Blowin’ in the wind – Wind Turbines benefit from Schaeffler bearings

Wind power is one of the fastest growing sustainable technologies – with 93GW of new capacity installed in 2020 – a record year for the industry. Today, there is 743GW of wind power capacity worldwide, helping to avoid over 1.1 billion tonnes of CO₂.

Yet this level of adoption is not sufficient to make sure the world achieves net zero by 2050. In fact, countries across the world need to be installing wind power three times faster over the next decade to meet this target and avoid the worst effects of climate change.

Minimising total cost of ownership

As more wind turbines are installed, the issues that could hinder their operational effectiveness are under increasing scrutiny. Obviously, if a wind turbine is not being used, it cannot produce clean energy, while maintenance, repair and operations (MRO) costs can soar, particularly in the case of offshore wind farms. The reliability of components therefore plays an essential role in minimising TCO, maximising operational efficiency, achieving regulatory compliance, and enhancing worker safety.

The development of larger, multi-megawatt wind turbines has resulted in significantly higher forces, torques, and loads. With such a wide range of bearings performing different functions within a wind turbine’s structure, white etching cracks (WECs) have become a major cause for concern.

A solutions provider

The solution that Schaeffler recommends – which has been statistically verified – for the efficient and cost-effective reduction of WEC damage is the through-hardening of the bearings, in combination with a black oxide coating on the inner ring, outer ring, and rolling elements – with Schaeffler experts developing an ideal coating system that significantly increases a bearing’s resistance to WECs.

The Durotect B coating system has been developed from conventional black oxide finishes to give increased performance, minimising the risk of damage caused by slippage, improving run-in behaviour, increasing corrosion resistance, and the enhancing the level of protection against WECs.

In fact, research has shown that WECs have occurred in less than 100 out of 1 million through-hardened bearings with black oxide or Durotect B coating that were produced and delivered by Schaeffler for use in wind turbines since 2005. This corresponds to an incredibly low failure rate of less than 0.01%.

For applications that require high load ratings, Schaeffler also offers rolling bearings made from Mancrodur carbonitrided steel and coated with Durotect B. For those who aren’t familiar, carbonitriding involves subjecting the bearings to a special heating process in which the bearing surface is enriched with carbon and nitrogen, increasing surface hardness and wear resistance.

Strength and durability

Similarly, Cronidur special steel with high chromium content can be used to completely eliminate the risk of WECs. Cronidur 30 is a martensitic through-hardened steel that, due to its alloy composition – carbon, nitrogen, chromium, and molybdenum – exhibits exceptional corrosion resistance, strength, durability, and high temperature hardness.

An inspection programme carried out by Schaeffler to determine individual solutions for different applications and additional stresses showed that no cases of WECs occurred in bearings with Cronidur 30.

Bearings for wind turbines can also suffer damage due to the passage of electrical current, so in order to prevent this, Schaeffler has developed a ceramic insulation coating. Commonly used for wind turbine generators, Insutect A is applied using the plasma spray method, then sealed and applied to the outer ring (J20AA) or inner ring (J20C).

Avoid costly unplanned downtime

Another method of avoiding premature failure of your bearings is to ensure that the main bearing arrangement and its lubrication are perfectly in sync. For example, 10MW offshore wind turbines that are intended to be operational for a minimum of 25 years, costly maintenance work must be kept down.

This is essential, as the cost of dismounting bearings and replacing components can incur exponential costs. The rental costs of boats, cranes, and other equipment for replacing a main shaft bearing alone, can be as high as €800,000.

In these circumstances, any unplanned downtime can last up to 20 days. If the customer loses 2.2 million kilowatt hours during those 20 days, costs can rise to a further €200,000.

Therefore, the savings achieved by avoiding unplanned production stoppages can reach approximately €1 million, proving that the correct amount of grease for the main shaft bearing is truly essential.

Take the best foot forward

Machine elements in modern mechanical systems are subjected to increasingly harsh operating conditions and wind turbines are no exception.

WECs continue to be a cause of the premature failure of rolling bearings, and while research from Schaeffler into what causes this to happen remains ongoing, the good news is that there is a practical and proven coating system that significantly increases a bearing’s resistance. 

For more information on Bearing & Lubrication solutions and to get in touch with one of our ERIKS Bearings Specialists or Lubrication Engineers, please contact your local ERIKS Service Centre, who will be happy to discuss your options.

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