Rolling is a common and compulsory process that is done in the manufacturing world for applications that involve the use of sheet metals. The rolling process is a metalworking process that helps to reduce the thickness of metal and make the thickness uniform.
Today we’ll be looking at the classification of a rolling process which includes; hot rolling and cold rolling process.
Hot and Cold rolling:
As earlier mentioned, in metalworking process hot rolling occurs above the recrystallization temperature of the material. Though, the recrystallization prevents the metal from work hardening. The material fed for rolling is usually large pieces of metal, like semi-finished casting products, such as slabs, billets, and blooms. Products from continuous casting operation are usually fed directly into the rolling mills at a suitable temperature. However, in smaller operations, the material begins at room temperature which must be heated. This can be performed in a gas- or oil-fired soaking pit for larger workpieces and for smaller workpieces, induction heating is used. After the working of the material, the temperature is monitored to ensures it remains above the recrystallization temperature. Hot-rolled metals typically have little directionality in their mechanical properties and deformation-induced stresses.
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Unlike hot rolling, cold rolling occurs below the recrystallization temperature of the material usually at room temperature. this increases the strength to about 20% high through strain hardening and enhances the surface finish and also holds tighter tolerances. Products that usually undergo cold-rolled process include sheets, rods strips, and bars; these products are usually smaller than the same products that are hot rolled. This is because of the smaller size of the workpiece and their greater strength as compared to hot-rolled material. This process uses four-high or cluster types of mills for its working. Cold rolling cannot be used to perfectly reduce the thickness of a workpiece as much as hot rolling in a single pass.
Cold-rolled sheets and strips are available in various conditions such as full-hard, half-hard, quarter-hard, and skin-rolled. The material thickness reduces by 50% in full-hard rolling, while others involve less of a reduction. Cold rolled steel is then annealed to induce ductility in the cold-rolled steel which is called a Cold Rolled and Close Annealed. Skin rolling which is also known as skin-pass, it is used to produce a smooth surface, uniform thickness and reduce the yield point. Skin-rolled stock is usually used in subsequent cold-working processes where good ductility is needed.
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Other shapes can be cold-rolled if the transverse dimension is relatively small and if the cross-section is relatively uniform. Cold rolling requires some shaping operations, usually, along the line of sizing, breakdown, roughing, semi-roughing, semi-finishing, and finishing.
That’s it for this article, classification of rolling process “hot and cold rolling”. I hope you enjoyed the reading, if so, kindly comment, share and check other related topics below. Thanks!