What is the difference between pitch bearing and yaw bearing?
1. Anticorrosion treatment of the outer surface
For the anti-corrosion requirements of yaw bearings, we use arc spraying long-term anti-corrosion technology. It uses special arc spraying equipment to melt, atomize and spray corrosion-resistant metal (pure aluminum or zinc) to the surface of the workpiece to form a metal arc spraying layer, and then seal it with a highly permeable corrosion-resistant coating to form an arc spraying long Effective anti-corrosion composite coating. Its technical characteristics are: ① long anti-corrosion life, up to more than 20 years; ② high coating adhesion; ③ good coating quality. The process route: semi-finished preparation of the inner and outer rings of the bearing → pre-cleaning → workpiece pre-protection → sandblasting → arc spraying → sealing treatment, which are described as follows.
1) Preparation of semi-finished products of inner and outer rings of bearings
In order to ensure that the yaw bearing has a high appearance quality, the anti-corrosion spraying process is arranged after all machining, and the sprayed bearing parts are directly put into storage after the assembly is completed to ensure that the anti-corrosion layer will not be scratched.
Use organic solvent for degreasing treatment, there may be oil stains on the surface of the semi-finished bearing after machining, in order to ensure the spraying quality, a cleaning process must be arranged before spraying.
3) Workpiece pre-protection
Before sandblasting and spraying, special surface pre-protection tooling is used to protect the workpiece arc raceway, threaded holes and surfaces that do not need spraying.
The surface of the inner and outer rings of the bearing is roughened to increase the contact surface between the coating and the workpiece, so that the surface of the workpiece is more activated and the bonding strength of the coating is improved.
5) Arc spraying
Arc spraying (pure aluminum or zinc) equipment mainly includes DC power supply, spray gun, air compressor and air filter, etc., and mainly controls parameters such as arc voltage, current, wire feeding speed, compressed air pressure, and spraying distance.
6) Closed treatment
Since there are pores in the sprayed coating, it must be sealed to increase the corrosion resistance.
After the yaw bearing is sprayed and assembled, its main exposed machining surfaces are the gear surface, the mounting thread surface and the arc raceway surface. The first two are coated with anti-rust oil after assembly, and the latter is coated with lubricating grease during assembly. The inner packaging of the finished product is closed and wrapped with plastic film, and the outer layer is wrapped with plastic braided tape for protection, which can meet the requirements of anti-rust.
2 Damping torque
2.1 Formation mechanism
After the yaw bearing is assembled, there are two sources of damping torque: one is the frictional resistance of the raceway part, and the other is the frictional resistance of the sealing strip and the sealing surface. The latter is generally constant under the same processing conditions, so the magnitude of the damping moment after the yaw bearing is assembled mainly depends on the former.
The frictional resistance torque generated by the raceway part during rotation mainly depends on the size of the bearing clearance. The larger the gap, the smaller the resistance, and the smaller the gap, the larger the resistance. The yaw bearing requires zero clearance or negative clearance, and the amount of negative clearance is determined by the friction damping torque after assembly. Therefore, the size of the friction damping torque after assembly basically depends on the assembly clearance value of the yaw bearing, and the formation of this value mainly depends on: the size of the finishing car before the raceway quenching, the raceway surface quenching, and the raceway quenching after the quenching. The grinding size and the size of the rolling elements are matched in four links.
Wind power bearings (yaw bearings, pitch bearings) are subject to complex forces, and the bearings are subjected to relatively large shocks and vibrations. Therefore, the bearings are required to withstand both shocks and large loads. The life of the wind turbine main engine requires 20 years, and the cost of bearing installation is relatively large, so the life of the yaw and pitch bearings is required to reach 20 years.
Wind turbines may work in cold areas, the ambient temperature is as low as -400C, the working temperature of the bearing is around -200C, and the bearing must be able to withstand large impact loads under low temperature conditions.
Yaw and pitch bearings have special requirements in terms of clearance. Compared with the yaw bearing, the impact load of the pitch bearing is relatively large, and the wind blows to the blade and the vibration is also large, so the clearance of the pitch bearing is required to be zero clearance or slightly negative clearance value, so that in the case of vibration It can reduce the fretting wear of the bearing. Yaw bearings require small clearance values.
Wind turbine equipment works in the field, and part of the yaw and pitch bearings are exposed outside, which will be polluted by the atmosphere, and the high humidity environment will also corrode the bearing matrix. Therefore, the exposed yaw and pitch bearings will be exposed to the outside world. The parts require surface anti-corrosion treatment.