayton, Ohio .
In 1904 he left the bridge builder to work for a steel mill in his home town as a spare hand. He quickly learned about steel rolling and earned the respect of his coworkers. He always remembered the way the Fourdrinier machines produced paper rolls, and began to consider ways in which the process of steel rolling could be made more efficient. After eighteen months, he became the assistant of the sheet mill superintendent, Charlie Hook. During this time and afterwards, Tytus continued to research and think about improving steel rolling. In 1906 he was promoted to superintendent of the new mill in Zanesville, Ohio. The following year, he married Marjorie Denny. At the end of 1909, He was chosen to plan and activate Armco's East Works plant at Middleton as chief of operations.
In 1919 he had readied blueprints for a new plant incorporating techniques for continuous steel rolling, but the opportunity to put these plans into practice did not arise until 1921. He presented his plans and Armco made the difficult decision to implement them. The continuous rolling steel mill he designed and built began operation in Ashland in 1924 and became a model for the industry. In 1927 Tytus was made vice-president of Armco. In 1935 he received the Gary Memorial Award from the American Iron and Steel Institute. He died, June 2, 1944 of a heart attack.
Aerial view of Třinec Iron and Steel Works
Blast furnaces of Třinec Iron and Steel Works
Interior of a steel mill
A steel mill (British English and Australian English steelworks) is an industrial plant for the manufacture of steel.
Steel is an alloy of iron and carbon. It is produced in a two-stage process. First, iron ore is reduced or smelted with coke and limestone in a blast furnace, producing molten iron which is either cast into pig iron or carried to the next stage as molten iron. In the second stage, known as steelmaking, impurities such as sulfur, phosphorus, and excess carbon are removed and alloying elements such as manganese, nickel, chromium and vanadium added to produce the exact steel required. In the late 19th Century and early 20th Century the world's largest steel mill was located in Barrow-in-Furness, UK. Today, the world's largest steel mill is in Gwangyang, South Korea.
Steel mills turn molten steel into blooms, ingots, slabs and sheet through casting, hot rolling and cold rolling.
An integrated steel mill has all the functions for primary steel production:
iron making (conversion of ore to liquid iron),
steelmaking (conversion of pig iron to liquid steel),
casting (solidification of the liquid steel),
roughing rolling/billet rolling (reducing size of blocks)
product rolling (finished shapes).
The principal raw materials for an integrated mill are iron ore, limestone, and coal (or coke). These materials are charged in batches into a blast furnace where the iron compounds in the ore give up excess oxygen and become liquid iron. At intervals of a few hours, the accumulated liquid iron is tapped from the blast furnace and either cast into pig iron or directed to other vessels for further steelmaking operations. Historically the Bessemer process was a major advancement in the production of economical steel, but it has now been entirely replaced by other processes such as the basic oxygen furnace.
Molten steel is cast into large blocks called "blooms". During the casting process various methods are used, such as addition of aluminum, so that impurities in the steel float to the surface where they can be cut off the finished bloom.
Because of the energy cost and structural stress associated with heating and cooling a blast furnace, typically these primary steelmaking vessels will operate on a continuous production campaign of several years duration. Even during periods of low steel demand, it may not be feasible to let the blast furnace grow cold, though some adjustment of the production rate is possible.
Integrated mills are large facilities that are typically only economical to build in 2,000,000 ton per year annual capacity and up. Final products made by an integrated plant are usually large structural sections, heavy plate, strip, wire rod, railway rails, and occasionally long products such as bars and pipe.
A major environmental hazard associated with integrated steel mills is the pollution produced in the manufacture of coke, which is an essential intermediate product in the reduction of iron ore in a blast furnace.
Integrated mills may also adopt some of the processes used in mini-mills, such as arc furnaces and direct casting, to reduce production costs.
World integrated steel production capacity is at or close to world demand, so competition between suppliers results in only the most efficient producers remaining viable. However, due to the large employment of integrated plants, often governments will financially assist an obsolescent facility rather than take the risk of having thousands of workers thrown out of jobs. Such measures result in products then sold in international trade lead to allegations of dumping.
A mini-mill is traditionally a secondary steel producer; however, Nucor (one of the world's largest steel producers), as well as one of its competitors, Commercial Metals Company (CMC) use mini-mills exclusively. Usually it obtains most of its iron from scrap steel, recycled from used automobiles and equipment or byproducts of manufacturing. Direct reduced iron (DRI) is sometimes used with scrap, to help maintain desired chemistry of the steel, though usually DRI is too expensive to use as the primary raw steelmaking material. A typical mini-mill will have an electric arc furnace for scrap melting, a ladle furnace or vacuum furnace for precision control of chemistry, a strip or billet continuous caster for converting molten steel to solid form, a reheat furnace and a rolling mill.
Originally the mini-mill concept was adapted to production of bar products only, such as concrete reinforcing bar, flats, angles, channels, pipe, and light rails. Since the late 1980s, successful introduction of the direct strip casting process has made mini-mill production of strip feasible. Often a mini-mill will be constructed in an area with no other steel production, to take advantage of local resources and lower-cost labour. Mini-mill plants may specialize, for example, making coils of rod for wire-drawing use, or pipe, or in special sections for transportation and agriculture.
Capacities of mini-mills vary; some plants may make as much as 3,000,000 tons per year, a typical size is in the range 200,000 to 400,000 tons per year, and some old or specialty plants may make as little as 50,000 tons per year of finished product. Nucor Corporation, for example, annually produces around 9,100,000 tons of sheet steel from its 4 sheet mills, 6,700,000 tons of bar steel from its 10 bar mills and 2,100,000 tons of plate steel from its 2 plate mills.
Since the electric arc furnace can be easily started and stopped on a regular basis, mini-mills can follow the market demand for their products easily, operating on 24 hour schedules when demand is high and cutting back production when sales are lower.
Sheet metal embossing
Sheet metal embossing is a process for producing raised or sunken designs or relief in sheet metal. This process can be made by means of matched male and female roller dies, or by passing sheet or a strip of metal between rolls of the desired pattern.
Albert Gilles was the person who mastered the metal embossing operations at a young age. He made very good metal works during his career. Walt Disney, Pope Pius XII, and a very good number of North American churches were part of his clients book.
The metal sheet embossing operation is commonly accomplished with a combination of heat and pressure on the sheet metal depending on what type of embossing is required. Theoretically, with any of these procedures, the metal thickness has change in its composition.
Metal sheet is drawn through the male and female roller dies producing a pattern or design on the metal sheet. Depending on the roller dies used, different patterns can be produced on the metal sheet. This pressure and a combination of heat actually "irons" while raising the level of the image higher than the substrate to make it smooth. The term "impressing" enables one to distinguish an image lowered into the surface of a material, in distinction to an image raised out of the surface of a material
In most of the pressure embossing operation machines, the upper roll blocks are stationary, while the bottom roll blocks are movable. The pressure with which the bottom roll is raised is referred to as the tonnage capacity.
Embossing machines are generally sized to give 2" of strip clearance on each side of an engraved embossing roll. Many embossing machines are custom-manufactured, so there are no industry-standard widths. It is not uncommon to find embossing machines in operation producing patterns less than 6" wide all the way up to machines producing patterns 70"+ wide.
The ability to form ductile metals
Use in medium to high production runs
The ability to maintain the same metal thickness before and after embossing
The ability to produce unlimited patterns, depending on the roll dies
The ability to reproduce product with no variation
Structural steel is steel construction material, a profile, formed with a specific shape or cross section and certain standards of chemical composition and strength. Structural steel shape, size, composition, strength, storage, etc, is regulated in most industrialized countries.
Structural steel members, such as I-beams, have high second moments of area, which allow them to be very stiff in respect to their cross-sectional area.
A steel I-beam, in this case used to support wood beams in a house.
Structural steel in construction: A primed steel beam is holding up the floor above, which consists of a metal deck (Q-Deck), upon which a concrete slab has been poured.
Steel beam through-penetration with incomplete fireproofing.
Metal deck and OWSJ (Open Web Steel Joist), receiving first coat of spray fireproofing plaster, made of polystyrene leavened gypsum.
Common structural shapes
In most developed countries, the shapes available are set out in published standards, although a number of specialist and proprietary cross sections are also available.
I-beam (I-shaped cross-section - in Britain these include Universal Beams (UB) and Universal Columns (UC); in Europe it includes the IPE, HE, HL, HD and other sections; in the US it includes Wide Flange (WF) and H sections)
Z-Shape (half a flange in opposite directions)
HSS-Shape (Hollow structural section also known as SHS (structural hollow section) and including square, rectangular, circular (pipe) and elliptical cross sections)
Angle (L-shaped cross-section)
Channel (C-shaped cross-section)
Tee (T-shaped cross-section)
Rail profile (asymmetrical I-beam)
Flanged T rail
Bar, a piece of metal, rectangular cross sectioned (flat) and long, but not so wide so as to be called a sheet.
Rod, a round or square and long piece of metal or wood, see also rebar and dowel.
Plate, sheet metal thicker than 6 mm or 1/4 in.
Open web steel joist
While many sections are made by hot or cold rolling, others are made by welding together flat or bent plates (for example, the largest circular hollow sections are made from flat plate bent into a circle and seam-welded).
Most industrialized countries prescribe a range of standard steel grades with different strengths, corrosion resistance and other properties.
Standard structural steels (Europe)
Most steels used throughout Europe are specified to comply with the European standard EN 10025. However, many national standards also remain in force.
Typical grades are described as 'S275J2' or 'S355K2W'. In these examples, 'S' denotes structural rather than engineering steel; 275 or 355 denotes the yield strength in newtons per square millimetre or the equivalent megapascals; J2 or K2 denotes the materials toughness by reference to Charpy impact test values; and the 'W' denotes weathering steel. Further letters can be used to designate normalized steel ('N' or 'NL'); quenched and tempered steel ('Q' or 'QL'); and thermomechanically rolled steel ('M' or 'ML').
The normal yield strength grades available are 195, 235, 275, 355, 420, and 460, although some grades are more commonly used than others e.g. in the UK, almost all structural steel is grades S275 and S355. Higher grades are available in quenched and tempered material (500, 550, 620, 690, 890 and 960 - although grades above 690 receive little if any use in construction at present).
Standard structural steels (USA)
Steels used for building construction in the US use standard alloys identified and specified by ASTM International. These steels have an alloy identification beginning with A and then two, three, or four numbers. The four-number AISI steel grades commonly used for mechanical engineering, machines, and vehicles are a completely different specification series.
The standard commonly used structural steels are: Carbon steels
A36 - structural shapes and plate
A53 - structural pipe and tubing
A500 - structural pipe and tubing
A501 - structural pipe and tubing
A529 - structural shapes and plate
High strength low alloy steels
A441 - structural shapes and plates
A572 - structural shapes and plates
A618 - structural pipe and tubing
A992 - W shapes beams only
A270 - structural shapes and plates
Corrosion resistant high strength low alloy steels
A242 - structural shapes and plates
A588 - structural shapes and plates
Quenched and tempered alloy steels
A514 - structural shapes and plates
A517 - boilers and pressure vessels
Steel vs. concrete
As raw material prices fluctuate, often so does building design. During times of lower steel prices, more steel and less concrete is used, and vice versa. Each set of vendors and users typically maintain national industry associations that advocate the use of its materials versus the other. However, both materials are typically used together. Concrete without steel reinforcement (usually ribbed round bars called Rebar) crumbles under tensile loads. Steel on its own, without solid concrete floors, is likewise not a preferred building method.
While rebar is almost always steel, it is not considered a structural steel and is described separately in the Rebar and Reinforced concrete articles.
The properties of steel vary widely, depending on its alloying elements.
The austenizing temperature, the temperature where a steel transforms to an austenite crystal structure, for steel starts at 900°C for pure iron, then, as more carbon is added, the temperature falls to a minimum 724°C for eutectic steel (steel with only .83% by weight of carbon in it). As 2.1% carbon (by mass) is approached, the austenizing temperature climbs back up, to 1130°C. Similarly, the melting point of steel changes based on the alloy.
The lowest temperature at which a plain carbon steel can begin to melt, its solidus, is 1130 °C. Steel never turns into a liquid below this temperature. Pure Iron ('Steel' with 0% Carbon) starts to melt at 1492 °C (2720 °F), and is completely liquid upon reaching 1539 °C (2802 °F). Steel with 2.1% Carbon by weight begins melting at 1130 °C (2066 °F), and is completely molten upon reaching 1315 °C (2400 °F). 'Steel' with more than 2.1% Carbon is no longer Steel, but is known as Cast iron.
Fireproofing of structural steel
In order for a fireproofing product to qualify for a certification listing of structural steel, through a fire test, the critical temperature is set by the national standard, which governs the test. In Japan, this is below 400°C. In China, Europe and North America, it is set at ca. 540°C. The time it takes for the steel element that is being tested to reach the temperature set by the national standard determines the duration of the fire-resistance rating.
Care must be taken to ensure that thermal expansion of structural elements does not damage fire-resistance rated wall and floor assemblies. Penetrants in a firewalls and ferrous cable trays in organic firestops should be installed in accordance with an appropriate certification listing that complies with the local building code.
Open Web Steel Joists (OWSJ) require a great deal of spray fireproofing because they are not very massive and also because they are so open, that a lot of the sprayed plaster flies right past its constituent parts during the coating process.
Structural steel requires external insulation (fireproofing) in order to prevent the steel from weakening in the event of a fire. When heated, steel expands and softens, eventually losing its structural integrity. Given enough energy, it can also melt. Heat transfer to the steel can be slowed by the use of fireproofing materials. While concrete structures that comprise buildings are able to achieve fire-resistance ratings without additional fireproofing, concrete can be subject to severe spalling, particularly if it has an elevated moisture content. Fireproofing is available for concrete but this is typically not used in buildings. Instead, it is used in traffic tunnels and locations where a hydrocarbon fire is likely to break out. Thus, steel and concrete compete against one another not only on the basis of the price per unit of mass but also on the basis of the pricing for the fireproofing that must be added in order to satisfy the passive fire protection requirements that are mandated through building codes. Common fireproofing methods for structural steel include intumescent, endothermic and plaster coatings as well as drywall,calcium silicate cladding, and mineral or high temperature insulation wool in the form of blanket.
Profile rolling (to manufacture a cone)
Rolling is a fabricating process in which the metal, plastic, paper, glass, etc. is passed through a pair (or pairs) of rolls. There are two types of rolling process, flat and profile rolling. In flat rolling the final shape of the product is either classed as sheet (typically thickness less than 3 mm, also called "strip") or plate (typically thickness more than 3 mm). In profile rolling the final product may be a round rod or other shaped bar, such as a structural section (beam, channel, joist etc). Rolling is also classified according to the temperature of the metal rolled. If the temperature of the metal is above its recrystallization temperature, then the process is termed as hot rolling. If the temperature of the metal is below its recrystallization temperature, the process is termed as cold rolling. Another process also termed as 'hot bending' is induction bending, whereby the section is heated in small sections and dragged into a required radius.
Heavy plates tend to be formed using a press process, which is termed forming, rather than rolling.
Hot/Cold Rolling Animation
Hot rolling is a hot working metalworking process where large pieces of metal, such as slabs or billets, are heated above their recrystallization temperature and then deformed between rollers to form thinner cross sections. Hot rolling produces thinner cross sections than cold rolling processes with the same number of stages. Hot rolling, due to recrystallization, will reduce the average grain size of a metal while maintaining an equiaxed microstructure where as cold rolling will produce a hardened microstructure.
Hot Rolling Process
A slab or billet is passed or deformed between a set of work rolls and the temperature of the metal is generally above its recrystallization temperature, as opposed to cold rolling, which takes place below this temperature. Hot rolling permits large deformations of the metal to be achieved with a low number of rolling cycles. As the rolling process breaks up the grains, they recrystallize maintaining an equiaxed structure and preventing the metal from hardening. Hot rolled material typically does not require annealing and the high temperature will prevent residual stress from accumulating in the material resulting better dimensional stability than cold worked materials.
Hot rolling is primarily concerned with manipulating material shape and geometry rather than mechanical properties. This is achieved by heating a component or material to its upper critical temperature and then applying controlled load which forms the material to a desired specification or size.
Hot Rolling Applications
Hot rolling is used mainly to produce sheet metal or simple cross sections such as rail road bars from billets.
Mechanical properties of the material in its final 'as-rolled' form are a function of:
rate of temperature decrease during deformation,
rate of deformation,
heat of deformation,
recrystallisation time, and
subsequent rate of cooling after deformation.
Types of Hot Rolling Mills
Prior to continuous casting technology, ingots were rolled to approximately 200 millimetres (7.9 in) thick in a slab or bloom mill. Blooms have a nominal square cross section, whereas slabs are rectangular in cross section.
Slabs are the feed material for hot strip mills or plate mills and blooms are rolled to billets in a billet mill or large sections in a structural mill.
The output from a strip mill is coiled and, subsequently, used as the feed for a cold rolling mill or used directly by fabricators. Billets, for re-rolling, are subsequently rolled in either a merchant, bar or rod mill.
Merchant or bar mills produce a variety of shaped products such as angles, channels, beams, rounds (long or coiled) and hexagons. Rounds less than 16 millimetres (0.63 in) in diameter are more efficiently rolled from billet in a rod mill.
Rolling mill for cold rolling metal sheet like this piece of brass sheet.
Cold rolling is a metalworking process in which metal is deformed by passing it through rollers at a temperature below its recrystallization temperature. Cold rolling increases the yield strength and hardness of a metal by introducing defects into the metal's crystal structure. These defects prevent further slip and can reduce the grain size of the metal, resulting in Hall-Petch hardening.
Cold rolling is most often used to decrease the thickness of plate and sheet metal.
Physical metallurgy of cold rolling
Cold rolling is a method of cold working a metal. When a metal is cold worked, microscopic defects are nucleated throughout the deformed area. These defects can be either point defects (a vacancy on the crystal lattice) or a line defect (an extra half plane of atoms jammed in a crystal). As defects accumulate through deformation, it becomes increasingly more difficult for slip, or the movement of defects, to occur. This results in a hardening of the metal.
If enough grains split apart, a grain may split into two or more grains in order to minimize the strain energy of the system. When large grains split into smaller grains, the alloy hardens as a result of the Hall-Petch relationship. If cold work is continued, the hardened metal may fracture.
During cold rolling, metal absorbs a great deal of energy. Some of this energy is used to nucleate and move defects (and subsequently deform the metal). The remainder of the energy is released as heat.
While cold rolling increases the hardness and strength of a metal, it also results in a large decrease in ductility. Thus metals strengthened by cold rolling are more sensitive to the presence of cracks and are prone to brittle fracture.
A metal that has been hardened by cold rolling can be softened by annealing. Annealing will relieve stresses, allow grain growth, and restore the original properties of the alloy. Ductility is also restored by annealing. Thus, after annealing, the metal may be further cold rolled without fracturing.
Degree of cold work
Cold rolled metal is given a rating based on the degree it was cold worked. "Skin-rolled" metal undergoes the least rolling, being compressed only 0.5-1% to harden the surface of the metal and make it more easily workable for later processes. Higher ratings are "quarter hard," "half hard" and "full hard"; in the last of these, the thickness of the metal is reduced by 50%.
Cold rolling as a manufacturing process
Cold rolling is a common manufacturing process. It is often used to form sheet metal. Beverage cans are closed by rolling, and steel food cans are strengthened by rolling ribs into their sides. Rolling mills are commonly used to precisely reduce the thickness of strip and sheet metals.
Foil rolling is a continuous deformation process compressing metal between a pair of rollers called work rolls. Another term for this process is called plate roll bending. This is defined as a cold forming process where plate and steel metal is formed into cylindrical shapes by a combination of three rolls arranged in a pyramid formation. Two of the rolls are power driven, in a fixed position, and the third is adjustable to suit the desired bend radius and workpiece thickness.
Foil is produced for several applications:
Thermal insulation for the construction industry
Fin stock for air conditioners
Electrical coils for transformers
Capacitors for radios and televisions
Insulation for storage tanks
Containers and packaging
Foil stock is reduced in thickness by a rolling mill, where the material is passed several times through metal work rolls. As the sheets of metal pass through the rolls, they are squeezed thinner and extruded through the gap between the rolls. The work rolls are paired with heavier rolls called backup rolls, which apply pressure to help maintain the stability of the work rolls. The work and backup rolls rotate in opposite directions. As the foil sheets come through the rollers, they are trimmed and slitted with circular or razor-like knives installed on the rolling mill. Trimming refers to the edges of the foil, while slitting involves cutting it into several sheets.
Aluminium alloys are most commonly produced in the foil rolling process because the raw materials necessary for its manufacture are abundant. Aluminium foil is inexpensive, durable, non-toxic, and greaseproof. Iron, silicon, and manganese are all major alloying elements. Sheet metals with a thickness below 200 micrometers are considered foils (Some foils may be as thin as 6.3 micrometers).Plate Roll Bending
Profile rolling (to manufacture a cone)
"Plate Roll Bending is a cold forming process. Plate or steel metal is formed into cylindrical shapes by a combination of three rolls arranged in a pyramid formation. Two of the rolls are power driven, in a fixed position, and the third is adjustable to suit the desired bend radius and workpiece thickness."
"Shapes produced range from simple cylindrically shaped parts to more complex parts, such as conical and flattened from 1/16in to 6in, and lengths of up to 20in, or more, can be formed by this method."
Progressive Roll Forming
Roll forming, also spelled rollforming, is a continuous bending operation in which a long strip of metal (typically coiled steel) is passed through consecutive sets of rolls, or stands, each performing only an incremental part of the bend, until the desired cross-section profile is obtained. Roll forming is ideal for producing parts with long lengths or in large quantities.
The geometric possibilities can be very broad and even include enclosed shapes so long as it is the same cross-section throughout. Typical sheeting thicknesses range from 0.025in. to 0.25in., but they can exceed that. Length is almost unaffected by the rolling process. The part widths typically aren't smaller than 1in. however they can exceed 20in.
History of Steelworks' Plant and Equipment
The rapid advance of mechanical engineering in the latter part of the eighteenth and in the nineteenth centuries accelerated the progress by placing better and more powerful machinery at the disposal of the Ironmasters, whilst at the same time creating a demand for Iron.
Important dates are 1728, when Payn and Hanbury introduced their Rolling Mill for the production of Sheet Iron; 1760, when Smeaton substituted Cast Iron blowing tubs for the wooden and leather bellows previously in use; and 1783, when Cort introduced grooved rolls for Merchant bars. Most important of all, however, were the introduction of the steam engine at the end of the eighteenth and beginning of the nineteenth century, of the railroad about 1825, and the invention, by Nasmyth, of the steam hammer in 1838.
The next important invention was at Clyde Iron Works, in 1828, when J. B. Neilson invented the process of heating the blast. This greatly improved fuel economy, although the blast was at first heated by burning raw coal in the stoves; but in 1832 the work of heating the blast was done by the waste gases at Wasseralfingen in Bavaria; and this method was then universally adopted.
The First "Open Hearth"The Open Hearth furnace owes its inception to the brothers Frederick and William Siemens.
In a lecture which Mr. C. W. Siemens, F.R.S . (later Sir William Siemens) delivered at a meeting of the Chemical Society in 1868, he presented many interesting facts about the early history of the manufacture of Steel in the Open Hearth Furnace. Heath, the discoverer of the beneficial action of Manganese, was the first, he said, to make the attempt in 1845. His method was to melt pig-iron in a cupola, and transfer it in the molten state to a reverberatory furnace. Wrought iron scrap was introduced at another part of the furnace, between the bath of molten metal and the chimney, to be preheated before being pushed amongst the molten pig metal. "Fearing the effect of the ashes from a common fire-place, Heath proposed to heat his furnace by jets of gas; and there is every probability that his experiments would have been successful if he had possessed the means of imparting the intensity of heat to the flame, and at the same time the absence of cutting draught, which are essentially necessary."
Early Experiments - and FailuresAfter referring to other earlier experimenters, Mr Siemens comes to the Regenerative Gas Furnace invented by his brother, but developed and improved by the brothers jointly; a licence to use this was granted to Mr. Charles Attwood, in 1862, but he failed to make good steel on the Open Hearth and converted the furnace for heating crucibles. A licence was next granted to a French firm, Messrs Boigue, Bambour & Co, to erect a furnace in their works at Montlucon for a process devised by M Le Chatelier, but which did not turn out very well; upon which the company became discouraged and gave up the attempt, although, as Siemens pointed out, they had a very powerful furnace and one which would have done all that was required if the company had displayed the least determination to succeed.
Meanwhile, a licence had been granted to Emile and Pierre Martin, of the Sirenil Works in France, to melt steel both in crucibles and on the open hearth; and they built a furnace in 1864, chiefly intended as a heating furnace but, having been built of Dinas bricks, it was also available as a melting furnace. Siemens continued,"With this furnace, which was really less suitable than those previously erected, MM Martin have succeeded in producing cast-steel of good quality and various tempers; and their produce was awarded a Gold Medal at the great French Exhibition of last year (1867). MM Martin have since patented various arrangements of their own, such as the employment of particular fluxes to cover the surface of the molten metal, the application of a separate furnace for heating the iron before charging it into the melting furnace, and the employment of particular brands of cast and wrought-iron which may be useful under special circumstances, but which form no essential part of the general solution of the problem."
Siemens' Sample Steel WorksSiemens went on to say that "Having been so often disappointed by the indifference of manufacturers and the antagonism of their workmen, I determined in 1865 to erect experimental or 'Sample Steel Works' of my own at Birmingham, for the purpose of maturing the details of these processes before inviting manufacturers to adopt them. The first furnace erected at these works is one for melting the higher qualities of steel in closed pots, and contains 16 pots of the usual capacity. The second, erected in 1867, is an open bath furnace, capable of melting a charge of 24 cwt, of steel every 6 hours.""Although these works have been carried on under every disadvantage, inasmuch as I had to educate a set of men capable of managing steel furnaces, the result has been most beneficial in affording me an opportunity, of working out the details of processes for producing cast-steel from scrap-iron of ordinary quality, and also directly from the ore, and in proving these results to others."
Rolling MillsRolling mills have been used, in association with slitting mills since the 1590s for producing iron strips. Early rolling mills were small and water driven, such as the one still in existence at Wortley Ironworks Lower Forge in Sheffield.
Wider iron sheets, for making tinplate, were produced by John Hanbury in about 1720, and in 1784 Henry Court (of puddling furnace fame) was using grooved rolls to produce round and other sections.In 1781 Matthew Boulton suggested, when on a visit to an ironworks in Wales, using a steam engine for driving a rolling mill, and on his return home he had a coupled steam engine made and connected to a forge train. This was adopted for the first steam driven rolling and slitting mill by John Wilkinson, in collaboration with Boulton and Watt, at his Bradley Works. It was driven by an engine that Watt invented with two cylinders and two beams, astonishing the other ironmasters, and was the forerunner of numerous other mills in his own works, and in those of envious rivals who followed this enterprising pioneer.
For many years after this it was the practice to have a Beam Engine, either condensing or non- condensing, in the centre of the mill, driving, a line of shafting from which mills were driven, these being situated right and left of the engine.
As mills became more powerful the central drive was found to be a disadvantage: for one thing, if anything went wrong either with the engine or the line shafting, the whole works was stopped. Accordingly it became the practice to drive the mills individually, and Horizontal Engines displaced the old Beam Engines.With the advent of steel and the handling of heavier pieces, the individual drive became an absolute necessity.For the earlier continuously rotating mills, engines with fly wheels could be used. The advantage of the fly wheel is that it stores energy at periods when little work is being done (as for example, when the piece is being passed back over the top of the rolls) which it can give out again when the maximum demand for power occurs - that is, when the piece is in the rolls. In this way the engine cylinders only require to be designed for something slightly over the average power required.
With a view to avoiding the loss of time while the piece was being passed back over the top of the rolls, Mr. James Naysmith (inventor of the Steam Hammer in 1838), suggested the use of Reversing Engines. This was tried at Crewe and found satisfactory, with the result that the standard drive for reversing Rolling Mills, became either a two or a three crank Reversing Engine. It was of course impossible to use a fly wheel with these engines, as there was no reserve of stored energy to draw upon to take the peak loads; with the result that the cylinders had to be made large enough to take the maximum load. Thus the engine was running well under its' power for most of its time, which did not make for economy. Such engines were therefore referred to as "steam eaters."
For heavy plates the reversing mill has many advantages, and it was obvious that if it could be driven by an engine provided with a fly wheel to store energy, and give it out at the peak loads, considerable economy in steam, and fuel, would result.
Attempts were made to do this by the use of trains of gearing and clutches. The upkeep and breakage were, however, so serious as to more than absorb any saving in fuel; and so the less efficient but more reliable reversing engine held the field.
The problem of obtaining a more efficient drive for the reversing mill still remained open; and it was the A E G Company of Berlin that solved the problem using the Ilgner system of electric driving.The first mill to be so driven was at the Hildegardehutte Works in Austrian Silesia. This was a large bar mill having four stands of housings, the rolls being 29 inch diameter. The mill was originally driven by a twin reversing engine. On a vacant piece of ground beyond the engine the electric plant was erected. It consisted of three DC motors in series, mounted on a shaft connected through an intermediate shaft, which took the place of the engine crankshaft. These motors had a normal capacity of 3,000 HP and a maximum of 10,350 HP and were capable of running at 120 RPM. The fly wheel converter set consisted of a three phase motor in the centre of 1,500kW normal and 4,300 kW maximum operating on a 3,000 Volt circuit at 50 Hz. On each side of the motor was a flywheel 13 ft in diameter, weighing 26 tons, and beyond these two variable voltage generators in series, each of 1,500 kW normal and 4,300 kW maximum rating.The whole equipment was built on the most liberal proportions and was able to take momentary overloads of 200 per cent., to run for half-an-hour with 75 per cent, and for two hours with 40 per cent overload. The cost of the whole equipment was said to have between twenty and twenty two thousand pounds British money.
The manufacture of rolls for mills became wide spread in the latter half of the 1800's. The first company in the UK set up specifically to make rolls was the Guest and Cranage, Victoria Roll Foundry, in England in 1854. In 1857 R B Tennant Ltd set up a foundry in Coatbridge for roll making.
Slabbing / Cogging MillIn Clydebridge the Cogging Mill was also referred to as the Slabbing Mill. Apparently Cogging Mill is a British term and Slabbing Mill is the American term. Before these mills came into use, ingots were converted into slabs for the rolling mill using Naysmith type Slabbing Hammers. Dalzell works started out with 2 Slabbing Hammers and when the Cogging Mill was installed it allowed larger ingots to be used, and it also greatly speeded up production.
The term Cogging may refer to the use of gear teeth (cog wheels) for the mill drive but is more likely to be derived from tilt hammers, which were also operated by cogs which lifted the helve hammer to allow it to drop back down on the piece being worked.
Cogging Mills were first used in a blooming mill at Dowlais in Wales in 1866 and were in use.in America, at Cambria, in 1871. The first universal cogging mill was that of James Riley, General Manager of the Steel Company of Scotland, at Blochairn Works in Glasgow, in 1884. In this mill slabs were turned up on edge for rolling their sides.
A second heavier cogging mill was designed for Blochairn in 1890 to embody improvements suggested by James Riley. Up to that time the widest slabs made did not exceed 36 inches. This new cogging mill was designed to produce armour plates up to 5 foot wide with finished edges to minimise further machining. It was decided not to turn the slabs up on edge, as the tilting gear was cumbersome and expensive, and the mill was designed as a Universal Mill, with two vertical rolls, for rolling the slab sides, in addition to the usual horizontal rolls. One of the vertical rolls moved across the mill to allow slab widths of between 32 inches and 60 inches to be worked along the edges. This mill dispensed with live-roller gearing for moving the slabs to and from the mill, using instead dead rollers and a hydraulically actuated pusher carriage, whose stroke was multiplied by chains and pulleys. The mill was controlled by five people, one at the screwing gear, one at the pusher carriage, one at the mill engines, with an assistant for the necessary oiling etc., and the roller in overall charge of the mill.
James Riley became General Manager of the Glasgow Iron and Steel Company in 1894, at which time a new cogging mill was built for the Wishaw Steel Works of the company. This cogging mill was built by Messers Lamberton & Co, with rolls 8 feet 6 inches wide and 40 inches diameter, with end grooves for rolling slabs up to 54 inches wide tilted up on edge. The mill was driven by a pair of steam engines with cylinders 46 inches diameter by 60 inches stroke. The mill also had a pair of steam engines driving the screw down gear for setting the mills roll gap draught. A further steam engine (9 inch cylinder and 15 inch stroke) drove the live geared rollers carrying the slabs into and out of the mill.
Slab ShearsJames Riley used water hydraulic powered slab shears for both of the Blochairn cogging mills. These shears were made by Messers Tannentt, Walker & Co, of Leeds. The second, 1890, Blochairn slab shear had a bed plate and cast steel entablature with four corner columns and three hydraulic cylinders, two of 22 inches at the sides and a centre cylinder 31 inches diameter. A further ram held down the slab during shearing. A weight loaded hydraulic accumulator provided a pressure of one ton per square inch. The pipe work was all lead to a position to allow one man to control the shear.Also about this time Messers Lamberton & Co designed steam slab shears for David Colville & Sons Dalzell works, to cut slabs 60 inches wide by 12 inches thick. The drive was provided by coupled steam engines driving an eccentric shaft shearing motion through reduction gearing.An important consideration for slab shearing was the speed of shearing, because if the blades remained in contact with a hot slab for too long they would loose their sharp edge, necessary for making a clean cut.
Pull-Over MillPlate mills have been constructed in several types such as Pull-Over Mills, Reversing Mills, 3-high Mills, 4-High Mills, Universal Mills.
Early rolling mills (pull-over mills) had two work rolls that were driven by a water wheel, and later by steam engine. As the mill rotated continuously in one direction the plate was rolled through the mill then hand fed back over the top roll, to the rollers side of the mill.
At the British great Exposition in 1851 the Consett Iron Company displayed a plate 20 feet long, 3 1/2 feet wide and 7/16 inch thick. This weighed 1,125 pounds and was considered the largest plate rolled up to that time.
Reversing MillThe first reversing plate mill was at Parkgate works, and it rolled the plates for I K Brunel's "Great Eastern" in 1854.
Pull-over difficulties were encountered by J Ramsbottom, Chief Engineer to the London and North Western Railway Co, who wanted to make the frame plates of locomotives all in one piece, but the handling of long plates was difficult at a pull-over mill and the time taken allowed the plates to cool and reduced the output of the mill. He mentioned the problem to Mr Naysmith, the inventor of the steam hammer, who suggested reversing the mill, so that the plates would not have to be lifted and could be worked in both directions, thus doubling the output of the mill. To test the practicality of this, Mr Ramsbottom placed a pinion on the driving axle of a locomotive, geared to the mill in such a ratio that when the locomotive was running at the rate of 60 miles per hour the mill was at its normal rolling speed. The experiment proved quite successful, in spite of prophesies by the practical men at the mill that it would be impossible to roll plates without a fly wheel, with the result that a reversing engine was made with 36 inch steam cylinders, and set to work in 1866. This arrangement worked from the start without a hitch.
On the 4th December 1866 James Naysmith received the following letter from Mr Ramsbottom:
"Dear Sir - I must crave your forgiveness for my great delay in acknowledging the receipt of your kind letter of the 29th August, in which you refer to the successful carrying out at these works of your idea of a 'Reversible Rolling Mill without a Fly-wheel.' It has long been to me a matter of astonishment that your idea has not been reduced to practice years ago, particularly when it is considered how well the arrangement is adapted to the rolling of Armour Plates, or other work requiring a sustained effort, whilst it is at the same time more effective than the ordinary mill arrangement for very light work. So much is this latter true, that the men who are left to their own choice in the matter, will reverse the mill rather than pass a light sheet of 8 or 10 lbs. weight over the upper roll. This country is much indebted to you for so valuable a suggestion; and now that it has been brought to a successful issue, I have no doubt but it will be widely acted upon. I need not add that it will afford me much pleasure to show you the mill, and also what we are doing generally, if you should at any time visit Crewe."
James Naysmith also passed on the invention to Mr. Thomas Gillott of the Farnley Ironworks, Yorkshire, and received from him the following letter, dated the 2nd January 1877:
"Dear Sir - I was much gratified to see by your letter in Engineering the interest you have shown with respect to the large Reversing Plate Mill erected by me at these works, and drawn on the plan suggested by you. Allow me to thank you for the complimentary manner in which you have mentioned my work. Since the notice appeared, we have done a deal of heavy work in this mill; and a plate large enough to shear 11' 0" and 10' 2" and 1/2" thick has been rolled in five minutes. The slab went through the roll 17 times before being rolled to the width and turned round, and 18 times after turning and of the full width; making a total of 35 passes--the turning occupying 20 seconds. When it is remembered how rapidly a thin plate cools, this performance will sufficiently indicate the severe work this mill is capable of doing; notwithstanding the many predictions that such large plates could not be rolled without a fly-wheel. As to repairs, none have been required; so I cannot compare this with the Clutch systems. In respect of steam used, the direct acting engines compare favourably with an expansion beam condensing engine doing similar but lighter work. Should it ever be your wish to see this mill at work, I should be much pleased to have the opportunity of showing it to you.Although Naysmith's reversing mills, with direct-acting engines, fitted with link-motion and without fly wheels, had been proved satisfactory, there was still a prejudice against them in many places. They were accused of being "steam eaters", which they were. There was also a disinclination to scrap engines which were in good condition, so reversing the mills by trains of gearing was tried.
At the Glasgow meeting of the Iron and Steel Institute, in August, 1872, under the Presidency of Mr (afterwards Sir) Henry Bessemer, two papers were read describing reversing gears for Rolling Mills : one by Mr R. D. Napier of Glasgow and the other by Mr. Graham Stevenson of Airdrie. Both used friction clutches, which were no doubt a great improvement on positive claw clutches. Several reversing gears of these and other types were made and used in various parts of the country; but it was soon found that the wear and tear of the gearing, together with the frequent breakdowns, were causing greater loss than the extra steam used by the reversing engines; and they soon became obsolete.
The early plate mills tended to have two, or more, stands. The first stand was a roughing mill, and usually both the top and bottom roll were driven. The second stand was a finishing mill and usually only the bottom roll was driven. This was to avoid slip between the rolls, damage to the plate, and wear on the rolls and pinions if the rolls were not perfectly matched in diameter. A consequence of this, in fast running reversing mills, was that the free top roll would continue running, as a flywheel of stored energy, and could cause severe shock loadings through contact with the work piece as it re-entered the mill in the reverse direction. One partial solution to this problem was to fit a brake to the end of the top roll, however, even if stopped the top roll had still to be brought rapidly up to speed to match the already turning bottom roll during initial contact with the work piece. Another solution was to fit a light clutched drive to the top roll that would allow slip to take place.
The rolls fitted to the mills are subject to severe loadings and require a hard surface but a tough core. The initial roughing stand was usually fitted with grain cast iron 'soft' rolls and the finishing stand with chilled cast iron 'hard' rolls. Later, alloy cast steel rolls were used in the roughing stands.
The engine, initially usually a beam engine but later usually a horizontal twin compound engine, was located between the stands, driving a line of underground shafting, on which were mounted pinions to drive the several mills. The slabs / plates were hand manipulated through the rolls onto hand bogies or dead (undriven) roller tables. The roller table could be moved across between the hard and soft roller stands.
Incidentally, the Kelham Island Museum in Sheffield holds the largest remaining steamed engine in the UK - the1905 River Don Steelworks 12,000 horsepower vertical three cylinder armour plate rolling mill engine. To see this almost silent monster move is to see raw power and to see it instantly go into reverse is astonishing. A quote from the oldenginehouse web site says it all - "If you only ever see one steam engine moving in your life this should probably be the one!"
The early reversing mills were without live rollers, or indeed, any mechanical appliances for handling the material being rolled. A bogie on each side of the mill operated by men received the plate after each pass. With the increasing size and weight of plates this method became increasingly unsatisfactory, and steam-driven live roller racks were then introduced. The rollers at the back of the mill were at first mounted on a travelling carriage which, when the plate was sufficiently reduced in the soft rolls, could be moved across with the plate on it to the hard rolls. This arrangement was abandoned on most mills by the 1920s in favour of individual racks for each stand of rolls; the piece being transferred from the soft to the hard rolls by some form of pull-over gear. The racks and other auxiliary gear were also being electrically driven.
US / UK Trends 1895At a presentation made by James Riley at the Institution of Mechanical Engineers, in July 1895, comparisons were made between British and American practice for plate mills. Most American plate mills were three high mills; that rotated constantly in one direction with the plate passing under and over the centre roll in successive passes through the mill. American plates were rolled in these mills direct from flat ingots cast from the bottom (although a cogging mill was used at Carnegie's Homestead works). In Britain this had been tried in the late 1880s but was abandoned in the belief that the Lloyds and Board of Trade tests could not be assured without the preliminary working to improve steel properties in a cogging mill, particularly for thicker plates. At the time the US did not have the same shipbuilding trade as the UK. However, Mr Jeremiah Head a past president of the IMechE who had recently toured US works noted that in the US plates were subject to Bureau Veritas tests, equivalent to Lloyds, and he had seen plates 10 feet wide rolled on a three-high mills and had seen a 4,000 ton cargo ship building at Cleveland, on Lake Erie, with plates in her hull up to an inch thick.
3-High Fritz MillA problem with rolling mills is that the high rolling loads tend to bend the rolls and this produces a plate which is thicher in the middle than at the sides. Profiling the rolls in a slight barrel shape provided some compensation, but another solution is to provide further larger diameter 'back-up' rolls of a that provide a higher resistance to bending. The first solution was a 3-high mill. The plate could be passed between the smaller diameter driven middle roll and the bottom larger roll in one direction and between the middle roll and the larger top roll in the other direction.
The 3-High Mill is usually thought to have been first invented by John Fritz in 1857, when he was Engineer Manager to the Cambria Iron Company in the United States. However, there are accounts, written at the time, of 3-High mills in use in Staffordshire in 1815, and the first modern three high mill recorded is in a patent to R Roden at Abersychen iron Works in 1853.
The first mill built by Fritz was a rail mill, and its inception, as detailed in his autobiography by "Uncle Fritz" as he became known, is worth quoting to show how an idea has to be fought for in the face of ignorance and prejudice. The original two-high mill had proved to be a failure for several reasons, and Uncle Fritz goes on to say:
" To continue to run the mill as it was, I could see nothing ahead but a most disastrous failure. Having previously given the whole subject my most thoughtful consideration, even to its most minute detail, I was prepared to submit my plans and recommendations to the new Company. My proposal was to build a new train of rolls three-high and twenty inches in diameter. This involved a new engine that would run with safety one hundred revolutions per minute, and it practically meant an entirely new mill. To this proposition they demurred, saying that it could not be done as the expense was too great; besides, the mill they had was entirely new and was supposed to be the best mill in the country, and they were at a loss to see why good rails could not be made on it.
After some time and a great amount of earnest talk, I succeeded in convincing some of the representative shareholders that it was absolutely necessary to make some changes and improvements, and that, if my suggestions were adopted, success was sure.
At the next meeting the subject was taken up with a full Board, and, as I was informed afterwards, the matter was fully discussed, and it was decided to build an eighteen inch two-high train, geared, to replace the train we had, and I was ordered to go ahead at once with it. This was to me a very severe set-back, as I supposed I had Mr. Townsend converted to the three-high direct-action mill. To this order I replied most emphatically that I would not build the geared mill, as it would be money thrown away and time lost. In reply to my refusal to build the mill as ordered, they said my position was high-handed and most arbitrary, and one I had no right to assume, as I was in their employ on a salary for the purpose of managing their works and had no right to dictate to them what they should do. I, in a measure, assented to this, at the same time telling them that if they persisted in running their works on the lines they had laid down for me, there would be a humiliating funeral, and I did not want to remain to attend it, especially as one of the mourners. In a few days after receiving my reply, they gave me permission to build the mill as I wanted it, but suggested that I make the roll eighteen inches instead of twenty. I consented as a compromise - a great mistake - and commenced at once to build the mill, and make other important improvements.
How the Shareholders Protested.
About the time the patterns for the new train and also for the engine were completed, a protest was received at the works in the form of a legal document from the minority partners, notifying the Managing Directors that they would hold them personally responsible for the building of the new Mill. This was a most unexpected set-back, and all the work on the new mill was suspended for a time, and the Directors made another effort to get me to change my plans and build the old two-high geared mill, which the Company had previously, so earnestly urged me to do. I told them I was tired out trying to make rails on the old mill. They suggested that I could make a better mill two-high that would give less trouble, and consequently do more work. I admitted that it could be done, but the advantage to be gained would not warrant the expenditure, and the only thing that could possibly be done to make the enterprise a success was to build the three-high mill.
The next Sunday morning Mr Townsend came to the mill, where he found me in the midst of the regular Sunday repairs. After I was pretty well through with them he took me aside and showed me the protest. My hands being greasy, I asked him to read it to me, which he did. After all these years have passed there is no person other than myself who can fully appreciate the trying position the Managers were placed in. On the one hand I was urging them to build a mill, on an untried plan, as a strong minority called it, this minority also legally notifying the managers that they would hold them personally responsible for the result. On the other hand, I was absolutely refusing to build the mill they wanted; and, besides all this, they ridiculed the idea of adopting a new and untried method that was against all practice in this and the old country, from which at that time we obtained our most experienced Iron-workers. Moreover, the prominent Iron-makers in all parts of the country had said to Mr Morrell that the whole thing was a wild experiment and was sure to end in failure, and that young, determined, crack-brained Fritz would ruin him.
The Heaters and Rollers all opposed the three-high mill, and appointed a Committee to see the Managers and to say to them that the three-high mill would never work, and that they themselves would suffer by reason of its adoption; but if the Managers would put up a two-high geared train, which they said was the proper thing to do, the mill would go all right.
As I now look back to that eventful Sunday, morning, many long years ago, sitting on a pile of discarded rails, with evidence of failure on every side, Mr. Townsend and myself quietly and seriously talking over the history of the past, the difficulties of the present, and the uncertainties of the future, I cannot but feel in view of what since has come to pass that it was not only a critical epoch in the history of the Cambria Company, but that as well the future well-being of my life was in the balance. For, as Mr. Townsend was about to leave, after a full discussion of the Cambria Iron Company's conditions at that time, he turned to me and said, 'Fritz, go ahead and build the mill as you want it.' I asked, 'Do you say that officially ? ' to which he replied, ' I will make it official,' and he did so; and here I wish to say that to no other person so deservedly belongs the credit, not only of the introduction of the three-high roll train, but also of the wonderful prosperity that came to the Cambria Company, as it does to Mr. Edward Y. Townsend, then its Vice-President.
"A Grand Old Smash Up."
Notwithstanding, I now had the consent of the Company to go on with my plan for the new mill, many of my warmest friends, some of whom were practical ironmen, came to me and urged me not to try such an experiment. They said I had taken a wrong position in refusing to build the kind of mill the Company wanted. 'By so doing,' they said, 'you have assumed the entire responsibility, and in all probability the mill you are going to build will prove a failure, and being a young man your reputation will be ruined for life.' To this I replied that probably they were right, but that I had given the subject the most careful consideration and was willing to take my chances.
The work was now pushed on as fast as possible. In the construction of the mill train I made a radical departure from the old practice, which was to place breaking pieces at dangerous points in the train: these pieces were expected to give way under certain strains so as to save the roll from breaking. One of the previous methods was to make the coupling boxes and spindles light so that they would break when any extra strain came on them; and the leading spindle had a groove cut round it to weaken it, so that it would be sure to break before the rolls, The result was the constant breaking of some of these safety devices. In addition to all these devices, there was what was called a special breaking box on top of the rolls which held the rolls in place. This was made hollow so as to crush if the strain on the rolls became too great. I directed the Patternmaker to make this box solid. The Mill Manager, seeing the pattern was solid, went to the Patternmaker to have it changed and made hollow, as he supposed it had been made solid through a mistake. The Patternmaker refused to alter the pattern, saying the old man (as they called me over fifty years ago) had ordered it to be made that way. 'Well,' said the Manager, the old man has gone crazy; and if the box is put in as it is, the mill will be smashed to pieces, and I am going to see him about it.' This he did, and I told him the box was going in solid, as I would rather have a grand smash-up once in a while than he constantly annoyed by the breaking of leading spindles, couplings, and breaking boxes; to which he replied, ' By God, you'll get it ! '
When it became known that I had abandoned all safety devices, another violent storm arose, and it was of such a character as to much annoy Mr. Morrell. He was a very clever gentleman, without experience in the manufacturing end of the business, and, being known as the General Manager of the plant, he was naturally worried. This, of course, gave me much trouble to keep him in line, as every person he would meet that knew anything about the business would tell him of the great failure that was in store for the Cumbria Iron Works. Some one told Mr. Wood, the President of the Company, all about what was going to take place when the mill was started. I was afterwards told that he listened attentively to what they had to say and then said to them: Mr. Fritz has done many clever things for us that were said would never work, but always did and I shall not interfere with him or his plans.' . . . "
How the Mill was "Tried Out"
The train was now practically completed, with all breaking devices abandoned. The old mill was stopped on the evening of the 3rd July, 1857, and after the 4th I commenced to tear the old mill out and get ready to put the new one in, and also to put the new engine in place at the same time.
Everything in the Mill Department was remodelled and the floor line raised two feet. On the 29th of the same month everything was completed and the mill was ready to start. I need not tell you that it was an extremely anxious time for me: nor need I add that no engraved invitation cards were sent out, that not being the custom in the early days of Iron making: had it been, it would not have been observed on that occasion.
As the Heaters to a man were opposed to the new kind of mill, we did not want them about at the start. We secured one, however, out of the lot, who was the most reasonable one amongst them, to heat the piles for us. We had kept the furnace smoking for several days as a blind. At last, everything being ready we charged six piles, At about ten o'clock in the morning the first pile was drawn, and it went through the rolls without the least hitch of any kind, making a perfect rail.
You can judge what my feelings were as I looked upon that perfect and first rail ever made on a three-high Mill; and you may know in part how grateful I felt to the few faithful and anxious men who stood by me during all my trials and difficulties among whom were Alexander Hamilton, the Superintendent of the Mill, Thomas Lapsley, who had charge of the Rail Department, William Canam, and my brother, George.
We next proceeded to roll the other five piles. When two more perfect rails were rolled we were obliged to stop the engine, as the men were all so intently watching the rolls that the engine had been neglected, and, being new, the eccentric had heated and bent the eccentric rod so that the engine could no longer be worked. As it would have taken some time to straighten the rod and reset the valves, the remaining piles were drawn out of the furnace on to the mill floor.
"About this time the Heaters, hearing the exhaust of the engine, came into the mill in a body, and from the opposite end to where the rails were. Seeing the unrolled piles lying on the mill floor, they took it for granted that the new train was a failure and their remarks about it were far from being ill the least complimentary. Mr. Hamilton, coming along that time and hearing what they were saying about the mill, turned around, and in language more forcible than polite told the Heaters, who were Welsh, that if they would go to the other end of the mill they would see three handsomer rails than had ever been made in Wales, where the greater part of the rails used in this country at that time came from, as well as the Heaters who were so bitterly opposed to the three-high mill.
The above is a first-hand account from the inventor himself of how the Three-High Mill came to have a place in the sun. Uncle Fritz's trouble did not end there. The mill started on a Thursday and worked the whole of Friday, day and night shifts, on to noon on Saturday, when work was stopped for the week. On Saturday night the mill building, which was of wood, was set fire to by some incendiaries and burned to the ground. The mill was, however, re-started within 30 days of the fire, but without a roof ; and the new buildings, which were of brick, were finished and roofed over with the mill running full time during the progress of the work.
Three-High Lauth MillIn the type of mill invented by Fritz the middle roll was fixed, and the top and bottom rolls were adjustable. This was quite practicable for Section Mills when the rolls did not require to be adjusted between every pass. For Plate Mill work, however, this type of Mill was superseded by the one invented and patented by Mr. Bernard L. Lauth of Pittsburg, U.S.A.
In the Lauth mill the bottom roll was fixed; the middle roll, which was smaller than the top and bottom rolls, being raised and lowered by a power operated lever alternately as the piece passed under or over it, The top roll was adjusted by screw gear to give the draft in the usual was. The small middle roll was not subject to bending stress, as it was always in contact with one or other of the large rolls.Mr Lauth read a paper at the Glasgow meeting of the Iron and Steel Institute in 1872, in which he described his mill as follows:
"In the United States there are about 23 mills running three-high, and the character of these mills is as follows. The hard rolls are of the usual size, but between them there is a roll of smaller diameter: thus for a 4 feet roll by 20 inches diameter, the small roll would be 13 inches diameter and for a roll 6 feet long by 22 inches diameter, the middle roll would be 16 inches diameter. The rolls are all turned perfectly straight and level, so that they bear all over, and a stream of water is constantly kept on each roll to keep it perfectly cool.
The effect is that there is no expansion and contraction of the rolls, and the sheet or plate is rolled to a perfect level free from all buckling. The surface of the sheet or plate is very smooth, the water having the effect of washing off all the scale and preventing it sticking to the rolls. Some people are under the impression that by using so much water the sheets and plates would get cold. Such, however is not the case, as the water runs off in globular form, and in practice it is no impediment. By the old system of rolling, the Plates and Sheets are usually thinker in the middle than at the edges. By this system they are rolled all over to a uniform gauge, in consequence of the rolls being kept cold.
The reducing power of the middle roll is very marked and this is accounted for by reason of the smaller area which is covered by the grip of the plate, in consequence of the diameter of the roll being smaller. The effect is, that a larger draft can be put upon the plate or sheet than by the old system with the same power involved in the machinery."
The Clydebridge 3-High Plate Mill, that operated between 1922 and 1960, was a fine example of a Lauth mill. It was made by Davy Brothers Ltd, Sheffield. The top and bottom rolls were 36 inch diameter, whilst the middle roll was 24 inch diameter. The length of all rolls was 9 feet on the barrel. The roll necks for the top and bottom were 26 inch and those for the middle roll were 16 inch diameter, the lengths being 24 inches. The pinions were machine cut double helical teeth 56 inches wide on the face. The housing screws were 12 inches diameter and operated by a DC motor of 100 HP. The lifting tables on each side of the mill had seventeen 17 inch diameter rollers, each 7 ft 3 ins long, with journals 5 ins x 10 ins. Each table was provided with two 60 HP DC motors. The lifting rig was operated by a DC motor of 100 HP. The mill was driven by a double armature motor of 13,000 HP at 65 RPM. The motor gave constant torque from 0 to 65 RPM, and constant HP from 65 to 110 RPM.
Four-High MillThe 3-High Mill has been superseded for plates and strip by the 4-High Mill, where the piece passes between two driven work rolls, each supported by larger, un-driven, back-up roll, one above and one below the work rolls. This allows the power to be transferred through the smaller work rolls and ensures that these remain horizontal and parallel, despite the rolling loads, through the support from the larger back-up rolls. The Clydebridge 4-High Plate Mill (1962) work rolls were 39 inch diameter by 132 inches wide at the barrell, and the back-up rolls were 60 inch diameter. Similar mills were installed at Consett (closed in 1980) and at Rautaruukki in Finland (modernised and still operating) and the mill shared parts, such as the 27 ton drive spindles, with the Ravenscraig Roughing Mill. The newer Dalzell heavy plate mill has 72 inch diameter back-up rolls (each about 74 tons), which are so large that special railway carriages had to be constructed for their transport to the Works.
ShearsAn early plate mill would have a steam or water powered shear and the plate would be manipulated round to be shorn at the ends, or sides, or for splitting. In early shears, and with light plates, the plate would be manipulated by hand, with a trestle, called "the horse" being used to support the plate when being cut. As plates got heavier upturned castors were introduced, first in America, to support the plates. Later mechanical tables were developed, such as the Ennis table, (designed by Mr Ennis of Dorman Long & Co) used at the side shears in Clydebridge in the 1920s. This was a moveable roller table, the whole of which could be moved past the shear; and the table included electro magnets for adjusting the plates in front of the shears. These were all replaced with continuous roller tables, magnet manipulators and hydraulic clamps when the side cut shears were upgraded and new end cut shears installed in the early 1960s. Despite this the side cut shears were often still referred to as the Castor Shears.
For thinner plates a Schloemann Rotary Shear was installed at Clydebridge in the 1960s. This sheared both sides of a plate continuously with 2 circular blades at either side of the plate (rather like the operation of a rotary tin opener). The strips cut from the side fed through rotary chopper heads, which were 2 contra rotating drums with helical cutting blades. Other heavier shears installed at this time for cutting the ends of plates were electrically driven through reduction gearing located on top of the shear.
The basic drawing process for a wire, bar or tube.
Drawing is a metalworking process which uses tensile forces to stretch metal. It is broken up into two types: sheet metal drawing and wire, bar, and tube drawing. The specific definition for sheet metal drawing is that it involves plastic deformation over a curved axis. For wire, bar, and, tube drawing the starting stock is drawn through a die to reduce its diameter and increase its length. Drawing is usually done at room temperature, thus classified a cold working process, however it may be performed at elevated temperatures to hot work large wires, rods or hollow sections in order to reduce forces.Processes
The success of forming is in relation to two things, the flow and stretch of material. As a die forms a shape from a flat sheet of metal, there is a need for the material to move into the shape of the die. The flow of material is controlled through pressure applied to the blank and lubrication applied to the die or the blank. If the form moves too easily, wrinkles will occur in the part. To correct this, more pressure or less lubrication is applied to the blank to limit the flow of material and cause the material to stretch or thin. If too much pressure is applied, the part will become too thin and break. Drawing metal is the science of finding the correct balance between wrinkles and breaking to achieve a successful part.
Drawing can also be used to pull metal over a die (male mold) to create a specific shape. For example, stainless steel kitchen sinks are formed by drawing the stainless steel sheet metal stock over a form (the die) in the shape of the sink. Beverage cans are formed by drawing aluminium stock over can-shaped dies. By comparison, hydroforming forces metal into a female mold using pressure.
Bar, tube & wire
Bar, tube, and wire drawing all work upon the same principle: the starting stock drawn through a die to reduce the diameter and increase the length. Usually the die is mounted on a draw bench. The end of the workpiece is reduced or pointed to get the end through the die. The end is then placed in grips and the rest of the workpiece is pulled through the die. Steels, copper alloys, and aluminium alloys are common materials that are drawn.
Drawing can also be used to produce a cold formed shaped cross-section. Cold drawn cross-sections are more precise and have a better surface finish than hot extruded parts. Inexpensive materials can be used instead of expensive alloys for strength requirements, due to work hardening.
Bars or rods that are drawn cannot be coiled therefore straight-pull draw benches are used. Chain drives are used to draw workpieces up to 30 m (98 ft). Hydraulic cylinders are used for shorter length workpieces.
The reduction in area is usually restricted to 20 to 50%, because greater reductions would exceed the tensile strength of the material, depending on its ductility. To achieved a certain size or shape multiple passes through progressively smaller dies or intermediate anneals may be required.
Tube drawing is very similar to bar drawing, except the beginning stock is a tube. It used to decrease the diameter, improve surface finish and improve dimensional accuracy. A mandrel may or may not be used depending on the specific process used.
This technique has long been used to produce flexible metal wire by drawing the material through a series of dies of decreasing size. These dies are manufactured from a number of materials, the most common being tungsten carbide and diamond.
Deep drawing is a sheet metal forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. It is thus a shape transformation process with material retention. The flange region (sheet metal in the die shoulder area) experiences a radial drawing stress and a tangential compressive stress due to the material retention property. These compressive stresses (hoop stresses) result in flange wrinkles (wrinkles of the first order). Wrinkles can be prevented by using a blank holder, the function of which is to facilitate controlled material flow into the die radius.
The total drawing load consists of the ideal forming load and an additional component to compensate for friction in the contacting areas of the flange region and bending forces at the die radius. The forming load is transferred from the punch radius through the drawn part wall into the deformation region (sheet metal flange). Due to tensile forces acting in the part wall, wall thinning is prominent and results in an uneven part wall thickness. It can be observed that the part wall thickness is lowest at the point where the part wall loses contact with the punch, i.e. at the punch radius. The thinnest part thickness determines the maximum stress that can be transferred to the deformation zone. Due to material volume constancy, the flange thickens and results in blank holder contact at the outer boundary rather than on the entire surface. The maximum stress that can be safely transferred from the punch to the blank sets a limit on the maximum blank size (initial blank diameter in the case of rotationally symmetrical blanks). An indicator of material formability is the limiting drawing ratio (LDR), defined as the ratio of the maximum blank diameter that can be safely drawn into a cup without flange to the punch diameter. Determination of the LDR for complex components is difficult and hence the part is inspected for critical areas for which an approximation is possible.
Commercial applications of this metal shaping process often involve complex geometries with straight sides and radii. In such a case, the term stamping is used in order to distinguish between the deep drawing (radial tension-tangential compression) and stretch-and-bend (along the straight sides) components.
Deep drawing has been classified into conventional and unconventional deep drawing. The main aim of any unconventional deep drawing process is to extend the formability limits of the process. Some of the unconventional processes include hydromechanical deep drawing, Hydroform process, Aquadraw process, Guerin process, Marform process and the hydraulic deep drawing process to name a few.
The Marform process, for example, operates using the principle of rubber pad forming techniques. Deep-recessed parts with e,ither vertical or slopped walls can be formed. In this type of forming, the die rig employs a rubber pad as one tool half and a solid tool half, similar to the die in a conventional die set, to form a component into its final shape. Dies are made of cast light alloys and the rubber pad is 1.5-2 times thicker than the component to be formed. For Marforming, single-action presses are equipped with die cushions and blank holders. The blank is held against the rubber pad by a blank holder, through which a punch is acting as in conventional deep drawing. It is a double-acting apparatus: at first the ram slides down, then the blank holder moves: this feature allows it to perform deep drawings (30-40% transverse dimension) with no wrinkles.
Industrial uses of deep drawing processes include automotive body and structural parts, aircraft components, utensils and white goods. Complex parts are normally formed using progressive dies in a single forming press or by using a press line.
Workpiece Materials and Power Requirements
Softer matierials are much easier to deform and therefore require less force to draw. The following is a table demontstrating the Draw force (lbs) to percent reduction of commonly used materials.
Percent Reduction 39% 43% 47% 50%
=Material= Aluminum 19,800 22,600 25,400 28,300
Brass 26,400 30,200 34,000 37,700
steel 28,600 32,700 36,800 40,800
Stainless steel 37,400 42,700 48,100 53,400
Punches and Dies are typically made of tool steel, however carbon steel is cheaper, but not as hard and is therefore used in less severe applications, it is also common to see Cemented carbides used where high wear and abrasive resistance is present. Alloy steels are normally used for the ejector system to kick the part out and in durable and heat resistant blankholders.
Tube drawing is a metalworking process to size tube by shrinking a large diameter tube into a smaller one, by drawing the tube through a die. This process produces high quality tubing with precise dimensions, good surface finish, and the added strength of cold working. Because it is so versatile, tube drawing is suitable for both large and small scale production.
There are five types of tube drawing: tube sinking, mandrel drawing, stationary mandrel, moving mandrel, and floating mandrel.
Tube sinking, also known as free tube drawing, reduces the diameter of the tube without a mandrel inside the tube. The inner diameter (ID) is determined by the inner and outer diameter of the stock tube, the outer diameter of the final product, the length of the die landing, the amount of back tension, and the friction between the tube and the die. This type of drawing operation is the most economical, especially on thick-walled tubes and tubes smaller than 12 mm (0.47 in) in diameter, but does not give the best surface finish. As the tube thickness increases the surface finish quality decreases. This process is often used for the tubing on low cost lawn furniture.
Rod drawing is the process that draws the tube with a mandrel inside the tube; the mandrel is drawn with the tube. The advantage to this process is that the mandrel defines the ID and the surface finish and has a quick setup time for short runs. The disadvantages are that lengths are limited by the length of the mandrel, usually no more than 100 feet (30 m), and that a second operation is required to remove the mandrel, called reeling. This type of process is usually used on heavy walled or small ID tubes. Common applications include super-high pressure tubing and hydraulic tubing (with the addition of a finishing tube sinking operation). This process is also use for precision manufacturing of trombone handslides.
Fixed plug drawing
Fixed plug drawing, also known as stationary mandrel drawing, uses a mandrel at the end of the die to shape the ID of the tube. This process is slow and the area reductions are limited, but it gives the best inner surface finish of any of the processes. This is the oldest tube drawing method.Floating plug drawing
Floating plug drawing, also known as floating mandrel drawing, uses a mandrel that is not anchored whatsoever to shape the ID of the tube. The mandrel is held in by the friction forces between the mandrel and the tube. This axial force is given by friction and pressure. This greatest advantage of this that it can be used on extremely long lengths, sometimes up to 1,000 feet (300 m). The disadvantage is it requires a precise design otherwise it will give inadequate results. This process is often used for oil-well tubing.
Tethered plug drawing
Tethered plug drawing, also known as semi-floating mandrel drawing, is a mix between floating plug drawing and fixed plug drawing. The mandrel is allowed to float, but it still anchored via a tether. This process gives similar results to the floating plug process, except that it is designed for straight tubes. It gives a better inner surface finish than rod drawing.
Drawing silver wire by hand pulling.
Drawing thicker silver wire by cranked pulling.
Wire drawing is a metalworking process used to reduce the diameter of a wire by pulling the wire through a single, or series of, drawing die(s). There are many applications for wire drawing, including electrical wiring, cables, tension-loaded structural components, springs, paper clips, spokes for wheels, and stringed musical instruments. Although similar in process, drawing is different than extrusion, because in drawing the wire is pulled, rather than pushed, through the die. Drawing is usually performed at room temperature, thus classified a cold working process, but it may be performed at elevated temperatures for large wires to reduce forces. Wires can also be drawn into different shapes, although this is much more difficult than diameter reductions. More recently drawing has been used with molten glass to produce high quality optical fibers.
Wire drawing concept
The wire drawing process is quite simple in concept. The wire is prepared by shrinking the beginning of it, by hammering, filing, rolling or swaging, so that it will fit through the die; the wire is then pulled through the die. As the wire is pulled through the die, its volume remains the same, so as the diameter decreases, the length increases. Usually the wire will require more than one draw, through successively smaller dies, to reach the desired size. This can be done on a small scale with a draw plate, or on a large commercial scale using automated machinery.
The areal reduction of small wires are 15–25% and larger wires are 20–45%. Very fine wires are usually drawn in bundles. In a bundle, the wires are separated by a metal with similar properties, but with lower chemical resistance so that it can be removed after drawing.
Commercial wire drawing usually starts with a coil of hot rolled 9 mm (0.35 in) diameter wire. The surface is first treated to remove scales. It is then fed into either a single block or continuous wire drawing machine.
Single block wire drawing machines include means for holding the dies accurately in position and for drawing the wire steadily through the holes. The usual design consists of a cast-iron bench or table having a bracket standing up to hold the die, and a vertical drum which rotates and by coiling the wire around its surface pulls it through the die, the coil of wire being stored upon another drum or "swift" which lies behind the die and reels off the wire as fast as required. The wire drum or "block" is provided with means for rapidly coupling or uncoupling it to its vertical shaft, so that the motion of the wire may be stopped or started instantly. The block is also tapered, so that the coil of wire may be easily slipped off upwards when finished. Before the wire can be attached to the block, a sufficient length of it must be pulled through the die; this is effected by a pair of gripping pincers on the end of a chain which is wound around a revolving drum, so drawing the wire until enough can be coiled two or three times on the block, where the end is secured by a small screw clamp or vice. When the wire is on the block, it is set in motion and the wire is drawn steadily through the die; it is very important that the block rotates evenly and that it runs true and pulls the wire at a constant velocity, otherwise "snatching" occurs which will weaken or even break the wire. The speed at which the wire is drawn vary greatly, according to the material and the amount of reduction.
Continuous wire drawing machines differ from the single block machines in having a series of dies through which the wire passes in a continuous manner. The difficulty of feeding between each die is solved by introducing a block between each die. The speeds of the blocks are increased successively, so that the elongation is taken up and any slip compensated for. One of these machines may contain 3 to 12 dies. The operation of threading the wire through all the dies and around the blocks is termed "stringing-up". The arrangements for lubrication include a pump which floods the dies, and in many cases also the bottom portions of the blocks run in lubricant.
Often intermediate anneals are required to counter the effects of cold working, and to allow more further drawing. A final anneal may also be used on the finished product to maximize ductility and conductivity.
An example of product produced in a continuous wire drawing machine is telephone wire. It is drawn 20 to 30 times from hot rolled rod stock.
Lubrication in the drawing process is essential for maintaining good surface finish and long die life. The following are different methods of lubrication:
Wet drawing: the dies and wire or rod are completely immersed in lubricant
Dry drawing: the wire or rod passes through a container of lubricant which coats the surface of the wire or rod
Metal coating: the wire or rod is coated with a soft metal which acts as a solid lubricant
Ultrasonic vibration: the dies and mandrels are vibrated, which helps to reduce forces and allow larger reductions per pass
Various lubricants, such as oil, are employed. Another lubrication method is to immerse the wire in a copper (II) sulfate solution, such that a film of copper is deposited which forms a kind of lubricant. In some classes of wire the copper is left after the final drawing to serve as a preventive of rust or to allow easy soldering.
Diagram of a carbide wire drawing die
Drawing dies are typically made of tool steel, tungsten carbide, or diamond, with tungsten carbide and manufactured diamond being the most common. Synthetic diamond is usually used in the early stages of the drawing process, whereas natural diamond dies are used in the final stages. For drawing very fine wire a single crystal diamond die is used. For hot drawing, cast-steel dies are used. For steel wire drawing, a tungsten carbide die is used. The dies are placed in a steel casing, which backs the die and allow for easy die changes. Die angles usually range from 6–15°, and each die has at least 2 different angles: the entering angle and approach angle.
Hydraulic force increase.
A hydraulic press is a hydraulic mechanism for applying a large lifting or compressive force. It is the hydraulic equivalent of a mechanical lever, and is also known as a Bramah press after the inventor, Joseph Bramah, of England. He invented and was issued a patent on this press in 1795. Hydraulic presses are the most commonly-used and efficient form of modern press.
How it works
The hydraulic press depends on Pascal's principle: the pressure throughout a closed system is constant. At one end of the system is a piston with a small cross-sectional area driven by a lever to increase the force. Small-diameter tubing leads to the other end of the system.
Pascal's law: Pressure on a confined fluid is transmitted undiminished and acts with equal force on equal areas and at 90 degrees to the container wall.
A fluid, such as oil, is displaced when either piston is pushed inward. The small piston, for a given distance of movement, displaces a smaller amount of volume than the large piston, which is proportional to the ratio of areas of the heads of the pistons. Therefore, the small piston must be moved a large distance to get the large piston to move significantly. The distance the large piston will move is the distance that the small piston is moved divided by the ratio of the areas of the heads of the pistons.
Hydraulic Press in a machine shop. This press is commonly used for hydroforming.
For example, if the ratio of the areas is 5, a force of 100 newtons on the small piston will produce a force of 500 newtons on the large piston, and the small piston must be pushed 50 cm to get the large piston to rise 10 cm. This is how energy, in the form of work in this case, is conserved and the Law of Conservation of Energy is satisfied. Work is force times distance, and since the force is increased on the larger piston, the distance the force is applied over must be decreased. The work of the small piston, 100 newtons multiplied by 0.5 meter (50 cm) is 50 joules (J), which is the same as the work of the large piston, 500 newtons multiplied by 0.1 meter (10 cm).
Hydroforming (or hydramolding) is a cost-effective way of shaping malleable metals such as aluminum or brass into lightweight, structurally stiff and strong pieces. One of the largest applications of hydroforming is the automotive industry, which makes use of the complex shapes possible by hydroforming to produce stronger, lighter, and more rigid unibody structures for vehicles. This technique is particularly popular with the high-end sports car industry and is also frequently employed in the shaping of aluminium tubes for bicycle frames.
Hydroforming is a specialized type of die forming that uses a high pressure hydraulic fluid to press room temperature working material into a die. To hydroform aluminum into a vehicle's frame rail, a hollow tube of aluminum is placed inside a negative mold that has the shape of the desired end result. High pressure hydraulic pistons then inject a fluid at very high pressure inside the aluminum which causes it to expand until it matches the mold. The hydroformed aluminum is then removed from the mold.
Hydroforming allows complex shapes with concavities to be formed, which would be difficult or impossible with standard solid die stamping. Hydroformed parts can often be made with a higher stiffness to weight ratio and at a lower per unit cost than traditional stamped or stamped and welded parts.
This process is based on the 1950s patent for hydramolding by Milton Garvin of the Schaible Company of Cincinnati, OH. It was originally used in producing kitchen spouts. This was done because in addition to the strengthening of the metal, hydramolding also produced less "grainy" parts, allowing for easier metal finishing.
In sheet hydroforming there is Bladder forming (where there is a bladder that contains the liquid, no liquid contacts the sheet) and hydroforming where the fluid contacts the sheet (no bladder). A work piece is placed on a draw ring (blank holder) over a male punch then a hydraulic chamber surrounds the work piece and a relatively low initial pressure seats the work piece against the punch. The punch then is raised into the hydraulic chamber and pressure is increased to as high as 15000 psi which forms the part around the punch. Then the pressure is released and punch retracted and hydraulic chamber lifted and the process is complete.
In tube hydroforming there are two major practices: high pressure and low pressure: Under high pressure the tube is fully enclosed in a die prior to presurization of the tube. In low pressure the tube is slightly pressurized to a fixed volume during the closing of the die (used to be call the Variform process). In tube hydroforming pressure is applied to the inside of a tube that is held by dies with the desired cross sections and forms. When the dies are closed on the tube the ends are sealed and the tube is filled with hydraulic fluid the internal pressure causes the tube to conform to the die. Punches may also be incorporated in the forming die to punch holes in the work piece during the forming process.
Industrial hydroforming machines use a piston to generate pressure in the hydraulic fluid used in hydroforming, but an experimental alternative is the use of explosives to generate the pressure. Called explosive hydroforming, this method places an explosive charge, with or without an additional working fluid, on the high pressure side of the material. When the explosive is detonated, the pressure forces the working material into the die, at pressures of up to millions of pounds per square inch. See also explosive welding, which allows metals of different types to be bonded at an atomic level. Since both explosive hydroforming and explosive welding use similar techniques, it is possible to combine the two methods to both shape and weld metals simultaneously.
Setup and equipment:
Tools and punches can be interchanged for different part requirements.Typical Tools:
One advantage to hydroforming is the savings on tools. For sheet metal only a draw ring and punch or male die is required. The bladder of the hydro form itself acts as the female die eliminating the need to fabricate a matching female die. This allows for changes in material thickness to be made with usually no necessary changes to the tool. However dies must be highly polished and in tube hydroforming a two piece die is required to allow opening and closing.
One advantage of hydroforming is that complex shapes can be made in one step. In sheet hydroforming with the bladder acting as the female die almost limitless geometries can be produced. Tube hydroforming can produce many geometric options as well but is limited by a few factors: Forming pressure, tube wall thickness, material yield strength and die design.
Tolerances and Surface Finish:
Hydroforming is capable of producing parts within tight tolerances including aircraft tolerances where a common tolerance for sheet metal parts is within thirty thousandths of an inch. Sheet metal hydroforming also allows for a smoother finish as draw marks produced by the traditional method of pressing a male and female die together are eliminated.
Effect on Work material:
When a blank is hydroformed the metal flows around the die rather than stretching which causes less reduction in material thickness and also less effects of cold work aand strain hardening which could eliminate the need for an annealing process on some parts that would need further deformation.
Manual goldsmith press
A press, or a machine press is a tool used to work metal (typically steel) by changing its shape and internal structure.
A forge press reforms the work piece into a three dimensional object—not only changing its visible shape but also the internal structure of the material. A stronger part results from this process than if the object was machined.
Bending is a typical operation performed and occurs by a machine pressing, or applying direct pressure, to the material and forcing it to change shape. A press brake is a typical machine for this operation.
An easy to understand type of machine press is a set of rollers. Metal is fed into the rollers, which are turning to pull the material through. The space between the rollers is smaller than the unfinished metal, and thus the metal is made thinner and/or wider.
Another kind of press is a set of plates with a relief, or depth-based design, in them. The metal is placed between the plates, and the plates are pressed up against each other, deforming the metal in the desired fashion. This may be coining or embossing or forming. A punch press is used for forming holes. Capping Presses form caps from rolls of aluminium foil at up to 660 per minute.
Progressive stamping is a manufacturing method that can encompass punching, coining, bending and several ways of modifying the metal, combined with an automatic feeding system. The feeding system pushes a coil of metal through all of the stations of a progressive stamping die. Each station performs one or more operations until a finished part is made per the requirements on the print. The final operation is a cut-off operation, which separates the finished part from the carrying web. The carrying web, along with metal that is punched away in previous operations, is considered scrap metal.
Power press with a fixed barrier guard
A brake press is a special type of machine press that bends sheet metal into shape.
A good example of the type of work a brake press can do is the backplate of a computer case. Other examples include brackets, frame pieces and electronic enclosures just to name a few. Some press brakes have CNC controls and can form parts with accuracy to a fraction of a millimetre. These machines can be dangerous considering the knife-edge bending dies and forces in excess of 4,000 kilonewtons (900,000 lbf) However in the hands of a skilled operator the machine presents minimum hazard.
Machine presses are used extensively around the world for shaping all kinds of metals to a desired shape. A typical toaster (for bread) has a metal case that has been bent and pressed into shape by a machine press.
Machine presses can be hazardous, so safety measures must always be taken. Injuries in a press may be permanent, because of the large forces used. Bimanual controls (controls the use of which requires both hands to be on the buttons to operate) are a very good way to prevent accidents, as are light sensors that keep the machine from working if the operator is in range of the die.
Types of presses
Allsteel hydro-mechanical press
Fine blanking press
Forging press (Hammer press)
Screw press or fly press
Rack-and-pinion press, for example, an arbor press
Historically, metal was shaped by hand using a hammer. Later, larger hammers were constructed to press more metal at once, or to press thicker materials. Often a smith would employ a helper or apprentice to swing the sledgehammer while the smith concentrated on positioning the workpiece. Adding windmill or steam power yielded still larger hammers such as steam hammers. Most modern machine presses use a combination of electric motors and hydraulics to achieve the necessary pressure. Along with the evolution of presses came the evolution of the dies used within them.
Shearing is a metalworking process which cuts stock without the formation of chips or the use of burning or melting. Strictly speaking, if the cutting blades are straight the process is called shearing; if the cutting blades are curved then they are shearing-type operations. The most commonly sheared materials are in the form of sheet metal or plates, however rods can also be sheared. Shearing-type operations include: blanking, piercing, roll slitting, and trimming.
A punch (or moving blade) is used to push the workpiece against the die (or fixed blade), which is fixed. Usually the clearance between the two is 5 to 10% of the thickness of the material, but dependent on the material. Clearance is defined as the separation between the blades, measured at the point where the cutting action takes place and perpendicular to the direction of blade movement. It affects the finish of the cut (burr) and the machine's power consumption. This causes the material to experience highly localized shear stresses between the punch and die. The material will then fail when the punch has moved 15 to 60% the thickness of the material, because the shear stresses are greater than the shear strength of the material and the remainder of the material is torn. Two distinct sections can be seen on a sheared workpiece, the first part being plastic deformation and the second being fractured. Because of normal inhomogeneities in materials and inconsistencies in clearance between the punch and die, the shearing action does not occur in a uniform manner. The fracture will begin at the weakest point and progress to the next weakest point until the entire workpiece has been sheared; this is what causes the rough edge. The rough edge can be reduced if the workpiece is clamped from the top with a die cushion. Above a certain pressure the fracture zone can be completely eliminated.
Straight shearing is done on sheet metal, coils, and plates. The machine used is called a squaring shear, power shear, or guillotine. The machine may be foot powered (or less commonly hand powered), or mechanically powered. It works by first clamping the material with a ram. A moving blade then comes down across a fixed blade to shear the material. For larger shears the moving blade may be set on an angle or "rocked" in order to shear the material progressively from one side to the other; this angle is referred to as the shear angle. This decreases the amount of force required, but increases the stroke. The amount of energy used is still the same. The moving blade may also be inclined 0.5 to 2.5°, this angle is called the rake angle, to keep the material from becoming wedged between the blades, however it compromises the squareness of the edge.
The design of press tools is an engineering compromise. A sharp edge, strength and durability are ideal, however a sharp edge is not very strong or durable so blades for metal work tend to be square-edged rather than knife-edged.
A punch press is a type of machine press used for forming and cutting material. It can be small and manually operated and hold one simple Die set, or be very large, CNC operated, and hold a much larger and complex die set.
A Die set consists of a set of (male) punches and (female) dies which, when pressed together, may form a hole in a workpiece or may deform the workpiece in some desired manner. The punches and dies are removable with the punch being temporarily attached to the end of a ram during the punching process. The ram moves up and down in a vertically linear motion.
Commonly machines are large metal framed equipment having two types of machine frames. A 'C' type frame or a 'portal' type frame. The C type commonly has the hydraulic ram at the top foremost part to enable the punching process to be carried out, whereas the portal frame is much akin to a complete circle with the ram being centered within the frame to stop frame deflection or distortion.
All punch press machines have a table or bed with brushes or rollers mounted in the tables to allow the sheet metal workpiece to traverse with low friction. Brushes are commonly used in production environments where minimal scratching to the workpiece is required, such as brushed aluminium or high polished materials.
The main bed of most machines is called the 'Y' Axis with the 'X' Axis being at right angles to that and allowed to traverse under CNC control. Dependent on the size of the machine, the beds and the sheet metal workpiece weight, then the motors required to move these axis tables can vary in size and power. Older styles of machines used DC motors to move, however with advances in technology, today's machine mostly use AC brush less motors for drives.
Punching is a shearing process in which a scrap slug is separated from the workpiece when the punch enter the die. The sidewall of the resulting hole displays a burnished area, rollover and die break.
The process of operation begins with the CNC controller commanding the drives to move a particular axis to a desired position. Once in position, the control initiates the punching sequence and pushes the ram to Bottom Dead Centre and returns it to Top Dead Center. the Origins of BDC and TDC go back to older machines where this was a pitman type press with a Pneumatic or Hyrdraulic operated clutch system. On today's machines BDC/TDC does not actually exist but is commonly used as a term to derive the top and bottom of a stroke of the ram. The Punch enters the Sheet metal, and pushes it through the die, obtaining the required shape of the punch and die set. This will form a slug of metal that is collected underneath the die and ejected through a bolster plate into a scrap container.
The whole punching process on modern machines is extremely fast compared to older pitman style machines and thus gives rise to increased production volumes. The sequence takes approximately 0.5 milli seconds to complete (variant from machine to machine and manufacturer) and signals to the control the next movement command allowed after the ram has reached the top of its stroke.
As a metal forming process, the punch press is used for the highest volume production. Cycle times are often measured in sheet yield as a percentage of waste to parts required ratios per sheet processed. As most programming is done by skilled CAD/CAM operators parts within the sheet workpiece are commonly nested.Machine setters are mostly used to set up tooling and programming but thereafter once the machine is running an operator of low skill can oversee its continued operation. Often one operator will monitor several punch presses simultaneously making this one of the lowest cost metal manufacturing processes.
Punch presses are usually referred to by their tonnage. In a production environment a 20 ton press is mostly the prevalent machine used today. The tonnage needed to cut and form the material is well known so sizing tooling for a specific job is a fairly straightforward task.
Most punch presses today are hydraulically powered, however there remains a legacy of older machines which are mechanically driven rams, meaning the power to the ram is provided by a heavy, constantly-rotating flywheel. The flywheel drives the ram using a Pitman arm. In the 19th century, the flywheels were powered by leather drive belts attached to line shafting, which in turn ran to a steam plant. In the modern workplace, the flywheel is powered by a large electric motor.
Mechanical punch press
Mechanical punch presses fall into two distinct types, depending on the type of clutch or braking system with which they are equipped. Generally older presses are "full revolution" presses that require a full revolution of the flywheel for them to come to a stop. This is because the braking mechanism depends on a set of raised keys or "dogs" to fall into matching slots to stop the flywheel. A full revolution clutch can only bring the flywheel to a stop at the same location- top dead center. Newer presses are often "part revolution" presses equipped with braking systems identical to the brakes on commercial trucks. When air is applied, a band-type brake expands and allows the flywheel to revolve. When the stopping mechanism is applied the air is bled, causing the clutch or braking system to close, stopping the flywheel in any part of its rotation.
Hydraulic punch press
Hydraulic punch presses, which power the ram with a hydraulic cylinder rather than a flywheel, and are either valve controlled or valve and feedback controlled. Valve controlled machines usually allow a one stroke operation allowing the ram to stroke up and down when commanded. Controlled feedback systems allow the ram to be proportionally controlled to within fixed points as commanded. This allows greater control over the stroke of the ram, and increases punching rates as the ram no longer has to complete the traditional full stroke up and down but can operate within a very short window of stroke.
Power press with a fixed barrier guard
A stamping press is a metalworking machine tool used to shape or cut metal by deforming it with a die.
A press has a press frame, a bolster plate and a ram. The bolster plate (or bed) is a large block of metal upon which the bottom portion of a die is clamped; the bolster plate is stationary. Large presses (like the ones used in the automotive industry) have a die cushion integrated in the bolster plate to apply blank holder forces. This is necessary when a single acting press is used for deep drawing. The ram is also a solid piece of metal that is clamped to the top portion of a (progressive) stamping die and provides the stroke (up and down movement). This action causes the die to produce parts from the metal being fed through it.
Stamping presses can be subdivided into mechanically driven presses and hydraulically driven presses. The most common mechanical presses use an eccentric drive to move the presses ram, whereas hydraulic cylinders are used in hydraulic presses. The nature of drive system determines the force progression during the rams stroke. The advantage of hydraulic presses is the constant press force during the stroke. Mechanical presses have a press force progression towards the bottom dead center depending on the drive- and hinge-system. Mechanical presses therefore can reach higher cycles per time and are usually more common in industrial press shops.
Another classification is single acting presses versus double (seldom triple) acting presses. Single acting presses have one single ram. Double acting presses have a subdivided ram, to manage for example blank holding (to avoid wrinkles) with one ram segment and the forming operation with the second ram segment.
Typically, presses are electronically linked (with a programmable logic controller) to an automatic feeder which feeds metal raw material through the die. The raw material is fed into the automatic feeder after it has been unrolled from a coil and put through a straightener. A tonnage monitor may be provided to observe the amount of force used for each stroke.
A brass vase spun by hand. Mounted to the lathe spindle is the mandrel for the body of the vase a shell sits on the "T" rest. The foreground shows the mandrel for the base. Behind the finished vase are the spinning tools used to shape the metal.
Metal spinning, also known as spin forming or spinning, is a metalworking process by which a disc or tube of metal is rotated at high speed and formed into an axially symmetric part. Spinning can be performed by hand or by a CNC lathe.
Metal spinning ranges from an artisan's specialty to the most advantageous way to form round metal parts for commercial applications. Artisans use the process to produce architectural detail, specialty lighting, decorative household goods and urns. Commercial applications include rocket nose cones, cookware, gas cylinders, brass instrument bells, and public waste receptacles. Virtually any ductile metal may be formed, from aluminum or stainless steel, to high-strength, high-temperature alloys. The diameter and depth of formed parts are limited only by the size of the equipment available.
The spinning process is fairly simple. A mandrel, also known as a form, is mounted in the drive section of a lathe. A pre-sized metal disk is then clamped against the mandrel by a pressure pad, which is attached to the tailstock. The mandrel and workpiece are then rotated together at high speeds. A localized force is then applied to the workpiece to cause it to flow over the mandrel. The force is usually applied via various levered tools. Simple workpieces are just removed from the mandrel, but more complex shapes may require a multi-piece mandrel. Extremely complex shapes can be spun over ice forms, which then melt away after spinning. Because the final diameter of the workpiece is always less than the starting diameter the workpiece must thicken, elongated radially, or buckle circumferentially.
A more involved process, known as reducing or necking, allows a spun workpiece to include reentrant geometries. If surface finish and form are not critical, then the workpiece is "spun on air"; no mandrel is used. If the finish or form are critical then an eccentrically mounted mandrel is used.
"Hot Spinning". This process involves spinning a piece of metal on a lathe and with high heat from a torch the metal is heated. Once heated, the metal is then shaped as the tool on the lathe presses against the heated surface forcing it to distort as it spins. Parts can then be shaped or necked down to a smaller diameter with little force exerted, providing a seamless shoulder.
The basic hand metal spinning tool is called a spoon, though many other tools (be they commercially produced, ad hoc, or improvised) can be used to effect varied results. Spinning tools can be made of hardened steel for using with aluminium or solid brass for spinning stainless steel or mild steel.
Some metal spinning tools are allowed to spin on bearings during the forming process. This reduces friction and heating of the tool, extending tool life and improving surface finish. Rotating tools may also be coated with thin film of ceramic to prolong tool life. Rotating tools are commonly used during CNC metal spinning operations.
Commercially, rollers mounted on the end of levers are generally used to form the material down to the mandrel in both hand spinning and CNC metal spinning. Rollers vary in diameter and thickness depending the intended use. The wider the roller the smoother the surface of the spinning; the thinner rollers can be used to form smaller radii.
Cutting of the metal is done by hand held cutters, often foot long hollow bars with tool steel shaped/sharpened files attached. In CNC applications, traditional carbide or tool steel cut-off tools are used.
The mandrel does not incur excessive forces, as found in other metalworking processes, so it can be made from wood, plastic, or ice. For hard materials or high volume use, the mandrel is usually made of metal.
Advantages & disadvantages
Several operations can be performed in one set-up. Work pieces may have re-entrant profiles and the profile in relation to the center line virtually unrestricted.
Forming parameters and part geometry can be altered quickly, at less cost than traditional metal forming techniques. Tooling and production costs are also comparatively low. Spin forming is easily automated and an effective production method for prototypes as well as high production runs.
Other methods of forming round metal parts include hydroforming, stamping and forging or casting. Hydroforming and stamping generally have a higher fixed cost, but a lower variable cost than metal spinning. Forging or casting have a comparable fixed cost, but generally a higher variable cost. As machinery for commercial applications has improved, parts are being spun with thicker materials in excess of 1" thick steel. Conventional spinning also wastes a considerably smaller amount of material than other methods.
Objects can be built using one piece of material to produce parts without seams. Without seams, a part can withstand higher internal or external pressure exerted on it. For example: scuba tanks, co2 cartridges, and oxyacetylene tanks.
One disadvantage of metal spinning is if a crack forms or the object has a dent, it either must be thrown away, or a lot of work involved in fixing it; neither are cost effective.
Forging is the term for shaping metal by using localized compressive forces. Cold forging is done at room temperature or near room temperature. Hot forging is done at a high temperature, which makes metal easier to shape and less likely to fracture. Warm forging is done at intermediate temperature between room temperature and hot forging temperatures. Forged parts can range in weight from less than a kilogram to 170 metric tons. Forged parts usually require further processing to achieve a finished part.
Forging is one of the oldest known metalworking processes.
Forging was done historically by a smith using hammer and anvil, and though the use of water power in the production and working of iron dates to the 12th century, the hammer and anvil are not obsolete. The smithy has evolved over centuries to the forge shop with engineered processes, production equipment, tooling, raw materials and products to meet the demands of modern industry.
In modern times, industrial forging is done either with presses or with hammers powered by compressed air, electricity, hydraulics or steam. These hammers are large, having reciprocating weights in the thousands of pounds. Smaller power hammers, 500 lb (230 kg) or less reciprocating weight, and hydraulic presses are common in art smithies as well. Steam hammers are becoming obsolete.
Advantages and disadvantages
Forging results in metal that is stronger than cast or machined metal parts. This stems from the grain flow caused through forging. As the metal is pounded the grains deform to follow the shape of the part, thus the grains are unbroken throughout the part. Some modern parts take advantage of this for a high strength-to-weight ratio.
Many metals are forged cold, but iron and its alloys are almost always forged hot. This is for two reasons: first, if work hardening were allowed to progress, hard materials such as iron and steel would become extremely difficult to work with; secondly, steel can be strengthened by other means than cold-working, thus it is more economical to hot forge and then heat treat. Alloys that are amenable to precipitation hardening, such as most alloys of aluminium and titanium, can also be hot forged then hardened. Other materials must be strengthened by the forging process itself.
Hot forging is defined as working a metal above its recrystallization temperature. The main advantage of hot forging is that as the metal is deformed the strain-hardening effects are negated by the recrystallization process.
Cold forging is defined as working a metal below its recrystallization temperature, but usually around room temperature. If the temperature is above 0.3 times the melting temperature (on an absolute scale) then it qualifies as warm forging.
A cross-section of a forged connecting rod that has been etched to show the grain flow.
There are many different kinds of forging processes available, however they can be grouped into three main classes:
Drawn out: length increases, cross-section decreases
Upset: Length decreases, cross-section increases
Squeezed in closed compression dies: produces multidirectional flow
Common forging processes include: roll forging, swaging, cogging, open-die forging, impression-die forging, press forging, automatic hot forging and upsetting.
Open-die drop-hammer forging
Open-die forging is also known as smith forging. In open-die forging a hammer comes down and deforms the workpieces, which is placed on a stationary anvil. Open-die forging gets its name from the fact that the dies (the working surfaces of the forge that contract the workpiece) do not enclose the workpiece, allowing it to flow except where contacted by the dies. Therefore the operator needs to orient and position the workpiece to get the desired shape. The dies are usually flat in shape, but some have a specially shaped surface for specialized operations. For instance, the die may have a round, concave, or convex surface or be a tool to form holes or be a cut-off tool.
Open-die forging lends itself to short runs and is appropriate for art smithing and custom work. Other times open-die forging is used to rough shape ingots to prepare them for further operations. This can also orient the grains to increase strength in the required direction.
Impression-die drop-hammer forging
Impression-die forging is also called closed-die forging. In impression-die work metal is placed in a die resembling a mold, which is attached to the anvil. Usually the hammer die is shaped as well. The hammer is then dropped on the workpiece, causing the metal to flow and fill the die cavities. The hammer is generally in contact with the workpiece on the scale of milliseconds. Depending on the size and complexity of the part the hammer may be dropped multiple times in quick succession. Excess metal is squeezed out of the die cavities; this is called flash. The flash cools more rapidly than the rest of the material; this cool metal is stronger than the metal in the die so it helps prevent more flash from forming. This also forces the metal to completely fill the die cavity. After forging the flash is trimmed off.
In commercial impression-die forging the workpiece is usually moved through a series of cavities in a die to get from an ingot to the final form. The first impression is used to distribute the metal into the rough shape in accordance to the needs of later cavities; this impression is called a edging, fullering, or bending impression. The following cavities are called blocking cavities in which the workpiece is working into a shape that more and more resembles the final product. These stages usually impart the workpiece with generous bends and large fillets. The final shape is forged in a final or finisher impression cavity. If there is only a short run of parts to be done it may be more economical for the die to lack a final impression cavity and rather machine the final features.
Impression-die forging has been further improved in recent years through increased automation which includes induction heating, mechanical feeding, positioning and manipulation, and the direct heat treatment of parts after forging.
One variation of impression-die forging is called flashless forging, or true closed-die forging. In this type of forging the die cavities are completely closed, which keeps the workpiece from forming flash. The major advantage to this process is that less metal is lost to flash. Flash can account for 20 to 45% of the starting material. The disadvantages of this process included: additional cost due to a more complex die design, the need for better lubrication, and better workpiece placement.
There are other variations of part formation that integrate impression-die forging. One method incorporates casting a forging preform from liquid metal. The casting is removed after it has solidified, but while still hot. It is then finished in a single cavity die. The flash is trimmed and then quenched to room temperature to harden the part. Another variation follows the same process as outlined above, except the preform is produced by the spraying deposition of metal droplet into shaped collectors (similar to the Osprey process).
Closed-die forging has a high initial cost due to the creation of dies and required design work to make working die cavities. However, it has low recurring costs for each part, thus forgings become more economical with more volume. This is one of the major reasons forgings are often used in the automotive and tool industry. Another reason forgings are common in these industrial sectors is because forgings generally have about a 20% higher strength to weight ratio compared to cast or machined parts of the same material.
Design of impression-die forgings and tooling
Forging dies are usually made of high-alloy or tool steel. Dies must be impact resistant, wear resistant, maintain strength at high temperatures, and have the ability to withstand cycles of rapid heating and cooling. In order to produce a better, more economical die the following rules should be followed:
The dies should part along a single, flat plane if at all possible, If not the parting plan should follow the contour of the part.
The parting surface should be a plane through the center of the forging and not near an upper or lower edge.
Adequate draft should be provided; a good guideline is at least 3° for aluminum and 5° to 7° for steel
Generous fillets and radii should be used
Ribs should be low and wide
The various sections should be balanced to avoid extreme difference in metal flow
Full advantage should be taken of fiver flow lines
Dimensional tolerances should not be closer than necessary
The dimensional tolerances of a steel part produced using the impression-die forging method are outlined in the table below. It should be noted that the dimensions across the paring plane are affected by the closure of the dies, and are therefore dependent die wear and the thickness of the final flash. Dimensions that are completely contained within a single die segment or half can be maintained at a significantly greater level of accuracy.
Dimensional tolerances for impression-die forgings
Mass [kg (lbs)] Minus tolerance [mm (in.)] Plus tolerance [mm (in.)]
0.45 (1) 0.15 (0.006) 0.48 (0.018)
0.91 (2) 0.20 (0.008) 0.61 (0.024)
2.27 (5) 0.25 (0.010) 0.76 (0.030)
4.54 (10) 0.28 (0.011) 0.84 (0.033)
9.07 (20) 0.33 (0.013) 0.99 (0.039)
22.68 (50) 0.48 (0.019) 1.45 (0.057)
45.36 (100) 0.74 (0.029) 2.21 (0.087)
A lubricant is always used when forging to reduce friction and wear. It is also used to as a thermal barrier to restrict heat transfer from the workpiece to the die. Finally the lubricant acts as a parting compound to prevent the part from sticking in one of the dies.
Press forging is variation of drop-hammer forging. Unlike drop-hammer forging, press forges work slowly by applying continuous pressure or force. The amount of time the dies are in contact with the workpiece is measured in seconds (as compared to the milliseconds of drop-hammer forges). The press forging operation can be done either cold or hot.
The main advantage of press forging, as compared to drop-hammer forging, is its ability to deform the complete workpiece. Drop-hammer forging usually only deforms the surfaces of the workpiece in contact with the hammer and anvil; the interior of the workpiece will stay relatively undeformed. Another advantage to the process includes the knowledge of the new parts strain rate. We specifically know what kind of strain can be put on the part, because the compression rate of the press forging operation is controlled. There are a few disadvantages to this process, most stemming from the workpiece being in contact with the dies for such an extended period of time. The operation is a time consuming process due to the amount of steps and how long each of them take. The workpiece will cool faster because the dies are in contact with workpiece; the dies facilitate drastically more heat transfer than the surrounding atmosphere. As the workpiece cools it becomes stronger and less ductile, which may induce cracking if deformation continues. Therefore heated dies are usually used to reduce heat loss, promote surface flow, and enable the production of finer details and closer tolerances. The workpiece may also need to be reheated. When done in high productivity, press forging is more economical than hammer forging. The operation also creates closer tolerances. In hammer forging a lot of the work is absorbed by the machinery, when in press forging, the greater percentage of work is used in the work piece. Another advantage is that the operation can be used to create any size part because there is no limit to the size of the press forging machine. New press forging techniques have been able to create a higher degree of mechanical and orientation integrity. By the constraint of oxidation to the outer most layers of the part material, reduced levels of microcracking take place in the finished part.
Press forging can be used to perform all types of forging, including open-die and impression-die forging. Impression-die press forging usually requires less draft than drop forging and has better dimensional accuracy. Also, press forgings can often be done in one closing of the dies, allowing for easy automation.
Upset forging increases the diameter of the workpiece by compressing its length. Based on number of pieces produced this is the most widely used forging process. A few examples of common parts produced using the upset forging process are engine valves, couplings, bolts, screws, and other fasteners.
Upset forging is usually done in special high speed machines called crank presses, but upsetting can also be done in a vertical crank press or a hydraulic press. The machines are usually set up to work in the horizontal plane, to facilitate the quick exchange of workpieces from one station to the next. The initial workpiece is usually wire or rod, but some machines can accept bars up to 25 cm (10 in.) in diameter and a capacity of over 1000 tons. The standard upsetting machine employs split dies that contain multiple cavities. The dies open enough to allow the workpiece to move from one cavity to the next; the dies then close and the heading tool, or ram, then moves longitudinally against the bar, upsetting it into the cavity. If all of the cavities are utilized on every cycle then a finished part will be produced with every cycle, which is why this process is ideal for mass production.
The following three rules must be followed when designing parts to be upset forged:
The length of unsupported metal that can be upset in one blow without injurious buckling should be limited to three times the diameter of the bar.
Lengths of stock greater than three times the diameter may be upset successfully provided that the diameter of the upset is not more than 1.5 times the diameter of the stock.
In an upset requiring stock length greater than three times the diameter of the stock, and where the diameter of the cavity is not more than 1.5 times the diameter of the stock, the length of unsupported metal beyond the face of the die must not exceed the diameter of the bar.
Automatic hot forging
The automatic hot forging process involves feeding mill-length steel bars (typically 7 m or 24 ft long) into one end of the machine at room temperature and hot forged products emerge from the other end. This all occurs very quickly; small parts can be made at a rate of 180 parts per minute (ppm) and larger can be made at a rate of 90 ppm. The parts can be solid or hollow, round or symmetrical, up to 6 kg (12 lbs), and up to 18 cm (7 in.) in diameter. The main advantages to this process are its high output rate and ability to accept low cost materials. Little labor is required to operate the machinery. There is no flash produced so material savings are between 20 - 30% over conventional forging. The final product is a consistent 1050 °C (1900 °F) so air cooling will result in a part that is still easily machinable (the advantage being the lack of annealing required after forging). Tolerances are usually ±0.3 mm (±0.012 in.), surfaces are clean, and draft angles are 0.5 to 1°. Tool life is nearly double that of conventional forging because contact times are on the order of 6/100 of a second. The downside to the process is it only feasible on smaller symmetric parts and cost; the initial investment can be over $10 million, so large quantities are required to justify this process.
The process starts by heating up the bar to 1200 to 1300 °C (2200 to 2350 °F) in less than 60 seconds using high power induction coils. It is then descaled with rollers, sheared into blanks, and transferred several successive forming stages, during which it is upset, preformed, final forged, and pierced (if necessary). This process can also be couple with high speed cold forming operations. Generally, the cold forming operation will do the finishing stage so that the advantages of cold-working can be obtained, while maintaining the high speed of automatic hot forging.
Examples of parts made by this process are: wheel hub unit bearings, transmission gears, tapered roller bearing races, stainless steel coupling flanges, and neck rings for LP gas cylinders. Manual transmission gears are an example of automatic hot forging used in conjunction with cold working.
Roll forging is a process where round or flat bar stock is reduced in thickness and increased in length. Roll forging is performed using two cylindrical or semi-cylindrical rolls, each containing one or more shaped grooves. A heated bar is inserted into the rolls and when it hits a stop the rolls rotate and the bar is progressively shaped as it is rolled out of the machine. The work piece is then transferred to the next set of grooves or turned around and reinserted into the same grooves. This continues until the desired shape and size is achieved. The advantage of this process is there is no flash and it imparts a favorable grain structure into the workpiece.
Examples of products produced using this method include axles, tapered levers and leaf springs.
Net-shape and near-net-shape forging
This process is also known as precision forging. This process was developed to minimize cost and waste associated with post forging operations. Therefore the final product from a precision forging needs little to no final machining. Cost savings are gained from the use of less material, and thus less scrap, the overall decrease in energy used, and the reduction or elimination of machining. Precision forging also requires less of a draft, 1° to 0°. The downsize of this process is its cost, therefore it is only implemented if significant cost reduction can be achieved.
Unlike the above processes, induction forging is based on the type of heating style used. Many of the above processes can be used in conjunction with this heating method. Equipment
(a) Material flow of a conventionally forged disc; (b) Material flow of a impactor forged disc.
The most common type of forging equipment is the hammer and anvil. Principles behind the hammer and anvil are still used today in drop-hammer equipment. The principle behind the machine is very simple--raise the hammer and then drop it or propel it into the workpiece, which rests on the anvil. The main variations between drop-hammers are in the way the hammer is powered; the most common being air and steam hammers. Drop-hammers usually operate in a vertical position. The main reason for this is excess energy (energy that isn't used to deform the workpiece) that isn't released as heat or sound needs to be transmitted to the foundation. Moreover, a large machine base is needed to absorb the impacts.
To overcome some of the shortcomings of the drop-hammer, the counterblow machine or impactor is used. In a counterblow machine both the hammer and anvil move and the workpiece is held between them. Here excess energy becomes recoil. This allows the machine to work horizontally and consist of a smaller base. Other advantages include less noise, heat and vibration. It also produces a distinctly different flow pattern. Both of these machines can be used for open die or closed die forging.
A forging press, often just called a press, is used for press forging. There are two main types: mechanical and hydraulic presses. Mechanical presses function by using cams, cranks or toggles to produce a preset (a predetermined force at a certain location in the stroke) and reproducible stroke. Due to the nature of this type of system difference forces are available at different stroke positions. Mechanical presses are faster than their hydraulic counterparts (up to 50 strokes per minute). Their capacities range from 3 to 160 MN (300 to 18,000 tons). Hydraulic presses use fluid pressure and a piston to generate force. The advantages of a hydraulic press over a mechanical press are its flexibility and greater capacity. The disadvantages are that it is slower, larger, and more costly to operate.
The roll forging, upsetting, and automatic hot forging processes all use specialized machinery.
Pipe and tube bender
Tube and pipe benders are machines which bend tube, pipe and solid metals. Pipe bending machines can either be human powered, hydraulic assisted, or hydraulic motor driven. In the pipe bending operation the tube may be supported internally or externally to preserve the cross section of the pipe. In operations where there is flexibility in the shape of the pipe, the pipe does not need to be supported, however there will be some deformation in the cross section of the pipe.
Tube Bending Process
Tube bending as a process starts with loading a tube is loaded into a pipe bender and is clapped into place by two dies, the clamping block and the forming die and also loosely held by two other dies, the wiper die and the pressure die. After that has been completed the mechanist will start the bender, while the tube is pulled around the forming die creating a elbow, U-bend, 2-D or 3-D bent tubes. Three dimensional tube is a tube with each opening on different planes. Two dimensional tube is a tube with each opening on the same plane. Also the foot pound power required to bend certain tubes can range 4ft-lbs to 300ft-lbs depending on the diameter and material such as, steel and copper.
Many times after a tube is bent the finish on the in side of the bend will have wrinkles and a stretched wall on the outside wall. The finish on the inner side usually does not wrinkle due to mandrels used in the bending process. Although the inner side of the bend does not wrinkle often the outer side of the bend most often thins due to the stress and strain put on the tube while being bent, but is not thin enough to worry in most cases.Mandrels
A mandrel is a steel rod or linked ball inserted into the tube while it is being bent to give the tube extra support to reduce wrinkling and braking the tube during this process. The different types of mandrels are as follows.
Plug mandrel, a solid rod used on normal bends.
Form mandrel, a solid rod with curved end used on bend when more support is need.
Ball mandrel without cable, unlinked steel ball bearings inserted into tube, used on critical and precise bends.
Ball mandrel with cable, linked ball bearings inserted into tube, used on critical bend and precise bends.
Sand, sand packed into tube, most non used method for bending support.
Probably the first bending process used on cold pipes and tubing. In this process a die in the shape of the bend is pressed against the pipe forcing the pipe to fit the shape of the bend. Because the pipe is not supported internally there is some deformation of the shape of the pipe giving an ovular cross section. This process is used where a consistent cross section of the pipe is not required.
Rotary draw benders
Rotary draw benders (RDB) are precise in that they bend using tooling or "die sets" which have a constant center line radius (CLR). The die set consists of two parts: The former die creates the shape to which the material will be bent. The counter die does the work of pushing the material into the former die while traveling the length of the bend. Rotary draw benders can be programmable to store multiple bend jobs with varying degrees of bending. Often a positioning index table (IDX) is attached to the bender allowing the operator to reproduce complex bends which can have multiple bends and differing planes.
Rotary draw benders are the most popular machines for use in bending tube, pipe and solids for applications like: handrails, frames, motor vehicle roll cages, handles, lines and much more. Rotary draw benders create aesthetically pleasing bends when the right tooling is matched to the application.
Mandrel benders (MB) are machines designed to bend tube to a tight radius with little to no change in the shape of the tube. Typically a mandrel bender is needed when bending thin wall tubing to a radius much tighter than the material can bend without collapsing or distorting. The word mandrel refers to the part of the tooling set up which is inserted into the tube and remains inside the tube during the bend process. This internal mandrel helps to support the shape of the wall when bending. Performance automotive or motorcycle exhaust pipe is a common application for a mandrel bender.
An induction coil is placed around a small section of the pipe at the bend point. It is then heated to between 800 and 2,200 degrees Fahrenheit. While the pipe is hot, pressure is placed on the pipe to bend it. The pipe is then quenched with either air or water spray. Heat-Induction bending is used on large pipes such as freeway signs, power plants, and petroleum pipe lines.
During the roll bending process the pipe, extrusion, or solid is passed through a series of rollers (typically 3) that apply pressure to the pipe gradually changing the bend radius in the pipe. The pyramid style roll benders have one moving roll, usually the top roll. Double pinch type roll benders have two adjustable rolls, usually the bottom rolls, and a fixed top roll. This method of bending causes very little deformation in the cross section of the pipe. This process is suited to producing coils of pipe as well as long gentle bends like those used in truss systems.
Sand-packing / hot-slab forming
In the sand packing process the pipe is filled with fine sand and the ends are capped. The pipe is then heated in a furnace to 1600 °F or higher. The pipe is then placed on a slab with pins set in it. The pipe is then bent around the pins using a winch, crane, or some other mechanical force. The sand in the pipe minimizes distortion in the pipe cross section.
These are strong but flexible springs inserted into a pipe to support the pipe walls during manual bending. They have diameters only slightly less than the internal diameter of the pipe to be bent. They are only suitable for bending 15 mm and 22 mm soft copper pipe (typically used in household plumbing).
The spring is pushed into the pipe until its center is roughly where the bend is to be. A length of flexible wire can be attached to the end of the spring to facilitate its removal. The pipe is generally held against the flexed knee, and the ends of the pipe are pulled up to create the bend. To make it easier to retrieve the spring from the pipe, it is a good idea to bend the pipe slightly more than required, and then slacken it off a little. They are less cumbersome than rotary benders, but are not suitable for bending short lengths of piping when it is difficult to get the requires leverage on the pipe ends.
Bending springs for smaller diameter pipes (10 mm copper pipe) slide over the pipe instead of inside.
All electric tube bending + cutting
One kinds of mandrel benders.This type CNC tube benders designed for Bending and Cutting in 1 pipe bender. Equipped with all Electric axis, it offers boost bending facility for 1D bending and minimum wall thinning with cutoff after each part is finished. The superior performance allows for speed up production of many parts from a single tube length.
This CNC tube bending machine is ideal for the high volume producer particularly in the field of exhaust pipe systems, manifolds and hydraulic connectors.
A working blacksmith in 1970
A smith, or metalsmith, is a person involved in the shaping of metal objects.
In pre-industrialized times, smiths held high or special social standing since they supplied the metal tools needed for farming (especially the plough) and warfare.
Etymology of smith
Illustration by Theodor Kittelsen for Johan Herman Wessel's The Smith and the Baker
The word smith is cognate with the somewhat archaic English word, "smite", meaning "to hit" or "to strike". Originally, smiths practiced their crafts by forming metal with hammer blows.
As an English suffix, -smith connotes a meaning of specialized craftsmen — for example, wordsmith and tunesmith are nouns synonymous with writer or songwriter, respectively.
Types of smiths
Types of smiths include:
a blacksmith works with iron and steel; (this is what is usually meant when referring just to "Smith")
an arrowsmith forges arrow heads;
a bladesmith forges knives, swords, and other blades;
a coppersmith, or brownsmith, works with copper;
a fendersmith makes and repairs the metal fender before fireplaces, protecting rugs and furniture in mansions and fine estates, and frequently cares for the fires as well;
a goldsmith works with gold;
a gunsmith works with guns;
a locksmith works with locks;
a pewtersmith works with pewter;
a silversmith, or brightsmith, works with silver;
a tinsmith, tinner, or tinker works with light metal (such as tinware) and can refer to someone who deals in tinware;
a swordsmith is a bladesmith who forges only swords;
a whitesmith works with white metal (tin) and can refer to someone who polishes or finishes the metal rather than forging it.
Sometimes, terms similar to the above are created metaphorically, for categories of people not working with metal at all - for example, "songsmith".
Artisans and craftpeople
The ancient traditional tool of the smith is a forge or smithy, which is a furnace designed to allow compressed air (through a bellows) to superheat the inside, allowing for efficient melting, soldering and annealing of metals. Today, this tool is still widely used by blacksmiths as it was traditionally.
The term, metalsmith, often refers to artisans and craftpersons who practice their craft in many different metals, including gold, copper and silver. Jewelers often refer to their craft as metalsmithing, and many universities offer degree programs in metalsmithing, jewelry and blacksmithing under the auspices of their fine arts programs.
Machinists are metalsmiths who produce high-precision parts and tools. The most advanced of these tools, CNC machines, are computer controlled and largely automated.
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating and maintaining a suitable temperature, and then cooling. Annealing is used to induce ductility, relieve internal stresses, refine the structure and improve cold working properties.
In the cases of copper, steel, and brass this process is performed by substantially heating the material (generally until glowing) for a while and allowing it to cool slowly. In this fashion the metal is softened and prepared for further work such as shaping, stamping, or forming.
Thermodynamics of annealing
Annealing occurs by the diffusion of atoms within a solid material, so that the material progresses towards its equilibrium state. Heat is needed to increase the rate of diffusion by providing the energy needed to break bonds. The movement of atoms has the effect of redistributing and destroying the dislocations in metals and (to a lesser extent) in ceramics. This alteration in dislocations allows metals to deform more easily, so increases their ductility.
The amount of process-initiating Gibbs free energy in a deformed metal is also reduced by the annealing process. In practice and industry, this reduction of Gibbs free energy is termed "stress relief".
The relief of internal stresses is a thermodynamically spontaneous process; however, at room temperatures, it is a very slow process. The high temperatures at which the annealing process occurs serve to accelerate this process.
The reaction facilitating the return of the cold-worked metal to its stress-free state has many reaction pathways, mostly involving the elimination of lattice vacancy gradients within the body of the metal. The creation of lattice vacancies are governed by the Arrhenius equation, and the migration/diffusion of lattice vacancies are governed by Fick’s laws of diffusion.
Mechanical properties, such as hardness and ductility, change as dislocations are eliminated and the metal's crystal lattice is altered. On heating at specific temperature and cooling it is possible to bring the atom at the right lattice site and new grain growth can improve the mechanical properties.
Stages of annealing
There are three stages in the annealing process, with the first being the recovery phase, which results in softening of the metal through removal of crystal defects (the primary type of which is the linear defect called a dislocation) and the internal stresses which they cause. Recovery phase covers all annealing phenomena that occur before the appearance of new strain-free grains. The second phase is recrystallization, where new strain-free grains nucleate and grow to replace those deformed by internal stresses. If annealing is allowed to continue once recrystallization has been completed, grain growth will occur, in which the microstructure starts to coarsen and may cause the metal to have less than satisfactory mechanical properties.
Annealing in a controlled atmosphere
The low temperature of annealing (about 50 °F above C3 line) may result in oxidation of the metal’s surface, resulting in scale. If scale is to be avoided, annealing is carried out in an oxygen-, carbon-, and nitrogen-free atmosphere (to avoid oxidation, carburization, and nitriding respectively) such as endothermic gas (a mixture of carbon monoxide, hydrogen gas, and nitrogen).
The magnetic properties of mu-metal (Espey cores) are introduced by annealing the alloy in a hydrogen atmosphere.
Diffusion annealing of semiconductors
In the semiconductor industry, silicon wafers are annealed, so that dopant atoms, usually boron, phosphorus or arsenic, can diffuse into substitutional positions in the crystal lattice, resulting in drastic changes in the electrical properties of the semiconducting material.
Specialized annealing cycles
Normalization is an annealing process in which a metal is cooled in air after heating.
This process is typically confined to hardenable steel. It is used to refine grains which have been deformed through cold work, and can improve ductility and toughness of the steel. It involves heating the steel to just above its upper critical point. It is soaked for a short period then allowed to cool in air. Small grains are formed which give a much harder and tougher metal with normal tensile strength and not the maximum ductility achieved by annealing.
Process annealing, also called "intermediate annealing", "subcritical annealing", or "in-process annealing", is a heat treatment cycle that restores some of the ductility to a work piece allowing it be worked further without breaking. Ductility is important in shaping and creating a more refined piece of work through processes such as rolling, drawing, forging, spinning, extruding and heading. The piece is heated to a temperature typically below the austenizing temperature, and held there for long enough to relieve stresses in the metal. The piece is finally cooled slowly in to room temperature. It is then ready again for additional cold working. This can also be used to ensure there is reduced risk of distortion of the work piece during machining, welding, or further heat treatment cycles.
The temperature range for process annealing is ranges from 500 ºF to 1400 ºF, depending on the alloy in question.
Full annealing temperature ranges
A full anneal typically results in the most ductile state a metal can assume for metal alloy. To perform a full anneal, a metal is heated to its annealing point (about 50°c above the austenic temperature as graph shows) and held for sufficient time to allow the material to fully austenitize, to form austenite or austenite-cementite grain structure. The material is then allowed to cool slowly so that the equilibrium microstructure is obtained. In some cases this means the material is allowed to air cool. In other cases the material is allowed to furnace cool. The details of the process depend on the type of metal and the precise alloy involved. In any case the result is a more ductile material that has greater stretch ratio and reduction of area properties but a lower yield strength and a lower tensile strength. This process is also called LP annealing for lamellar pearlite in the steel industry as opposed to a process anneal which does not specify a microstructure and only has the goal of softening the material. Often material that is annealed will be machined and then be followed by further heat treatment to obtain the final desired properties.
Short cycle anneal
Short cycle annealing is used for turning normal ferrite into malleable ferrite. It consists of heating, cooling, and then heating again from 4 to 8 hours.
Heat treatment is a method used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering and quenching. It is noteworthy that while the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.
Heat treatment of metals and alloys
Metallic materials consist of a microstructure of small crystals called "grains" or crystallites. The nature of the grains (i.e. grain size and composition) is one of the most effective factors that can determine the overall mechanical behavior of the metal. Heat treatment provides an efficient way to manipulate the properties of the metal by controlling rate of diffusion, and the rate of cooling within the microstructure.
Complex heat treating schedules are often devised by metallurgists to optimize an alloy's mechanical properties. In the aerospace industry, a super alloy may undergo five or more different heat treating operations to develop the desired properties. This can lead to quality problems depending on the accuracy of the furnace's temperature controls and timer.
Annealing is a technique used to recover cold work and relax stresses within a metal. Annealing typically results in a soft, ductile metal. When an annealed part is allowed to cool in the furnace, it is called a "full anneal" heat treatment. When an annealed part is removed from the furnace and allowed to cool in air, it is called a "normalizing" heat treatment. During annealing, small grains recrystallize to form larger grains. In precipitation hardening alloys, precipitates dissolve into the matrix, "solutionizing" the alloy.
Typical annealing processes include, "normalizing", "stress relief" annealing to recover cold work, and full annealing.
Hardening and tempering (quenching and tempering)
To harden by quenching, a metal (usually steel or cast iron) must be heated into the austenitic crystal phase and then quickly cooled. Depending on the alloy and other considerations (such as concern for maximum hardness vs. cracking and distortion), cooling may be done with forced air or other gas (such as nitrogen), oil, polymer dissolved in water, or brine. Upon being rapidly cooled, a portion of austentite (dependent on alloy composition) will transform to martensite, a hard brittle crystalline structure. The quenched hardness of a metal depends upon its chemical composition and quenching method. Cooling speeds, from fastest to slowest, go from polymer (i.e.silicon), brine, fresh water, oil, and forced air. However, quenching a certain steel too fast can result in cracking, which is why High-tensile steels like AISI 4140 should be quenched in oil, tool steels such as 2767 or H13 hot work tool steel should be quenched in forced air, and low alloy or medium-tensile steels such as XK1320 or AISI 1040 should be quenched in brine or water. However, metals such as austenitic stainless steel (304, 316), and copper, produce an opposite effect when these are quenched; they anneal. Austenitic stainless steels must be quench-annealed to become fully corrosion resistant, as they work-harden significantly.
Untempered martensite, while very hard and strong, is too brittle to be useful for most applications. A method for alleviating this problem is called tempering. Most applications require that quenched parts be tempered (heat treated at a low temperature, often three hundred degree Fahrenheit or one hundred fifty degrees Celsius) to impart some toughness. Higher tempering temperatures (may be up to thirteen hundred degrees Fahrenheit, depending on alloy and application) are sometimes used to impart further ductility, although some yield strength is lost.
Some metals are classified as precipitation hardening metals. When a precipitation hardening alloy is quenched, its alloying elements will be trapped in solution, resulting in a soft metal. Aging a "solutionized" metal will allow the alloying elements to diffuse through the microstructure and form intermetallic particles. These intermetallic particles will nucleate and fall out of solution and act as a reinforcing phase, thereby increasing the strength of the alloy. Alloys may age "naturally" meaning that the precipitates form at room temperature, or they may age "artificially" when precipitates only form at elevated temperatures. In some applications, naturally aging alloys may be stored in a freezer to prevent hardening until after further operations - assembly of rivets, for example, may be easier with a softer part.
Examples of precipitation hardening alloys include 2000 series, 6000 series, and 7000 series aluminium alloy, as well as some superalloys and some stainless steels.
Some techniques allow different areas of a single object to receive different heat treatments. This is called differential hardening. It is common in high quality knives and swords. The Chinese jian is one of the earliest known examples of this, and the Japanese katana the most widely known. The Nepalese Khukuri is another example.
Precipitation hardening, also called age hardening or dispersion hardening, is a heat treatment technique used to strengthen malleable materials, including most structural alloys of aluminium, magnesium, nickel and titanium, and some stainless steels. It relies on changes in solid solubility with temperature to produce fine particles of an impurity phase, which impede the movement of dislocations, or defects in a crystal's lattice. Since dislocations are often the dominant carriers of plasticity, this serves to harden the material. The impurities play the same role as the particle substances in particle-reinforced composite materials. Just as the formation of ice in air can produce clouds, snow, or hail, depending upon the thermal history of a given portion of the atmosphere, precipitation in solids can produce many different sizes of particles, which have radically different properties. Unlike ordinary tempering, alloys must be kept at elevated temperature for hours to allow precipitation to take place. This time delay is called ageing.
Note that two different heat treatments involving precipitates can alter the strength of a material: solution heat treating and precipitation heat treating. Solution heat treating involves formation of a single-phase solid solution via quenching and leaves a material softer. Precipitation heat treating involves the addition of impurity particles to increase a material's strength. Precipitation hardening via precipitation heat treatment is the main topic of discussion in this article.
Kinetics versus thermodynamics
This technique exploits the phenomenon of supersaturation, and involves careful balancing of the driving force for precipitation and the thermal activation energy available for both desirable and undesirable processes.
Nucleation occurs at a relatively high temperature (often just below the solubility limit) so that the kinetic barrier of surface energy can be more easily overcome and the maximum number of precipitate particles can form. These particles are then allowed to grow at lower temperature in a process called aging. This is carried out under conditions of low solubility so that thermodynamics drive a greater total volume of precipitate formation.
Diffusion's exponential dependence upon temperature makes precipitation strengthening, like all heat treatments, a fairly delicate process. Too little diffusion (under aging), and the particles will be too small to impede dislocations effectively; too much (over aging), and they will be too large and dispersed to interact with the majority of dislocations.
Precipitation strengthening is possible if the line of solid solubility slopes strongly toward the center of a phase diagram. While a large volume of precipitate particles is desirable, little enough of the alloying element should be added that it remains easily soluble at some reasonable annealing temperature.
Elements used for precipitation strengthening of typical aluminum and titanium alloys make up about 10% of their composition. While binary alloys are more easily understood as an academic exercise, commercial alloys often use three components for precipitation strengthening, in compositions such as Al(Mg, Cu) and Ti(Al, V). A large number of other constituents may be unintentional, but benign, or may be added for other purposes such as grain refinement or corrosion resistance. In some cases, such as many aluminum alloys, an increase in strength is achieved at the expense of corrosion resistance.
The addition of large amounts of nickel and chromium needed for corrosion resistance in stainless steels means that traditional hardening and tempering methods are not effective. However, precipitates of chromium, copper or other elements can strengthen the steel by similar amounts to hardening and tempering. The strength can be tailored by adjusting the precipitation temperature, with lower temperatures resulting in higher strengths.
Many alloy systems allow the aging temperature to be adjusted. For instance, some aluminium alloys used to make rivets for aircraft construction are kept in dry ice from their initial heat treatment until they are installed in the structure. After this type of rivet is deformed into its final shape, aging occurs at room temperature and increases its strength, locking the structure together. Higher aging temperatures would risk over-aging other parts of the structure, and require expensive post-assembly heat treatment.
The primary species of precipitation strengthening are second phase particles. These particles impede the movement of dislocations throughout the lattice. You can determine whether or not second phase particles will precipitate into solution from the solidus line on the phase diagram for the particles. Physically, this strengthening effect can be attributed both to size and modulus effects, and to interfacial or surface energy.
The presence of second phase particles often causes lattice distortions. These lattice distortions result when the precipitate particles differ in size from the host atoms. Smaller precipitate particles in a host lattice leads to a tensile stress, whereas larger precipitate particles leads to a compressive stress. Dislocation defects also create a stress field. Above the dislocation there is a compressive stress and below there is a tensile stress. Consequently, there is a negative interaction energy between a dislocation and a precipitate that each respectively cause a compressive and a tensile stress or vice versa. In other words, the dislocation will be attracted to the precipitate. In addition, there is a positive interaction energy between a dislocation and a precipitate that have the same type of stress field. This means that the dislocation will be repulsed by the precipitate.
Precipitate particles also serve by locally changing the stiffness of a material. Dislocations are repulsed by regions of higher stiffness. Conversely, if the precipitate causes the material to be locally more compliant, then the dislocation will be attracted to that region.
Furthermore, a dislocation may cut through a precipitate particle. This interaction causes an increase in the surface area of the particle. The area created is
where, r is the radius of the particle and b is the magnitude of the burgers vector. The resulting increase in surface energy is
where is the surface energy. The dislocation can also bow around a precipitate particle.
There are two equations to describe the two mechanisms for precipitation hardening:
Dislocations cutting through particles:
where τ is material strength, r is the second phase particle radius, γ is the surface energy, b is the magnitude of the Burgers vector, and L is the spacing between pinning points. This governing equation shows that the strength is proportional to r, the radius of the precipitate particles. This means that it is easier for dislocations to cut through a material with smaller second phase particles (small r). As the size of the second phase particles increases, the particles impede dislocation movement and it becomes increasingly difficult for the particles to cut through the material. In other words, the strength of a material increases with increasing r.
Dislocations bowing around particle:
where τ is the material strength, G is the shear modulus, b is the magnitude of the Burgers vector, L is the distance between pinning points, and r is the second phase particle radius. This governing equation shows that for dislocation bowing the strength is inversely proportional to the second phase particle radius r. Dislocation bowing is more likely to occur when there are large particles present in the material.
These governing equations show that the precipitation hardening mechanism depends on the size of the precipitate particles. At small r, cutting will be the dominant strengthening mechanism, while at large r, bowing will be the dominant strengthening mechanism.
Looking at the plot of both equations, it is clear that there is a critical radius at which max strengthening occurs. This critical radius is typically 5-30 nm.
10 inch, manual rotary table
A rotary table is a precision work positioning device used in metalworking. It enables the operator to drill or cut work at exact intervals around a fixed (usually horizontal or vertical) axis. Some rotary tables allow the use of index plates for indexing operations, and some can also be fitted with dividing plates that enable regular work positioning at divisions for which indexing plates are not available. A rotary fixture used in this fashion is more appropriately called a dividing head (indexing head).
The table shown is a manually operated type. Powered tables under the control of CNC machines are now available, and provide a fourth axis to CNC milling machines. Rotary tables are made with a solid base, which has provision for clamping onto another table or fixture. The actual table is a precision-machined disc to which the work piece is clamped (T slots are generally provided for this purpose). This disc can rotate freely, for indexing, or under the control of a worm (handwheel), with the worm wheel portion being made part of the actual table. High precision tables are driven by backlash compensating duplex worms.
The ratio between worm and table is generally 40:1, 72:1 or 90:1 but may be any ratio that can be easily divided exactly into 360°. This is for ease of use when indexing plates are available. A graduated dial and, often, a vernier scale enable the operator to position the table, and thus the work affixed to it with great accuracy.
A through hole is usually machined into the table. Most commonly, this hole is machined to admit a Morse taper center or fixture.
Rotary tables are most commonly mounted "flat", with the table rotating around a vertical axis, in the same plane as the cutter of a vertical milling machine. An alternate setup is to mount the rotary table on its end (or mount it "flat" on a 90° angle plate), so that it rotates about a horizontal axis. In this configuration a tailstock can also be used, thus holding the workpiece "between centers."
With the table mounted on a secondary table, the workpiece is accurately centered around the rotary table's axis, which in turn is centered around the cutting tool's axis. All three axes are thus coaxial. From this point, the secondary table can be offset in either the X or Y direction to set the cutter the desired distance from the workpiece's center. This allows concentric machining operations on the workpiece. Placing the workpiece eccentrically a set distance from the center permits more complex curves to be cut. As with other setups on a vertical mill, the milling operation can be either drilling a series of concentric, and possibly equidistant holes, or face or end milling either circular or semicircular shapes and contours.
Billet refers to a cast semi finished product. It is also referred to as ingot, particularly for smaller sizes. A billet is typically cast to a rectangular, hexagonal or round cross section compatible with secondary processing, e.g. forging. It can be produced either as coil or cut lengths. Ingots and billets are collectively known as bar stock.