Abstract:
The objective of this thesis was to study the factors related to the mixed proportions used in sand casting, containing sand, bentonite and water. The sample factory had problems with the quality of casting items that did not meet the standards. As a result, the surface defects of castings were as high as 5-6 percent of all types of them. Therefore, it was necessary to improve the mixing ratio of the sand mold to reduce the problem of casting surface defects.
An experimental design was used in this research by determining 3 main factors, including sand (x) with mixed proportion of 94.00 96.50 percent, divided into 8 levels. Bentonite (y) had a ratio of 3.00 5.00 percent, divided into 8 levels, and water (z) had a ratio of 0.5-1 percent, divided into 8 levels. Thus, 8 experiments were conducted with 3 replications for each level total of 24 trials.
The results showed that the most suitable mix ratio used to make sand castings, when x+y+z = 100 percent. Therefore, the equations obtained were: 1) the value equation of compact (C) = 50.444x + 35.983y + 103.198z; 2) perm (P) equation or P = 67.977x + 130.753y 251.266z; 3) green compressive strength equation (GCS) = 0.533x + 2.737y 7.916z; and 4) moisture equation (M) or M = 68.348x + 64.64y + 85.369z. When using 94% sand, 5% bentonite, and 1% water, substitute the values in the four equations, the sand casting mixture met the standards. When this ratio was used in the sample factory, it was found that the surface defects of the casting parts of the 1-inch 90 degree elbow decreased from 6.15 to 2.13 percent.