INTERACTION BETWEEN MOVING CELLULAR SOLIDIFICATION FRONT AND GRAPHITEPARTICLES DURING CENTRIFUGAL CASTING

Particle pushing phenomena during solidification in the melt containin g a particle lighter than the melt under the influence of centrifugal forces is described. This phenomena is observed in centrifugally cast copper alloys originally containing an average of 7 vol% graphite part icles, cast in a 9.5-cm outer diameter mold rotating at 800 and 1900 r pm. A model to calculate the critical interface velocity, depending on the centrifugal force and the location of the cellular interface wher e the particle interacts with the interface, is proposed, and the part icle pushing criterion is discussed. It is found that as the particle velocity increases with increasing the rotational speed of the mold, t he effect of the particle velocity on the critical intel face velocity increases; in addition the critical interface velocity is lowest at t he tip of the cellular interface, and increases with distance from the tip of the interface. The critical interface velocity calculated in c opper alloy containing 5 mu m graphite cast in a 9.5-cm outer diameter mold rotating at 800 rpm (1.5 x 10(-3) m s(-1)) is higher than the in terface velocity calculated for casting in a mold rotating at 1750 rpm (5 x 10(-4) ms(-1)) obtained numerically by Kang and Rohatgi (C.G. Ka ng, P.K. Rohatgi, Met. Trans. 27B (1996) 277). The fact that the actua l interface velocity is lower than the critical interface velocity lea ds to pushing of particles by the growing dendrites in the last freezi ng interdendritic regions, as observed experimentally. (C) 1998 Elsevi er Science S.A. All rights reserved.