The melting process of a gold bar involves three basic stages: heat the precious metal until it melts, pour the molten charge into a mold cavity, and cooling and solidification in the shape of the mold cavity. It is important to indicate that much of the art and science of the melting process is concerned with control of things that happen to gold as it solidifies. Basically, an understanding of how gold solidify, therefore it is important to the gold metallurgical operation. In this way the control of the melting, and solidification to produce better products is essential in order to identify the problems found in the melting process.
It has been noted that the change from hot molten charge to cool solid bars takes place in three main stages. The first one is the cooling of the metal from the pouring temperature to the solidification temperature. Essentially, the difference between the pouring temperature and the solidification temperature is known as the amount of superheat, which determines the amount of time the operator has available work with the molten charge before it starts to solidify.
The second stage is related to the cooling of the gold bar through the range of temperature at which it solidifies. It has been established that during this stage, the quality of the gold or Dore bar is established. Shrink holes, blow holes, hot cracks and other problems are produced while precious metals solidify. The last stage is referred to the cooling of the solid gold alloy to room temperature. It is during this stage of cooling that warpage and metal stresses occur.
Gold bar cooled in water
Gold Bar Solidification Process | Gold Contraction | Gold Bar Crystallization | Heat Transfer from the Gold Bar | Effect of Trapped Gases on Gold Bar Quality | Gold Bar Pouring Temperature | Molten Gold Pouring | Common Defects of Gold Bars | How to Identify Gold | Flux Mixture and Melting Gold | Gold Bars with Serrated Edges | Molds and Gold Bars |