The supplied by Eddie Bell is very good and here are a
few more comments.
At area of contact between rolls and material, the rolls flatten and
forms a flat along the roll. On leaving, the rolled product returns
elastically to their radius.
The smaller the diameter of the roll, the faster the curve of the
roll falls away from the product and a smaller width of flat is made
- thus leaving more of the available torque to flatten the product
rather than deform the rolls surface. In other words, more of the
rolls separating force can be used to thin the product.
As a rough formula an idea of the thinnest thickness can be found by
dividing the roll diameter by a factor 700. This factor is only a
guide and can vary from 600 - 1000 depending on product material,
it's hardness, roll quality and rigidity of machine. Also, adding
tension to the product at entry or exit of the rolls (or both)
assists in making a thinner product as does frequent annealing.
Durston Rolling Mills