Front and back end crop-losses in slab ingot rolling

Abstract

When a rolling schedule for slab ingots is planned, designers usually take a keep interest in the rolled form developed at the front and back end. Usually, these parts assume a concave shape, such overlaps making up crop losses, which have to be minimized by using the proper rolling technique. Crop losses may make up 3% of the total slab- or bloom-weight and even figures of 10% have been reported from industry. The shape of overlaps formed at the front and back end in slab ingot rolling has been studied theoretically and experimentally and the influence of roll radius, height of workpiece and reduction has been analysed. The theory has been carried out by means of plane-strain upper-bound solutions, whilst the experiments were performed with plasticine (Filia wax) and aluminium in the cold condition: the main part of the experimental programme was accomplished using plasticine. The end shapes obtained from theory and experiment are of the same nature and in good qualitative agreement. However, the experimental results obtained by means of plasticine and aluminuim differ. The best quantitative correspondence with theory is found for the plasticine crop-loss volumes. It is concluded that overhangs and crop-loss volumes formed at the front end are larger than those at the back end. The overhangs and the crop-loss volumes decrease when large rolls are used — especially for heavy reductions — but this phenomenon is, however, less pronounced when considering the back end. When large rolls and heavy reductions are used for small workpiece heights, the concave end-shapes gradually become convex.