Ejection and green strength of die pressed compacts

摘要

The ejection characteristics and the green strengths of a range of die pressed cyclindrical alumina compacts, prepared by uniaxial pressing in cylindrical moulds, is reported. The value of static ejection force is seem to vary with the die-wall frictional forces and depended upon the aspect ratio, the state of lubrication, and the ultimate compaction pressure. The presence of a wall lubricant, during the compaction process, significantly decreases the ejection pressure, due to a reduction in the frictional forces at the powder - die wall itnerface. The data show that the strength of the green compacts increases up to a certain compaction pressure. Upon further increasing the compaction pressure, the strength of the green compacts decreases due to formation of the laminar cracks. The positions of these laminar cracks, in the green compacts, were manifested in the ejection force profiles at the location of lamianr cracks.