Bearing Considerations for High-Temperature Applications
- Apr 19, 2018 -
Potential Heat Issues for Bearings
Additional Wear and Tear
Over time, excess heat can change the microstructure of the steel causing a reduction in the estimated life of the bearing. The friction created when a bearing rotates creates heat, which can make an already hot environment even more extreme. The resulting heat can cause a myriad of problems and can change natural wear and tear into unnatural wear, ruining your bearing in the process.
Heat causes metal to expand, which can create warping issues. When the metal in a bearing expands, it can reduce the clearance between the ball and the raceways. This change in clearance can cause the bearing to tighten, which can eventual force it to seize up and fail.
Like the rest of the bearing, seals need to be stabilized to survive extreme temperatures. Traditional rubber seals are only rated for certain temperatures, so extreme temperature can render these seals useless without the proper material or stabilization. This can also cause bearing grease to purge the oil which can and migrate onto other components. Depending on the application, this can be an unwanted side effect, especially if the grease falls onto new products.
Like seals, special greases are required for high-temperature environments. Standard greases are effective up to 300 degrees, but will purge all oils leaving a dried-up soap base in hotter conditions. Without that grease, bearings are subject to more friction, leading to even increased wear and shorter life.
Bearing Considerations for High-Temperature Environments
There are some considerations to make when choosing heat-treated bearings.
As we mentioned before, the natural friction caused by rotation creates heat. Heat stabilized bearings combat this by operating at a lower RPM than their standard bearing counterparts. As a result, you’ll want to consider the RPMs for your high-temperature bearing options to make sure they match the needs of your applications. Some bearing manufacturers offer multiple versions of the same bearing so that you can pick and choose which temperature range best matches your application.
As you modify the heat treatment for the appropriate temperature range the hardness of the steel with be reduced to stabilize the steel. Traditional bearings that are rated for up to 300 degrees have a Rockwell hardness range of 60 to 64. The hardness rating will be adjusted based upon operating temperatures for heat- stabilized bearings. With lower steel hardness the potential for increased wear is greater at higher speeds, so keep that in mind when selecting your high-temperature bearing solutions.
Due to the need for heat stabilized steels, finding a bearing with proper load support is also crucial. The higher the operating temperature inherently support lower loads, so alternate solutions may be necessary. One suggestion is switching to a material with a higher natural temperature range. For example, a 440 stainless steel bearing can be used to meet higher load needs when a heat-treated chrome bearing isn’t enough.
Due to their special qualities, heat-treated bearings aren’t always readily available. Many plants need to manufacture a certain number of these types of bearings to make a profit. As a result, there may be minimum quantities attached to factory orders for high-temperature bearings. This may not be an issue depending on how many bearings your application requires, but it’s important to consider when looking for products.
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