Improvement of Surface Cracks in Aluminum Alloy Strip Casting Using a Grooved Roll in a Vertical-Type High-Speed Twin Roll Caster

A vertical-type high-speed twin roll caster can cast aluminum alloy strip at speeds from 20 to 90 m/min; however, surface cracks occur on the cast strip. In Al-Si alloys, surface cracks are known to occur when the Si content is less than 5 mass%. The condition of the surface cracks in cast strips is affected by the roll load. When deep drawing is conducted on a cold-rolled strip, surface cracks occur in the casting direction. The purpose of this study was to investigate the use of a roll with a groove to eliminate the occurrence of surface cracks. The grooves were formed by knurling in the width direction of the roll, and the effect of groove shape on the occurrence of surface cracks was assessed. The roll speed was 60 m/min, and the roll load was 3 N/mm. Eight groove shapes with depths ranging from 0.1 to 0.3 mm were tested. Previous research investigated the effects of casting-direction and diamond-pattern grooves on surface crack elimination, but these grooves were not sufficiently effective. Width-direction grooves were expected to make deformation of the strip surface at the roll bite more uniform and thus improve surface crack elimination. However, this effect was not examined in previous studies. Surface crack elimination was evaluated by penetrant testing of the cast and cold-rolled strips and by deep drawing of the cold-rolled strip. The results showed that surface cracks could be eliminated using an appropriately grooved roll.