REGENERATIVE TREATMENT OF CLAY-BONDED USED CASTING SAND BY ATTRITION, DUST REMOVAL AND PRE-DRYING SAND BEFORE TREATMENT

摘要

A process is described for the recovery treatment of predominantly clay-bonded used foundry sand to allow its re-use in place of new sand. In such processes the sand grains are repeatedly accelerated and decelerated and are rubbed against one another by a combined impact stress and shearing stress so as to free the adherent shell from the sand cores and the shell material thus freed is removed pneumatically. According to the invention the process further comprises the step of setting the water content of the old sand before the stress treatment at most one per cent by weight. The low water content avoids the formation of lumps during the recovery process.