Filter systems for high velocity liquid metal flow

Liquid cast iron (carbon equivalent, CE=4-3%) and Al-12.5Si were poured down a 500 mm tall sprue and cast in a straight fluidity test channel, with and without a filter system. Different arrangements of filter and bubble trap were compared to assess their effectiveness. The filling sequence was recorded on videotape by the use of real time x-ray radiography. Measurements were made of the speed of the metal and the distance to which it flowed in the fluidity casting. A critical finding was that the soundness of samples revealed a relationship with the velocity of the melt; the lower the velocity, the fewer the defects. The final design of a filtering system seems to require a mechanism for the detrainment of bubbles and the reduction in velocity of the melt from over 2 m s(-1) to 0.4-0.8 m s(-1). In consequence, the fluidity of the melt is reduced, but the internal quality of the casting improved from being unacceptably impaired by entrained bubbles to being substantially free from such defects. (C) 2004 W. S. Maney Son Ltd.