CONTROL OF FIBER ORIENTATION IN INJECTION-MOLDED CERAMIC COMPOSITES

A ceramic injection moulding suspension containing 60 vol% solids of w hich 12 vol% was in the form of short-staple fibres was prepared by tw in screw extrusion. The material was moulded in the form of large and small end-gated rectangular bars using a machine which applied modulat ed pressure after mould filling. The orientation of fibres in conventi onal and modulated pressure moulding was compared. The former showed t he well-known arrangement of sub-skin alignment and disorder near the centre. In the latter, the fibres were preferentially oriented in the flowing direction throughout the moulding. The uniformity of preferred orientation throughout the bar was sensitive to oscillation frequency . This is because of the high thermal diffusivity and hence rapid soli dification of the ceramic suspensions compared to unfilled polymers. T he solidification front progresses rapidly to occlude fibres which wer e incompletely oriented during the period in each cycle when the melt was stationary. (C) 1997 Published by Elsevier Science Limited.