Low-friction coatings from General Magnaplate Corp., Linden, N.J. (magnaplate.com), prevent stainless-steel feeders that meter dry solids from getting gummed up. The volumetric and gravimetric feeders must survive 20 grueling years of daily use, says their manufacturer Acrison Inc., Moonachie, N.J. (acrison.com). A key design goal for the company is ensuring minimum downtime as well as low cost of ownership for customers.
"Metal coatings play a critical part in the performance of our products primarily because of the variety of applications they serve," reports Acrison senior mechanical engineer Paul Matarazzo. "The principle issue is reducing friction to keep materials from sticking on the inside of the metal feeders."
A coating of low coefficient of friction (COF) materials prevents buildup on the machinery. This is of primary importance to manufacturers using pigments. In these applications accuracy is critical. Any metering error will directly affect endproduct color. "Obviously, this can have huge cost implications in the food industry," says Matarazzo, "where they use extremely expensive color additives." Precise pigment metering is important in automotive parts and consumer products where color is often part of brand recognition and product differentiation.
Low COF coatings that touch food must be FDA or USDA approved. And abrasion of machinery from dry bulk solids is also of great concern, says Matarazzo. "Certain materials vigorously abrade machinery causing damage that not only leads to production downtime but can also contaminate the products being metered. Tungsten carbide and silicon-type materials are particularly abrasive, leading to meter and feeder damage."
Some applications involve materials that react with stainless steel. There, explains Matarazzo, designers must specify coatings that will prevent corrosion from aggressive cleaning solutions used on packaging lines, for example.
"We also use metal coatings for applications that require a release property in high temperatures, as for feeding into a furnace at up to 1,000°F. These coatings, unlike Teflon, can withstand such high temperature."