The purposes of this study were to investigate the impact of proportions of cast iron scrap, steel scrap, carbon and ferro silicon on hardness and the quality of cast iron and to obtain an appropriate proportion of the four components in iron casting process using a mixture experimental design, analysis of variance and response surface methodology coupled with desirability function. Monte Carlo simulation was used to demonstrate the impacts of different proportions of the four components by varying the proportions of components within ±5% of the four components. Microstructures of the cast iron sample obtained from a company and the cast iron samples casted with the appropriate proportions of the four components were examined to see the differences of size and spacing of pearlite particle. The results showed that linear mixture components were statistically significant implying a high proportion of total variability for hardness of the cast iron samples explained by the casting mixtures of raw materials. The graphite of the sample casted from the appropriate proportion has shorter length and more uniform distribution than that from the company. When varying percentages of the four components within ±5% of the appropriate proportion, simulated hardness values were in the range of 237 to 256 HB.

Sand molding casting has been widely used for a long time. But, one of its main drawbacks is that surface quality of the castings is not good enough for some applications. The purposes of this research were to investigate the effect of addition of sawdust ash of rubber wood (SARW) on molding sand properties and the surface quality of iron castings and to find an appropriate level of SARW with the appropriate properties of the iron castings. The molding sand compositions for making a sand mold consisted of the recycled molding sand, bentonite, water and SARW. The percentage levels of SARW were 0%, 0.1%, 0.2%, 0.3% and 0.4%. The different proportions of molding sand samples were investigated for the molding sand properties including permeability, compression strength and hardness. The results showed that addition of SARW had an effect on the molding sand properties. The appropriate percentage proportion of molding sand was obtained at 95.8% recycled molding sand, 0.8% bentonite, 3% water and 0.4% SARW. There were statistically significant differences of mean surface roughness and hardness values of the iron castings made from molding sand samples without SARW addition and the appropriate percentage proportion of molding sand. In addition, the average surface roughness value of the iron castings made from the sand mold with the appropriate percentage proportion of molding sand was ~40% lower than those of the iron castings made from molding sand samples without SARW addition.