Abstract

The permeability, green compressive and tensile strength of foundry cores bonded with composite mixtures of bentonite clay with each of grades 1 and 2 Nigerian acacia exudates were determined. Silica sand grains were used as base for the specimens which in accordance with foundry standard were cylindrically shaped for green permeability and compressive strength but shaped like figure eight for tensile strength test. A standard permeability meter and a shatter machine were used to test air permeability and collapsibility of cores. A standard universal strength machine was used to test the compressive and tensile strength of core specimens. The tensile strength specimens were baked at 200°C for 1 - 3 h and then oven cooled before test. The result showed that bentonite clay addition to acacia bonded cores had beneficial effects on only permeability of cores. It caused an average in permeability by 62 and 8% for grades 1 and 2 acacia bonded cores respectively. Averagely it depressed green compressive strength by 10%, tensile strength by 2 - 4% and shatter index by 6%. This means that when grades 1 and 2 acacia species is used as main binders for sand cores for casting alloys that require high permeability like iron and steel casting of intricate shapes bentonite clay addition will serve without wide adversity on other important core properties.

Key words: Foundry, cores, bentonute clay, acacia exudates.