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www.metalcastingdesign.com for an article on the investment casting of precious metals in jewelry.
Casting the Metal Michael Arvay loves his precious.
Precious metals, that is. 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. Permanent mold casting involves the use of coated metal molds to produce products with good mechanical prop- erties and smooth surface fi nishes. One of Market Harmony’s machines
is a tilt-pour apparatus that automati- cally tilts to fi ll 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 geometri- cally simple, Arvay and operations like his encounter some of the same concerns that casters of the most intricate products come across, spe- cifi cally surface fi nish 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.” While Arvay’s casting shop is a
small boutique operation serving cus- tomers with extensive hands-on labor, other types of precious metals casting facilities also exist. Valcambi, one of the world’s largest producers of gold bars, runs a highly automated shop that produces both permanent mold
castings and continuous 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 solidifi ed. After the rest of the product is solid, the bar is notched and broken off in the appro- priate lengths. Valcambi’s permanent mold and continuous casting lines work much like those in an automated production metalcasting shop, with robots per- forming the work that would normally be done by human employees. “We were the fi rst company to have
a fully automated unit to produce gold bars,” said a Valcambi spokesperson who wished not to be named. Because little premium is placed on
the geometric design of bullion bars, producers of the products focus on controlling a few casting process param- eters to fi nd success—alloy temperature and consistency, mold material/tem- perature and mold release agent. The ideal casting temperature of
gold is 2,080F (1,138C). According to Arvay, going over that temperature (superheating) is not advisable; falling below it is worse.
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.
24 Metal casting Design anD purchasing March/april 2010
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