BEARING RING WITH INSULATING COATING

Abstract

A non-conventional, low temperature, process for applying a thin electrically insulating coating arrangement with high density, high purity, minimal porosity, and improved adhesion strength to a steel bearing component is provided. The bearing component is formed from steel and machined or otherwise formed to a near net shape. A high purity aluminum is electro-chemically deposited on the steel bearing component using a non-aqueous electrolyte in an inert environment to form a high purity aluminum coating at least over a portion of the steel bearing component. A surface of the high purity aluminum coating is then converted by an acid-bath into aluminum oxide to form an insulating layer. A bearing component and a bearing having such components is also provided.

Claims

1. A method for providing an electrically insulating coating to a bearing component, comprising: providing a bearing component formed from steel and machined or otherwise formed to a near net shape; electro-chemically depositing a high purity aluminum on the steel bearing component using a non-aqueous electrolyte in an inert environment to form a high purity aluminum coating at least over a portion of the steel bearing component; and converting a surface of the high purity aluminum coating using an acid-bath into aluminum oxide to form an insulating layer.

2. The method of claim 1, further comprising: sealing the insulating layer.

3. The method of claim 1, wherein the high purity aluminum has a final thickness of 25-200 μm.

4. The method of claim 1, wherein the insulating layer has a final thickness of 25-200 μm.

5. The method of claim 1, wherein the high purity aluminum and the aluminum oxide insulating layer have less than 2% voids or inclusions.

6. The method of claim 5, wherein the high purity aluminum and the aluminum oxide insulating layer virtually zero voids or inclusions in a test sample examined at a 2500:1 scale enlargement.

7. The method of claim 1, further comprising: roughening a surface of the steel bearing component to be coated with the high purity aluminum to a surface roughness Ra of greater than 6 μm.

8. The method of claim 1, further comprising: masking a raceway surface of the bearing component prior to at least one of the electro-chemical depositing of the high purity aluminum or the conversion of the surface of the high purity aluminum coating using the acid-bath into aluminum oxide.

9. The method of claim 1, wherein the insulating layer has a resistance of at least 10 MΩ at 50 VDC.

10. The method of claim 1, further comprising: finishing a raceway surface of the steel bearing component after forming the insulating layer.

11. A rolling bearing having a steel bearing component with the insulating layer formed by the method according to claim 1.

12. A rolling bearing comprising: an inner ring; an outer ring; a plurality of rolling elements located between the inner ring and the outer ring; wherein at least one of the inner ring or the outer ring include, at least over a portion thereof, an insulating coating arrangement comprised of a layer of high purity aluminum located on a steel base component used to form the inner ring or the outer ring and an aluminum oxide insulating layer formed on the high purity aluminum.

13. The rolling bearing of claim 12, further comprising a sealing layer on the aluminum oxide insulating layer.

14. The rolling bearing of claim 12, wherein an outer mounting surface of the outer ring includes the insulating layer arrangement.

15. The rolling bearing of claim 12, wherein an inner mounting surface of the inner ring includes the insulating layer arrangement.

16. The rolling bearing of claim 12, wherein an outer mounting surface of the outer ring and an inner mounting surface of the inner ring include the insulating layer arrangement.

17. The rolling bearing of claim 12, wherein the layer of the high purity aluminum has a final thickness of 25-200 μm.

18. The rolling bearing of claim 12, wherein the insulating layer has a final thickness of 25-200 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The foregoing Summary as well as the following Detailed Description will be best understood when read in conjunction with the appended drawings. In the drawings:

[0027] FIG. 1 is an elevational view of a rolling bearing including one or more bearing components with an insulating coating.

[0028] FIG. 2 is a greatly enlarged cross-sectional view through either of the bearing rings as indicated by lines 2-2 in FIG. 1 showing the insulating coating applied to one or both of the bearing rings.

[0029] FIG. 3 is a greatly enlarged cross-sectional view showing the insulating coating on the bearing component of FIG. 2.

[0030] FIG. 4 is a flow chart showing the process for applying and insulating coating on a bearing component according to one embodiment.

[0031] FIG. 5 is a 500× magnification photo of an example of the insulating coating on the bearing component.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Certain terminology is used in the following description for convenience only and is not limiting. The words “inner,” “outer,” “inwardly,” and “outwardly” refer to directions towards and away from the parts referenced in the drawings. A reference to a list of items that are cited as “at least one of a, b, or c” (where a, b, and c represent the items being listed) means any single one of the items a, b, c or combinations thereof. The terminology includes the words specifically noted above, derivatives thereof, and words of similar import.

[0033] Referring to FIG. 1, a rolling bearing 10 including an outer ring 12 and an inner ring 14 is shown. The outer ring 12 and the inner ring 14 are bearing components formed of bearing grade steel. Rolling elements 16 are located between the outer ring 12 and the inner ring 14. The rolling elements are preferably spaced apart via a cage 18.

[0034] As shown in detail in FIG. 2, at least one of the inner ring 14 or the outer ring 12 include, at least over a portion thereof, an insulating coating arrangement 30 having a layer of high purity aluminum 32 located on the steel used to form the inner ring 14 or the outer ring 12. The high purity aluminum coating 32 includes an aluminum oxide insulating layer 34 on an outer surface thereof that is formed from the high purity aluminum layer 32. The layers in FIG. 2 are not shown to scale.

[0035] The high purity aluminum layer 32 and the aluminum oxide insulating layer 34 preferably have less than 2% voids or inclusions, and more preferably less than 0.2% voids or inclusions. In accordance with one embodiment, there are virtually zero voids or inclusions as indicated by a test sample examined at a 500:1 scale enlargement. This is shown in FIG. 5.

[0036] As shown in detail in FIG. 3, the aluminum oxide insulating layer 34 can be sealed, as indicated by seal layer 36. This seal layer can be formed via a hot water seal in which the aluminum oxide layer or at least an outer surface thereof is converted to a hydrated form which reduces the pore size. A further coating such as Teflon or any other insulating sealant can optionally be used with or in place of the hot water seal.

[0037] As shown in FIG. 2, preferably the insulating coating arrangement 30 is located on the outer mounting surface 26 of the outer ring 12 and the raceway 22 does not include the insulating layer. Alternatively, the inner mounting surface 28 of the inner ring 14 includes the insulating coating arrangement 30 and the raceway 24 of the inner ring 14 does not include the insulating coating arrangement 30. It is also possible for both the outer ring 12 and the inner ring 14 to include the insulating coating arrangement 30. The aluminum oxide insulating layer 34 preferably has an electrical resistance of at least 10 MΩ at 50 VDC. More preferably, the aluminum oxide insulating layer 34 or aluminum oxide insulating layer 34 with the seal layer 36 has a resistance of at least 50 MΩ at 1000 VDC.

[0038] Preferably, the high purity aluminum layer 32 has a final thickness of 25-200 μm. Additionally, the aluminum oxide insulating layer 34 has a final thickness of 25-200 μm. More preferably, the high purity aluminum layer 32 and the aluminum oxide insulating layer 34 each have a thickness of 40-75 μm. Preferably, the total coating thickness is 50-400 μm and more preferably in the range of 75-125 μm.

[0039] Referring to FIG. 4, a method for providing an electrically insulating coating on a bearing component, which can be the outer ring 12 and/or the inner ring 14 is provided in the flowchart 40. The method includes providing the bearing component formed from steel and machined or otherwise form to a near net shape. As show in box 41, this semi-finished bearing component is preferably a bearing ring and all surfaces are finished to final dimensions with the possible exception of the raceway which may need final finishing after the insulating coating arrangement 30 is applied. Preferably, these bearing components are washed or cleaned as indicated in box 42. This cleaning is by known processes, using detergents and/or solvents. If necessary, the surface of the bearing components to be coated can be roughened as indicated in box 43. Preferably, roughening is done only on the areas to be coated and not the raceways 22, 24, and a surface roughness of Ra≧6 μm is provided to enhance bonding of high purity aluminum onto the surfaces of the bearing component to be coated. A final cleaning step can be provided as indicated in box 44 which can include rinsing with a solvent and/or detergent to remove any impurities including surface oils which could prevent proper adhesion of the coatings to be applied. As indicated in box 45, preferably the raceways 22, 24 of the bearing components in the form of bearing rings 12, 14 are masked. The masking can be clone with a polyester film or tape and an appropriate adhesive, which can be silicone based, or can be done with caps or plugs which are resistant to the electroplating chemicals and/or the anodizing acid. The mask is applied in a known manner to areas that are not to be coated or treated, such as the raceways 22, 24.

[0040] As shown in box 46, an anode is applied to each of the bearing components, in the form of the outer and inner rings 12, 14, and the bearing components are electroplated with high density pure aluminum, as shown in box 47, preferably to a thickness of at least about 50 μm (0.002 in). The coated thickness may vary between 25 and 200 μm depending on the application and the further processing to be carried out. The electroplating is carried out using a non-acquiesce electrolyte, such as toluene, in an inert environment which allows the pure aluminum to be deposited onto the steel bearing components in a highly pure and dense state without inclusions or voids. As shown in box 48, preferably the thickness of the aluminum is verified.

[0041] This highly pure aluminum is then hard coat anodized as indicated in box 49, preferably to 50% to 60% of the thickness of the high purity aluminum layer 32, resulting in the layer of pure aluminum 32 as well as the anodized insulating layer 34 as shown in FIG. 3 which are formed on the steel bearing component in the form of the bearing rings 12, 14. Preferably, the anodization is a sulfuric acid anodization or alternately oxalic acid anodization with the bearing component forming the anode of the electrical circuit in the anodization bath. As shown in box 50, optionally a dye may be applied to the anodized surface in order to provide a color of choice to the bearing component. The anodized insulating layer 34 can optionally be sealed.

[0042] As shown in box 51, preferably the total thickness of the anodized layer 34 and the pure aluminum layer 32 is non-destructively verified. The total layer thickness for each layer is preferably in range of 50-200, and more preferably μm 40-75 μm. Preferably, the total coating thickness is 50-400 μm and more preferably in the range of 75-125 μm. In one embodiment, the total layer thickness is nominally 100 μm (0.004 in).

[0043] As shown in box 52, the raceway masking can then be removed and any final finishing or machining of the raceways 22, 24 can then be performed. Finally, as indicated in box 53, preferably electrical testing of the coating is performed to ensure that the insulating layer has a resistance of at least 10 MΩ at 50 VDC more preferably a resistance of at least 50 MΩ at 1000 VDC.

[0044] This arrangement provides for an EDM resistant rolling bearing component and more preferably a EDM resistant roiling bearing assembly such as the rolling bearing 10 shown in FIG. 1 in which one or both of the rings 12, 14 include the insulating coating arrangement 30.

[0045] The embodiments described above are considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore to be embraced therein.