This study developing mathematical model to optimize heat treatment process to obtain the most significant parameter that affected tensile strength of duralium through multistage artificial aging. The process parameters in this study were temperature of aging, holding time of aging, and artificial aging process was conducted in double stages. The experiments were conducted according to central composite design matrix. The adequacy of developed model was analysed by analysis of variance (ANOVA). The optimum parameter of multistage artificial aging was obtained for maximum tensile strength of duralium.

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Bucket teeth are a part of the coal process circuit in bucket excavator machine. It is used to dredge the overburden or a piece of the land that covers coal piles. Bandung Polytechnic of Manufacturing produces the product with AISI 4140 steel. The problem with batch production is that it has a wide variety of hardness as the result of using a quenching by blower. Therefore, there needs an alternative to a thinner hardness of bucket teeth. This research explores the possibility of using spray quenching method. The method uses the spray to quench the samples on the rotated concrete steel shelf evenly. The Shore scleroscope hardness test performs three times on the products at two points: the tip and 80 mm from the tip. The results are averaged later on. They show that spray quenching produced a thinner hardness variety compared to the blower product. Product using blower has the hardness of 25.16 HRB at point 1 and 15.66 HRB at point 2. Product with the first spray quenching has the hardness of 15.1 HRB at point 1 and 11.56 HRB at point 2, and after the second spray quenching became 7.3 HRB at point 1 and 8.4 HRB at point 2. Thus, spray quenching provides a more uniform hardness along the teeth and can be a substitute for the traditional quenching method.

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During the solidification process, metal liquids turn into solid geometry units including the riser and gating system. The disruption in the liquid flow often causes shrinkage in the object. Critical Solid Fraction Point is a critical point where the continuous liquid supply turned solid and unable to pour to some sections. Simulation software can predict the critical solid fraction time of an object and the liquid supply behavior. The simulation helps the designer in the casting design. The application of low steel alloys in the cement industry, e.g., the Diaphragm, needs development to minimize the shrinkage. This research aimed to analyze the critical solid fraction point in the diaphragm steel casting products. The primary objective of this research was to predict the critical solid fraction point during solidification, started from the longest time in the riser/feeder using SOLIDCast 8.1.1 casting software and provided improvement recommendation to minimize the shrinkage.