Compaction of homogeneous (Mn, Zn)-ferrite potcores

Abstract

The compaction of thin-walled potcore compacts (height 10 mm, diameter 15 mm, wall thickness 1 mm) with a high homogeneity is analysed. High homogeneity implies that the density is uniform throughout the compact. In order to attain this goal, internal and external friction are minimized while the mode of pressing and pressing velocity are optimized. Internal friction refers to friction between the powder particles, which is influenced by the particle size distribution and additives. The use of five different additives is evaluated. External friction relates to the friction between the powder and the die wall, which is influenced by the relative hardness of the die wall and lubricants. The effects of three different coatings and a lubricant on friction with the die wall have been investigated. The homogeneity of compacts with complicated shapes is affected by the formation of large local density gradients, which lead to differential shrinkage during sintering. By characterizing the shape of sintered products, it is shown that the inhomogeneity in compacts is reduced by optimizing the pressing mode and the pressing velocity. This improves the variation of the diameter over the height of the sintered potcores from 3 to 1.0%