Yaw and Pitch Rolling Bearing Design Types

Modern wind turbines use large slewing rings at the root of each blade to enable pitch angle changes and thus aerodynamic performance and load control. Yaw bearings are used for angular realignment of the nacelle into the predominant wind direction. These applications require long periods in nearly stationary positions with large stochastic loads. Due to this demanding load environment and the fact that bearings exist in the critical load path, their design becomes critical to the safety and reliability of most turbine designs.
Large wind turbines (those rated at more than 250 kW) use ball or roller bearings with special configurations for blade retention pitch bearing and yaw bearing locations. The bearings consist of two ring-rolled forgings forming the outer and inner raceways and a complement of either balls or rollers. The inner and outer continuous-ring forgings have mounting holes that allow the bearing to be bolted directly to the supporting structures. The balls or rollers are inserted into the bearing through a radial cylindrical hole in one of the rings. The hole then is closed using a removable loading plug con-toured to the ball path or roller path surface. 
It is common practice to cut a spur gear integral with one of the bearing rings, especially for the yaw bearing application. Individual plastic spacers or thin section cage arc segments are used to separate the balls. The spacers are cylindrical with a hemispherical end. The individual rollers in the cross-roller bearing are separated by plastic, saddle-shaped spacers. The rollers in the cross-roller bearing alternate in their orientation to carry load.
The inner and outer rings are hardened from 250 to 300 Brinell hardness (HB). This is referred to as the “core hardness” of the ring. This core hardness should provide adequate core yield and fatigue strength, yet remain at a hardness low enough to facilitate machining of the rings, gear teeth, and mounting-bolt holes. The actual ball or roller path (rolling contact surface) is induction heated, quenched, and tempered to provide a hard surface or “case.” The surface hardness of the raceway is a minimum of 58 HRC (Rockwell C scale hardness). The depth of the hardened case is defined as the depth to a hardness of 50 HRC.
The two-row, eight-point contact ball bearing type is more costly to manufacture than the single-row, four-point contact ball bearing. In addition to having a second row of balls and separators, the two-row bearing must be repeatedly assembled and disassembled during manufacture to accurately measure and match the internal diametral clearance or preload of the two ball rows.
The main advantages of the eight-point contact ball bearing, as compared to the four-point contact ball bearing, are:
• Lower ball loads;
• Lower Hertz stresses;
• Less required case depth; and
• Increased fatigue life.

Wind Power Generator Slewing Ring Cages or Separators

Most yaw and pitch bearings are supplied with plastic spacers between each rolling element. A four-point contact ball bearing has cylindrical spacers with hemispherical indented ends. The cross roller bearing has plastic saddle-type spacers, which conform to the two adjacent rollers with axes of rotation 90 degrees apart. The ball spacers for larger balls (50-mm diameter and larger) often have a steel-plate reinforcement cast into the plastic.
Use of segmented cages is very rare for yaw and pitch bearings. The opening that the cage requires between the raceways significantly reduces the available load-carrying ball path. The bearing manufacturer should be consulted about spacer design. The spacer material also must be compatible with the selected lubricant.

offshore wind,wave and tidal energy

Harnessing energy from offshore winds, waves, and tides holds great promise for our nation's clean energy future. Energy production is just one of the valuable resources our oceans and coastal ecosystems provide. We can successfully develop offshore renewable energy by ensuring that energy projects are sited, designed, and constructed in a manner that protects our fragile ocean ecosystems.

Bearings selection and calculations for wind power plants

The demands placed on bearings for wind power plants are extremely high. Therefore, the procedures for bearing selection and lifetime calculations are fundamentally different than selecting bearings in other application areas.
When selecting bearings for industrial use, design engineers can choose bearings for a defined bearing location relatively easily, working together with their suppliers if necessary, and basing their decisions on parameters such as rotary speed and torque, radial and axial load, and the required rigidity and preload or clearance. 
In wind power technology, the procedures leading up to the selection of a bearing are fundamentally different, essentially because of a single parameter: the bearing lifetime. The manufacturers of wind power plants and the gears for those plants require a bearing lifetime of 20 years (i.e. 175,000 hours) for their bearings. This is already an extreme value, but it does not cover all requirements. In addition, it must be taken into account that external loads acting on the bearing are highly dynamic (that is, irregular) because of the wind. The unfavorable environmental conditions for offshore facilities, used ever more frequently, are another factor: sea air is highly corrosive. For generator plants, electrical corrosion must also be taken into account. Finally, the service options available to wind farm operators are extremely limited, and any unscheduled downtime for a bearing will result in significant costs.

Slewing ring for wind energy

UWE is a leading Chinese supplier of blade bearing and yaw bearings for wind energy, from Small Wind Turbines of 750kW to the latest Multi-MW Offshore turbines up to 5MW.
The custom designed UWE slewing bearings are engineered in close cooperation with turbine manufacturers: our dedicated engineering team is at your service for new developments and design optimisation.UWE slewing bearings are delivered worldwide.

Wind turbine pitch bearing

The pitch bearing is a significant component of the safety concept of a turbine.The bolted joint that connects the rotor blade via the blade bearing to the rotor hub is subjected to extremely dynamic loads.the blade angle must always be optimally adjusted to the wind speed via the rotary motion of the blade bearing.As an interface to component developers and suppliers verified load specifications act for components like main bearing, blade bearing, yaw drives and tower foundation.For example, the pitch system was broken down into the components rotor blade, blade bolts, blade bearing, yaw ring, pitch gear, etc. 

Wind turbine blade bearing friction

Wind turbine blade bearing enables pitching of blades for power control and rotor braking and is a critical component. High blade bearing friction is undesirable, as it may be associated with excessive heating of the surfaces, damage and inefficient operation. Thus, continuous observation of bearing friction level is crucial for blade bearing health monitoring systems. A novel algorithm for online monitoring of bearing friction level is developed combining physical knowledge about pitch system dynamics with state estimator, i.e. observer theory and signal processing assuming realistic sensor availability. Results show estimation of bearing friction torque required for condition monitoring, and a corresponding indicator signal which represents estimation of a relative friction coefficient.

Wind turbine bearing

UWE bearing provide yaw, blade/pitch bearing and yaw bearing to our customers reliably. UWE wind turbine generator bearing is for 3KW-5MW wind turbine.Each wind turbine generator comprises of one yaw bearing and three pitch bearings, the material of the rolling rings is 42CrMo with quenching and tempering. Raceway surface intermediate frequency induction hardened. Due to complexity of the stress situation, the bearing must bear impact and carry high load. 20 years is a required lifetime for the wind turbine generator, it is also required by yaw bearing and pitch bearings as the mounting cost is too high.


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