Preparation of a mineral casting for eventual recycling

摘要

Large mineral castings, such as machine beds or frames, are difficult to break apart when they have reached the end of their working lives. The task can be eased by casting in steel rods of about 8 mm diameter, in a zigzag pattern, whose ends protrude for about 10 mm from the casting. The protrusions are the contacts to a low voltage (1-5V) generator that can produce up to 15 kA. This heats the rods in a few minutes to near 250 deg C so that they expand rapidly and, together with gases formed from any resin components, exert a force of about 130 MPa on the casting, which usually has poor thermal conductivity. The heating rods are concentrated in areas of least cross-section to limit the time for heat transfer. In uniformly thick sections they are placed on the centerline.