Rolling Of Billet
Rolling is one of the most important industrial metal forming operations. Hot rolling is employed for breaking the ingots down into wrought products such as blooms and billets which are subsequently rolled to other products like plates, sheets etc. It is the plastic deformation of materials caused by compressive force applied through a set of roles. The material gets squeezed between a pair of rolls, as a result of which the thickness gets reduced and the length is increased.
It is done at high temperature called hot rolling because of requirement of large deformations. Hot rolling results in residual stress-free product. Cold rolling of sheets, foils etc is gaining importance due to high accuracy and lack of oxide scaling. It also strengthens the product due to work hardening. The ingot is soaked at the hot rolling temperature of 1200 degree Celsius and then rolled into blooms or billets or slabs. Billets are rolled into bars, rods. Bars and rods are raw materials for extrusion, drawing, forging, machining etc.
Flatness of rolled billets can be increased by roller levelling. In this process, the sheet is passed between a pair of rolls which are driven by individual motors and are slightly offset. Rolled billets should have stiffness, hardness and strength.