Wheel bearing applications in the field of wind power

In recent years, as a rotating turntable bearing support structure appears more and more large-scale machinery and equipment , such as large rotary machines , offshore drilling platforms, port machinery , truck crane, radar, tanks, wind turbines and so on. Large machinery and equipment has also become an important connecting link, especially in the wind turbine , and is a necessary part of the pitch and yaw systems.
        Wind turbines typically run in the wild , desert, hills and other harsh environments , so installation is expensive , tedious process , but also the requirements for wind turbines have a higher capacity and stable operation . The use of wheel bearings directly affect the smooth operation of the machine , but also in the design, selection , manufacture, installation and maintenance process, in strict accordance with the relevant standards should be based on the specific use , and strive to design rationalization , stable , maximize life.
        Aiming wheel bearing applications and precautions to be in the field of wind power analysis , hoping to provide a reference for the design of wind turbines , installation and maintenance personnel. Many types of wheel bearings , used in wind turbines in the main single-row four-point contact ball double four -point contact ball two. One single row of compact four- point contact ball bearing turntable structure, light weight , and circular raceway ball four point contact , can withstand the axial force, radial force and overturning moment , low cost, high performance, yaw bearings for wind power is usually shown in Figure 1.
        Double four -point contact ball bearing turntable long life, strong bearing capacity , allowing a large amount of wear on the mounting base is less demanding, often used for wind power pitch bearing , in large MW wind turbine is also sometimes chosen in yaw bearing shown in Figure 2 . There are also double Reducing the ball , single row cross roller type , three -row roller and other forms of cross roller wheel bearings , although high precision, long life, high dynamic load capacity , but the base have high rigidity and precision requirements, and the roller in contact with the raceway is prone to edge effects , taking into account the wind turbine by external loads is more complex and require a higher safety factor cost and other factors, are rarely on the blower to use.
        A major component of wheel bearings
        1.1 turntable bearing inner rings and outer rings rings, rings of material is generally preferred 42CrMo, 5CrMnMo, 50Mn , respectively, corresponding to the standard GB / T 3077, GB / T 1299, GB / T 699, you can have the same selection materials processing and manufacturing performance , but the performance can not be lower than the above types of materials . Quenched state hardness of 210 ~ 260 HB, normalizing the status hardness of 180 ~ 240 HB, hardness requirements on wind turbines will be higher , for wind turbine temperature -20 ℃ impact energy required to do no less than 27 J, for cryogenic wind turbine needs to be done -40 ℃ impact energy test . Between the inner and outer rings around the raceway, the entire wheel bearing raceway is the weakest link , hardened raceways required to achieve the appropriate hardness and depth to combat wear and prevent raceway spalling , the hardened layer depth and hardness in accordance with standard JB / T in the 2300 regulations.
        1.2 rolling wheel bearing rolling elements located between the inner and outer rings, inner and outer rings relative rotation , mainly exposed to the wind overturning moment loads generated effects . Material usually used GCr15 rolling and GCr15SiMn, hardness values ​​shown in Table 1 , and should meet the standards GB / T 308 or GB / T 18254.
        1.3 Gear
        Wheel bearings and other bearing the biggest difference is with the drive gear when the wheel bearings and drive gear to engage the outside , gear cutting on the outer rings , and when the drive wheel bearings within the gear engages the ring gear is machined into account on . Standard spur gear involute cylindrical gears , usually modification coefficient , modulus gear shall comply with GB / T 1357, gear precision execution by GB / T 10095 stipulates that need hardened gear tooth surface according to the actual needs into hardened , full gear tooth hardening and quenching , quenching is generally part of the surface hardness 50 ~ 60 HRC, the effective depth DS ( ≥ 40 HRC hardness of the skin depth ) as shown in Table 2 .
        1.4 Seal ring material SNT7453 type nitrile rubber , while meeting the requirements HG / T 2811 's . Although nitrile rubber is the most commonly used oil materials , cheap, and good oil, heat and abrasion resistance and is widely used in many areas of life , but it does not apply to phosphate ester hydraulic fluids and additives gear oil, does not apply to ketones, ozone, and chloroform environment and therefore must be considered in the use of the sealing material and the working environment of grease nitrile rubber seals.
        2 wheel bearings are now working principle and mechanical failures often
        Large wind turbines are mainly primary drive system , the electric pitch system and yaw system , which pitch system and yaw system works through the wheel bearings are realized , in whole generation process, the need pitch and yaw , the main control system based on wind speed and direction feedback signal to start triple meter , driven by pinion bearing turntable action to change the pitch angle of the blades and the wind angle , to ensure maximum air flow catching machine .
        From past experience, the process of running the fan wheel bearings easily arise mainly in the following areas: installation and maintenance , with the gap between the ring gear , lubrication and sealing ring gear meshing with the drive gear at , corrosion , etc., so for these issues raised following precautions.
        3 wind turbine wheel bearings Precautions
        Wind turbines due to poor living environment , force complex, on the basis of the above provisions can be improved to meet the actual requirements of the relevant values ​​. If the inner and outer ring raceway , as the weakest link in the raceway , wheel bearings in use damaged 98% of the damage from the raceway , so as to ensure the turntable bearing life of 20 years to meet the requirements of the raceway hardened layer depth and surface hardness should be made more stringent requirements .
        In the design , installation, maintenance phase should note the following:
        1 ) of the wind turbine during operation of the power by the gas is changed, changes in the size and direction of the wind speed will not change , resulting gyroscopic torque , which acts on the blades is a variation of inertia load , the load on the rotating blade is changed, also the excitation source . The vibration of the blade vibration source , the blades are fixed by bolts on the bearing inner ring pitch , blade vibration loosening the fixing bolts , and then evenly discontinuity blade , fretting wear, and therefore , in the design process , to prevent the fixing bolts loose wheel bearings caused by bearing displacement arising from wear and tear, in ensuring the bolt fatigue life , as far as taking greater tightening torque value ( wind mechanical standard assembly manual has been given the reference torque value can be used as a reference ) . But the need to develop practical maintenance requirements according to the actual situation , such as the installation and initial start- slewing working in continuous operation for 100 h , check the mounting bolts should be fully meets the requirements of preload , after 500 h of continuous operation per repeat the inspection when loosening the bolt angle exceeds 30 °, to bolt to this note or replacement due to loose bolts to prevent aggravated wheel bearing wear .
        2 ) control the assembly clearance will also have a serious impact on the force and the life of the bearing . Clearance between the wheel bearing inner and outer rings , directly affects the load distribution turntable bearings , slewing sensitivity, precision rotation , vibration characteristics , for JB / T 2300-1999, JG / T 66-1999, JB 10705 [ 3,4 ] and other standards are on the wheel bearing clearance made ​​clear requirements , wind power in yaw bearings and pitch bearings usually requires zero clearance or slightly negative clearance to increase bearing capacity , reduce fatigue . Wheel bearings and gear pitch or yaw gear reducer gear backlash , generally require minimum backlash is (0.03 ~ 0.04) × modulus, after final tightening wheel bearings, the entire circumference of the small gear backlash gear to re- check to ensure that the gap is moderate , improving transmission accuracy and reduce the impact load .
        3 ) lubrication and sealing are also factors to be considered , using the wind turbine wheel bearings are low overload conditions, poor lubrication prone molecules fused to the metal surface , leaving the raceway pits accelerated bearing wear , so must ensure good lubrication between the tooth surface , is formed between the rolling element and raceway protective film , reducing fretting wear between the contact surfaces , reducing the turning moment of resistance , avoid direct metal to metal contact , while immediate dispose of waste oil , and other hard to avoid dust particles into the mating surfaces , causing broken teeth and even tooth wear and prolong the life of wheel bearings .
        Many common types of grease , grease the main consideration when selecting environmental and lubricating properties to use , if it comes to low-temperature environment , it is important to ensure that the grease will continue to work at the lowest temperatures ; establish reasonable procedures lubrication system , bearing grease injection volume and cycle to the data provided by the manufacturer as a reference, formulated in line with the actual conditions of the lubrication program ; equipment before and after the operation is stopped for a long time , it must also be greased , avoid starting an instant wear ; filling grease the grease when you want to make sure the model and clean , and definitely not mix different types of grease , but can not make any impurities , especially iron participation lubrication, lubrication to avoid injury . In the case of a conditional periodic manual control of the blade 360 ° rotation, while injection grease guaranteed each rolling element raceway can adequately lubricated.
        4 ) wheel bearing grease seals to prevent the outflow of the outside world but also to prevent dust , water vapor , impurities and corrosive gases from entering, to reduce bearing wear . Seal life is generally 5-7 years , so the design must consider how to replace the seals. Maintenance personnel must be regularly checked in accordance with the maintenance manual ring of aging , especially in larger temperature difference between regions, early aging of the rubber sealing lip lost more tightness ; while also doing nacelle seal to prevent direct sunlight shot in a sealed the ring, the seal ring premature aging. But found a ring dislocation or fracture, oil outflow , it is timely to reset or updated to ensure raceways and balls from wear and tear . In addition to prevent bearing over-current , galvanic corrosion occurs , as well as pay attention to the installation process should be with the Lord hardened the soft load area with a 90 °, to ensure the accuracy of details such as the installation work can not be ignored in the installation and commissioning process must be strictly in accordance with the design specifications execution.
        4 Conclusion
        Wheel bearings in wind turbines to play an important role , once the wheel bearings in need of repair or replacement , lifting transport costs will have to spend hundreds of thousands or even hundreds of million , costly , and therefore in the selection process of wheel bearings must be fully demonstrated , checking , in strict accordance with the instruction manual , fully understand its working principle and characteristics of the importance of its maintenance , to ensure that its rated life.