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

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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

unreasonable

 

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.

Analysis of the causes and preventive measures of bearing cracks in grinding processing

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Mechanical grinding is a method of manufacturing a common metal cutting, the bearing processing industry also been widely used, the bearing parts of heat hardening, or reticular cracking may occur more rules during grinding arrangement of small cracks, known as grinding cracks, it not only affects the appearance of bearing parts, more importantly, also directly affect the quality of the bearing parts. This paper analyzes the causes of bearing parts produced grinding cracks in the grinding process, then take preventive measures, so as to effectively prevent the generation of grinding cracks.
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First, the reasons bearing grinding cracks
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Generating bearing grinding cracks caused by the grinding heat, the surface temperature of the bearing up to 800-1000 ° C or more grinding. Tissue quenched steel is of martensite and residual austenite certain number of them are in a expanded state (without tempering). With increasing expansion and contraction of martensite steel carbon content increases, the steel grinding cracks generated surface of the bearing is particularly important. Effect of grinding heat of retained austenite in hardened steel that is subject to decomposition during grinding, gradually transformed into martensite, martensite this renewed focus on the surface of the part, causing local expansion of the bearing surface, increased parts of the surface stress, stress concentration resulting in grinding, will continue to accelerate the grinding surface of the grinding cracks produced; in addition, the nascent large Chuai martensite, grinding easily accelerate the production of grinding cracks.
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On the other hand, grinding when the grinding machine parts, parts of both pressure and tensile force is, contributing to the generation of grinding cracks. If the cooling is insufficient at the grinding, since the heat generated during grinding, the grinding surface of the sheet sufficient to re-austenitization, quenching and then quenched again into martensite, so that the surface layer of additional stress in the organization, coupled with the amount of heat generated by the grinding surface of the bearing temperature rises fast, fast cooling, which is superimposed the stress and thermal stress may lead to the grinding surface of the grinding cracks generation.
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Second, it characterized in bearing grinding crack
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Usually the grinding cracks significantly different quenching cracks, cracks occur only in the grinding surface of the grinding, shallow, and substantially uniform depth. Lighter grinding cracks perpendicular or nearly parallel to a line perpendicular to the grinding direction and are regularly arranged strips crack, which is a kind of cracks, crack more severe form of tortoiseshell (closed network like), a depth of approximately 0.03 ~ 0.15ram, with obvious cracks after acid etching, which is the second crack.
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Third, grinding cracks Prevention
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From the above analysis of the root cause to know that the generation of the grinding cracks are in a quenched martensite expanded state, the presence of stress. To reduce or eliminate such stress, the stress to be tempered i.e. quenching, tempering is performed, waste of time must be more than 4h. With increasing tempering time, the possibility of grinding cracks decreases. In addition, bearing in rapidly heated to about 100 degrees C and rapid cooling will crack. To prevent cold cracks, the part should be tempered at about 150 to 200 degrees Celsius, if heated to 300 degrees Celsius to continue bearing surface shrinkage cracks again, to prevent the generation of cracks, the bearings should be tempered at about 300 degrees Celsius. It is noteworthy that, bearing around 300 degrees Celsius tempering the hardness will drop, something should not be used. Is produced through a tempering still grinding cracks, which can be tempered or secondary artificial aging treatment, this method is very effective.

Slewing ring

It produces grinding cracks due to heat caused by grinding, so reducing the grinding heat is the key to solve the grinding cracks. Wet milling method is generally employed, but in any case the injection coolant, the coolant no method to arrive at the grinding surface grinding, grinding heat and therefore can not reduce the grinding point. Coolant only part of the grinding point of the grinding wheel and grinding after cooling being passed instantaneously, while the quenching effect of the cooling liquid to make the grinding point. Thus increasing the amount of coolant is one of the main measures to minimize the grinding zone of the grinding heat. If dry milling process, grinding feed less, grinding cracks can be reduced. However, this method is not very significant, and dusty, affecting the work of a bad environment, should not be taken.
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Selection softer durometer, coarser sand to the grinding wheel, grinding heat can be reduced. However, coarser particles can affect parts of the surface roughness, high surface roughness for the part, can not use this method, and therefore subject to certain restrictions. The crude fraction, grinding, selection of both coarse particles coarser soft grinding wheel, the grinding facilitate strength, improve efficiency, and then be fine-grained grinding wheel, grinding feed amount is small. Two points were roughing and finishing, this is the ideal method.
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Self-sharpening properties of a good choice of abrasive wheel, the grinding wheel surface timely removal of waste material, reducing the grinding feed, increasing the number of grinding table speed is reduced, which is an effective way to grinding cracks is reduced.
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The rotational speed of the grinding wheel and part of one of the factors is the main, large wheel rotation runout, ran large parts are grinding cracks incentives. Increase in time accuracy of the grinding wheel and the rotary part so as to eliminate the grinding cracks caused by various factors as much as possible.
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Fourth, the method of preventing the surface of the bearing steel grinding cracks
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In grinding, the grinding cracks generated surface bearing steel, the main method for preventing:
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① reduce grinding heat to solve the grinding cracks.
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② points coarse, fine grinding, both coarse particles selected coarse grinding soft grinding wheel.
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③ Selection good performance since the sharp abrasive wheel, the grinding wheel surface timely removal of waste material, reducing the grinding feed, increasing the number of grinding table speed is reduced.
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④ increase in time accuracy of the grinding wheel and the rotating parts so as to eliminate cracks caused by grinding possible.
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These are the bearings on the causes and preventive measures of cracks in the grinding process analysis reports, I hope you can help look after. Luoyang permanent crown diameter slewing bearings are mainly production of 50-9800mm / wheel bearings and various high-precision rotary bearing, a large thrust ball bearings, bearings and other non-standard shaped products, precision covering P0, P6, P5, P4 four grades, the product type comprises a single row four-point contact ball structure, cross-cylindrical roller structure, a triple-row cylindrical roller structure, a double structure volleyball, the ball joint structure of columns, thin-walled flange structure, large thrust ball structure. Welcome to the needs of friends to call detailed consultation.

High speed low noise slewing bearing bearings are shipped

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Recently, the high-end slewing bearing for medical CT machine designed and produced by our company for customers has been successfully rolled off the production line, and all the indicators of the finished product have passed the inspection.

For the CT machine special slewing bearing, we understand the various technical requirements of the customer, and calculate the bearing capacity and service life according to this requirement. After more than a month of full technical communication, Technical parameters, confirmed the production drawings. This product has an outer diameter of 1180mm and an inner diameter of 980mm. It has a toothless four-point contact ball slewing bearing structure with P5 accuracy. It is a high-end precision slewing bearing; and because it is medical, it has extremely high requirements for noise reduction.

According to the actual working conditions of customers, our technical engineers actively improve the product processing technology, and strive to make products that meet the actual needs of customers. First, the 42CrMo quenched and tempered material is used to make the material performance better and more stable, which guarantees the product quality from the source; secondly, the product raceway and appearance are comprehensively polished to ensure high product precision; thirdly, for the product’s silent requirements, A special segmented nylon cage device is used to lock the ball in the cage pocket while ensuring that the steel ball can rotate freely, thereby reducing the noise impact caused by the free movement of the cage in the raceway. Reduce rotating noise. Through the above efforts, we ensure that the finished products of the slewing ring meet various technical requirements.

 

After the finished product came out, after trial assembly test, it has fully met the requirements of the confirmed drawings of both the customer and us, and the rotation is flexible and light, and the rotation is silent. At present, this product is already on the way to customers.

 

The vision of “Let the world fall in love with Made in China” is not only a slogan, but also implemented in practical actions. It requires countless Chinese companies to constantly challenge themselves technologically and seize the right to speak for China in the core field of manufacturing. In the era of high-tech industry, only Chinese manufacturing can win the “tough battle” and truly realize “Let the world fall in love with Chinese manufacturing!” We Hengguan people carry this great dream and actively practice it! The road is long and long, Hengguan people will persevere in pursuit! May you and I walk along this great journey…

How long does the turntable bearing grease is filled?

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The turntable bearings are widely used in construction machinery and other equipment platforms. During the use of turntable bearings, the lubrication work is very important that there is no lubrication will greatly reduce the life of the bearing, to ensure that the bearing is effective, reliable, and the bearings must be sufficient. Lubrication, lubrication is the basic component of the bearing. Therefore, the filling of the grease has an important role in the normal use of the turntable bearing. So, how long does it know how long the turntable bearing grease is filled?
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First, the filler of turntable bearing grease
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1, fill grease
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Before running the bearing machine, it is necessary to make a supplemental finale. When filled with grease, the bearing should be rotated while the bearing is filled, and the grease is uniformly distributed until the sealing strip is observed at the sealing strip of the bearing. Overflow.

Tuto bearing

2, daily automatic fetipple
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After the incident, the automatic filling system can be opened, and the quantitative oil is injected daily (timing), which satisfies the normal use of the bearing, and the amount of the inclusions in the two months should at least reach the cavity volume value of the inside of the turntable bearing, in order to ensure the sufficient amount of oil Bearings, on the one hand, pay attention to the consumption of grease, on the other hand, to periodically detect oil passages to prevent leakage.
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At around three months, a concentrated finale should be carried out inside the turntable bearing, and the upper row-to-mouth hole should inject a large amount of grease to the upper sealing strip, and fresh grease spillage is uniform.
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Second, three row roller turntable bearing grease
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The bearing structure is protruding the rolling cavity ZUI, and the upper roller grease will move in the downward roller, and the upper row grease should be appropriate, the reference value is the middle row and the lower row 130% of the amount of oxime.

Tuto bearing

Third, what are the lubricates commonly used by turntable bearing
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Commonly used grease is calcium based grease, lithium-based grease, aluminum-based grease, and high temperature grease, and the user can select a suitable grease according to the particular situation.
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The above is about how long to fill a solution, and the timely filling grease is important, but the regular cleaning is also important, the turntable bearing is cleaned up, and the plane of the support driver is cleaned up, and the above oil, Burring and some debris removal, there is a clean working environment before installation. Further, the turntable bearing must be added to the new grease grease or a lithium-containing lithium-containing lithium-containing molybdenum containing molybdenum.

Talking about the cold treatment process of bearing steel

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The heat treatment operation of continuously cooling the quenched workpiece from normal temperature to a lower temperature to transform the retained austenite into martensite is called cold treatment. The purpose of cold treatment is to improve the hardness and wear resistance of steel, and stabilize the size of the workpiece. It is mainly used for bearings, tools and some carburized parts.

 

  1. Cold treatment process of bearing steel

 

The cold treatment of bearing steel often uses a freezer and dry ice alcohol solution. Precision bearings have higher requirements for dimensional stability; after the ring is quenched (especially staged quenching), the internal structure still retains more retained austenite. This retained austenite is an unstable structure. When storing and using the bearing In the process, changes will continue to change the accuracy of the bearing. For this reason, the cold treatment process is adopted, which can reduce the retained austenite in the structure and slightly increase the hardness of the parts.

 

After quenching and cooling the workpiece to room temperature, it is immediately placed in an environment below room temperature for a certain period of time, and then taken out and placed at room temperature. This treatment below room temperature is called cold treatment. The cold treatment of bearing steel often uses a freezer and dry ice alcohol solution. Stay at room temperature after quenching: After quenching, the material must be cooled uniformly inside and outside to room temperature and then cold treated, otherwise it will be easy to crack. Cold treatment immediately after cooling to room temperature (generally no more than 30min), otherwise it will stop the transformation of austenite to martensite change.

 

2, cold treatment temperature

 

The temperature of the cold treatment is mainly based on the martensitic transformation termination temperature Mf of the steel. In addition, the influence of the cold treatment on the mechanical properties and the manufacturability should also be considered. For GCr15 steel, the cold treatment is -70℃; when the precision requirements of ferrules or equipment are limited, the cold treatment temperature can be -40～-70℃; for ultra-precision bearings, it can be between -70℃～-80℃ Perform cold treatment in between. The temperature of the subcooling affects the impact fatigue and contact life of the bearing.

 

3, cold treatment heat preservation

 

Although the transformation of a large amount of martensite is completed when it is cooled to a certain temperature, in order to make the surface and core of a batch of ferrules reach the cold treatment temperature uniformly, a certain holding time is required, generally 1～1.5h.

 

 

  1. Tempering after cold treatment

 

The ferrule is placed in the air after cold treatment, and its temperature is slowly raised to room temperature and then tempered in time. The temperature rise should not be too fast, otherwise it is easy to crack; the tempering is timely, otherwise the larger residual stress inside the ferrule will cause the ferrule to crack, generally not more than 2h.

 

  1. cold treatment time

 

For the length of holding time of cold treatment, some scholars believe that the amount of retained austenite transformed into martensite depends only on the temperature reached by cooling, and the retention time at low temperature does not matter, because retained austenite-martensite transforms at low temperature The cooling is completed in an instant, so there is no need to keep it at a low temperature, just let the workpiece cool from the outside to the inside. It is also believed that the cold treatment time should be determined according to the thermal conductivity of the workpiece, the volume, the time required for cooling through, and the stability of the transformation of retained austenite. The retained austenite in the steel is fully transformed and is more conducive to the formation of carbide particles. After the transformation is completed, the hardness of the parts will not change significantly. Therefore, the holding time of cold treatment also needs to be reasonably controlled according to the actual situation.

 

In fact, there are many studies on cold treatment of bearing steel, including GCr15 steel, aviation high temperature bearing steel, carburized bearing steel, etc., except for the reduction in toughness (decreased impact toughness, 21% reduction), almost all of the research All show the many advantages of cold treatment: reduced Paralympics; increased hardness; increased wear resistance; increased tensile strength; fine carbide precipitation, increased fatigue life, etc.