RELATIONSHIPS OF PRESSURE RATIOS FOR COPPER POWDERS

초록

Pressure ratio is defined as the ratio of bottom punch (stationary punch) pressure to compacting pressure on the top punch (moving punch). Its use should be of great interest in quantitatively studying the effect of lubricants added to the powder or sprayed on the die-walls [1]. Duwez [2] tried to measure the pressure ratio with their experimental equipments, but were, in this case, unable to compensate for the movement of dynamometer in the die-wall, which disturbs uniform flow and the ability of powder to support shear. In order to evaluate the performance of various lubricants, it is necessary to express the interface friction quantitatively, in terms of a factor or a coefficient. Friction of a lubricant is most commonly measured by the ring test in metal forming [3]. Similarly in powdered metal compaction, the pressure ratio transmitted between the top and bottom punches could be a parameter measured by the uniaxial compaction of the solid cylinders and could predict the friction coefficient.