The Role of Wet-Tensile Strength of Foundry Sands in the Surface Finish of Aluminium Sand Casting

Abstract

0NE of the most striking features of industrial deve-lopment during the past decade has been the rapid growth in the use of aluminium and it, alloys in the form of castings. To obtain sound casting has always been a prob-lem for the foundry engineer, as the qualities required of it moulding sand are in some measure contradictory and a compromise must be made. Thus permeability is favoured by a low clay content and coarse particle size, whereas a smooth finish calls for a line sand with a higher clay content.Similarly, green strength is impr- oved by the addition of clay up to a certain point but permeability is reduced. Further permeability and green strength depend largely on the moisture content. These conventional green properties do not allow conclusions of sand properties on casting conditions 1 2, because all these are tested at room temperature, where temper-ature and material distributions are uniform inside the moulding sand. To overcome the above difficulties a new concept of Wet-Tensile Strength has been developed recently in the Foundry institute of Rhcinsch- West falischen Technischen Hoehschule Aachen (West Germany. It shows a very good correlation with the scabbing tendency of moulding materials and has been found to be of practical importance in order to control the quality of' aluminium castings in the foundry