Billet Sump Modification of Al-Billets for the Prevention of Starting Cracks

Abstract

Depending on the cast alloy, starting cracks are a common problem while casting aluminium extrusion billets. Hot crack formation is well investigated in theory as well as the formation of the sump shape using different casting technologies. Nevertheless, starting cracks are a problem in DC casting. Because TRIMET ALUMINIUM AG Essen uses the spout and float technology for DC-casting of aluminium this paper presents an investigation into methods for the prevention of starting cracks in Al-billets using float and spout DC-casting and covers the research methods, the results of crack prevention and the results of implementing these methods. The main topics to be considered are the control of sump formation and the correlation between sump geometry and hot cracks in the billet. Our experimental research covers DC-casting with varied casting parameters (stop-and-go casting, casting speed etc.), sump depth measurements, ultrasonic tests and metallographic examinations. We discuss crack prevention in the analysis and interpretation sections given consideration of the sump depth measurements. On the basis of these measurements the effect of the different casting technologies and parameters are shown. Finally, the methods we describe have to be implemented in production. The essential points are the upscaling and the automation of the casting process, especially the start-up phase. The results of this investigation provide excellent possibilities for crack prevention for DC-casting.