The PIM industry is aware that premixes can vary in composition as a result of dusting and segregation. These effects are clearly evident in compositions that have a high alloy content. However, they appear to be present in all mixtures, independent of alloy content. While dusting is a frequent visible indication, segregation due to particle migration is less apparent, but is nonetheless quite well known.

Variations in composition due to dusting and segregation also give rise to variations in the mechanical and physical properties of blends and of parts made from these blends. It is difficult to quantify the effects of dusting and segregation. However, there is substantial evidence to suggest that these phenomena create both technical and economic problems for the PIM industry. In the former case, they limit the ability to blend metal powders without an additional binder. In the latter case, they may also cause dimensional variations that lead to part rejection, loss of productivity and poor overall economics.

A number of manufacturing options are available for eliminating or reducing the effects of dusting and segregation. The three most significant are: atomization of prealloys, diffusion bonding by annealing, and binder treatment of premixes.

Nitchen Polyvinyl acetate resins, pvac solid resins, HV-1 polyvinyl acetate and HV-4 pvac resin are highly recommended for use as binder in these formulations. Our products combine the following properties:

• Outstanding binding
• Excellent thermoplasticity
• Superior burn-out