STUDY OF SPECIFIC SURFACE & WATER ABSORPTION, CAPACITY OF THE LOCAL SANDS,.

Abstract

Although the performance of moulding sand depends upon its constituents namely sand, binder and the additive, if any, but the sand being the major constituent affects the performance to a greater extent. The influence of sand is mainly determined by its physical and chemical characteristics. Under the physical characteristic, the most important ones are as follows :- 1. Sand grain shape 2. Sand grain size and distribution 3. Sp. surface area of sand grains and 4. Water absorption capacity. According to shape the sand grains are classi-fied as round, sub-angular, angular and compound. But this classification does not give any idea as to how much the grains deviate from sphericity i.e. the degree of angularity. As such, to have a clear picture of the same some definite index must be found which should indicate its degree of angularity. For determining the grain size and grain size distribution the sand is subjected to the conventional sieve analysis. The surface area can also be measured by sieve analysis after doing some minor calculation but this does not give the actual surface area since in sieve analysis the sand grains are assumed to be spherical in shape which is never true. The determination of specific surface alone can be of interest for the preparation of core sands. Surface area of sand grains has a decided effect on film thickness of binders - an imp&rtant consideration in the CO2 and shell moulding processes. The quantity of binder required depends on the sp. surface. However, this relationship exists only for pure silica sand where each grain is a single , rolled, compact crystal of quartz. There are however, certain silica sands containing a large quantity of porous grains which require more binder than the specific surface would indicate due to porosity of the grains and which does not act as a binder. In the light of above facts in one aspect of the thesis, it is proposed to determine the actual specific surface of the local sand grains and thereby to find out the true performance of the local sand. In fact the survey of literature indicates that some work has been reported by previous workers in this fia d but this work has been limited to the study of either foreign sand or so me standard sands which of course are not of much use to our Indian Foundries. The second aspect of the thesis is to determine the water absorption capacity of local sands„ and to find out the possible correlation with the physical properties of moulding sands. It is felt that the above investigation will be useful to the foundrymen in the selection and development of sands for casting various alloys..