Temperature’s Effects on Mounted Bearings
David Boyer pens an article regarding the effect temperature has on mounted bearings:
“I can’t lay my hand on the bearing because it’s operating too hot!”While this is a commonly heard complaint, most sleeve and rolling element bearings can operate successfully at temperatures well above the pain threshold of a human hand. The stabilized operating temperature of a bearing is the result of many factors. The key influences on operational temperature are bearing style, lubrication type, operational factors, environmental conditions and level of maintenance The particular bearing style (ball, roller, sleeve, etc.), the shaft mounting style (slip fit, adapter mounted, press fit, etc.) and auxiliary items (housings, seals, shields, flingers, etc.) all contribute to a final operating temperature. For a given set of application conditions, a particular bearing type will generate friction given off as heat. A typical bearing temperature rise range would be 40° to 80°F (4° to 27°C) for most industrial applications. However, a bearing temperature rise over ambient of up to a 120°F (49°C) can be observed at extreme conditions.
(Editor’s Note: H/T courtesy of Jacob Henke “The 40°F, 80°F, and 120°F differentials become 22.2°C, 44.4°C and 66.6°C respectively.”)
It should be noted when bearings operate at higher than normal temperatures, service life may suffer due to a deterioration of the lubricant oil film thickness and quality. The initial bearing selection should either be chosen with adequate design life hours to compensate for the anticipated reduction in service life or an appropriate lubricant for high temperature operation should be selected.Bearings may be exposed to abnormally high ambient temperatures or elevated temperatures in equipment such as furnaces, fans, ovens, blowers, steel mill/foundry casters, roll out tables, dryers, electric motors and generators, to name a few. In many of these cases, bearings are expected to operate above the limits for standard bearing products.If at all possible, locating bearings out of the immediate heat zones or providing provisions to reduce bearing heat are preferred means to achieve optimum bearing service life performance. This can be accomplished by insulation procedures to reduce radiant heat. Also, shaft heat flingers or cooling wheels coupled with heat resistant shaft materials can reduce bearing temperatures. The use of water or air cooled bearing units is another method to reduce bearing temperatures to a more manageable range. Though these steps incur higher installation costs, long term benefits may be gained by reducing lubrication and maintenance problems often encountered with high temperature bearing applications.When there is no way to avoid heat exposure, bearings can be specially modified to accommodate high temperature applications. Bearings having optional components materials, special internal radial clearances, high temperature lubricants and special heat treatments (if necessary) can operate successfully at very high temperatures, as shown.
|Bearing Type-Special Modifications||Allowable Max.
|Normal, Medium & Heavy Duty Bearings||Up to +550°|
|Spherical Roller Bearing Units||Up to +450°|
|Split Block Roller Bearing Units||Up to +450°|
|Cylindrical Roller Bearings||Up to +300°|
|Sleeve Bearings All Types||Limit by Bushing Matl|
The above maximum operating temperatures are limited by either the standard bearing unit features, component materials or lubrication provided.Bearings can provide years of service while operating at temperatures well above ambient and at levels well above what is commonly called “too hot.” As with any equipment component, proper bearing selection, correct lubrication and adequate maintenance procedures are vital to satisfactory service life.