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| Temperature?s
Effects on Mounted Bearings |
| By David Boyer, Link-Belt
Bearing Div., Rexnord Corporation, Milwaukee, WI |
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"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. |
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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. |
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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. |
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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. |
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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. Temperature (°F) |
| 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 Mat?l |
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The above maximum operating temperatures are limited by either the standard
bearing unit features, component materials or lubrication provided. |
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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. |
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This article is furnished
courtesy of PTDA
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to Bearings Reference Articles Index |
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