Development and testing of exchangeable carbon-bonded alumina foam filter systems for the continuous casting of steel

Reference Presenter Authors
14-056 Tony Wetzig Wetzig, T.(TU Bergakademie Freiberg); Dudczig, S.(TU Bergakademie Freiberg); Hubálková, J.(TU Bergakademie Freiberg); Aneziris, C.G.(TU Bergakademie Freiberg);

Ceramic foam filters became a popular tool in the foundry industry to remove non-metallic inclusions from the melt and to improve the casting quality. In the past, much effort was expended on transferring the principle of metal melt filtration to the continuous casting of steel. In the long casting sequences, installed filter systems are subject to severe conditions. Additionally, excessive filter clogging may force the premature stop of the casting sequence. Therefore, a new approach is necessary allowing the exchange of the filters on demand. Prior to industrial tests, such an exchangeable filter system had to be developed and evaluated in lab scale investigations.

Cylindrical carbon-bonded alumina foam filters with 200 mm diameter and height were prepared by replication of polyurethane templates. Therefore, different coating techniques were applied including centrifugation, dip-coating and spray-coating. After coking at 800°C, the produced filters were investigated regarding their porosity, mechanical strength, strut thickness distribution and homogeneity.

Due to their higher strength, filters produced by triple coating were considered most suitable for further tests. One filter prepared by this route then was tested on its behavior in contact with molten steel with the aid of a steel casting simulator. 100 kg of molten 42CrMo4 steel was cast on the filter under argon atmosphere at 1650.5 °C. The filter then was investigated by computed tomography and scanning electron microscopy in order to investigate potential damage due to the steel impact, the shrinkage during the casting and the change of the filter surface. It was shown that the filter has sufficient thermal shock resistance and mechanical strength to withstand the impact of the melt. During the casting, the filter showed a radial shrinkage of 2%. Furthermore, the surface of the filter showed a typical layer buildup due to its carbo-thermal reactivity.