The main features of wind power bearings
1. The use environment is harsh;
2. High maintenance cost;
3. High life expectancy is required;
Classification of wind power bearings
Bearings for wind turbines mainly include:
Yaw bearings, pitch bearings, spindle bearings, gearbox bearings, generator bearings.
Namely: pitch bearing, yaw bearing, transmission system bearing (main shaft and gearbox bearing).
Generator bearings
Bearing types: deep groove ball bearings, angular contact bearings, etc.
Working condition characteristics: high speed (1000-1500rpm), high temperature (90-120℃) and heavy load.
Requirements for grease: excellent shear stability, good oxidation stability, good anti-wear performance, excellent low-temperature starting performance, etc.
Spindle bearing
Bearing types: tapered roller bearings, spherical bearings, etc.
Working conditions characteristics: low speed (<25rpm), wide temperature, heavy load and large changes, vibration, high humidity.
Requirements for grease: excellent anti-wear performance, good oxidation stability, excellent low temperature starting performance, good water resistance, etc.
Pitch/Yaw Bearing
Bearing type: four-point contact ball bearing, etc.
Working condition characteristics: stop more than turn, wide temperature, heavy load, vibration, high humidity.
Requirements for grease: excellent anti-corrosion and fretting resistance, excellent low-temperature starting performance, good water resistance, good oxidation stability, etc.
Each wind turbine equipment uses 1 set of yaw bearing (slewing bearing), 3 sets of pitch bearing (slewing bearing) (some wind turbines below the megawatt level are non-adjustable blades, and variable pitch bearings may not be used) to generate electricity Machine bearings (deep groove ball bearings, cylindrical roller bearings) 3 sets of spindle bearings (spherical roller bearings) 2 sets, a total of 9 sets.
In addition, there are gearbox bearings, and the gearbox has three structural forms. The first form requires 15 sets of bearings, the second form requires 18 sets of bearings, and the third form requires 23 sets of bearings. In this way, the average number of wind turbine bearings is 27 sets.
The structural forms of bearings for wind turbines mainly include four-point contact ball bearings, crossed roller bearings, cylindrical roller bearings, spherical roller bearings, and deep groove ball bearings. The yaw bearing is installed at the connection between the tower and the cabin, and the pitch bearing is installed at the connection between the root of each blade and the hub.
Some wind turbine bearing varieties produced by some manufacturers
Wind power bearing production process requirements
1. The forging temperature should be controlled well, and the grains should not be coarse;
2. It is necessary to control the tempering process to ensure the tempered structure of its heart, so as to ensure its mechanical properties;
3. Control of the depth of the intermediate frequency quenching hardened layer on the surface;
4. Avoid micro-cracks on the surface.
Lubrication Analysis of Wind Power Bearings
The speed of the input shaft of the wind power gearbox is generally 10-20 rpm. Due to the relatively low speed, the oil film of the input shaft bearing (that is, the planet carrier support bearing) is difficult to form.
The function of the oil film is to separate the two metal contact surfaces when the bearing is running to avoid direct metal-to-metal contact.
We can introduce a parameter λ to characterize the lubrication effect of the bearing.
(λ is defined as the ratio of the thickness of the oil film to the sum of the roughness of the two contact surfaces)
If λ>1, it means that the thickness of the oil film is enough to separate the two metal surfaces, and the lubrication effect is good;
If λ<1, it means that the thickness of the oil film is not enough to completely separate the two metal surfaces, and the lubrication effect is not ideal.
Running under the condition of poor lubrication may cause damage to the bearing. Since wind power gearboxes generally use circulating lubricants with ISOVG320 viscosity, if λ is found to be less than 1, we generally can only improve the lubrication effect by reducing the roughness of the bearing raceways and rollers.
In addition, in the design of the gearbox, the planet carrier support bearing should try to avoid the size of one end bearing being too small. In the actual application analysis, we found that even if the service life meets the conditions, this design will cause the linear velocity of the small bearing to be very low and the oil film Even more unable to form.
Analysis of bearing area of wind power bearing
Generally, only a part of the rollers of a running bearing bear the load at the same time, and the area where this part of the roller is located is called the bearing area of the bearing.
The size of the load borne by the bearing and the size of the running clearance will affect the load-bearing area. If the load-bearing area is too small, the roller is prone to slipping during actual operation.
For wind power gearboxes, if the main shaft is designed with dual bearing support, theoretically only torque is transmitted to the gearbox. In this case, after a simple force analysis, it is not difficult to find that the load borne by the planet carrier support bearing is relatively small, so the bearing area of the bearing is often relatively small, and the rollers are prone to slippage. In the design of wind power gearboxes, planet carrier support bearings generally use two single-row tapered bearings or two full-roll cylindrical bearings.
We can increase the load-bearing area by properly preloading tapered roller bearings or reducing the clearance of cylindrical roller bearings. Figure 2 shows the comparison of the load-bearing area before and after reducing the clearance.
Wind power bearing technology
Design and analysis: The design is still based on empirical analogy, and the study of force analysis and load spectrum is almost blank. Among the difficult technologies are the trouble-free operation of the spindle bearing for more than 13*104h and the reliability of more than 95%; the high load capacity design for the high damage rate of the gearbox bearing.
Material: Different materials and heat treatments are used for different parts of the bearing, such as improving the low temperature of 40CrMo steel for yaw and pitch bearings (ambient temperature -40℃∽-30℃, bearing working temperature around -20℃), impact energy and other mechanics Performance heat treatment method, surface induction hardening hardening layer depth, surface hardness, soft belt width and surface crack control; speed increaser bearing is equivalent to the development of foreign STF, HTF steel and control the optimal content of retained austenite The main shaft bearing is made of electroslag remelting carburizing steel ZG20Cr2Ni4A when there is still a certain gap in the quality of domestic vacuum degassed steel.
