Black oxide bearings - improving operational reliability in the wind industry

Climate change is one of the single most important challenges that our planet currently faces. Consumers and businesses alike are rapidly trying to move towards a more sustainable way of working to reduce the impact upon the planet. The energy industry is no different, with providers looking towards renewable energy sources as they move away from fossil fuels.

As a result, the requirement for reliable and productive wind turbines is increasing every day, as the demand for affordable wind-generated energy soars. This means that wind farms need to be smarter than ever before, optimising their productivity and working to minimise downtime.

In this article, we’ll take a look at how black oxide bearings could help to improve operational reliability in wind turbines, by driving down maintenance requirements and minimising machine breakdowns.

When reliability needs to come first

The world needs a plentiful supply of renewable energy at a low cost to make it a viable option. As a result, wind turbines are being pushed to their limits to generate affordable clean energy. Turbine blades are increasing in size whilst generators and gearboxes are being designed lighter. Whilst this means that wind energy can be produced more efficiently than ever before, it also increases the demands on the mechanical components, increasing the risks of problems occurring.

Not only this, but the environmental conditions that a wind turbine is exposed to can often be challenging. This can include ice, rain, salt water, varying temperatures, and high wind speeds. These are challenging conditions for any bearing, which threaten reliability and put operations at risk.

The real cost of maintenance to the wind industry

The high levels of demand placed on wind turbines, combined with the arduous operating environment means that regular maintenance is required to fix any issues that occur and prevent extended periods of downtime.

In fact, Operation and Maintenance (O&M) costs in the wind industry typically add up to around 25% of the costs of running a wind turbine throughout its lifecycle. So, there’s no wonder that manufacturers and maintenance service providers are looking to implement technology to reduce maintenance requirements and associated downtime.

But is there really an effective solution that can minimise downtime and cut maintenance requirements in wind turbines?

Introducing black oxide bearings

Black oxidation is a surface treatment that can be applied to bearings used in wind turbines to improve operational reliability. This treatment is highly resistant to both chemicals and corrosion, whilst protecting the bearing during the crucial running-in phase and facilitating lubricant adhesion.  

This high-tech bearing surface treatment is created through a multistage chemical reaction that is applied to the bearing steel of the inner and outer rings, as well as the rolling elements of the bearing. This results in a dark black protective layer of mixed ferrous oxide being formed on the outer surfaces of the bearing.

The black oxidation process

Many people think of black oxide as a coating that is applied to a bearing. However, rather than a coating, black oxide is a surface treatment that is the result of a chemical reaction in the bearing steel. This means that black oxidation does not change the size of the bearing.

To create the black oxide reaction, the bearing components are fully immersed in an alkaline salt solution that is kept between 130°C and 150°C. There are usually around 15 different stages to this immersion process, using different temperatures, concentrations, and immersion times.

During this process, the iron contained within the bearing steel reacts with the saline solution to create a black oxide layer on the outside of the bearing components. This oxide layer consists of a mix of FeO, Fe2O3 and Fe3O4 and gives the bearing the dark black appearance that is synonymous with black oxide bearings.

Benefits of black oxide bearings

Treating a bearing with black oxidation can help to protect the bearing against some of the most common causes of premature bearing failure. This includes:

  • Corrosion
  • Friction
  • Wear
  • Micropitting
  • Smearing
  • Cracking

Let’s take a look at some of the benefits of black oxide bearings.

1. Improved wear resistance

Bearings that are treated with black oxide help to deliver improved wear resistance whilst offering protection against bending to facilitate an extended service life. This is because black oxide helps to protect the bearing from corrosion, friction, micropitting and cracking.

This increased wear resistance means that wind turbines can enjoy extended service intervals, as well as higher levels of productivity. And of course, who doesn’t want increased reliability for their machinery?

2. Enhanced lubricant retention

The black oxide layer that forms on the bearing is porous by nature. This helps the lubricant to adhere to the bearing, aiding in the retention of the lubricant.  Improved lubricant retention means that maintenance intervals can be extended, whilst ensuring that the components of the bearing remain well-protected throughout its service life. This improvement in lubricant conditions is particularly valuable in the run-in and start-up phases.

3. Facilitates efficient run-in

The run-in phase of any bearing is critical, but this stage is particularly important in the wind industry. Treating bearings with black oxide results in excellent run-in properties, keeping wear during the run-in phase to a minimum and helping to extend the overall service life of the bearing. Not only that, but bearings treated with black oxide also benefit from a shorter run-in period when compared to a standard rolling element bearing.

4. Protection against environmental factors

Environmental conditions in the wind industry are notoriously tough. Thankfully, black oxide bearings provide outstanding protection against the effects of the environment. Not only does black oxide deliver excellent protection against corrosion, but it also helps to guard against chemical reactions with lubricant ingredients, as well as aiding in the prevention of fretting corrosion and hydrogen diffusion.

5. Reduce bearing failure

Treating bearings with black oxide can have a dramatic impact on the lifespan of bearings in the wind industry. For example, one wind gearbox manufacturer took a sample of 1,000 standard cylindrical roller bearings and reported a failure rate of 40% - 70% within two years. However, in a sample of 1,150 SKF black oxide coated cylindrical roller bearings, the failure rate fell to just 0.1% within two years. This demonstrates the tangible difference that a black oxide treatment can make.

Drive down maintenance and enhance reliability with SKF black oxide bearings

Black oxide bearings can be used as a drop-in replacement to upgrade existing installations, as well as being ideal for use in new turbines. But what brand of black oxide bearing should you choose?

SKF’s black oxide bearings offer superior performance in the most demanding of conditions. This includes in high levels of vibration, heavy contamination, and low lubrication, making them ideal for use in the wind industry.

Through many years of development, research and testing, SKF black oxide bearings have gone through a process of continuous optimisation and refinement to deliver enhanced protection against damage to even the most sensitive of bearing components.

Thanks to SKF’s extended research and development, the black oxidation process can be applied to every type of bearing used within the wind industry. These bearings are particularly useful in wind turbine gearbox systems, where bearings are under high levels of stress and demands are tough.

Where to buy SKF black oxide bearings

SKF black oxide bearings offer a reliable and cost-effective method of extending service life and reducing maintenance intervals in the wind industry. If you’re considering making the switch to SKF black oxide bearings in your wind application, we’re here to help.

At ACORN®, our experts are highly experienced in the challenges faced by the wind industry. This gives us a unique ability when it comes to delivering innovative solutions to increase reliability and reduce downtime.

To find out more about how black oxide bearings could benefit your wind turbines, or for more help on improving reliability in the wind industry, contact your local knowledgeable sales team today.

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