[Measurement of casting shrinkage with U-type tungsten die (author's transl)].

Abstract

A simple method was developed for the accurate measurement of casting shrinkage using a U-type tungsten die. A wax pattern was prepared on the die and both were invested together in phosphate bonded investment. Cobalt-chromium alloy, Regalloy shot 2, was cast and its shrinkage was calculated from the distance of the gap created between the die and the cast piece. In order to evaluate the effects of some manipulative variables on the cast shrinkage value of the alloy, mold temperature, kind of liquid for the investment and powder/liquid ratio were varied and shrinkage values were obtained. The results showed that the shrinkage value was not affected by the kind of liquid and the power/liquid ratio, but significantly decreased as the mold temperature raised up to 600 degree C. However, this effect was eliminated by means of substractive correction of the thermal expansion of the tungsten die. Thus, the casting shrinkage of the cobalt-chromium alloy, Regalloy shot 2, was calculated to be 2.08 +/- 0.02%. The casting shrinkage of pure gold was also measured with the same procedure. The casting shrinkage was calculated to be 1.73 +/- 0.04% and highly consistent with the value (1.74%) reported by R. Earnshaw. This suggested that the developed method was sufficiently effective for the accurate measurement of casting shrinkage.