METAL FORMING *Metals may be formed into useful shapes in two basic ways: 1. By plastic deformation processes in which the volume and mass of metal are conserved and the metal is displaced from one location to another. 2. By metal removal or machining processes in which material is removed in order to give it the required shape.
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*Metal forming processes may be classified into only a few categories on the basis of the type of forces applied to the work-piece as it is formed into shape. Direct-compression-type processes Indirect-compression processes Tension type processes Bending processes Shearing processes
ROLLING • The process of plastically deforming metal by passing it between the rolls is known as rolling. • The work is subjected to high compressive stresses from squeezing action of rolls. • The frictional force between metal and rolls is responsible for drawing the metal into the rolls. Classification of Rolling Process i) Hot Rolling ii) Cold Rolling
Hot Rolling: • Hot working ---- above the re-crystallization temperature • It is employed where large reduction in cross-sectional area is required. • Used for bars, rods, rails etc.
Cold Rolling: • Cold working ---- below the re-crystallization temperature • Employed for finishing the metal to given specification of sizes and surface quality. • Produces sheets, strips and foils with good surface finish and increased mechanical strength.
ROLLED PRODUCTS i) Bloom: • First breakdown product of ingots with a minimum cross-sectional area of 36 in 2. • Generally, square in cross-section. ii) Billet: • Further reduction of bloom by rolling results in a billet. • Cross-sectional area 1.5 in. X 1.5 in.
iii) Slab: â€˘ A hot rolled ingot with a width to thickness ratio of 2:1 at least. â€˘ Cross-sectional area over 16 sq. in. **Blooms, billets and slabs are known as semi-finished products because they are subsequently formed into other mill products.
iv) Plate: • It has thickness greater than ¼ in. v) Sheet and Strip: • Generally have thickness lesser than ¼ in. vi) Foil: • Thickness is very small just as 0.002 in. * Billets and other unfinished rollings are further rolled to I-sections, T-sections, Angles, Channels, Girders etc.
Rolling Process: â€˘
In the process of rolling the billet is fed from one side into the rolls and reduces in thickness according to the section and gap between the rolls. â€˘ The reduction ratios have maximum allowable values for different metals beyond which reduction is not practicable in a single process. â€˘ Rolling sets in series may be employed. ** There are fundamentally two types of rolls: i) Supporting rolls ii) Driving rolls ** the rolls must be rigid or the rolled material will have a loop like shape.
ROLLING MILLS: • A rolling mill is a machine or factory for shaping metal by passing it between a pair of work rolls. • A rolling mill consists basically of rolls, bearings, a housing for containing these parts, and a drive for applying power to the rolls and controlling their speeds. • High forces are involved ------ large motors • Continuous mills ----- high initial investment • Rolling mills can be conventionally classified with respect to the number and arrangement of the rolls.
Classification of rolling mills: i) Two-high mills ii) Two-high reversing mills iii)Three-high mills iv) Four-high mills v) Cluster mills vi) Continuous mills vii)Planetary mills
Rolling mill for plates and wires
Rolling mill with twin chamber reheating furnace
2 Hi Hot Rolling Mills for Ferrous/ Non-Ferrous Flats
3 high mill pinion housing, for steel rolling mill.
4 Hi Cold Rolling Mill for Aluminium
Continuous Rolling Mills
Steel angles and channels
Two-high Mill: • The simplest and most common type. • Rolls of equals size are rotated in one direction. • The stock is returned to entrance, or rear, of the rolls for further reduction by hand carrying or by means of a platform which can be raised to pass the work above the rolls. • Improvement --- a two-high reversing mill, in which the work can be passed back and forth through the rolls by reversing their direction of rotation.
Three-high Mill: • It consists of an upper and lower driven roll and a middle roll which rotates by friction.
Four-high Mill: Four rolls ---- two small rolls supported by largediameter backup rolls. ** Very thin sheet can be rolled to very close tolerance on a mill with small-diameter work rolls. Cluster Mill: Each of the work rolls is supported by two backing rolls. Continuous Mill: high production
Planetary Mill: • It consists of a pair of heavy backing rolls surrounded by a large number of small planetary rolls. • The chief feature of this mill is that it hot reduces a slab directly to strip in one pass through the mill. • The overall reduction is the summation of a serious of small reductions by each pair of rolls in turn following each other in rapid succession.