Influence of paraffin wax characteristics on the formulation of wax-based binders and their debinding from green molded parts using two comparative techniques

The influence of paraffin wax characteristics on the formulation of wax-based binders has been examined. Four paraffin waxes (PW1, PW2, PW3 and PW4) were physically and molecularly evaluated and four binder systems 1-4 were formulated by mixing the major binder consisting of the paraffin wax with stearic acid (SA) and the minor binder: poly (ethylene-co-vinyl acetate) (EVA). Differential scanning calorimetric (DSC) and thermo, gravimetric analysis (TGA) were used to evaluate the thermal characteristics of the pure binder components and the formulated binder systems. Also, the rheological properties of the formulated binder systems and feedstock were studied to measure their viscosities. Data indicated that the binder system no. 4 consisted of 35 wt.% EVA (containing vinyl acetate content of 9 wt.%), 62 wt.% Of PW4 and 3 wt.% of SA is the preferable binder for powder compression or injection molding. Also, in order to compare between the two debinding techniques (solvent evaporation-condensation and solvent immersion techniques) to extract the soluble binder components (paraffin wax and SA) completely from the green molded parts, powder compression molded parts were prepared and subjected to both techniques. It can be concluded that solvent immersion is a preferable technique as it saves the amount of solvent used as compared with the evaporation-condensation technique. Consequently, the solvent immersion technique using cyclohexane solvent at extraction temperature of 40 degrees C and after extraction time of 5 h are the most suitable conditions for extracting the major binder and SA constituents completely from the binder mixture in the green molded part. (C) 2009 Elsevier B.V. All rights reserved.