Powder injection molding: A comparison of two debinding procedures based on solvent extraction

As-injected Fe-2%Ni samples with a binder containing 3.3 wt.% polypropylene (PP), 2.8 wt.% paraffin wax (PW) and 1.7 wt.% ethylene-vinyl-acetate (EVA) were subjected to a two step debinding process, i.e., chemical (solvent) combined with thermal extraction. The chemical debinding was carried out by: (i) immersing the samples in boiling hexane; (ii) exposing the samples to condensing hexane vapor. In order to evaluate the debinding rate, samples were taken at different exposing times and the mass loss was measured, The pore structure evolvement was then evaluated by mercury porosimetry and scanning electron microscopy. Although the mass loss under condensing vapor conditions at the beginning (t < 2 h) was lower than in the case of immersion extraction, for both procedures it tends to level off at 4.5 wt.% when time approaches 4 h. From the mass loss and DSC analyses it can be concluded that at this stage most of the PW and EVA was extracted. SEM observations show that after solvent debinding the powder particles are held together by a web-like structure of PP.