Experimental measurements in melting ingots in the melt of the same material

Abstract

This study concerns the melting of ingots of different materials in melt of the same material. We investigated the pure materials ice, lead, tin, and zinc, the magnesium alloys AZ91 and AM50, and the aluminum alloy A226. We used melting pots made from steel (for Pb, Sn, Zn, AZ91, AM50) and clay graphite (for A226) with a volume of 16 L, inserted into a resistance furnace. Some experiments with AZ91 were also carried out in a 2500 kg industrial furnace. The ice ingots were melted in a 20 L beaker. The temperature profile adjacent to the melting ingot was recorded over time. From this profile, the mean temperature of the melt adjacent to the ingots was calculated. Together with the geometrical and thermophysical properties of the investigated materials, the dimensionless Nusselt, Rayleigh, Prandtl, and Stefan numbers were calculated and interpreted as an empirical function, Nu=0.114·(Ra·Pr)0.291·Ste0.754. This function describes the melting behavior of all of the materials considered. This partly agrees with results from the literature, but considerable deviations were also determined. Once the mean temperature is known, the time needed to melt the different materials in different geometrical shapes can be estimated along with the maximum melting rate. This simple model helps understand technical processes where melting of materials is relevant, for example when calculating energy consumption in the foundry industry.