Densification of the Plastic Ball Compacts during the Hot-Pressing

Abstract

For the purpose of getting a better insight into the initial stages of densification during the hot-pressing, the hot-pressing experiments using the compacts of amorphous polystyrene sphere were performed. The size of the amorphous polystyrene plastic sphere was 0.695mm in diameter.
The obtained experimental data showed that the densification curves were divided into three parts. These parts were characterized by an initial rapid densification followed by an intermediate stage such as Murray's relation and finally a much slower process. On the other hand, it has been reported that the rapid densification in the initial stage was attributed to; (a) the particle rearrangement, (b) the influence of the porosity on the applied load, (c) the plastic flow within the solid particle.
To ensure these effects, the creep experiments using the sintered polystyrene sphere compacts which had various porosities were performed. From these experiments, it was found that the visco-elastic deformation within polystyrene itself and the influence of the porosity on the applied load could be effective, the former in paticular. In spite of these facts, the rearrangment of the spheres within the sintered body could not be observed in these experimental conditions. These were the contrast to the reports which had been presented.
In the intermediate stage of densification, Murry's relation was valid for the experimental data. In this stage, it was reasonable that the densification proceeded by the viscous flow characteristics of polystyrene sphere.
The final stage of the densification which was a much slower process was attributed to the pore closure as some investigaters reported.
Besides, the effects of porosity to the creep rate in the sintered polystyrene plastic sphere compacts were determined. As the results, the following experimental equations were obtained.
J/J₀=1+5P
J=J₀ exp 3.7P
J₀: creep compliance for the zero porosity specimen
J: creep compliance for the P % porosity specimen
P: prorosity %