Effect of Powder Lubricants on Dimensional Change of Iron Powder Compacts

Abstract

The dimensional changes in the axial direction of iron powder compacts (10 mm diameter, 10 mm height) pressed under 2-8 t/cm² (196-784 MPa) were measured along the process of production; these are, after unloading, ejecting, dewaxing at 600°C (873 K) for 30 min and sintering at 1100°C (1373 K) for 60 min in cracked-ammonia.
When 0.7 wt% of powder lubricant was added to iron powder, the magnitude of the axial spring-back was larger than that observed when die-wall was lubricated. But, each powder lubricant did not give appreciable difference in magnitude.
Some compacts swelled in dewaxing. Greater swelling was observed on compacts pressed under high pressure using lubricants which were viscous in the molten state.
Shrinkage by sintering grew large with the increase of the sum of spring-back and swelling. But, this tendency disappeared when the sum surpassed 3%.