Abstract
Heretofore it has been discussed chiefly on the ground of experience, what degree of the surface hardness of the backing-up roll for the four-high mill would be suitable. Hence, some one suffices himself at the softer surface with about 45 of Shore hardness, another prefers the harder roll with about 80-85 of Shore hardness, leaving the user in distress for selecting the suitable hardness. The author studied this problem in the line of elastic-dynamies, investigated the distribution of stress in the material proximate to the roll surface, explained the phenomenon of surface spalling by fatiguebreakage of the roll material, and gave the theoretical reason for seleeting the optimum surface hardness. Besides, the author made a calculation on the cold strip mills in operation at the Yawata Iron Works and correlated the calculated value with the theoretical.
