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US-12618439-B2 - Bearing element for a bearing unit, and bearing unit with an increased life

US12618439B2US 12618439 B2US12618439 B2US 12618439B2US-12618439-B2

Abstract

A bearing element of a bearing unit includes a substrate, a first coating on the substrate and a second coating on the first coating. The first coating is configured to increase a wear resistance of the substrate and includes a first solid lubricant, and the second coating is softer than the first coating and includes a second solid lubricant. The solid lubricants of the first and second coatings may be MoS 2 , and the first coating may include between 3 and 30 at % Ti.

Inventors

  • Paul Dietl
  • Xiaobo Zhou

Assignees

  • AKTIEBOLAGET SKF

Dates

Publication Date
20260505
Application Date
20230413
Priority Date
20220422

Claims (17)

  1. 1 . A bearing element of a bearing unit, comprising: a substrate, a first coating on the substrate, the first coating being configured to increase a wear resistance of the substrate and comprising a first solid lubricant, and a second coating on the first coating, the second coating being softer than the first coating and comprising a second solid lubricant, wherein the first solid lubricant and the second solid lubricant each comprise MoS 2 .
  2. 2 . The bearing element according to claim 1 , wherein the first coating comprises Ti.
  3. 3 . The bearing element claim 2 , wherein the first coating has a hardness between 750 and 2500 HV.
  4. 4 . The bearing element according to claim 3 , wherein the first coating has a thickness between 0.2 and 4 micron.
  5. 5 . The bearing element according to claim 3 , wherein the second coating further comprises an adhesive or a binder.
  6. 6 . The bearing element according to claim 5 , wherein a hardness of the second coating is less than 150 HV.
  7. 7 . The bearing element according to claim 6 , including a bonding layer between the substrate and the first coating.
  8. 8 . The bearing element according to claim 3 , wherein the second coating further comprises an epoxy.
  9. 9 . A bearing unit comprising at least one bearing element according to claim 1 , wherein the bearing element is a ring, a rolling element, a cage, a separator, or a spacer.
  10. 10 . The bearing element according to claim 1 , wherein the first coating comprises MoS 2 and Ti and has a hardness between 750 and 2500 HV, and wherein the second coating comprises MoS 2 and has a hardness of less than 150 HV.
  11. 11 . The bearing element according to claim 10 , wherein the second coating consists essentially of MoS 2 and an epoxy.
  12. 12 . The bearing element according to claim 1 , wherein the first coating consists essentially of MoS 2 and Ti and has a hardness between 750 and 2500 HV, and wherein the second coating consists essentially of MoS 2 and has a hardness of less than 150 HV.
  13. 13 . The bearing element according to claim 12 , including a bonding layer between the substrate and the first coating.
  14. 14 . The bearing element according to claim 12 , wherein the first coating is formed of a plurality of alternating first layers consisting essentially of titanium and second layers consisting essentially of MoS 2 .
  15. 15 . The bearing element according to claim 1 , wherein the substrate comprises PEEK or PA6.6.
  16. 16 . The bearing element according to claim 1 , wherein the substrate comprises a ceramic material.
  17. 17 . The bearing element according to claim 1 , wherein the substrate comprises a bearing steel.

Description

CROSS-REFERENCE This application claims priority to French patent application no. 2203737 filed on Apr. 22, 2022, the contents of which are fully incorporated herein by reference. TECHNOLOGICAL FIELD The disclosure is directed to a bearing element, in particular, a rolling-element bearing, of a bearing unit and to a bearing unit including the bearing element. BACKGROUND In some applications, for instance in a vacuum, it is not possible or desirable to use grease or oil to lubricate a contact area of a bearing unit, for instance a contact between a rolling element and a raceway or a cage. In such circumstances it is known to use a solid lubricant such as graphite or molybdenum disulfide MoS2 in order to lubricate a contact area. In order to reduce the resistance to the wear of a contact area and at the same time provide a solid lubricant in the contact area, it is known from EP 1 470 343 B1 (family member of US 2005/213860) to coat an element of a bearing unit with a hard solid lubricant comprising metal doped MoS2. However, further improvements are still possible. SUMMARY An aspect of the disclosure is to provide a bearing element of a bearing unit having a longer service life thanks to a combination of an increased resistance to wear and an increased ability to lubricate a contact surface between the bearing element and another bearing element. The bearing element comprises a substrate and a first coating for increasing the wear resistance of the substrate. The first coating is applied on the substrate and comprises a solid lubricant. The bearing element comprises a second coating which is softer than the first coating. The second coating is applied on the first coating and comprises a solid lubricant. According to further aspects of the disclosure which are advantageous but not compulsory, such a bearing element may incorporate one or several of the following features: the solid lubricant of the first and second coatings is MoS2;the first coating comprises Ti, the content of which is between 3 and 30 at %;the first coating has a hardness between 750 and 2500 HV;the first coating has a thickness between 0.2 and 4 micron;the solid lubricant of the second coating has a content between 20 and 60 at %;the second coating further comprises an adhesive or a binder such as epoxy;the hardness of the second coating is below 150 HV;the first coating comprises a bonding layer which is first applied on the substrate. Another aspect of the disclosure comprises a bearing element of a bearing unit, where the bearing unit comprises a substrate, a first coating on the substrate, the first coating being configured to increase a wear resistance of the substrate and comprising a first solid lubricant, and a second coating on the first coating, the second coating being softer than the first coating and comprising a second solid lubricant. Furthermore, the first coating consists essentially of MoS2 and 3 to 30 at % Ti and has a hardness between 750 and 2500 HV, and the second coating consists essentially of MoS2 and has a hardness of less than 150 HV. Another aspect of the disclosure is a bearing unit comprising a bearing element according to the disclosure. The bearing element can be for instance a ring, a rolling element, a cage, a separator or a spacer. The disclosed coating increases the life of the bearing unit, especially when the bearing unit runs in severe or extreme conditions in terms of acceleration, speed, loading or temperature. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be explained in connection with the annexed figures, as illustrative examples, without restricting the scope of the invention. In the annexed figures: FIG. 1 is a longitudinal cross section of a bearing unit according to an embodiment of the present disclosure. FIG. 2 is a schematic detail view of part of a bearing element of the bearing unit of FIG. 1. DETAILED DESCRIPTION The bearing unit according to the disclosure comprises an inner ring and an outer ring. The inner and outer rings are rotatable with respect to each other along a common rotational axis. In a preferred embodiment, the bearing unit is a plain bearing so that the inner and outer rings are in direct sliding contact with each other when one rotates relative to the other. In another preferred embodiment, the bearing unit further comprises rolling elements between the inner and outer rings. In another preferred embodiment, the bearing unit further comprises a cage (in one or several adjacent parts) for holding the rolling elements at a predetermined relative position with respect to each other. In another preferred embodiment, the bearing unit further comprises a plurality of spacers, each spacer separating two adjacent rolling element. In another preferred embodiment, the bearing unit is a full complement bearing, with rolling elements between the inner and the outer rings, but without any cage or spacer for separating the rolling elements. In a preferred