Influence of investment granulometry on the castability and surface roughness of castings obtained with Ni/Cr alloys

Abstract

The aim of this study was to verify the influence of investment granulometry on the castability and surface roughness of Ni/Cr castings. Four investments were selected for casting according to decreasing order of granulometry: Heat Shock > Micro Fine 1700 > Gilvest HS > Castotal. Castability was verified by means of 40 specimens made with a polyester screen and determined from the number of segments completely filled by the cast alloy. To analyze the roughness, 40 disk-shaped wax patterns were made (15 x 3 mm), and after inclusion in the investments, they were cast and analyzed, before and after polishing (Mitutoyo SJ-201). The measurements were statistically analyzed (1-ANOVA - Tukey - p < 0.05) and it was verified that Heat Shock provided the worst castability with significant difference (p < 0.05) when compared with other investments. This material and Castotal presented similar roughness before and after polishing, with statistically significant difference (p < 0.05) between them and Gilvest and Micro Fine. It was concluded that investments with smaller granulometry provided castings that were more complete, but not smoother.