It¡¯s been said a wind turbine is only as good as its components, and a turbine¡¯s bearings are extremely important ones. Although bearings are used many places throughout a nacelle, such as on generators and in the yaw and pitch system, those on main shafts and gearboxes are typically most problematic.
Timken ES302 is a thin-?lm, hard diamond-like carbon coating used to protect bearings. The ES302 coating uses a physical vapor-deposition technique that produces a vapor of material (which is then deposited on the object as a thin film) for an optimal level of friction reduction.
Not too long ago, wind operators and engineers began noticing a trend: roller bearings in turbine main shafts and gearboxes experienced premature damage, resulting in major rebuilds costing up to $300,000.
Bearings in turbines must withstand extreme environmental conditions, vibrations, and loads. What¡¯s more is bearings are subject to combinations of dynamic loads that create high-contact stresses on rollers and raceways, which can lead to damage. These stresses are difficult to predict and challenge bearing manufacturers to develop new approaches to reducing premature wear.
¡°You never want the steel surfaces to touch in a bearing,¡± says Ryan Evans, director of research and development for bearings with The Timken Company. That seems like a tough demand because when you look at a roller bearing, you see rollers moving around in a tight space. But that¡¯s the reason for lubrication ¡ª so there¡¯s always a film between the roller and the inner raceway ring.¡±
Unfortunately, lubricant films are challenging to maintain consistently.
¡°So as engineers struggled to solve the steel-on-steel contact problems of a turbine¡¯s bearings, a R&D team began developing a coating for roller bearings,¡± shared Evans.
Eventually, the team adopted a novel approach: making bearing rollers less ¡°steel-like.¡± ¡°We put a super-thin ¡ª fractions of a human hair thick ¡ª layer of a composite material on them,¡± says Evans. ¡°It¡¯s an engineered combination of ceramic and a polymer or, in other words, a plastic-like thin layer of material full of tiny ceramic particles.¡±
From this research, Timken¡¯s ES302 coating was developed, which is a specially engineered nanostructure coating that aims to provide maximum durability where metal-on-metal contact occurs. To help wind-farm operators avoid unnecessary O&M costs, Timken can apply its ES302 coating to the rollers of main-shaft and gearbox bearings, resulting in a highly wear-resistant bearing that is ideal for low-speed, high-load applications.
Researchers first introduced ES302 in 2010 and conducted extensive analysis at the time that suggested an ES302-coated bearing (compared to an equivalent uncoated bearing) could experience up to six times greater life when operated in standard conditions, and up to three times greater life under debris-contaminated conditions in wind turbines.
Recently, these lab results were confirmed when an ES302-coated main-shaft spherical roller bearing was returned to the company (due to non-bearing-related issues) after seven years of service in a 1.5-MW wind turbine. Extensive laboratory analysis revealed the bearing would have continued to provide reliable, trouble-free operation into the 15 to 20-year time frame had it not been taken out of service.
