A Passive Approach to Butt Swell Management

The thickening of the base of rolling slab ingots is colloquially known as butt swell. Because traditional DC casting systems are vertical and not truly continuous, this remains one of the remaining sectors of recovery loss in the casthouse and at the scalper. Butt swell is currently managed by using dynamic molds which adjust the mold bore as a function of casting recipe to deliver flat ingot profiles. In this paper, we analyze the metallurgical origin of butt swell in the DC casting process. Based on this analysis, a novel bottom block design is proposed which reduces the extent of the butt swell in the start-up regime of casting. Experimental results are reported in comparison to a standard reference case demonstrating a reduction in butt swell. Subsequent rolling trials also indicate additional scrap reduction in the flat rolling process.