The effect of powder characteristics on pressure sensitivity of powder injection moulding compounds

Pressure effect on the rheological behaviour of powder-polymer compounds intended for powder injection moulding was determined. A single-piston capillary rheometer modified by addition of a second chamber with a restricting needle valve generating backpressure increasing the pressure in the melted material during the flow through the die was employed to determine pressure sensitivity coefficients. The results obtained for three compounds varying in the characteristics of powders used confirmed that compounds at the loading level close to the maximum packing are more sensitive to pressure than polymer binder. It is shown that pressure sensitivity coefficients of these materials are strongly dependent on powder characteristics — particle size and particle size distribution. The highest coefficient (32.9 GPa) was found for compound containing broad particle size distributed powder having a perceptible portion of small particles.