By Carl D. Forth, Editor
— Reprinted with permission from Modern Metals Magazine, July 1995.
This 10 in. diameter tube forming roll is sectioned, which allows it to be treated only on the working areas to reduce treating expense.
Diffused vanadium-carbide layer process increases roll form tooling life.
A thermal diffusion process is being used by roll formers to improve tooling life and reduce corrosion and wear. The TD technology is available for tooling in a variety of industries.
Jeff Wheeler, roll forming supervisor for Superior Metal Products, Lima, Ohio, said that his company has employed this process on tooling that roll forms stainless steel, cold rolled and galvanized steel.
“On our critical areas, it seems to work really well,” he said.
The TD process is not used on all of the rolls in the roll former, only about one-third of the rolls that are most likely to be prematurely worn.
“I only put it on the ones that are working in an area that seems to scuff up,” Wheeler said. “We would normally take [those] rolls and put chrome on them. Depending on how hard it works in the forming process, within a half-hour's time [the chrome] would come off and leave a ring around the roll, which in turn leaves an imperfection on the piece.”
Wheeler said that the TD process tooling has beaten that time. “I've got some that have lasted for two years that I haven't touched,” he said.
Designed to reduce wear
According to the TD Center, thermal diffusion reduces galling, seizure, corrosion and wear, and helps to minimize lubrication, tool maintenanceand replacement costs.
TD is a thermal reactive technology that diffuses a very hard vanadium carbide layer into and onto the surface of metal substrates. The vanadium carbide layer is 0.0001 to 0.0008 in. thick and has a hardness of 3200 to 3800 Vickers.
Parts to be treated are immersed in a fused salt bath at temperatures of 1600 to 1900°F for one to eight hours. Vanadium dispersed in the salt bath combines with carbon atoms contained in the tooling substrate (the substrate must contain a carbon content of 0.3 percent or greater for the reaction to take place).
The process is designed to extend the life of wear-related components used in a variety of industries and applications, such as roll forming, metal forming and bending.
According to the TD Center, the process can be used with many tool steels, such as cold and hot working die steels, high speed steels, specialty steels, cemented carbide and low alloy steels.
First developed in Japan
The TD Center was formed in 1987, when Arvin signed a license agreement with Toyota Central Research and Development Laboratories to use a thermal diffusion tool treatment process developed in Japan. (The process is still used much more widely in Japan.)
Arvin officials visiting Japan became interested in the TD Process when they saw production parts being run with little or no lubricant compared to production in the United States.
The TD Center treated its first tooling in Columbus, Indiana, in early 1988. Later that year, it was granted a commercial license for North America, and in 1991 received the rights from Toyota to sub-license the process in North and South America.
At Superior, tooling is removed from the roll forming machine and sent to another company location in Spring Lake, Michigan, for inspection. Spring Lake will check to see if the roll is still good, then send it to Columbus for treatment. The whole process takes two or three weeks.
An assembled and disassembled roll. Roll form tooling is sent to TD Center by roll formers for treatment.
Substrate Is Important
Jon Knapp, vice president and general manager of TD Center, said that in some cases surface coating alone doesn't solve an operator's problem with tooling wear. In very high lead forming, if the substrate cannot support the coating, the surface of the substrate chips away, taking the coating with it.
In those cases, Knapp said, TD Center works on the substrate selection first, and then recommends a coating if needed.
Another problem area is surface finish. Knapp said that the technology can make the operator's rolls too slick, which causes slipping in the forming equipment. In those cases TD Center works to find the appropriate finish to allow the material to drive through the equipment.
TD developer joins TD Center
Several months ago, the TD Center announced that Dr. Tohru Arai, who originally developed the thermal diffusion technology, was joining the center as a technical advisor. Dr. Arai, who attended the Metalform trade show in Chicago in March, will assist in finding new applications for the technology and in developing new processing methods. He will also work with customers using the process to help reduce tool wear and lubricant usage.