Like hot rolling, cold rolling can be done using two-and-four-high roll arrangements.
Two types of cold rolling mills commonly used are:
(i) Sendzimir mill
(ii) Saxl pendulum mill
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Both of these mills make use of small diameter rolls. The former type makes use of elaborate system of backing rolls of increasing diameter as shown in Fig. 6.1. It will be noted that work rolls just in contact with the work-piece are of smallest diameter. These are backed up by 2 intermediate rolls, which in turn are backed up by 3 intermediate rolls and these are finally backed up by 4 biggest diameter final back up rolls.
Latter type of mill is similar to the planetary mill. It utilises a small freely rotating roll, mounted at the end of an arm which is forced to reciprocate like a pendulum at high speed over the deforming metal. The metal is fed towards the pendulum roll by feed rolls at around a speed of 10 mm/sec. The reduction in thickness achieved on this machine is tremendous and the metal entering the machine at a speed of 10 mm/sec may leave at speed of 100 mm/sec.
As against these speeds, the roll surface speed may be of the order of 2000 mm/sec. Due to high reduction in thickness, the temperature rise of metal is sufficient to reduce the tendency of the material to work-harden. However the work is annealed properly in controlled atmosphere to increase the ductility of work hardened material.
