rolling mill

Rolling mill for plates and wires (goldsmith tool).

Rolling mill for cold rolling metal sheet like this piece of brass sheet.

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A rolling mill is a machine or factory used to shape and process metal by passing it between a pair a working rolls. The metal is passed between two tough cylinders numerous times, with the distance between the cylinders being decreased with each pass so the metal becomes thinner and thinner. Depending on the temperature of the metalworking application rolling mills are typically hot or cold rolling mills.

History

The earliest documentation of the use of rolling mills can be traced back to a patent in 1679 covering the finish of bolts by rolling. In 1680 bars were being passed through plane-surfaced rolls to flatten out irregularities. In 1682 we can find one of the first operational rolling mills in Swalwell and Winlanton, near New Castle, England were hot rolling of ferrous materials was conducted.^[1] At these rolling mills bars were rolled into sheet and then cut at slitting mills. Major Hanbury is credited with one early designs of a rolling mill, but is not credited with the idea of hot rolling bars into thin sheets because it is believed the practice was prevalent in Europe by 1660 and in Germany early in the century. The earliest literature of rolling mills can be traced back to Christopher Polhem in 1761 in Patriotista Testamente where he mentions rolling mills for both plate and bar iron.^[2] He also explains how rolling mills can save on time and labor because a rolling mill can produce 10 to 20 and still more bars at the same time which is wanted to tilt only one bar with a hammer. In 1728 John Payne of England was issued a patent for rolling mill to roll hammered bars. Also a patent was granted to Thomas Blockley of England in 1759 for the polishing and rolling of metals. Another patent was granted in 1766 to Richard Ford of England for the first Tandem Mill.^[3] A tandem mill is where the metal is rolled in successive stands; Ford’s tandem mill was for hot rolling of wire rods.

Modern Rolling

The modern rolling practice can be contributed to the efforts of Henry Cort of Fontley Iron Mills, near Fareham, England. In 1783 a patent was issued to Henry Cort for his use of grooved rolls for rolling iron bars. With this new design mills were able to produce 15 times the output per day than with a tilt hammer.^[4] Although Cort was not the first to use grooved rolls; he was the first to combine the use of all the best features of various steelmaking and shaping processes known at the time. Thus the term “father of modern rolling” was giving to him by modern writers. The first rail rolling mill was established by John Birkenshaw in 1820 where he produced fish bellied wrought iron rails in lengths of 15 to 18 feet.^[5] With the advancement of technology in rolling mills the size of rolling mills grew rapidly along with the size products being rolled. Example of this is at the Great Exposition in 1851 a plate 20 feet long, 3 ½ feet wide, and 7/16 of inch thick, weighed 1,125 pounds was exhibited by the Consett Iron Company.^[6] Further evolution of the rolling mill came with the introduction of Three-high mills in 1853 used for rolling heavy sections.

Hot Rolling Mill

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.

Cold Rolling Mill

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.

Components of a Rolling Mill

The work rolls and their bearings- made of material harder than it is intended to roll

The backup rolls and its bearings-are intended to provide rigid support required by the working rolls to prevent their flexure or bending under the rolling load

The Mill Foundation- reinforced concrete for every ton of mill weight

Rolling balance system- to ensure that the upper work and back up rolls are maintain in proper position relative to lower rolls

Work Roll Changing devices-use of an overhead crane and a unit designed to attach to the neck of the roll to be removed from or inserted into the mill.

Mill protection devices- to ensure that forces applied to the backup roll chocks are not of such a magnitude to fracture the roll necks or damage the mill housing

Pinions- gears to divide power between the two spindles, rotating them at the same speed but in different directions

Gearing- to establish desired rolling speed

Motor Couplings- used to connect the shafts of motors to reduction gears in pinion stands

Drive motors- rolling narrow foil product to thousands of horsepower

Motor Generator Sets- constant and variable voltages applied to the motors

Coilers- provides high forward tensions

Mill Instrumentations- sensors to monitor all important parameter processes

Operating Controls- enable the mill operator to handle rolling process ^[7]

Classification of Rolling Mills

Mills classified in accordance with the name of the product which they roll, follow: Blooming, cogging and slabbing mills, being the preparatory mills to rolling finished rails, shapes or plates, respectively. If reversing, they are from 34 to 48 inches in diameter, and if three-high, from 28 to 42 inches in diameter.

• Billet mills, three-high, rolls from 24 to 32 inches in diameter, used for the further reduction of blooms down to 1J^ x IJ^-inch billets, being the preparatory mills for the bar and rod

• Beam mills, three-high, rolls from 28 to 36 inches in diameter, for the production of heavy beams and channels 12 inches and over.

• Rail mills with rolls from 26 to 40 inches in diameter.

• Shape mills with rolls from 20 to 26 inches in diameter, for smaller sizes of beams and channels and other structural shapes.

• Merchant bar mills with rolls from 16 to 20 inches in diameter.

• Small merchant bar mills with finishing rolls from 8 to 16 inches in diameter, generally arranged with a larger size roughing stand.

• Rod and wire mills with finishing rolls from 8 to 12 inches in diameter, always arranged with larger size roughing stands.

• Hoop and cotton tie mills, similar to small merchant bar mills11.

• Armor plate mills with rolls from 44 to 50 inches in diameter and 140 to 180-inch body.

Plate mills with rolls from 28 to 44 inches in diameter13.

• Sheet mills with rolls from 20 to 32 inches in diameter.

• Universal mills for the production of square-edged or so-called universal plates and various wide flanged shapes by a system of vertical and horizontal rolls

• Tube mills for the production of tubes.

• Special mills, such as slitting, piercing, tire wheel mills, etc.

• Cold mills.

^[8]

Finished Products of Rolling Mills (3 Groups)

First Group

Bars, rods, wire rods, bands and hoops, constituting the first group, are produced from blooms, slabs and billets by reducing this material to the simplest forms, such as squares, rounds and flats. These' forms resemble the cross-section of the material from which they are rolled, and their final "section determines their nomenclature. The materials of this group have great length compared with their width and thickness. The steel from which they are rolled is prepared to conform to certain specifications, and the section must be within certain limits as to size and weight, and must be suitable for further fabrication into bolts, nuts, spikes, chains, rivets, wire, wire nails, hoops, cotton ties, springs, etc. ^[9]

Second Group

Shapes, constituting the second group, are reduced from blooms, slabs or billets to forms having more or less irregular section. In the process of rolling, the original material is not only reduced in section, but it is also developed into a definite shape. The various shapes are given commercial names, such as rails, splice bars, I-beams, channels, zees, tees, angles, etc. The heavier and larger sizes of these shapes are frequently rolled direct in one heat from the ingot to the finished material. After leaving the rolling mill, shapes are cut to length and are cooled on cooling beds. The shapes are subsequently straightened by means of straightening rolls or presses, the latter work being performed in suitable shops adjoining the rolling mill, and in this condition they are known commercially as structural shapes. These shapes are further developed and worked into various products at shops specially adapted to carry out the character of the work for which they are intended. For example, the fabrication of products built for building construction is carried on in architectural iron works; bridges at bridge works; ships at ship yards, and railroad construction at car shops.^[10]

Third Group

Plates and skelp, of the third group, is the material obtained by rolling slabs and blooms in mills known as plate and skelp mills. A sheet is the product obtained by rolling sheet bars in sheet mills. While bars and shapes have great length compared with their other dimensions, this does not apply to plates and sheets where the width is also well developed; this form of product is known as sheets when rolled to a thickness less than No. 12 gage. The United States government limits this thickness to No. 10, United States standard gage. With reference to quality and use, plates may be divided into tank, bridge, ship and boiler plates. The steel entering into the material from which plates are rolled is prepared to conform to standard specifications governing the above classes. Boiler plates are further divided (with reference to the grade of steel to be used for certain parts of the boiler) into flange, fire box and extra soft steel. Plates, after being rolled, have frequently an uneven surface, which is flattened by passing them through straightening rolls. Long plates are straightened by being held in place against guides and are hammered flat with wooden hammers. Plates, after being straightened and cooled, are transferred to the shearing department, usually adjoining the plate mill, where they are cut to size. Plates having irregular edges must be sheared. Universal mill plates have their edges rolled and need only be sheared on the ends. Universal mill plates are rolled from 18 to 60 inches in width. .^[11]

Example of Process of a Rolling Mill:

You can imagine how this might be used in the process of making aluminum foil. An aluminum ingot enters the rolling mill with a thickness of 45 cm. after passing through a hot rolling mill 12 to 16 times it is reduced to a thickness of just 5 cm. The aluminum then goes to the cold rolling mill to reduce it to its final thickness of less than 0.20320 mm. (.008 in.).

Foot Notes

References

See also

• Bernard Lauth
• John B. Tytus
• Rolling (metalworking)
• Hot rolling
• Cold rolling
• Structural steel
• Steel mill

External links

• Photos of a steam-powered rolling mill.
• Pictures of many rolling mills and big steel plants
• History of Rolling Mills