Abstract: this paper introduces the current situation of design, production and application of special bearings for wind turbines at home and abroad, and looks forward to the considerable market prospect of wind turbine bearings in China in the next few years. 

In recent ten years, wind power generation, as a renewable and green new clean energy, has been highly valued and developed by many countries.The bearings used for wind turbines mainly include: yaw bearing assembly (660PME047), wind vane main shaft bearing (24044CC), transmission bearing, generator bearing, etc. The structural forms of bearings mainly include four-point contact ball bearing, cross roller bearing, cylindrical roller bearing, centering roller bearing, deep groove ball bearing, etc.Among them, large yaw bearing assembly and vane spindle bearing technology is more difficult, now basically rely on the import, is one of the difficulties of fan localization.Home-made fan bearings can improve the design and application level of the domestic bearing industry, narrow the gap with the advanced level of foreign countries, promote the development and technological progress of the domestic bearing industry, in addition, can reduce the cost of wind power, accelerate the development of new resources and renewable resources in China. 

Wind turbines work in the field, all the year round, the working condition is poor, temperature, humidity and bearing load change is very big, the wind speed up to 23 m/s, has the impact load, so the bearing with good sealing performance and lubricating performance, impact resistance, long life and high reliability, the generator when the wind is about to start at level 2 or 3, and can follow the wind of change, so the bearing structure need to be specially designed to ensure that the low friction, high sensitivity, large yaw bearing outer ring gear, so the bearing design, material, manufacturing, lubrication and sealing are specially designed. 

1. Technical analysis of fan bearing

1.1 yaw bearing assembly (660PME047)

Yaw bearing assembly is the fan timely tracking the wind direction of the change of guarantee.When the fan begins to deflect, the impact moment M=I (I is the inertia of the engine room) will be generated by the yaw acceleration.The higher the yaw speed Ω, produced by the acceleration epsilon.Because I is so large, this multiplies the already high impact.In addition, if the fan is deflected in the process of movement, the yaw gear will bear considerable gyro torque, which is easy to cause the fatigue failure of yaw bearing. 

According to the stress characteristics of the fan bearing, yaw bearing adopts "zero clearance" design of four-point contact ball bearing, special design and processing of the channel, can withstand large axial load and torque load.Yaw gear to choose the appropriate material, modulus, tooth surface profile and hardness, to ensure the life of the driving gear and the match.At the same time, the heat treatment measures should be taken to improve the strength of the tooth surface, so that the bearing has good wear resistance and impact resistance. 

The fan is exposed in the field, so there are strict requirements on the sealing performance of the bearing. It is necessary to optimize the sealing form of the bearing and conduct simulation test and research on the sealing performance of the bearing to ensure that the bearing life is the same as the fan life.The fan is installed at a height of 40m, and the installation and disassembly costs are expensive. Therefore, it must have very high reliability, which generally requires a 20-year service life. In addition, the bearing structure is complex. 

1.2 wind vane spindle bearing (24044CC)

The main shaft of the vane is supported by two aligning roller bearings.Because the wind vane spindle bears the load is very large, and the shaft is very long, easy to deformation, therefore, the requirements of the bearing must have a good centering performance. 

Determine the internal structural parameters of the bearing and the structural form of the cage, so that the bearing has good performance and long life. 

1.3 transmission bearing

There are many kinds of bearings in the gearbox, which are mainly lubricated by gear oil in the gearbox.There are more metal particles in the lubricating oil, which greatly shortens the bearing life. Therefore, special heat treatment process is needed to make the raceway surface compressive stress, reduce the sensitivity of raceway to particle impurities, and improve the bearing life.At the same time, according to the working conditions of the bearing, the bearing structure was redesigned, the bearing processing technology was improved, and the bearing performance was further improved. 

1.4 generator bearing

The generator bearings are cylindrical roller bearings and deep groove ball bearings.Through the structural design of the two kinds of bearings, the improvement of the processing technology, the control of the cleanliness of the production process and the optimization of the related components, the noise of the bearing vibration is reduced, and the bearing has a good low noise performance. 

1.5 bearing mounting test technology research

The actual performance of the bearing after installation is not only related to the performance of the bearing itself, but also closely related to the specific installation and use conditions of the bearing. Therefore, it is necessary to study the mating form and the neutral of the installation center when the bearing is installed, so that the bearing can get better performance in practical use. 

2. Current situation of fan bearing technology

At present, domestic development and production of fan bearings are mainly transmission bearings and motor bearings, but the performance and life is not up to the requirements.As a result, about 90 percent of transmission bearings and motor bearings still rely on imports.Yaw bearing assembly and wind vane spindle bearing assembly is still under development, in addition to a small number of large state-owned enterprises such as rod, tile shaft trial-produced, few manufacturers, the basic domestic blank. 

The main technical difficulties in the development of fan bearing are the sealing structure and grease required for long life, special raceway processing and heat treatment technology, special cage design and processing and manufacturing methods.There is a big gap between China's current technical level and foreign advanced level, but in recent years, some research units in China have made some breakthrough research results in these aspects, which must accelerate the process of home-made fan bearings. 

3. Fan bearing market analysis

China is rich in wind energy resources, with theoretical reserves of 1600000000KW and exploitable wind energy resources of 253000000KW.With the enhancement of people's awareness of environmental protection and the country's emphasis on renewable energy, wind power generation has been developing rapidly in China in recent years. 

China started the construction of wind farms in the 7th five-year plan period, and by the end of the 8th five-year plan period, 19 wind farms with a total installed capacity of 166,500kw had been established, accounting for 0.07% of the total capacity of the national power grid.During the ninth five-year plan period, China completed 21 more wind farms with an additional installed capacity of 223,790kw and another 9,0300kw under construction.According to China's total installed capacity of the power industry reached 350000000KW, including wind power, new energy accounted for 0.7%, reaching 2450000KW. 

In the past, China's wind turbines mainly rely on imports, equipment investment is expensive, electricity prices remain high, which affects the market-oriented operation of wind power generation.According to the analysis, if the large 600KW wind turbine is localized, the localization rate reaches 60%, the equipment cost can be reduced by 15%-20%, and the wind power cost can be reduced by 10%-14%.The localization rate reaches 80%, the equipment cost can be reduced by 25%, and the wind power cost can be reduced by 18%. 

At present, there are 81 research units and production enterprises engaged in the development, research and manufacturing of wind power machinery in China.Among them, off-grid type 20879 sets, 4975.2KW, respectively increased by 64.79% and 87.60% over the previous year.In 2001, China also produced 24 grid-connected wind power generating sets with 14760KW for the first time. 

Under the encouragement of a number of preferential policies on renewable pollution-free energy, China's wind power generation industry is bound to develop rapidly in the next few years.According to the tenth five-year development plan of China's power industry, wind power will develop at an average annual rate of 40%, and the production of China's wind power generation units will reach 80300 units by 2005. 

The supporting bearings for wind turbines are mainly used in yaw system, variable slurry system, transmission and engine, etc. Each unit mainly includes one set of yaw bearings, two sets of wind vane spindle bearings, about 15 sets of gearbox bearings, about 2 sets of generator bearings, and various types of bearing structure.Based on the average requirement of 20 sets of bearings for each unit, 1.66 million sets of bearings will be needed by 2005.Even at the current localised rate of 10% for gearboxes and motor bearings, there will be room for 166,000 units.If the bearing localization rate is increased to 20%, there will be a market capacity of 332,000 sets, which is about the improvement of the current production capacity. The matching bearing localization rate will be further improved. Therefore, the market prospect of special bearings for wind turbines is broad.