Machine designers and maintenance engineers need to deal with bearings in their rotating machines at different stages, first for selection and then for maintenance and troubleshooting. The main criteria for bearing selection were the calculation of bearing life according to the basic ISO 281 rated life formula:
l 10 = (C/P) p . 100,000 / 60.n
( C is the dynamic load coefficient and P is the equivalent load applied to the actual bearing, episode is the exponent that depends on the ball or rollers, pt is the number of rotations for constant speed machines).
What is often forgotten is that this is a probability calculation and does not express the “life” of each individual bearing. The probability is set at 90% survival, or in other words, if a significant number of bearings are exposed to the same operating conditions, 90% of them will meet or exceed the expected “useful life” rating, many will last longer, and even that means that 10% will not achieve that defined “life”.
But it is important to remember that the complete bearing can be seen as a system in which the useful life of each component, i.e. rolling elements, races, cage, lubricant and seals, when present, contributes equally and in some cases dictates the real life of the bearing. the bearing. Basically, the useful life of a bearing is determined by the useful life of the different components that make up the bearing system.
The ISO 281 bearing life calculation only takes into account the fatigue life of the raceway, so it does not include cage, lubricant or seals. In some cases, some useful life estimates can be made for these other items, but they are not integrated or standardized in ISO.
Additionally, there are other considerations when selecting the correct bearing for an application that go beyond calculating its theoretical life. For example, are there any special assembly or disassembly requirements? Are there special environmental considerations? Etc.
For a more complete process, SKF has introduced a revised bearing selection methodology that guides the engineer through the steps necessary to have a robust and reliable bearing application.
When choosing bearings for any purpose, you want to ensure that you achieve the required level of equipment performance and at the lowest possible cost. Robustness is also very important because the conditions under which your equipment is assembled, used and maintained may not be precisely known and may, in fact, vary over time.
In addition to bearing life, there are important factors to consider when gathering bearing specifications for an application, including:
- lubricant and feeding method
- shaft and housing fit together
- bearing clearance class
- cage material and guide
- dimensional stability
- accuracy requirements
- bearing seal
- assembly and maintenance method
These elements have been organized in a structured process and represented by easy-to-follow icons in the online catalog:
The process provides a simple step-by-step approach that shows the general relationship between each stage. By clearly defining and naming the steps in this way, it will be easier to find information on a specific topic. In reality, however, you will encounter interdependencies that require you to scroll back and forth between steps.
