2009 was 3,385.8 metric tons, which amounts to sales of $105.5 billion. In addition to gold bars, those figures in- clude consumption of gold in the form of jewelry, dental implants, electronics and industrial products, and other in- vestment products like coins. As with bullion, gold often finds its way into these products via the metalcasting process, but because the bars are not engineered components, they fly under the general metalcasting industry radar.


Casting the Metal Michael Arvay loves his precious.


Precious metals, that is.


The proper pouring temperature of gold is 2,080F (1,138C). Here, the material is poured into a metal mold to make a cast bullion bar in an automated permanent mold facility.


Arvay is owner and president of


Market Harmony LLC, Pittsburgh, a company that produces gold, silver and other bullion bars for the investor and collector. The company operates a small 6,000-sq.-ft. casting facility with four permanent mold casting lines, which produces bars with good mechanical properties and smooth surface finishes. One of Market Harmony’s machines


is a tilt-pour apparatus that automati- cally tilts to fill molds and is similar to those you would see in a production casting shop. The other three casting lines are comprised of dip-out furnaces and hand poured molds. The largest of the machines has a melt capacity of 1,000 lbs. of silver or 2,000 lbs. of gold. The small company’s production


numbers are limited to the demands of the volatile bullion market. “As the bullion prices go up, every-


one wants to have gold, so we have our highest production during those months, and the lowest production during market lulls,” Arvay said. While the operation is small and


manual and the products geometrically simple, Arvay and operations like his encounter some of the same concerns that casters of the most intricate prod- ucts come across, specifically surface finish defects and internal soundness. “When [we began] casting, the end


products would come out in a very raw state—dirty, malformed and ugly,” Ar- vay said. “We researched and innovated methods to try to solve these problems.” Precious metalcasters must be careful


not to introduce air into their castings and produce a part with excess poros- ity. According to a spokesperson for Valcambi, one of the world’s largest producers of gold bars, the bar must be plain, with no sharp edges, and it must show no deterioration from air pockets near the surface of the cast- ing. The spokesperson, who spoke on condition of anonymity, said porosity is more of a concern with silver castings than with gold, as silver has a higher affinity for oxygen. The Valcambi spokesperson also said


that steps can be taken in the casting process to eliminate porosity defects, just as in commercial plants. “You can put charcoal in the melt


to absorb oxygen,” he said. “Anything you can do in order to give the air a way out [of the mold cavity] helps. Then, it’s the temperature itself, the pouring speed and the temperature of the mold.”


The Gold and the New


While Arvay’s casting shop is a small boutique operation serving customers with extensive hands-on labor, other types of precious metals casting facili- ties also exist. Valcambi runs a highly automated shop that produces both permanent mold castings and con- tinuous bar stock castings. Continuous casting involves the feeding of molten metal through a graphite die machined to a desired shape. When the metal exits the die, the outer skin has solidi- fied. After the rest of the product is


Gold and other precious metals are refined into small grains to achieve the highest levels of purity possible before they are melted and poured into casting molds.


MODERN CASTING / September 2010 19


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