I. Wind Power Generation: The Most Hardest "Test Ground" for Bearings

Wind turbine generators are typically installed at altitudes of 50 meters or higher, or even standing in vast oceans. The bearings of wind turbines endure drastic changes in temperature, humidity, and load throughout the year. The wind speed can reach up to 23 m/s, and there are continuous impact loads. Once a bearing in a wind turbine fails, the disassembly and reinstallation costs are high and the process is lengthy - as the equipment is located at high altitudes, each repair requires the use of large lifting equipment and professional teams.

 

The lifespan of wind turbine generators is set at 20 years, so the reliability lifespan of wind turbine bearings must be the same as the generator's lifespan. A typical wind turbine generator consists of 4 sets of yaw/declutching bearings, 1 set of main bearings, 20 sets of gearbox bearings, and 2 sets of generator bearings. Each failure of a set of bearings can lead to unplanned shutdown of the entire wind turbine - in a wind farm, such shutdowns are costly.

 

Japanese NMT wind power generation-specific bearings, targeting the harsh conditions of the main shaft, yaw, declutching, and generator, adopt a systematic solution of self-aligning roller bearings, four-point contact ball bearings, and deep groove ball bearings to address the triple challenges of harsh environments, 20-year lifespan, and high reliability.

 

II. Main Shaft Bearings: The "Core Joint" Bearinging that Sustains the Largest Load

The main shaft bearing is the component in the wind turbine generator that bears the largest load. The main shaft of the rotor bears a very large load, and the shaft is long and prone to deformation, so the bearing must have good self-aligning performance and extremely high load-bearing capacity.

 

Three technical routes for main shaft bearings

 

Currently, wind turbine main bearings are mainly divided into three types: self-aligning roller bearings (SRB), tapered roller bearings (TRB), and three-row cylindrical roller bearings (CRB). Self-aligning roller bearings are mostly used in doubly-fed and 5MW or below models; large-power doubly-fed, direct-drive, and semi-direct-drive models mostly adopt tapered roller bearings and three-row cylindrical roller bearings.

 

In the typical two-point support form, the positioning end bearing not only needs to meet the main load-bearing requirements for radial and axial loads, but also requires good self-aligning performance (usually requiring more than 0.3°), and must be able to operate stably for 20 years under low-cost requirements.

 

NMT's response solution

 

NMT's self-aligning roller bearings feature a spherical raceway design, which automatically adjusts the contact position when the main shaft bends due to wind load, distributing the load evenly along the length of the roller, eliminating edge stress concentration. NMT uses precise forging and secondary quenching processes to reduce the non-metallic inclusions in the bearing steel to an extremely low level, increasing the fatigue limit by 38% compared to ordinary products.

 

For the special clearance requirements of main shaft bearings, NMT provides customized clearance solutions - considering the economic feasibility of actual processing and operating conditions, it is usually recommended to use half of the standard clearance as the wind turbine clearance, or to select special clearance based on actual application data. The bearing ring material uses high-performance steels such as 42CrNiMo, with an increase in tensile strength of 18%, and the quenching depth is increased from 5mm to 7.5mm.

 

III. Yaw and Declutching Bearings: The Precise Controller of Wind Direction Angle

Yaw bearings are installed at the connection between the tower and the nacelle, and declutching bearings are installed at the connection between each blade root and the hub. These two types of bearings are responsible for adjusting the windward angle of the rotor, allowing the wind turbine to always capture the wind energy in the optimal position.

 

The core challenges of yaw and declutching bearings

 

Yaw bearings and declutching bearings need to withstand large axial forces and overturning moments. According to the force characteristics, yaw bearings adopt small clearance design; declutching bearings adopt zero clearance or "negative clearance" design of four-point contact ball bearings, with the raceway specially designed and processed to withstand large axial load and moment load.

 

Due to the exposure of the wind turbine to the harsh environment outdoors, there are extremely strict requirements for the sealing performance of the bearings. The sealing form of the bearings must be optimized to ensure that the bearing life is the same as that of the fan (20 years). The bearing rings of yaw and pitch bearings are generally made of 42CrMo steel, and the heat treatment adopts overall quenching treatment. The raceway part is surface hardened, with a hardness of 55HRC-62HRC.

 

NMT's response plan

 

NMT's four-point contact ball bearings adopt zero-clearance or "negative clearance" precise pre-tightening design. A single set of bearings can withstand bidirectional axial loads and overturning moments. The precisely controlled groove geometry ensures that the rolling elements are uniformly in contact under the load, eliminating stress concentration.

 

For the sealing challenges of yaw and pitch bearings, NMT provides a full range of sealing solutions - contact rubber seals form a physical barrier between the inner and outer rings, effectively blocking sand, moisture, and salt fog from entering. In the actual application of NMT yaw system bearings in wind farms, the failure rate has decreased by 75%, and the annual maintenance cost has exceeded 500,000 yuan.

 

VII. Gearbox Bearings: The "Speed-Transmitting Hub" of Power Transmission

 

The gearbox is the part with the largest number of bearings and the most types in the wind turbine unit. A gearbox typically contains about 20 sets of bearings, involving various types such as self-aligning roller bearings, cylindrical roller bearings, spherical roller bearings, and four-point contact ball bearings.

 

The core challenge of gearbox bearings

 

The bearings in the gearbox mainly rely on gear oil for lubrication. The lubricating oil contains a lot of metal particles, which significantly affects the bearing life. During startup and braking, the bearings are subjected to huge impact loads, and at the same time, they require low friction torque and high operational flexibility at low-speed startup.

 

NMT's response plan

 

NMT's gearbox bearings adopt a special heat treatment process, creating compressive stress on the raceway surface, reducing the sensitivity of the raceway to particle impurities, and improving the bearing life. The optimized roller contour design eliminates edge stress concentration, allowing fatigue cracks to be delayed even under boundary lubrication conditions.

 

NMT's cylindrical roller bearings provide extremely high radial load capacity through a line contact structure, suitable for parts in the gearbox that bear heavy radial loads. The self-aligning roller bearings compensate for the deformation of the shaft system with spherical raceways, maintaining a uniform load distribution in long-axis gearboxes.

 

VII. Generator Bearings: The "Power Source for Clean Operation"

 

The generator is the final energy output end of the wind turbine unit. The bearings in the generator need to maintain low vibration, low noise, and long-term reliability at high rotational speeds. Generator bearings typically use a combination of cylindrical roller bearings and deep groove ball bearings.

 

The core challenge of generator bearings

 

The generator rotates at a high speed (usually 1000-1500 rpm), and the bearings need to maintain low vibration and low noise at high rotational speeds. The stability of the lubricating grease shear is crucial. At the same time, generator bearings are extremely sensitive to cleanliness, and any tiny particle intrusion can affect the power generation efficiency and bearing life.

 

NMT's response plan

 

NMT's deep groove ball bearings provide quiet and efficient rotational support for the generator with an extremely low friction coefficient (≤0.0015) and operating noise (≤20dB). The ultra-precision grinding of the raceway and the optimized arc design ensure uniform contact stress, with rotational accuracy reaching the ISO P2 standard.

 

NMT's long-lasting low-volatile lubricant has a volatility of ≤0.003mg/g and can achieve a maintenance cycle of up to 30,000 hours in a wide temperature range of -45℃ to 155℃, significantly reducing the maintenance frequency and operating costs of the generator.

 

VII. The Engineering Value of NMT Wind Turbine Bearings

The value of wind power equipment is not determined by the purchase price of a single unit, but by how many years it can operate safely, continuously, and reliably in harsh environments.

 

On the main shaft of the wind turbine, NMT's self-aligning roller bearings' high load-bearing capacity and self-aligning performance support each rotation for decades. In the yaw and pitch systems, the zero-clearance precision preload of NMT four-point contact ball bearings ensures that the wind turbines always face the wind at the optimal angle. In the gearbox, NMT cylindrical roller bearings and self-aligning roller bearings maintain long-term reliability under impact loads and metal particle environments. In the generator, the low-noise and long-life lubrication of NMT deep groove ball bearings enable each degree of electricity to be produced efficiently.

 

Choosing NMT wind power generation-specific bearings is to select a proven 20-year-life precise support solution for each core rotating part of the wind turbine - allowing each wind turbine to continue operating in the open fields and ensuring the stable output of each degree of clean energy.