Oil or grease lubricated bearings and plastic bearings can cause problems for users needing high temperature applications. However, there are alternatives. Metallized Carbon Corporation manufactures oil-free, self-lubricating, carbon-graphite materials for severe service applications, including bearings specially designed for dry running in high temperature applications.
DRY RUNNING AT HIGH TEMPERATURES
The Metcar high temperature bearings are designed for use at temperatures ranging from 350 to 1000 degrees Fahrenheit (176 to 537 degrees Celsius) in oxidizing atmospheres, and from 350 to 6000 degrees Fahrenheit (176 to 3315 degrees Celsius) in non-oxidizing atmospheres. At these high temperatures, oil-grease lubricated ball, roller, and sleeve bearings are problematic because the oil-grease lubricants can melt, volatilize or carbonize. Plastic and composite bearing materials can soften, deform or melt at such high temperatures.
Because Metcar carbon-graphite bearings rely on graphite for their self-lubricating properties, they are not subject to the shortcomings associated with petroleum-based lubricants at elevated temperatures. They are dimensionally stable, and are not subject to melting, softening, or deformation.
Metcar bearings are ideal for use in continuous dryers, high temperature conveyors, kiln cars, and high temperature ventilation dampers. They are also a great choice for other high temperature equipment, including continuous bakery ovens, screw conveyors, valves, and paint dryers. Several Metcar Grades have received FDA approval for use in contact with foods and pharmaceuticals.
Metcar bearings for dry running can be provided to customer prints or custom-designed for specific application dimensions and tolerances. Standard pillow blocks and flange blocks with Metcar bearing inserts are available with cast iron, stamped steel, or stamped stainless steel housings. Metcar high temperature bearings are also available shrink-fitted into metal housings or metal retaining rings.
CARBON-GRAPHITE BUSHINGS FOR AIRCRAFT ENGINE FUEL PUMPS
Another example of Metallized Carbon Corporation’s new approach are Metcar carbon-graphite bushings for use in gear pumps that pump aviation fuel for aircraft engines. This unique material offers numerous advantages over traditional metals. The carbon-graphite bushings are used to support both the drive gear shaft and the idler gear shaft.
Metcar carbon-graphite bushings are preferred for this application because they can use aviation fuel as the bushing lubricant. Aviation fuel is a low viscosity liquid that produces only an extremely thin hydrodynamic film, too thin to provide adequate lubrication for traditional metallic bushings. But since Metcar’s carbon-graphite material—in contrast—has no atomic attraction to a metallic shaft, the thin fuel film is sufficient to lubricate metallic shafts running in the carbon-graphite bushings.
A second major advantage of carbon-graphite bushings is that they are self-lubricating—they can run dry for short periods of time without catastrophic pump failure or significant wear. In addition, Metcar carbon-graphite bushings are dimensionally stable, which permits the close bushing to shaft running clearances that are required in gear pump applications.
Finally, these carbon-graphite bushings have a relatively low elastic modulus. While elastic enough that they can be press-fit into the metallic gear pump housing with no difficulty, after being properly press-fit, the Metcar bushings are pre-stressed in compression. Therefore, they exhibit nearly the same coefficient of thermal expansion as the metallic gear pump housing material. This assures that the running clearance between the shafts and the bushings will remain the same throughout the entire operating temperature range of the pump.
For More Information
Matthew Brennan is president and CEO of Metallized Carbon, an ISO certified and producer of the Metcar brand of solid, oil-free, self-lubricating materials. For additional information about the company and its services, visit www.metcar.com or call 914.941.3738.
MODERN PUMPING TODAY, January 2015
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