Capillary flow of hard-metal carbide powder compounds

Experimental data relating to capillary flow of hard-metal carbide powders compounded with various polymeric binders are presented. Such powder-binder mixtures are used for the production of sintered hard-metal carbide components, mainly by injection moulding. In addition to measurements of their rheological behaviour in a capillary rheometer, the compounds were also subjected to thermo-gravimetric analysis in order to assess the ability of the binder to debind properly. The binder composition was varied from paraffin wax and its combinations with polyethyleneglycols to multi-component binders consisting of polyethyleneglycol, polyethylene, ethylene/vinyl acetate copolymer, and paraffin wax. Two kinds of hard-metal carbide powders differing in particle size distribution (uni-modal, bi-modal) wee used. Although the compounds containing the simpler binder types had acceptable flow properties, their debinding behaviour was unsatisfactory. The multi-component compounds exhibited considerably better debinding; their flow was stable within a wide range of shear rates. Flow instabilities appearing at high solids loadings can limit the processability of the compounds used.