1/12/2010 3:00:00 PM |
Bearing Ratings |
Comments |
Jerry Fox |
You might ask yourself – what is a bearing rating? Timken defines a rating as a load which, when applied to a population of similar bearings under a controlled test environment, will allow 90% of the bearing population to survive for a required number of revolutions, while 10% of the bearing population will have experienced some minimum threshold of raceway damage. This rating is called C1 if the required number of revolutions is 1,000,000 and C90 if the required number of revolutions is 90,000,000.
When wind turbine designers perform bearing life calculations, they will determine the equivalent load P on the bearing and perform a calculation that compares it to the C1 or C90 rating – estimating the number of successful revolutions that can be expected on a probable basis from that bearing in service. This is called a Basic Life L10 calculation. Advanced life analyses using various codes are also made to consider the effects of the operating environment. The bearing rating C is used in most of these calculations, and is an essential building block in establishing wind turbine design and overall size.
Continuous improvement in steel and bearing manufacturing processes has yielded bearings with some of the highest ratings in our industry. Since 1986, customers in the auto, rail, aerospace, off-highway and metals industries have applied higher Timken bearing ratings in their bearing calculations with success.
See SAE paper 881232 entitled “Tapered Roller Bearing Performance for the 1990’s” for more detail.
Until now, it's been a different story in wind. In the standards, the certification bodies have specified that only ISO ratings may be applied to calculation of bearing L10 life.
After careful auditing and scrutiny of our steel and bearing manufacturing operations and life testing performance data,
Germanischer Lloyd has approved use of Timken bearing ratings for Timken tapered roller and cylindrical roller bearings applied in wind turbine applications. This is a breakthrough in design opportunity because the Timken rating is 9% higher than an ISO rating applied to most other brands– all geometry being equal.
For designers trying to select the most cost effective bearing possible while still meeting the reliability requirements of the turbine, the 9% increase in bearing rating equates to a 33% higher calculated bearing L10 life. We believe that the GL endorsement of the higher Timken bearing will offer new opportunities for downsizing the power train and creating leaner, more competitive designs.
We see immediate opportunities in applying this technology to main shaft support positions, planetary idler positions and low speed shafting, but we want your thoughts on the subject. Join the conversation and let us know how you think higher bearing ratings can benefit your wind turbine designs.