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The reason: Lead is a banned substance under the European Restrictions on Hazardous Substances (RoHS). “Lead may be the asbestos of the 21st Century,” comments Matt Hlavin, vice president of sales and marketing of Thogus Products, a custom injection molder based in Avon Lake, OH. “Lead is toxic, and you have the recycling costs, the handling issues. It is not environmentally friendly.”
The new material has a specific gravity of 11.0, the same as lead, and shields radiation as well, or better than, lead, according to Hlavin. Target applications are manufacturers of products such as x-ray tubes, collimators and housings, dental x-ray equipment and trays, nuclear medicine containers, gaskets and seals. Thogus Products has developed 50 lead-replacement applications since it first began working on the project five years ago with compounder PolyOne of Cleveland. About 18 months ago, Thogus also began to work with GE Plastics to expand resin formulations.
Ground tungsten is loaded at a 50 percent level into polymer matrices of nylon 6, and more recently, thermoplastic polyurethane, which allows flexible moldings. The molded products are about 96 percent tungsten by weight. The high cost of the tungsten filler is due to special treatment which allows it to be compounded with polymers. The compounds cost $42 to $60 a pound. Lead costs less than 70 cents a pound.
Net shape advantage
Thogus is targeting applications that can benefit from parts integration or insert molding. One example is collimators, instruments that filter streams of X- rays. “Their design is very complex with a lot of tight tolerances,” comments Hlavin. “The lead part is cast and then machined. There is a lot of secondary machining involved. We are able to redesign the product from a blank piece of paper for plastic.” The molded, net shape part is less expensive than the processed lead part. Thogus is also looking at applications that shield electronics. X-Ray applications for Homeland Security are also a big potential market. Even ammunition replacement is on the radar screen.
Not surprisingly, one of the problems is extreme wear of injection molding machine components, ranging from screws to tools. “It took us three years to optimize the process,” says Hlavin. “When we first started, we broke a lot of screw tips.” Thogus operates 31 injection molding machines, ranging in size from 25 to 400 tons. The smallest tungsten part molded by Thogus has been 20 grams; the largest is 26 pounds.
GE Plastics’ Thermocomp compounds are available in a variety of grades and densities. A denser Thermocomp material could be specified to reduce part thickness and materials costs, said Anne Burnell, the technology leader for GE Plastics’ compounding business.
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 Lead parts that require a significant amount of secondary operations are ideal candidates for parts made from molded tungsten compounds. |
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