A new generation of self-lubricating materials, now used in foodservice applications, are especially suited for commercial appliances because of the “hostile” environments in which they operate.
The key innovation with these new offerings, which are engineered to survive high temperatures and long service intervals, is that lubrication is provided by the bearing material itself, rather than an external compound.
The GRAPHALLOY material by Graphite Metallizing Corp, Yonkers, N.Y., is a self-lubricating bearing material based on the properties of certain graphite-metal alloys that have a metallurgical structure that can be compared to a deck of cards with individual layers that easily slide off the deck. This phenomenon gives the materials its self-lubricating ability.
These materials provide other properties that are beneficial in appliance-bearing applications. They maintain integrity when submerged in hostile liquids such as acids, alkalis, and other corrosive materials. The GRAPHALLOY material has an operational range from 1,000°F to -300°F. The materials provides a constant, low coefficient of friction rather than just a surface layer, helping to protect against catastrophic failure. Lubrication is maintained even during linear motion; the lubricant is not drawn out and dust is not pulled in. The result is that these materials provide excellent reliability under conditions found in tough appliance applications such as low-speed operation, frequent starts and stops and switchovers from standby to continuous running.
In a typical application, switching to a new graphite-alloy material eliminated the need for maintenance of bearings supporting spits in ovens used in a large restaurant chain. The ovens, which are designed to keep chickens warm prior to serving, are manufactured by Julien Industries, Montreal, Que., whose clients include Bombardier Inc., Prevost Car Inc., Frigidaire Canada Inc., the Canadian Armed Forces, Toronto’s Sky Dome, St. Hubert Rotisseries, AMTRAK, Montreal’s Molson Centre and many others.
The oven is not designed for cooking the chickens but rather for keeping them warm prior to serving while displaying them. The oven is about 5 ft. wide, 6 ft. high and 3 ft. deep, and has a single spit, with branches to hold the chickens, driven by a sprocket attached by a chain to an electric motor. Appearance is critical because the oven is designed to function as a point of purchase display. This made it critical to hide the bearings and other aspects of the mechanism.
The need to hide the bearings and mechanisms introduced complexities that made it difficult to relocate them to a cooler area of the oven. The ball bearings that were originally used in the oven had to be lubricated every two weeks because the 450° oven environment caused the grease to rapidly deteriorate. In the past the bearings needed to be lubricated every two weeks because high internal temperatures attacked the lubricants.
The challenge of obtaining and applying the right lubricant, not to mention the difficulty of performing regular maintenance in a busy restaurant, meant that these tasks were often neglected. The result was that a significant number of bearings failed in the field. Julien service engineers promptly replaced the bearings when that happened to avoid a disruption of service to the restaurant’s customers. This created a burden on the field service team, which spent a considerable proportion of their time on this single issue.
Search for a solution
Pierre Olivier Roy, research and development engineer for Julien, was assigned the task of solving the problem. Roy first investigated high temperature greases but was unable to find any that would meet the company’s performance requirements while supporting food service requirements. Roy also tried redesigning the oven to reduce the amount of heat experienced by the bearings, but found that even with a major redesign that would move the bearings outside the heated portion of the oven, enough heat was still transferred through the driving shaft to cause bearing problems. This approach would also have the serious disadvantage of not being able to be retrofitted to existing ovens.
Roy’s search led him to Graphite Metallizing Corp., and its GRAPHALLOY material. The GRAPHALLOY bushings are available in more than 100 grades of material in any desired size or geometry, including cylindrical with or without grooves, flange or double flange, split and metal-backed. Graphite Metallizing offered a bushing with exactly the same dimensions as the bearings used in the past.
Samples were ordered for installation in the field on an oven whose bearings had failed.
After observing the “test oven” for four months, Julien committed to the self-lubricating bushings and immediately saw a significant drop in phone calls to its service department.
Further, says Roy, “by eliminating the need for regular maintenance, the new bearing material has greatly simplified the job of maintaining the ovens. And as a bonus, the new bushings run more quietly than the bearings that we used in the past.”
