Experimental and Numerical Study of Permanent Mold Casting of Bismuth Bronze Pipe Fitting

The applicability of lead-free bronze to permanent mold casting has been reported only in fundamental studies. This study experimentally and analytically studied the applicability of bismuth bronze alloy to permanent mold castings with casting shapes similar to actual pipe fittings. The Vickers hardness of a permanent mold-cast bismuth bronze pipe fitting was 22 HV higher than that of the sand mold-cast bismuth bronze pipe fitting, and the increase in tensile strength of 75 MPa can be expected from the conversion formula between hardness and tensile strength. However, the permanent mold-cast bismuth bronze pipe fitting had defects such as shrinkage porosity, solidification cracking, and surface porosity. As a result, all permanent mold-cast pipe fittings leaked in the pressure leak test. From the results of the retained melt modulus analysis using casting simulation software, it was found that a relatively small amount of molten metal compensated for solidification shrinkage in the permanent mold casting. This caused the shrinkage porosity, hot tearing, and surface porosity in the permanent mold-cast pipe fittings. Therefore, the gating and risering system must be carefully considered for permanent mold casting of bismuth bronze products. This study showed that the retained melt modulus analysis is effective for considering gating and risering systems and predicting defects caused by insufficient feeding. In addition, surface porosity requires measures such as increasing machining allowance.