Materials and manufacturing processes vol:10 issue:3 pages:439-451
A two-component model binder system composed of the low molecular weight component stearic acid (SA) and the polymer polypropylene (PP) was chosen to study the kinetics of long-term conventional thermal debinding of SA from a metal powder compact formed from spherical stainless steel powder. The burnout temperature of the two binder components is widely different, so that the SA-weight loss could be followed in the lower temperature regime independently by thermogravimetric analysis. The experiment provides at constant temperature an exponential decrease of the SA-weight with debinding time. It is suggested that the debinding rate is controlled by diffusion of SA in the thermoplastic to inner surfaces of pores, which develop in the material during debinding. This is in correspondence with previous work on short-term debinding. The kinetics for the PP/SA-system are compared to previous results on binders with other polymer components. The second part of this paper reports about MIM-processing of commercial steel parts with a novel proprietary binder formulation which allows a distortion-free conventional thermal debinding within hours.