WICK-DEBINDING IN POWDER INJECTION-MOLDING

Powder injection moulding offers the possibility of producing powder c ompacts of intricate shape and design at the cost of the additional st ep of debinding. In order to reduce the duration of debinding, capilla ry extraction of the binder by wick powder may be employed. The presen t investigation examines the influence of four variables in the wickin g process in order to optimize it: specimen height, temperature, time, and wick powder size. The results confirm some aspects of a theoretic al model accepted for injection moulding, the dependence on height, an d on temperature through the binder viscosity. The dependence of fract ional debinding on time implied by the model is at variance with the e xperiments, as well as the total time of debinding and an explanation is given. The capillary pressure of the wick is reformulated in terms of pore dimensions. The permeability of the wick can be the limiting f actor, rather than the permeability of the metal powder A criterion to detect wicking action has been established and tested.