Microstructure and strength of needle coke modified ceramic casting molds

Properties of an investment casting mold using needle coke additions have been investigated in this work. The use of needle coke increases the mold thickness by a factor of 30% on flat section and 60% at sharp edges over that of a comparable full fused silica system. The extra mold thickness in the needle coke modified system, especially at edges, gives a higher load bear capacity. Ceramic molds modified with needle coke exhibit higher “green, dry” strength, and show less reduction in “green, wet” strength. The extra volume of cavity left after needle coke combustion is not acting as a significant defect which would reduce the hot strength of the mold.