Characterisation of Natural Moulding Sands from selected Deposits in Maiduguri-Nigeria for casting Applications

Abstract

Natural moulding sands consist of refractory sand grains associated with clay right from their deposit locations. In Maiduguri, there are some sand casting activities taking place. However, there seems to be no single graded source of moulding sand that the practitioners can use for producing qualitative sand castings. Therefore, this study was carried out to characterise moulding sands from five selected deposits in Maiduguri for possible use in sand casting applications. Chemical compositions of sand samples were determined using XRF Analyser while American Foundrymen‟s Society (AFS) standard laboratory tests were used to determine the physico-mechanical properties. The results of the characterisation revealed the following ranges of values; clay content from 21.8% to 47.2% corresponding to Pompomari and Gwange/Fori, grain fineness number from 50.94 AFS to 95.02 AFS corresponding to Pompomari and Gwange/Fori deposits.. Other physico-mechanical properties determined included; green and dry compressive strengths, permeability, loss on ignition and refractoriness. Results of chemical composition analysis show SiO2 having dominance in all the samples (90.10 % to 66.77 %) with trace elements of CaO, Fe2O3, Al2O3, MgO, TiO2, K2O, NaO2 also present within acceptable limits. The overall results show that all deposits have potential for use in sand casting applications for the casting of nonferrous metals and malleable and ductile iron. However, the clay content range given above is a major problem compared with the standards recommended by the American Foundry Society. This did not only limit their uses to low melting point alloys because of relatively lower refractoriness values but also possesses danger to their life expectancy. In conclusion, the use of the deposits characterised especially the Gwange/Fori deposit with clay content of 47.2 % should be used with caution because of the possibility of developing gas defects like blowholes and pinholes. All the other four deposits have been recommended for full exploitation for use in sand casting applications for casting of nonferrous metals as well as malleable and ductile irons. Finally, on the basis of the overall properties, the five deposits have rated in the following order of preferences; Dala Lawanti, Pompomari, Gwange/Fori, Gamboru and University of Maiduguri respectively.