Manufacturing of Large Steel Disk by Cross-rolling

Abstract

A cross-rolling technique was devised to manufacture large steel disks with high percentage yield and to improve their anisotropy of the impact value.The first half of this paper deals with a simple theory of the cross-rolling to make clear the influence of rolling conditions on the percentage yield of the disk. The last half is devoted to an experimental study of cross-rolling using plasticine as a model material to simulate the deformation of steel disks during hot cross-rolling. Finally a result oi trial manufacture of large steel disk is described.
The results obtained are summerized as follows:
(1) It is possible to expand the round disk keeping its shape unchanged by the orthogonal crossrolling, if the percentage reductions in the first-and second pass (cross-rolling pass) are equalized.
(2) The percentage yield (100η) of the disk is reduced by the spread during rolling, the difference of reduction in the first-and the second pass (Δr) and angular deviation of the rolling direction of the second pass from the orthogonal direction to the first pass (oblique angle θ); and η is given by the next formula, when |Δr|<<r and |Δθ|<<1.
where 2a and h₀: diameter and thickness of a disk before rolling, R: roll radius, r= (r₁+r₂)/2, Δr=r₁-r₂ (r₁ and r₂ are fractinal reduction in the first-and the second pass respectively)
(3) Concavities formed at the side surface of the disk in the early stage of repeated cross-rolling, when the thickness of the disk is relatively large, continue to grow in the suceeding rolling, causing to reduce the percentage yield of the final disk. But it is possible to increase the yield by upsettng disk before rolling to make barelling on the side surface, cross-rolling it with large reduction and reversing the direction of rolling.