14-12-2012, 06:17 PM
ROLLING PROCESS
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ROLLING PROCESS
“The rolling process is the rapid method of converting large section into desired shapes. The forming of sheets, plates, bars, angles, rails, I-beams and other structural sections is done by ‘rolling’. It is the process where the metal is compressed between two rotating rolls for reducing its cross-sectional area.This is one of the most widely used of all the metal working processes, because of its higher conductivity and low cost.”
The process consists of passing the ingot through least of two rolls rotating in opposite directions at the same speed. The gap between the two rolls is adjusted to conform to the desired thickness of the rolled section. Rough rolls would be able to achieve greater reduction than smoother rolls. The rolls squeeze the passing ingot to reduce its cross-section and increase in length. The reduction could be achieved with a given set of rolls is designated as the ‘angle of bite’. The angle of bite depends on the type of rolling and the conditions of the rolls. The volume of the metal that enters should be the same as leaving it except in initial passes where some metal lost due to filling o voids and cavities in the ingots. Between the entrance and exit, the velocity of the metal is continuously changing, whereas the rolls velocity remains constant . The material commonly rolled are aluminium, magnesium, copper, there alloy and many grades of steel.
‘TYPES OF ROLLING MILLS’
Two- high rolling mill:-
(a) Reversing mill
(b) Non-reversing mill
Three-high rolling mill
Four-high rolling mill
Tandem rolling mill
Cluster rolling mill
Planetary rolling mill
REVERSING MILL
A two-high rolling mill has two rolls only. In a two-high reversing mill the rolls rotate first in one direction and then in the other so that the rolled metal may pass back and fort through the rolls several times. Reversing mill is used in blooming and slabbing mills and for roughing work in rail, plate, structural and other mills.
NON-REVERSING MILL
A two- high non-reversing mill has two rolls which has two rolls which revolve continuously in the same direction. Therefore, smaller and less costly motive power can be used. However, every time, material is to be carried back over the top of the mill for again passing it through the rolls. It is used in mills through which the bar passes once and in open-train plate mills.
THREE-HIGH ROLLING MILL
It consist of three rolls. The upper and the bottom rolls rotate in the same direction whereas middle roll rotates in the opposite direction. It is used for rolling of two continuous passes in a rolling sequence without reversing the drives.