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New Product
Development of “DLC Coating Spherical Roller Bearing” for Wind Turbine Main Shaft
October 19, 2020New Products

Significantly improve wear-resistance by applying DLC coating with high adhesion to roller

NTN Corporation (hereafter, NTN) has developed the “DLC Coating Spherical Roller Bearing” for wind turbine main shaft with significantly improved wear-resistance by applying the DLC (diamond like carbon) coating*1 to the surface of rollers.

For wind turbine main shaft bearings (hereafter, main shaft bearings), spherical roller bearings, which has high-load capacity and excellent allowable capability for installation misalignment, are widely used. The main shaft bearing repeats starting and stopping according to wind conditions and it is used at extremely low speeds. The main shaft bearings used in such environment has a problem of the wear on the raceway surface and it will develop to flaking and cracking due to rolling sliding *2 specific to spherical roller bearing and metal to metal contacts on the raceway surface caused by insufficient lubrication.

We improved significantly wear-resistance of this developed product on raceway surface by applying a DLC coating that has high adhesion and is difficult to remove on the rolling surface of roller. The DLC coating has a three layer structure, (1) a metal under layer to increase adhesion to the base material, (2) an intermediate layer to avoid a sudden change in hardness between the under layer and the top layer, and (3) a very hard surface layer. Even under severe lubrication conditions, the DLC coating with high adhesion continuously provide high performance. Almost no wear occurs with this developed product under accelerated testing conditions in which the raceway surface of a standard product without a DLC coating make flaking from wear in one month.

We have already begun mass production of this developed product, and we will further propose this product as well as strengthening sales of this product as an aftermarket product that responds to premature damages caused by wear on the raceway surface in particular. The new coating technology can also be combined with asymmetrical designed product*3, which was developed in 2017 to make wind turbine more compact.

NTN is working on expanding sales in wind turbines market by expanding the product lineup so that customers can select the most suitable option from DLC coating and asymmetrical design of this developed product to meet the needs.

  1. Hard film with amorphous structure in which carbons having a diamond structure and a graphite structure are irregularly mixed
  2. Roling sliding: the sliding caused by rotational speed differences between roller and raceway contacts.
  3. Pressed Release on September 4, 2017:
    Development of “Asymmetrical Spherical Roller Bearings” for Wind Turbine Main Shafts


1. Significantly improved wear-resistance of raceway surface
2. DLC coating which has a high adhesion with a three layer structure
Three layer structure of the under layer, the intermediate layer, and the surface layer provides high adhesion to the film.
No flaking on DLC coating under the condition of boundary-lubrication*4, actual maximum contact stress *5 of the actual DLC coating, and rolling sliding.
  1. When the oil film is thinned and the 2 areas without oil film is locally contacting
  2. Contact stress when maximum load generated at the use in actual wind turbine


Industrial machinery used under severe lubrication conditions where it is difficult to form oil film, such as wind turbine

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Product image

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Applied parts

Applied parts Nacelle of wind turbine

Lineup of spherical roller bearing for wind turbine main shaft

Lineup of spherical roller bearing for wind turbine main shaft

Standard product
DLC coating product (Improve wear-resistance)
Asymmetrical design product (compact)
DLC coating + asymmetrical design product
(Improved wear-resistance + compact)