Analysis on the reasons of Grease Leakage of Pitch Bearings of Wind Turbine

With the increase of the operating time of the wind turbine, the sealing ring of the pitch bearing is gradually aging, the lubricating grease is gradually deteriorating, the waste grease is not drained smoothly and the pitch bearing is not completely rotated, resulting in uneven internal pressure, which will lead to the pitch bearing sealing ring. There are different degrees of grease leakage. If it is not handled in time, it may cause poor lubrication of the pitch bearing, thereby affecting the service life of the pitch bearing and the wind turbine. Today, the editor will conduct a detailed analysis of the causes of grease leakage in the pitch bearing of wind turbines for everyone to learn and understand.


The internal structure design of the pitch bearing is unreasonable


1, channel structure


The design of the pitch bearing channel affects the fluidity of the grease in the groove inside the bearing. Under normal circumstances, the variable pitch bearing is filled with grease from the grease hole. The pressure difference required to discharge the waste grease from the grease hole is less than the pressure value that the seal ring can withstand, and at the same time is greater than the resistance value of the grease flow, the seal ring No fat leakage. The required pressure difference is closely related to the resistance of the grease to flow. A small resistance requires a small pressure difference, and a large resistance requires a large pressure difference. If the design of the internal channel of the pitch bearing is unreasonable, the grease flow resistance will be large, which is not conducive to the uniform distribution of the grease and the internal pressure, and the grease cannot enter the grease discharge hole smoothly, resulting in poor grease discharge, resulting in grease at the seal ring overflow.


2, size and distribution of lipid pores


The grease injection holes and grease discharge holes of the variable pitch bearing should be distributed at reasonable intervals to ensure that the bearing can be smoothly injected with new grease and discharged. The distance between the adjacent grease injection hole and the grease discharge hole should be moderate. If the distance is too short, the pressure of the grease injection hole will be higher and the pressure of the grease discharge hole will be lower during grease filling, and the newly added grease will be easily discharged from the grease discharge hole; If the length is too long, the seal ring will bear greater local pressure when adding grease, which will easily lead to grease leakage. In addition, the cross-sectional diameter of the grease discharge hole is too small, the diameter of the grease collection bottle connected to the grease discharge hole is too small, and the distance between two adjacent rows of grease holes on the bearing is too large, which will also increase the resistance of grease discharge, resulting in poor grease discharge. Smooth, so that the internal pressure of the pitch bearing is too large, resulting in grease leakage.


Poor sealing


  1. Aging and wear of the sealing ring


Most of the pitch bearings use nitrile rubber seals, which will age after long-term use. The aging rate is related to the acrylonitrile content in the nitrile rubber, the rubber content of the formula, the antioxidant and the use environment. In general, the nitrile rubber The service life of the sealing ring is 5~10 years. The pitch bearing adopts a contact seal. During operation, the seal ring contacts the friction surface of the seal. As the running time increases, the seal ring will gradually wear out, resulting in a decrease in sealing performance and insufficient pressure on the seal ring. Grease may be removed from the seal ring. Leakage.


2, the seal ring structure design is unreasonable


Pitch bearings generally use double-lip seals. The outer lip can block moisture, dust and other harmful substances from entering the inside of the bearing, and the inner lip can prevent grease leakage. If the seal ring structure design is unreasonable, the sealing effect will be affected after installation, and the seal ring may be deformed after the pitch bearing is operated, resulting in insufficient sealing ability or sealing failure, and the grease is easy to leak.


  1. Improper installation and maintenance of the seal ring


Failure to install or maintain according to the process will result in uneven force on the seal ring. Poor interface bonding during the installation of the seal ring will cause the seal ring interface to break. After the subsequent pitch bearing grease injection operation, the seal ring is prone to bulging and warping (Figure 1 ) And the phenomenon of fracture, so that the grease will overflow from the gap, warpage and damage of the sealing ring.


4, the sealing ring is squeezed and damaged


When installing or maintaining the blades of wind turbines, hydraulic tensioners need to be used to apply torque to the connecting bolts between the blades and the pitch bearing. The distance between the connecting bolts and the sealing ring is relatively short, and the extension head of the hydraulic tensioner has a larger overall size. The stretching head is easy to press on the sealing ring to cause serious damage to the sealing ring, as shown in Figure 2. The subsequent operation of the pitch bearing may cause deformation and tearing of the sealing ring, resulting in a large amount of grease leakage.


Improper selection of grease or unreasonable setting of lubrication system


  1. Improper selection of grease


The choice of grease usually refers to the actual working conditions of the pitch bearing, and also needs to consider the consistency of the grease and the type of additives. The consistency of the grease is closely related to the ambient temperature. Every time the ambient temperature drops by 5 ℃, the consistency will double and the fluidity of the grease will deteriorate. If the consistency of the grease is not appropriate or the pressure resistance is insufficient, subsequent use is likely to occur The solidification phenomenon blocks the grease system, causing the grease to not be discharged normally and leak from the sealing ring, as shown in Figure 3.


2. The amount of grease injection and the setting of the centralized lubrication system are



The pitch bearing needs to be filled with a certain amount of grease before operation. The filling amount is about 60% to 80% of the inner space of the pitch bearing. Generally, the filling amount is about 70%. There are also individual pitch bearing suppliers to ensure sufficient Choose 80% filling amount for lubrication.


Most wind turbines at home and abroad use centralized lubrication systems to fill the pitch bearing with grease. Some wind turbine manufacturers use manual and regular grease filling to further reduce the maintenance cost of the pitch bearing. Both of these two methods of refilling grease have shortcomings: the grease injection amount and grease injection period for manual regular grease injection are often empirical data, and there is a large deviation from the actual grease required for the pitch bearing. The grease injection volume is usually In this case, the lubrication time of the pitch bearing cannot be guaranteed. In addition, about 80% of the grease may be added to the pitch bearing before leaving the factory, which will easily cause a large amount of local grease to accumulate in the pitch bearing channel. ; The centralized lubrication system adopts automatic grease injection method to make the bearing lubrication more adequate. Although the lubrication time and grease injection uniformity of the variable pitch bearing are guaranteed, the centralized lubrication is performed when the variable pitch bearing is not running or the unit is shut down for a long time The system continues to inject grease according to its preset fixed program, which is also likely to cause a large amount of local grease accumulation in the pitch bearing channel.


Under normal conditions, the sealing pressure of the sealing ring of the pitch bearing is about 2.8×105 Pa. The grease injection pressure required when the pitch bearing is stationary and not working is about (2.5~2.8) x105 Pa. The grease injection pressure required when the pitch bearing is running is only It is about 0.6 x105 Pa. Due to the poor fluidity of the grease used in the pitch bearing, the large accumulation of grease caused by the above two kinds of grease injection methods will increase the pressure of the grease channel in the pitch bearing channel, thereby increasing the injection required during grease injection. Fat pressure. When the grease injection pressure is greater than the sealing pressure of the pitch bearing seal ring, the grease will leak from the pitch bearing seal ring under the action of the grease injection thrust.


In addition, if the air in the pressure pump or grease pipe of the centralized lubrication system is not completely emptied, the air will enter the pitch bearing channel along with the grease, resulting in excessive local pressure in the channel. When the pressure is greater than the pitch bearing The sealing pressure of the sealing ring will open the sealing ring, causing serious grease leakage.


  1. Improper collection of waste fat


At present, the waste grease collection of pitch bearing of wind turbines generally adopts the method of installing grease collecting bottles in several waste grease discharge holes distributed on the circumference of the bearing. When new grease is added, the new grease squeezes the waste grease into the waste from the inner cavity of the bearing. Grease drains out of the small holes and drains into the fat collecting bottle, which needs to be cleaned regularly. In fact, as the running time of the pitch bearing increases, the waste grease collection effect is not good, and it is easy to leak grease.


The above is about the analysis and introduction of the reasons for the grease leakage of the pitch bearing of the wind turbine. As an important component of the wind turbine, the pitch bearing is used in a harsh environment, high maintenance costs, and complex forces, and directly affects the continuity of the entire pitch movement. Stability and accuracy. Therefore, in order to ensure the reliability of the life of the pitch bearing, the pitch bearing needs to be well sealed and lubricated to avoid grease leakage.