December 21, 2012 -- Carbon-graphite bearings and thrust washers are used in high temperature applications because oil/grease lubricated, metallic bearings can start to have problems at temperatures above about 350ºF (177ºC). Oil/grease lubricants can start to melt, volatilize or carbonize above this temperature. When this occurs, oil/grease-lubricated metallic bearings start to experience high friction, high wear, galling, vibration and even seizing.
At high temperatures, plastic and composite bearings are subject to other problems such as softening, melting, deformation and may extrude out of the bearing area all together.
Carbon graphite bearings are ideally suited for applications at elevated temperatures because they rely on graphite for their self-lubricating properties. These solid homogeneous bearing materials do not contain oil/grease lubricants and they do not rely on oil/grease for lubrication. Thus, bearings manufactured from these carbon graphite materials are not subject to the shortcomings associated with petroleum-based lubricants at elevated temperatures.
Because the carbon graphite matrix is very strong, it is not subject to the deformation, melting, or even softening that can occur with plastic bearings at these elevated temperatures.
Room Temperature or Cold Temperature Dry Running Applications
Carbon-graphite bearings are also used for dry running at room temperature or cold temperatures. This occurs in applications where oil/grease lubricated metal bearings can not be used because:
Oil/grease lubricants volatilize in vacuum
At low temperatures, oil/grease lubricants can congeal, freeze, or solidify
In environments containing abrasive dust which is attracted by oil/grease lubricants to form a paste that increases bearing wear.
In high load, slow roll, start-stop equipment where oil/grease lubricants can be squeezed out of the rubbing surface and cause metal-to-metal contact.
Where the bearings need to conduct an electric current.
In sanitary or clean conditions where oil/grease lubricants could leak out and destroy product such as food, textiles, pharmaceuticals, paper, etc.
Custom Bearing Design
Metcar Engineers will work with the customer to design the ideal bearing for your application. Design considerations include:
Bearing size (length, wall thickness, press-fit/shrink-fit interference, running clearance)
Bearing wear rate at required load, speed, and temperature
Optimum carbon-graphite material grade
Temperature limitation (oxidation)
Coefficient of Friction
Shaft material and surface finish
Metcar bearings for dry running can be provided to customer print or to customer approved dimensions and tolerances. Metcar bearings are also available shrink fitted into metal housings, or metal retaining rings.
For additional information about the company and its services, please visit us online at www.metcar.com, or call (914) 941-3738