The Mechanics of Drawing Tinplate through Rotatable Dies

Abstract

Experimental and theoretical studies were made into the mechanics of the S-mill rolling process, in which rolls reduce thin, hard materials by novel means without recourse to the conventional rigid roll gap. Essentially in the S-mill process, strip is drawn through rotatable dies; consequently the process is limited by the front tension which the strip will carry. Therefore any method which reduces the front tension could lead to an increase in the maximum strip reduction. Experimental, results indicated that the optimum operational conditions existed when the mill rolls were set to the minimum possible alpha-angle since then the lowest strip tensions and the greatest roll separating forces were generated. Moreover, for the smallest alpha-angle the work done by the torque was least and that by the tension difference was greatest. The maximum strip reduction obtained in a single pass was 54.2 percent, however, this reduction was increased further by passing the strip more than once through the mill. A short series of tests was carried out rolling stainless steel so that a comparison between different materials could be made. Results are presented in a non-dimensional form for future design calculations. Experiments were conducted with the larger work-roll driven. The results indicated that when the larger work-roll was supplied with positive torque little difference was detected in the strip tensions, although the roll separating forces were, in general, reduced. However, when the larger work-roll acted as a brake, substantial reductions were found in the front and back strip tensions. Considering the assumptions made, the theory proposed for the S-mill process gave accurate predictions for the roll separating forces. However, several factors, including an inability to estimate accurately the interstand tensions resulted in, as is usual in cold rolling theories based on an equilibrium analyses, poor predictions of roll torques.