Possibility and Problems in Injection Moulding of Wood Powders

Abstract

Injection tests of mixed wood powders of Cryptomeria japonica with Hinoki (Chamaecyparis) were carried out at various injection conditions ; injection pressure and its holding time, container and cavity temperatures, moisture content of wood powders, in order to confirm the possibility of near net shape forming of wood powders. Effects of injection conditions on the injection pressure-punch stroke relationships, the mechanical properties, bending strength and bulk density of injected products were discussed. The experimental results showed that the wood powders could not be injected into the cavity when a initial moisture content was 12% due to less fluidity of wood powders. The optimum conditions of container and cavity temperature existed regarding of the initial moisture content of wood powders. Successful injection mouldings were performed within the container temperature Tc=90-130°C and the cavity temperature Tv=150±20°C when the initial moisture content 100% powders were used. And also the injection pressure became small at the optimum mould temperature conditions since the fluidity of wood powders became improve. The bulk density and bending strength of injected product increase with increasing container and cavity temperature. However, an optimum condition existed for the initial moisture content of powders where the bulk density and bending strength became max. Maximum relative density and bending strength were 0.95 and 25 MPa at the container temperature Tc=130°C and the cavity temperature Tv=170°C with initial moisture content 100% wood powders. Finally, it was also found that if the arbitrary cavity was using under appropriate injection conditions, it was possible to obtain the wood powders products with arbitrary shape.