Debinding solvent extraction

Solvent extraction involves immersing the component in a liquid in which at least one binder can be dissolved, leaving an open porous structure for subsequent binder burnout. Full debinding is desirable because the resulting powder compaction will have almost no strength. The time t for debinding is given by [225] ... 

Thermoplastic based binders are by far the most widely used. These forms of binder usually contain a wax as a major component and a thermoplastic as the minor component. Additives are usually added for lubrication, viscosity control, wetting and improving powder-binder interaction. Debinding of such binders is normally achieved via thermal degradation, wicking, solvent extraction or even photo-degradation. Thermoplastics commonly used include polyethylene, polystyrene, polypropylene and ethylene vinyl acetate. Table 2 highlights some of the common thermoplastics used in PIM or MIM processes. 

Thermosets, such as phenolics and epoxies, are polymers that hardened irreversibly by means of a cross-linking reaction. This usually happens at elevated temperature or upon mixing the resin with a hardener. Once the reaction is completed, a three dimensional cross-linked network structure is formed and the reaction is irreversible. Debinding is also accomplished by thermal degradation or solvent extraction. Table 4 shows some example of thermoset used in MIM or PIM. 

In order to eliminate flaws inherent to thermal debinding and to shorten the duration of this stage, other techniques for the extraction of organic shaping additives have been developed. These techniques are based on an under- or overpressure of the treatment atmosphere, on microwave heating, capillary migration of molten binder, sublimation of a binder in aqueous phase, or solubilization by catalytic reaction or solvents. 

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