GB1448953A - Powder forming - Google Patents

Abstract

1448953 Making metal powder BOC INTERNATIONAL Ltd 3 Jan 1975 [14 Jan 1974] 01746/74 Heading B3A Metal powder is made from swarf, e.g. of steel or copper (including turnings, chippings, and the like) by removing oil and grease from the swarf, cooling the swarf to below - 20‹ C., and milling the cooled swarf to form powder. In Fig. 1, swarf from a conveyer 10 passes over a vibrating screen 12 above an oil collecting tray 14 and passes through a rotary crusher where its size is reduced to about 6 mm. Residual oil and grease are removed in a centrifuge, the particles passing into a hopper 22 and travelling up a screw conveyer 24 to the inlet 30 of a rotary hammer mill 32. Liquid nitrogen is fed into the conveyer and mill by pipes 28, 40 so as to form a liquid bath in the bottom of the conveyer and hopper 22. Cold nitrogen vapour passes up the hopper to effect precooling of the fragments, a large quantity of which is kept in the hopper to reduce the amount of cold vapour passing back to the centrifuge. In another embodiment, the screw conveyer is replaced by a belt conveyer in a freezing tunnel fed with liquid nitrogen. The mill may be a ball or rod mill. Other coolants which may be used are solid CO 2 , liquid air, liquid argon, or liquid natural gas, which may contact the swarf directly, or through a bath. Mechanical refrigeration may be used.