SQUARE-ROOT WICK DEBINDING MODEL FOR POWDER INJECTION-MOLDING

An alternative wick debinding model has been developed that predicts a square root dependence of degree of debinding on debinding time, in a greement with the known experimental behaviour of this quantity. The m odel is based on the inverse flow of the phase separating binder/air f ront, for which experimental evidence is presented. Debinding of flat specimens having both sides in contact with the wick proceeds with dou ble speed compared with one sided extraction. A review has been carrie d out of total debinding time which is found to vary over more than tw o orders of magnitude, corresponding roughly with a viscosity variatio n over a similar range. The discrepancy between the experimental value of the wick debinding time and a previously established theoretical v alue can be ascribed to two causes. First, the capillary pressure diff erence would be smaller by a factor of about 10 if the proper pore dim ensions were inserted: minima for the medium being depleted, maxima fo r the wick. The second cause is the permeability drop by a factor of a bout 100 due to artery formation in the draining compact. This is show n to be a natural consequence of the model.