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 June 2007

The Not-So-Invisible Metal

Zinc is sometimes called the invisible metal, but the truth is that zinc is everywhere. This is why one of ASTM International’s oldest standards, B 6, Specification for Zinc, is still an important and vital document that continues to evolve along with technology.

Photo illustrating zinc spray coating process.

“Frequently people don’t see zinc in the products it’s used in, or don’t realize it’s there,” says Richard F. Lynch, honorary chair of ASTM International Committee B02 on Nonferrous Metals and Alloys, and founder and president of Lynch and Associates, Inc., a metallurgical consulting firm. “The importance of zinc is monumental in terms of protecting iron and steel from corrosion.”

Lynch says that the major role of zinc today is to provide an outer coating for galvanized steel. This coating protects the steel used in automobiles, appliances and many other applications from rusting. “That’s the major role of zinc now and that is the part of the zinc business that is growing most significantly,” notes Lynch. “Cars don’t rust anymore because they have galvanized coatings under the paint. Bridges and guardrails don’t need painting for years due to zinc coatings.”

Zinc shows up in other areas. It is used in metal die-castings, on the exterior of cars, in many of the functional parts of automobile engines, in computers, electronic equipment and builders hardware as well.

In addition to all of this, Lynch says that zinc oxide is an activator during the rubber vulcanization process and works to improve the properties of rubber. It is used for similar reasons in the production of plastics and paint. And let’s not forget the United States penny—the coin is copper plated but has been 97.5 percent zinc since 1982.

All of these uses and others make zinc the fourth most used metal, so it makes sense that B 6 continues to be an important standard nearly 100 years after it was first published as “Specifications for Spelter.” Though “spelter” is not a commonly heard word now, in 1911 it was used to describe zinc cast in slabs for commercial use or crude zinc obtained in smelting zinc ores.

The original version of the standard listed four grades of zinc, two of which (High Grade and Prime Western Grade) are still listed in the recent major revision approved in 2006. Three additional grades, LME, Special High Grade and Intermediate Grade are also covered in the current edition of the standard.

“B 6 is the cornerstone specification for zinc in North America, Latin America and many other places throughout the world,” says Lynch. He feels that the central importance of the standard in industry internationally is that it controls the purity of zinc according to what’s required for a given application. “For example, in die casting, if there is too much tin, lead or cadmium, it results in catastrophic intergranular corrosion,” says Lynch. “It’s important that the ingot made from primary zinc metal that goes into die castings is maintained to a very high level of purity, which means that it has to meet the standard of Special High Grade in B 6.”

Lynch, who began his career with NL Industries and became heavily involved with zinc at the Zinc Institute in New York City before starting Lynch and Associates, has been an ASTM International member since 1982. The immediate past chair of Committee B02, Lynch currently serves as the chair of Subcommittees B02.04 on Zinc and Cadmium and B02.94 on Long Range Planning, as well as the chair of the long range planning subcommittee of Committee A05 on Metallic-Coated Iron and Steel Products, where he is a past vice chair. Lynch, who received the Award of Merit in 1990 and was also given the Committee B02 Gary M. Kralik Distinguished Service Award, believes that the ASTM consensus process has been instrumental in the success of B 6 in the face of ever-changing technology and industry needs. He also believes that the success of B 6 reflects the overall success of ASTM International.

“What I’ve experienced at ASTM is that the people involved are truly interested in developing good standards and I have made many good friends here,” says Lynch. “The world is a better place because of ASTM International.”