Square Root Wick Debinding Model for Powder Injection Moulding

Abstract

An alternative wick debinding model has been developed that predicts a square root dependence of degree of debinding on debinding time, in agreement with the known experimental behaviour of this quantity. The model is based on the inverse flow of the phase separating binder/air front, for which experimental evidence is presented. Debinding of flat specimens having both sides in contact with the wick proceeds with double speed compared with one sided extraction. A review has been carried out of total debinding time which is found to vary over more than two orders of magnitude, corresponding roughly with a viscosity variation over a similar range. The discrepancy between the experimental value of the wick debinding time and a previously established theoretical value can be ascribed to two causes. First, the capillary pressure difference would be smaller by a factor of about 10 if the proper pore dimensions were inserted: minima for the medium being depleted, maxima for the wick. The second cause is the permeability drop by a factor of about 100 due to artery formation in the draining compact. This is shown to be a natural consequence of the model. PM/0633