Getting your bearings: understanding industrial bearing specification
Published: 05 May, 2016
Bearing selection is driven by the application and environment in which it will be operating and it can be very difficult to make the right decision without a wealth of in-depth information. Stephen Finch, project engineer at ERIKS UK, shines a light on the process and outlines how end-users can achieve the best return on investment.
For those not familiar with bearing selection, a car can prove to be a good analogy; as choosing the right bearing for a car would be just as difficult as choosing which car would be best for a daily three hour commute.
Hundreds of models could do the job, and the cheapest way would be to buy a small one litre hatchback, however over time that would not last as long as an expensive grand tourer. Yet, given its expense, the grand tourer may not be a realistic option for such a regular and rigorous journey so a compromise must be made, and it is the same with bearings. In short you need to be specific. The more detail you have on the application, the easier it is to narrow down the bearing options and ultimately arrive at the most appropriate specification.
For example, if there is purely a large load, a roller bearing or a plain bearing would be the most appropriate; or if the application in question is operating at an extremely high speed, a ball bearing or even a ceramic balled bearing could be best suited. It is important to remember that there is never just one application characteristic to account for, as such thereís a wealth of information needed to ensure the selection is as accurate as possible.
The devilís in the detail
When it comes to making a preliminary recommendation, the most important aspects to consider would be: space window; loads, both radial and axial; speed; ambient temperature; and environment (i.e contamination risk). Once all these considerations have been discussed, and depending on the data collected, you should be able to create a shortlist of five to six options. The decision can then be made between initial purchase cost and the estimated life.
Looking beyond the cost v operational life discussion, there are a number of bearing options which can handle more specific problems.
Take bearing housing alignment for example. It can be very difficult to achieve perfect alignment therefore a bearing which can handle the resulting misalignment without any negative effects is needed, such as a spherical roller bearing or a split roller bearing.
Another scenario could involve an application which witnesses large temperature changes. Here, steps must be made to reduce potential damage from the axial expansion of the shaft and the fretting (corrosion caused by the lifting and moving of steel or iron and its rapid oxidation under friction from heat and pressure) which can take effect on the bearing. A CARB, needle or cylindrical roller bearing would accommodate this with little to no adverse effects.
End users may also find themselves in the situation where a bearing is not completing a full rotation. In a rolling element bearing this means only a few of the rolling elements take any load, and therefore only part of it does any work. As such, they wear much faster and the rolling elements could dig through the lubrication film and lead to steel-on-steel contact. For this scenario, a plain bearing with no rolling elements would be superior.
Ultimately, it is really important to be very accurate with the original data collection when selecting, as the final result will only be as good as the original specification. Getting it right will hopefully allow the final result and expectations to be achieved and even surpassed.
There are a few other areas which should be carefully considered during the specification stage. A considerable amount of premature bearing failure can be attributed to incorrect specification and inadequate application of lubricant. Getting the right lubricant, in the right quantity and at the correct interval levels is therefore essential.
A correct seal can also noticeably improve a bearingís chances of fulfilling its projected operational life. Even a tiny amount of contamination can adversely affect the operating life of a bearing which is why adequate sealing arrangements are key.
Finally, itís important to bear in mind that, as with any industrial installation or remedial work, the key to long-lasting success is to implement a regular and thorough maintenance programme. Regular interval checks for bearing are ideal, even if itís just visual, temperature and noise checks. Condition monitoring techniques such as vibration analysis can also be used to determine bearing status, enabling companies to address any issues early on and before any downtime occurs.
Given the importance of bearings to the overall efficiency of nearly all industrial applications, the specification and installation process should not be rushed. If anyone is in any doubt when it comes to selecting and installing new bearings, I would urge them to hold a detailed audit and discussion with their supplier. With new innovations constantly being introduced to the market, it pays to tap into the know-how of the experts, so donít leave things to chance as you may quickly lose your bearings in a very complicated industrial product field.
For more information please visit: www.eriks.co.uk/bearings