EFFECT OF WATER-CONTENT ON TENSILE FRACTURE FORCE AND DEFORMABILITY OF RAM EXTRUDED CYLINDERS

Wetted powder masses with varying amounts of water were used to study mechanistically the extrusion process in terms of brittleness and defo rmability of ram extruded cylinders. Mixtures of dicalcium phosphatedi hydrate (DCPD) and Avicel PH 101 (70/30%) were massed with water (mois ture contents 50, 60, 70, 80 w/w%). The masses were extruded in a ram extruder (25.0 mm in diameter) with a 10.0 mm diameter and 10 mm long die. The moist extrudates were cut to isodiametrical cylinders. The po rosity and degree of liquid saturation were determined. The extruded, isodiametrical cylinders were glued on to small brass cylinders and co nnected to a material testing instrument. The force as a function of d isplacement was recorded during tensile testing of the extruded cylind ers at a loading rate of 1 mm/min. The tensile fracture force (force a t failure) and the deformability during the measurement, i.e. an inver se number of the slope of the force displacement curves, were determin ed. The tensile fracture force of the extruded cylinders decreased wit h increased porosity. At the same time the deformability of the cylind ers increased for all the extruded masses, except the one with the hig hest porosity. (C) 1997 Elsevier Science B.V.