COMPACTION OF HOMOGENEOUS (MN, ZN)-FERRITE POTCORES

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 compac t. In order to attain this goal, internal and external friction are mi nimized while the mode of pressing and pressing velocity are optimized . Internal friction refers to friction between the powder particles, w hich is influenced by the particle size distribution and additives. Th e use of five different additives is evaluated. External friction rela tes to the friction between the powder and the die wall, which is infl uenced by the relative hardness of the die wall and lubricants. The ef fects of three different coatings and a lubricant on friction with the die wall have been investigated. The homogeneity of compacts with com plicated shapes is affected by the formation of large local density gr adients, which lead to differential shrinkage during sintering. By cha racterizing the shape of sintered products, it is shown that the inhom ogeneity in compacts is reduced by optimizing the pressing mode and th e pressing velocity. This improves the variation of the diameter over the height of the sintered potcores from 3 to 1.0%.