2017

Asymmetrical design of left and right roller rows for longer operating life and better wear-resistance characteristics

NTN Corporation (hereafter, NTN) has developed the “Asymmetrical Spherical Roller Bearings” for wind turbine main shafts that feature an asymmetrical design of left and right rollers within the bearing that improves the calculated operating life of the bearing by approximately 2.5-times compared to conventional products, and reduces the PV value*¹ by approximately 30% for better wear-resistance characteristics.

Spherical roller bearings with a high-load capacity and excellent allowable capability for installation misalignment are widely used as bearings for wind turbine main shafts (hereafter, main shaft bearings). Main shaft bearings are subjected to axial loads, where the wind load acts horizontally in the direction of the shaft, in addition to radial loads, where the weight of components including the rotors and blades act perpendicularly to the shaft. With these loads, main shaft bearings have a greater load acting on the rear row (further away from the blades) compared to the front row (closer to the blades). Spherical roller bearings have a characteristic of the rolling and sliding movement. Combined with metallic wear between the raceway surface and rollers caused by insufficient lubricant, the characteristic leads to wear developing on the raceway surface from areas with a high PV value. As a result, flaking and cracking could occur particularly in the outer ring of the rear side.

The newly developed “Asymmetrical Spherical Roller Bearings” features a modified roller design to suit the usage conditions specific to these wind turbine main shaft bearings to improve their operating life and wear-resistance characteristics. Compared to the conventional product, the contact angle of the developed product is smaller at the front row and larger at the rear row. The length of the rear row is longer than the front row, to support axial loads from the wind more efficiently on the rear row, and support radial loads mainly on the front row. Distributing loads appropriately between the front row and rear row rollers has achieved a longer operating life and better wear-resistance characteristics under application conditions specific to wind turbine main shaft bearings. The developed product can be designed with the same boundary dimensions*² as conventional products. The inner diameter can be reduced by approximately 10% and weight by approximately 30% when designing main shaft bearings with the same operating life as conventional products, which can contribute to making wind turbines more compact and lighter weight.

NTN will exhibit the developed product at “China Wind Power 2017” in Beijing, China between October 17 and 19, and propose the product to various manufacturers of wind turbines and wind turbine operators.

1. Value combining the contact surface pressure [P] and rolling sliding velocity [V]. (Rolling sliding is the sliding caused by the difference in speeds between the contact areas of the roller and raceway surface in the direction of rotation)
2. Refers to the inner diameter of inner ring, outer diameter of outer ring and width dimension.

Features

* Calculated by NTN under average fatigue load conditions acting on wind turbine main shaft bearings

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Product photo

The developed product	Cross-section of the developed product	Cross-section of the conventional product

Internal structure of wind turbine (example)	Axial load acting on wind turbine main shaft bearing

Applications

Main shaft bearings of wind turbines and other applications subjected to radial loads and axial loads in one direction