Square Rolling Slabs from Start of Casting-the Elimination of Butt Swell

The thickening of the bottom part of DC cast rolling slabs, butt-swell, is a well known problem in the aluminium business. The slabs are scalped, normally in the rolling plant, prior to rolling to a absolute rectangular shape. The rolling mill therefore prefers rolling slabs with geometry close to rectangular from the casthouse. Due to geometry specifications from the rolling mills the supplier casthouse has to cut off the bottom part of the slab before shipping. The bottom cut length is typically 0.3-0.6m (1-2') depending on the thickness and casting speed. This paper describes the basic principles behind the development of the flexible mould technology, and the operational experience so far from close to 15 years of operation. For 600mm thick ingots flexible moulds typically reduce the total scrap rate in the casthouse with more than 5% compared to conventional moulds with fixed geometry.