Influence of process carbon on the flow and compaction properties of bentonite bonded moulding sands

摘要

The changeover from jolt compaction to today's compaction processes has led to a fundamental change in the compaction characteristics with clay-bonded sands. The individual processes differ in particular with regard to the direction of movement of the compaction front. Whilst with jolting the compaction starts at the pattern, with squeezing and impact compaction a compaction front starts at the back of the mould and travels towards the pattern plate. In so doing the top sand layers are firstlythrust together and under further increasing compaction moved towards the pattern. The wedging together of the sand grains immediately produces considerable lateral pressures at the start of compaction, which in time considerably increase the friction atthe walls of the filling frame or flask. There is a marked decrease in the packing density in the edge zones, which results in non-uniform distribution of the mould hardness or mould strength. As a consequence of this there is an increase in the tendencyto swell in the critical areas. Moulds often do not properly fit together.