The possiblity of producing bronze oilless bearings from prealloyed copper-30% tin powder was investigated. The possibility of studying the dimensional change and homogenization during the sintering of Cu-Sn alloys with this prealloyed powder was also explored.
The copper-30% tin prealloyed powder was made by gas atomization. The specimens of bearing shape were prepared by usual powder metallurgy techniques from the mixture of copper powder and the prealloyed powder. The copper powder sizes were similar to the commercial grade powder and the prealloyed powders were -200∼270 mesh and -400 mesh. The specimens were sintered in hydrogen-nitrogen atmosphere at temperatures ranging from 740℃ to 820℃ for times up to 24 minutes.
Specimens sintered for 12 minutes showed large dimensional growth between 780℃ and 800℃ and the growth was larger for the specimens made from larger prealloyed powder. During sintering at 820℃ large dimensional growth occurred between 6 and 12 minutes and small growth up to 24 minutes. The changes occuring during sintering could be easily observed from the shape changes in the spherical prealloyed powders shown in the microstructure. The composition homogenization was also revealed in X-ray diffraction measurement. The results suggest that the dimensional growth occurs when the tin rich melt flows to copper clusters forming homogeneous α bronze.
Measurements of oil impregnation and radial crushing strength indicate that oilless bearings with satisfactory properties can be produced from the copper-30% tin prealloyed powder. The results also show that the Cu-30% Sn prealloyed powder may provide a useful tool for studying the dimensional growth and homogenization during sintering of Cu-Sn mixtures.
