The Effect of Lubricants on Closure of Large Pores During Powder Compaction

Abstract

The effect of several lubricants on the compaction behavior of spray dried alumina was examined The study investigated the ability of the lubricants to aid in the closure of residual intergranular porosity. Computer modeling was used to examine factors that affect closure of intergranular pores in powder compacts. Introduction There is a need to increase the quality of dry pressed parts. High volume markets for structural ceramics will be realized if low cost parts can be manufactured, making dry pressing a likely method of forming Also, there is a demand for increased quality for products that are currently dry pressed, such as spark plugs. [1] The compaction behavior of the powders and the quality of compacts pressed from several industrially spray dried powders was investigated. [2] The results indicated that quality issues lie in residual intergranular and other large pores in the microstructure of these compacts. The residual intergranular pores in the microstructure of compacts of industrially spray dried powder was found to reside in regions where granules did not deform, fracture, and knit with neighboring granules During the compaction process, organic additives in the spray dried powder are extruded or displaced from particle-particle contact and also provide lubrication to enhance particle-particle sliding. [3] These processes provide particle mobility to allow intergranular porosity to be eliminated during compaction. Computer modeling was conducted in conjunction with experimentation. The model examines the ability to deform a granule as a function of the coefficient of friction of the particles composing the granule. This will provide better understanding of compaction behavior.