POROSITY AND STRENGTH PROPERTIES OF GYPSUM BONDED INVESTMENT USING TERENGGANU LOCAL SILICA FOR COPPER ALLOYS CASTING

Abstract

In this study, several formulations of gypsum bonded investment (GBI) as a mould for copper alloy casting has been developed and their properties had been investigated. The mould was developed using Terengganu local silica sand with the average particle size of 220–250 µm, acted as a refractory and Plaster of Paris (POP) as a binder. The formulations used were 75% local silica, 25% plaster and various amounts (31–37%) of water. The compressive strength, tensile strength, porosity, core hardness and mould hardness properties of the prepared GBI were studied. It has been found that both compressive strength and tensile strength reduced with a water content due to an increment of mould porosity which was confirmed via Scanning Electron Microscopy analysis. The mould hardness was found unchanged, but the core hardness was slightly reduced with the increment of water. The compressive strength of GBI moulds developed in this work was in the range of 600–1100 kN/m2, which was sufficient for copper alloy casting.

Keywords

• Copper alloys casting
• Compressive strength
• Hardness
• Gypsum bonded investment