If you were to ask 10 people what temperature your bearings should be operating at, you'll get 10 different answers. The sad part is, they all might be right! Single roll ball bearings used in most blowers and motors have a wide range of applications and thereby temperature ranges.
According to Wikipedia, ball bearings have been around since the Stone Age. They may have even pre-dated the wheel. Wooden bearings can still be seen in old clocks or water mills where water was used for lubrication. Even "jeweled" watches use sapphire plain bearings to reduce friction thus allowing more precise time keeping. The first caged roller bearing was invented and used by a clockmaker. The first patented ball bearing in the mid-1800's was used in a bicycle to win the world's first bicycle road race.
How hot can a ball bearing today operate? Over 500 degrees F! Sleeve bearings don't generally operate quite as hot-maybe up to 300 degrees F. But to run a bearing anywhere near that hot not only requires excellent lubrication, but a very special bearing system. For blowers, pumps, and motors, with the correct lubrication system, the bearings are designed to safely operate in the 250 F range(+/- 50F).
So is this a good temp to operate in....of course not! The cooler a bearing operates, the longer the life. Without lubrication, a bearing will overheat and burn itself up. The purpose of lubrication is to reduce, and to a certain extent, carry away, the heat of friction in the bearing. Properly lubricated bearings keep the bearing operating at a "normal" temperature. Too much grease will not allow the heat to dissipate, so it runs hotter. Generally, for motors and blowers operating at 3600 rpm, normal temp is 100O F to 150O F.
However, there are exceptions. An oil mist lubrication system for a relatively large blower bearing had a normal temp of 225 F. It ran at that temp for years. Another steam "compressor" type blower handling very hot gasses, had a normal operating temp of 245 F. The main drawback to designing these machines to operate with hotter bearings, is the life of the bearing is shortened. Instead of lasting the normal design of say 10 years, the bearings may only last 5 years.
There are 4 stages of bearing failure. Stages #1 and #2 are only detectable using vibration spectrum analysis. Stage #3 has slightly increased overall vibration levels, increased noise, and increased temperature. When the bearing reaches Stage #4, the vibrations have become excessive, the ultrasonic noise has increased, and the bearing temp has spiked. You only have about one hour of bearing life left.
Prevent a catastrophic bearing failure of your rotating equipment by monitoring the vibration and temperature of the bearings. Wireless vibration and temp sensors are now readily available for most applications. Preventative maintenance monitoring tools may oftentimes be costly up front, but they can save you in the long run. Invest in PM, it will save you money!
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