Instrumented Compaction Experiments under Varied Climatic Conditions
From empirical observations in industrial practice it is known that compaction behaviour and quality of uniaxial pressed ceramic compacts may be significantly influenced by climatic conditions during granulate storage and processing. At the same time, the type of basic material, added binders and lubricants can play a major role in most cases. In the present study, an attempt was made to reach a better understanding of the interactions between climatic conditions and compaction behaviour of silicon nitride granulates with different binder/lubricant systems by using instrumented compaction experiments. In addition to the continuous measurement of the pressure-density development and the strength of the compacts, parameters are measured which characterize the friction conditions, the total compaction energy and their single parts, the elastic redeformation in axial and radial directions. From the calculation of shear and compressive stresses, conclusions can be drawn regarding acting failure mechanisms and predictions of the expected density distribution can be given. For the examined silicon nitride granulates a deleterious influence of moisture on the whole pressing process and the defect rate of the compacts after storage of granulates at a humidity of more than 50 % before compaction was verified. For this material the changes in compaction behaviour are not reversible after storage at lower humidity.