The influence of the refractory coating which is a mixture of silica flour and kaolin on the surface roughness of the plate castings produced using evaporative patterns had been considered in this work. The kaolin was used as a binder and ratio method was employed to form basis for the factorial design of experiment which led to nine runs of experiments. Methyl alcohol at 99% concentration was used as the carrier for the transfer of the coating to the surface of the patterns. Pouring temperature was observed as a process parameter alongside the mix ratios of the coating. Attempts were made to characterize the refractory coating by using two methods; differential thermal analysis (DTA) and X-ray diffraction. Attempt was also made to characterize the casting material. Gating system design was done for the plate casting to determine the correct proportions of the gating parameters in order to construct the gating system properly to avoid turbulence during pouring of liquid metal. A digital profilometer was used to take the measurements of the surface roughness. It was observed that the mix ratio 90% silica flour-10% kaolin produced the lowest value of the surface roughness of the plate castings and had the lowest material loss in the DTA test. The pouring temperature of 650 o C produced best casting.
This investigation aims at evaluating some process parameters for the production of aluminium alloy investment castings using polystyrene as pattern material and Plaster of Paris as investment slurry. The process parameters considered are the shell thickness, casting thickness and pouring temperature and the effect of varying these parameters on the mechanical properties of aluminium silicon magnesium alloy (A356) produced through the investment casting method is being investigated in this work. The effects of these variables were studied using design of experiments (D.O.E) via Taguchi's L9 orthogonal array method. The castings produced were subjected to mechanical tests such as tensile strength, impact strength and hardness test using Monsanto tensometer and Avery impact and Avery hardness testing machines respectively. The results obtained were analysed using Minitab software 17. The results showed that the tensile strength, impact strength and hardness were optimum when the shell thickness was 5 mm, pouring temperature was 665 o C and the bar cross section was 64 mm 2 respectively. The investigation concludes that investment shell of thin thickness, casting thickness of smaller bar sections and lower pouring temperatures in the range of 665 o C -690 o C were the most suitable parameters that produced optimum results with better mechanical properties in this study.
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