What is a Wind Turbine Bearing

Wind turbine bearings are a special kind of bearings, which are used in harsh environments, require high maintenance costs, and require high service life. Bearings for wind turbines mainly include: yaw bearings, pitch bearings, main shaft bearings, gearbox bearings, and generator bearings. Namely: pitch bearings, yaw bearings, transmission system bearings (main shaft and gearbox bearings). One set of yaw bearings (slewing bearings) and 3 sets of pitch bearings (slewing bearings) are used for each wind turbine (some wind turbines below the megawatt level have non-adjustable blades, and pitch bearings are not required). Machine bearings (deep groove ball bearings, cylindrical roller bearings) 3 sets of main shaft bearings (spherical roller bearings) 2 sets, 9 sets in total. In addition, there are gearbox bearings, and the gearbox has three structural forms. The first form requires 15 sets of bearings, the second form requires 18 sets of bearings, and the third form requires 23 sets of bearings. In this way, the average number of wind turbine bearings is 27 sets. The structural forms of bearings for wind turbines mainly include four-point contact ball bearings, crossed roller bearings, cylindrical roller bearings, spherical roller bearings, deep groove ball bearings, etc. The yaw bearing is installed at the connection between the tower and the cockpit, and the pitch bearing is installed at the connection between the root of each blade and the hub.

Bearings are the core components of wind turbines. Wind turbine bearings range from those used in the blades, main shaft and yaw, to high speed bearings used in gearboxes and generators. In recent years, wind power in emerging markets around the world has developed rapidly. Under the background of national policy support and tight energy supply, China's wind power equipment manufacturing industry has risen rapidly, and the market demand for wind power equipment has increased rapidly, which has also driven the development of wind turbine bearings.

Features of wind turbine bearings:

1. The use environment is harsh;

2. High maintenance cost;

3. High service life is required;

Classification of wind turbine bearings:

Bearings for wind turbines mainly include: yaw bearings, pitch bearings, main shaft bearings, gearbox bearings, and generator bearings. Namely: pitch bearings, yaw bearings, transmission system bearings (main shaft and gearbox bearings).

Generator bearing

Bearing types: deep groove ball bearings, angular contact bearings, etc.

Working condition characteristics: high speed (1000-1500rpm), high temperature (90-120°C) and heavy load.

Requirements for grease: excellent shear stability, good oxidation stability, good anti-magic performance, excellent low-temperature start-up performance, etc.

Spindle bearing

Bearing types: tapered roller bearings, spherical bearings, etc.

Working condition characteristics: low speed (<25rpm), wide temperature, heavy load with large changes, vibration, high humidity.

Requirements for lubricating grease: excellent anti-wear performance, good oxidation stability, excellent low-temperature start-up performance, good water spray resistance, etc.

Pitch/Yaw Bearings

Bearing type: four-point contact ball bearing, etc.

Working condition features: stop more than turn, wide temperature, heavy load, vibration, high humidity.

Requirements for lubricating grease: excellent anti-corrosion and anti-fretting wear performance, excellent low-temperature start-up performance, good water spray resistance, good oxidation stability, etc.

One set of yaw bearings (slewing bearings) and 3 sets of pitch bearings (slewing bearings) are used for each wind turbine (some wind turbines below the megawatt level have non-adjustable blades, and pitch bearings are not required). Machine bearings (deep groove ball bearings, cylindrical roller bearings) 3 sets of main shaft bearings (spherical roller bearings) 2 sets, 9 sets in total.

In addition, there are gearbox bearings, and the gearbox has three structural forms. The first form requires 15 sets of bearings, the second form requires 18 sets of bearings, and the third form requires 23 sets of bearings. In this way, the average number of wind turbine bearings is 27 sets.

Structural forms of bearings for wind turbines

The structural forms of bearings for wind turbines mainly include four-point contact ball bearings, crossed roller bearings, cylindrical roller bearings, spherical roller bearings, deep groove ball bearings, etc. The yaw bearing is installed at the connection between the tower and the cockpit, and the pitch bearing is installed at the connection between the root of each blade and the hub.

Some types of wind turbine bearings produced by some manufacturers

Manufacturing process for wind turbine bearings

1. The forging temperature should be well controlled, and the grains should not be coarse;

2. It is necessary to control the tempering process well to ensure the quenched and tempered structure of its core, so as to ensure its mechanical properties;

3. Control of the depth of intermediate frequency quenching hardening layer on the surface;

4. Avoid fine cracks on the surface.

Cleaning process for wind turbine bearings

1. Inspection of forging blanks

2. Rough car

3. Rough car aging

4. Fine car

5. Forming fine car

6. Heat treatment

7. Hobbing and gear milling

8. During drilling, it can be treated with bluing, phosphating, vulcanization, etc. according to customer requirements

9. Grinding process can be divided into rough grinding and fine grinding. 10. Part inspection

10. Demagnetization, cleaning, assembly, surface coating with anti-rust oil, filling grease, sealing nozzle, packaging (inner layer of plastic film bag, middle layer of kraft paper, outer layer of nylon plastic tape winding).

Lubrication Analysis of Wind Turbine Bearings

The speed of the input shaft of a wind power gearbox is generally 10-20 rpm. Due to the relatively low speed, it is often difficult to form an oil film on the input shaft bearing, that is, the planet carrier support bearing. The function of the oil film is to separate the two metal contact surfaces when the bearing is running, so as to avoid direct metal-to-metal contact. We can introduce a parameter λ to characterize the lubrication effect of the bearing (λ is defined as the ratio of the oil film thickness to the sum of the roughness of the two contact surfaces).

If λ is greater than 1, it means that the thickness of the oil film is enough to separate the two metal surfaces, and the lubrication effect is good; if λ is less than 1, it means that the thickness of the oil film is not enough to completely separate the two metal surfaces, and the lubrication effect is not ideal. In the case of poor lubrication, the bearing may be damaged as shown in Figure 1. Since wind power gearboxes generally use circulating lubricating oil with a viscosity of ISOVG320, if it is found that λ is less than 1, we generally can only improve the lubrication effect by reducing the roughness of the bearing raceway and rollers.

In addition, in the design of the gearbox, the planet carrier support bearing should try to avoid the size of the bearing at one end being too small. In the actual application analysis, we found that even if the service life meets the conditions, this design will lead to a very low linear velocity of the small bearing and oil film more impossible to form.

Load zone analysis of wind turbine bearings

Generally, only a part of the rollers of the running bearing bears the load at the same time, and the area where this part of the rollers is located is called the bearing area of the bearing. The size of the load borne by the bearing and the size of the running clearance will have an impact on the load-bearing area. If the range of the load-bearing area is too small, the rollers are prone to slipping in actual operation.

For wind power gearboxes, if the design of the main shaft adopts the scheme of double bearing support, then theoretically only the torque is transmitted to the gearbox. In this case, after a simple force analysis, it is not difficult to find that the load on the support bearing of the planet carrier is relatively small, so the load-bearing area of the bearing is often relatively small, and the rollers are prone to slipping. In the design of wind power gearbox, the support bearing of the planet carrier generally adopts the scheme of two single-row tapered bearings or two full-roller cylindrical bearings.

We can increase the load-bearing area by properly preloading tapered roller bearings or reducing the clearance of cylindrical roller bearings. Figure 2 shows the comparison of the bearing area before and after reducing the clearance.

Technologies used for wind turbine bearings

Design and analysis: Empirical analogy design is still the main method, and research on force analysis and load spectrum is almost blank. Among the difficult technologies are the requirements for the main shaft bearing to run for more than 13*104 hours without failure, and have a reliability of more than 95%; the high load capacity design for the high damage rate of the gearbox bearing, etc.

Materials: Bearings in different parts use different materials and heat treatment, such as improving the impact energy of 40CrMo steel for yaw and pitch bearings at low temperature (environment temperature -40°C∽-30°C, bearing working temperature around -20°C) and other mechanical properties The heat treatment method of performance, the depth of the hardened layer, the surface hardness, the width of the soft zone and the control of surface cracks of the surface induction hardening; the development of the bearings of the speed increaser is equivalent to the development of foreign STF and HTF steels and the control of the optimal content of retained austenite research; the main shaft bearing is made of electroslag remelted carburizing steel ZG20Cr2Ni4A when there is still a certain gap in the quality of domestic vacuum degassed steel.

How to find a trustworthy Wind Turbine Bearing suppliers?

 When it comes to choosing Wind Turbine Bearing suppliers, procurement departments rely on a number of qualitative, quantitative, subjective and objective criteria.

1. Supplier cost

Probably the most obvious – but equally important – factor to take into consideration when looking for new suppliers, is cost.

Of course, you’ll have a figure in mind as you’ll know which products you’re looking for, and how much you’re willing to pay. Even so, prices between suppliers can vary, so it’s important to shop around and see who offers the best deal. For instance, some suppliers may offer discounts on bulk-buying; or others may offset higher costs with better quality products.

You should weigh up all of the options when it comes to costs, before deciding which supplier is best in that respect.

2. Quality

There’s often a correlation between cost and quality: the more expensive the product, the better the quality. Regardless of price, there is still a predetermined, agreed level of quality, and you want to be sure that your expectations are met.

After all, the last thing you want to do is market your products as high-end, when your supplier sends you something completely different.

Quality doesn’t just refer to the physical product itself, but its associated aspects too. Are the products packaged adequately, protecting them in transit? Are they labelled correctly? Speak with potential suppliers to ensure that you’re fully aware of what they will offer you – you don’t want to sign a contract and then be disappointed.

 3. Reliability and previous experience

It’s important to remember that when choosing a supplier, you’re essentially entering into a long-term relationship with them. It’s similar to hiring a new recruit – you’ll want to see references. 

Don’t be afraid to ask for them: it makes sense that you would want to hear from businesses who have worked with specific suppliers in the past, as they can give you an honest account of what the partnership was like, and list any good or bad points.

If you’re deciding between two suppliers, references can make all the difference when deciding who to choose.

Your chosen supplier will directly reflect upon your business. If they send over a batch of products two weeks late, the customer who ordered that product will blame you, not your supplier. 

4. Shared culture

Expectations are only met when they are clear on both sides. A good supplier relationship is built on shared cultural goals and attitudes. Speak with suppliers directly to find out how they like to work with other businesses. If you want constant communication but they prefer to just “get on with it”, then realistically, that’s not going to work. 

Top-down view of people around a table on their laptops

When speaking with suppliers, whilst you’ll have questions to ask them; it’s likely they’ll have equally as many questions for you. Use this time to gauge whether your culture and expectations are similar, as you should get a good idea of whether or not the relationship will work. 

5. Location

When choosing a supplier, location is a big factor to consider. If you’re a local business that has built your brand on expertise in your area, then you’ll want to focus on finding a supplier who is located nearby, and shares your values.

Link-B2B is a professional supplier listing service platform which will provide high quality and trustworthy supplier list to international buyers. If you are looking for Wind Turbine Bearing suppliers, feel free to visit Link-B2B.com and send a request.