Some reasons for decreased service time of dies for Al hot extrusion

Abstract

In this contribution some important reasons for decreased service time of selected nitrided and coated dies for Al extrusion are explained. The influences of contact pressure, length of bearing surface, nitriding conditions and of the preparation of inlet edge of bearing surface at PVD CrN coating were studied. Laboratory tests of the wear at lower and increased contact pressure and an analysis of the wear on industrial dies were carried out. The die design and the flow of the extruded material should lead to a decrease of the contact pressure on the bearing surface. Two different modes of the initial wear progress on the area at the exit edge of the bearing surface were observed. Despite good adhesional and other relevant characteristics of CrN coating, the analysis revealed that inappropriate construction of the initial edge of the die bearing surface in combination with the maintenance of the die seems to be the main reasons for a considerably decreased service time of these dies as expected. © 2013 WIT Press.