Breaking up two-layer cast-ion rolling-mill rolls with a chill layer

Abstract

When the Magnitogorsk Metallurgical Combine began to make cast-iron rolls with a chill layer, it became necessary to break up the rolls after they had been removed from service. The rolls had to be divided into pieces no larger than 600 • 800 mm in order to be used as a component of the metallic charge for the production of alloyed cast iron in arc furnaces or induction furnaces. The combine conducted an experiment in which the rolls were broken up by two technologies already in use at the combine explosive fragmentation, with the blastholes for the explosive charges being perpendicular to the axis of the roll; breakup of the rolls on an impact breaker. The first method posed the danger of having fragments of the chill layer fly off as the blastholes were being drilled. In the second method, the body of the roll could not be broken up into pieces of the required dimensions, and the ball-weight of the impact breaker would itself be broken due to the high hardness of the body. Thus, two new technologies were proposed and tried out for breaking up two-layer cast-iron rolls explosive fragmentation in which the blastholes are located along the body of the roll; the use of an impact breaker after the roll body has been heated by a powerful mechanical cutter in the area where the roll is supposed to be divided. Explosive fragmentation with axial blastholes was chosen as the main technology after tests (two opposing blastholes are used). To perform a comparative analysis, nine rolls were broken up by the proposed fragmentation technology (A) and one was broken up by the existing technology (B). The results (in terms of one roll) are shown below: