Trapping Mechanisms of Blow Hole in Paraffin

Abstract

In the continuous casting process argon gas is usually blown into the tundish to suppress the formation of non-metallic inclusions which cause blocking of the nozzle. The gas which comes into the mold with the molten steel through the tundish nozzle, however, is sometimes trapped as small bubbles at the solidification front in the mold. It is well known that these trapped bubbles cause surface defects of the products. Many simulation studies have examined the trapping mechanisms of gas bubbles in the subsurface of the cast, however, there have been very few experimental studies. In this paper, we used paraffin liquid instead of molten steel to observe the bubble behavior as it is a more convenient substance.
The testing conditions were as follows: the temperature of paraffin liquid was 329K (the melting point is 325K), the tilting angle of solidification front in the direction of bubble flow was 30 degrees, measuring time was 30 sec, the average diameter of a bubble was about 1 mm and frequency of bubble flow was about 18 sec.
It was determined that decrease in the temperature of cooling water, which means an increase in the solidification speed of paraffin, causes an increase in the number of trapped bubbles.