When a powder is compacted the air present must either leave the die cavity or remain at higher than atmospheric pressure in the pores. On the release of the applied pressure this air can still be at high pressure and might force apart the bonds between the agglomerates and lead to horizontal cracks. Arrays of such cracks are known as laminations, and seem to be an ubiquitous problem in die and isostatic pressing. One aim of this paper is to show whether or not air pressure can cause laminations and it is found that it can. A simple mathematical model of the air movement has been devised and checked against the experimental results. This model is then used to find the optimal movement of the top-plate with time so as to expel the maximum amount of air in a fixed cycle time and for a fixed amount of compaction.
|Number of pages||4|
|Journal||British ceramic. Transactions and journal|
|Publication status||Published - 1 Nov 1990|