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Strong and robust

Putting tailored heat-treated gearbox bearings to the test

Robust bearings are the key to a long-lasting wind turbine. To evaluate their surface and subsurface robustness and minimize failures, SKF has further developed the SKF Generalized Bearing Life Model (GBLM). During the "Bearing World by FVA" conference, the company presented its application of the SKF high durability gearbox bearings for wind.

Improving performance while lowering costs is an essential part of staying competitive. Especially the energy market is under constant pressure to generate more power without increasing spending – simultaneously, the industry calls for bigger turbines, smaller components, more reliability, and less downtime.

Manufacturers in particular are challenged to live up to all these expectations, as the steadiness of small components like bearings is linked directly to the performance, costs, and service life of the entire wind turbine. Therefore, SKF is constantly striving for ways to improve bearing reliability and keep failure rates to a minimum.

Fighting the stresses

To no surprise, one common reason for gearbox bearing failure is surface damage, as this part endures the highest stresses. To ensure that the risk of downtime is kept as low as possible, the bearing’s contact surface must be particularly robust. For this purpose, SKF has developed a steel and heat treatment process that gives the top layer a tailored microstructure. This treatment increases the strength of the material which makes the top layer more durable. This way, the bearing can withstand marginal lubrication conditions or indentations and is more resilient to surface-induced failures and sub surface rolling contact fatigue.

A peek beneath the surface

Evaluating the hardened bearings using the SKF Generalized Bearing Life Model (GBLM) was an important part of the development process. The calculation model is used to determine the life of bearings as realistically as possible, while taking the real-life performance into consideration. SKF has been developing life models for more than 80 years and has been constantly improving them in line with the latest knowledge.

The newest model is the GBLM which is able to separate the bearing surface survival from the subsurface. It can point out the region where the damage originates more likely, either the surface or the subsurface. Thanks to these detailed insights, the bearing life calculation is now more realistic. And with the information gathered by using the GBLM, bearings and bearing applications can now be matched in a more consistent way, which has a positive impact on machine life and the total cost of ownership.

The GBLM models were developed and validated by extensive testing of typical high speed shaft bearings in specific test rigs at    different load and lubrication conditions.

The testing results clearly show that the SKF high durability gearbox bearings for wind are more resilient against surface and sub-surface fatigue, which leads to a significantly higher service life than usual.

In need of resilience

To conform to the industry’s need for more reliable and resistant yet smaller and lighter bearings, manufacturers need to look into advanced calculation methods like the SKF Generalized Bearing Life Model. The SKF process to develop rating life models and performance data and parameters has recently been successfully audited by Det Norske Veritas.

SKF is constantly working on improving various testing processes to make bearings even more failure-proof, thus reducing downtime and prolonging service life. If you want to dive deep into the calculation process, feel free to read this article on SKF Evolution.

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