STUDY OF SOME PARAMETERS INFLUENCING VACUUM PROCESS OF MAKING CASTINGS

Abstract

The Vacuum process of making castings in which a binderless, dry silica sand is enclosed between two plastic films and rigidised by the agency of vacuum to form a mold. The present investigations were carried out to explore this process extensively. Five silica sands with A.F.S. grain fineness number of 123, 108, 94, 77 and 70; three plastic films of 0.05, 0.075 and 0.10 mm thicknesses; and seven absolute pressures of 160, 260, 360, 410, 460, 510 and 560 Torr (ie. 600, 500, 400, 350, 3009 250 and 200 mm. of Hg Vacuum) respectively were selected. The molten aluminium was poured at a temperature of 620 ± 10°C and with the vacuum being still maintained. After cooling for about 4 minutes, the vacuum was released and casting just withdrawn. The surface finish, dimensional accuracy, metallograpb.ic structure, tensile strength and microhardness of test cast-ings were evaluated. In general, the surface finish, was found to be excellent, the dimensional accuracy was very high$- metall-ographic structure, tensile strength and microhardness were found to be altered.