Wind power bearings can be divided into three categories: yaw bearings, pitch bearings, transmission bearings (main shaft and gearbox bearings).Tower and yaw bearings are installed in the junction of tower and the cockpit; pitch bearings are installed in each blade root and hub joints. Each wind turbine equipment use three sets pitch bearings and a set of yaw bearing (part of the megawatt-class wind turbines is not below the adjustable blade, can not use pitch bearing.)
1 Identification code
Yaw and pitch bearing code use the method of slewing bearing in JB/T10471-2004 method. But in the wind turbine yaw, pitch bearings, double-row four-point contact ball slewing bearings appeared, and this structure bearing the code is not provided in the JB/T10471-2004, therefore, add the standard of double-row four point contact ball slewing bearing. Because single-row four point contact ball slewing bearing structure type code is 01, while double-row different dimater ball slewing bearing is 02,there provided that 03 stands for double-row four point contact ball slewing bearing.
2 Technical Requirements
2.1 material
This standard specifies the yaw, pitch bearing ring material select 42CrMo, treatment with the overall quenching, after quenching hardness 229HB-269HB, raceway select surface-hardening, quenching hardness of 55HRC-62HRC. As the wind turbine yaw, pitch bearing’s force is complex and bearings withstand large shock and vibration, therefore, required bearings to withstand both the impact and greater loads. Host wind turbine life requirements of 20 years, bearing the cost of installing large, thus requiring yaw, pitch bearing life have reached 20 years. Bearing rings matrix hardness is 229HB-269HB, so it is able to withstand shocks but no plastic deformation, meanwhile raceway surface quenching hardness reach to 55HRC-62HRC, also can increase the contact fatigue life, thus ensuring long life bearing requirements.
2.2 Low-temperature impact energy
This standard’s low temperature impact energy requirements for bearing rings:-20 ℃ Akv not less than 27J, under cold Akv value can be determined in consultation with users. Wind turbines may work in very cold areas, environmental temperature is about as low as -40 ℃, the bearing operating temperature is -20°C or so, bearing in low temperature conditions must be able to withstand large impact loads, therefore, required bearing ring material must be done low-temperature impact energy test after quenched, take part of the bearing rings to made sample or the same performance and same with the ring under the conditions of sample treatment, do impact energy test in the -20°C environment
2.3 bearing gear
As the wind turbine bearing drive accuracy is not high, and ring gear diameter is relatively large, gear modulus is relatively large, therefore, the accuracy of the general level of gear required GB/T10095.2---2001 of 9 or 10. However, because there has impact between the pinion and bearing ring under working conditions, therefore,the bearing gear need to quench,Generally, pinion tooth surface hardness reach to 60HRC, taking same life design into account, gear tooth surface hardness of the provisions of quenching not be less than 45HRC.
2.4 Clearance
Yaw, pitch bearings have special clearance requirements. Compared to yaw bearing, pitch bearing’s impact load relatively large, wind to the blade vibration is also large, so required pitch bearing clearance should be zero or slightly negative clearance value, so in the case of vibration, it can be reduced the fretting wear of bearings. Yaw bearing requirements for the small clearance value, that is 0-501 ~ m. In addition, because wind turbine yaw and pitch bearing rotation driven by the drive motor under the negative clearance or small clearance state therefore, bearing need to empty measurement to start friction torque after assembly, so specific torque value based on the different host drive system is not the same.
2.5 Antiseptic treatment
Wind turbine equipment work in the field, and part of the yaw, pitch bearing exposed, will be air pollution, high humidity also will corrosion bearing matrix , therefore, require surface anti-corrosion treatment, the general galvanized.