Analisa Penambahan Bentonit 3%, 5%, dan 7% Pasir Hitam Terhadap Hasil Pengecoran Aluminium

Casting process is a process of making objects by melting some metals and pouring it into a mold cavity and let it freeze. One of the factors that affected the results of castings is the mold that we used. The purpose of this study is to know the effect of bentonite on casting. This study use black sand types with variations of the addition of bentonite 3%, 5%, and 7%. The results showed that from the chemical composition testing, there are 3 elements that become most influential on cast aluminum, it was Si (9.27%), Fe (2.07%), and Cu (1.77%). Take a look on the from of elements, this material can be classified as aluminum alloy silicon metal (Al-Si). The percentage depreciation for the variation of 3% bentonite is 1.96%, for the variation of 5% bentonite is 2.04%, and the variation of 7% bentonite is 2.7%. Testing the density of 3% bentonite variation of 2.46 gr/ml, 5% bentonite variation of 2.35 gr/ml, and 7% bentonite of 2.31 gr/ml. From the observation of porosity, the variation of 3% bentonite is the least porosity compared to 5% and 7% bentonite variation. Defects that occured on this study is because of the low permeability value which causes the air cant come out from the sand mold. The permeability value of the 3% bentonite variation was 63.00 while in the 5% bentonite variation was 56.73 and the variation of the bentonite was 7% 50.17. The highest clay content results occurred in 7% bentonite variation with a value of 17.04%, while the 5% bentonite variation was 10.92% and the lowest value occurred in 3% bentonite variation which is 4.60%. The highest rockwell hardness results were found in 3% bentonite variation, reaching 62.4 HRB, while 5% bentonite variation was 62.2 HRB, and 7% variation was 61.1 HRB