GB1573913A

GB1573913A - Insulating bearing housings

Info

Publication number: GB1573913A
Application number: GB2997/76A
Authority: GB
Original assignee: Boatman P J F
Current assignee: Boatman P J F
Priority date: 1977-01-27
Filing date: 1977-01-27
Publication date: 1980-08-28
Also published as: ZA77379B

Description

(54) IMPROVEMENTS IN OR RELATING TO INSULATING BEARING HOUSINGS (71) I, PETER JAMES FRANCIS BOATMAN, a British subject, of 9 Deansberry Close, Trentham, Stoke-on-Trent, Staffordshire, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of electrically insulating bearing housings from their bearings and housings so insulated.

In electric machines, where shafts are rotatably mounted in bearings, the presence of undesired shaft voltages between the shafts and the stationary housings for the bearings creates currents passing across the engaging surfaces of the bearings. These currents can cause deterioration of the bearings due to breakdown of their oil films, and pitting of the bearings.

To prevent this it has been proposed to insulate the housings from the machine by means of insulating packers, to earth the housing by means of carbon brushes, and to use insulating materials which are loosely fitted between the bearings and their housings. However these methods are inconvenient and, in particular, the carbon brushes wear out relatively quickly and the loose materials are difficult to fit.

According to one aspect of the present invention there is provided a method of electrically insulating a bearing housing from its bearing, comprising blasting internal seating surfaces for the bearing with abrasive media before applying a coating of an electrically insulating material to the internal seating surfaces.

Preferably the internal seating surfaces are degreased prior to the coating being applied.

The internal seating surfaces are advantageously machined oversize prior to the coating being applied such that the coated faces can then be machined to the bearing diameter.

Preferably the internal seating surfaces of the housing are primed with adhesive prior to the application of the coating.

Preferably also the housing is heated to a predetermined temperature prior to the application of the coating, and at said predetermined temperature the coating of a synthetic material, for example a polyamide material is applied by means of an electrostatic spray and forms an integral part of the housing.

Alternatively the coating is applied by projecting particles of a ceramic material at a predetermined temperature on to the internal seating surfaces and forms an integral part of the housing.

According to another aspect of the present invention there is provided a housing for a bearing which can rotatably support a shaft in an electric machine, said housing having a coating of an electrically insulating material on internal seating surfaces for the bearing and formed in accordance with the method of any of the six preceding paragraphs.

Preferably the housing is provided with a cap, an internal seating surface of which has a coating of said material.

Advantageously the insulating material is a synthetic material, for example a polyamide material, preferably nylon.

Alternatively the insulating material is a ceramic material, preferably alumina or zirconia.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawing which is a sectional elevation of a bearing housing.

Referring to the drawing, a casting defines an annular housing 10 of conventional design supporting a bearing 12, the latter rotatably supporting one end of a shaft 14 of an electric machine. The housing 10 has, at one end, an external peripheral flange 16 and an internal peripheral flange 18, the latter defining an annular shoulder 20 against which the bearing 12 is located, and a central circular opening through which the shaft 14 extends into the housing 10 and the bearing 12.

The inner periphery of the housing 10 provides a seating face 26 for the bearing 12 and the surfaces of the face 26 and the shoulder 20 are provided with a coating 28 of electrically insulating material so as to insulate the housing 10 from the bearing 12, and thus the shaft 14, preventing shaft voltages from causing deterioration of the bearing due to the breakdown of the bearing oil film, and pitting of the bearing.

The insulating material used is preferably a plastics coating of a polyamide material, for example nylon. This material has all the necessary qualities to withstand expected working stresses and temperatures.

Before applying the coating, the casting is degreased and the surfaces to be coated are lightly shot blasted, the area not to be coated being blanked off. A primer adhesive is then applied to the surfaces which are to be coated and the casting is heated up to a temperature of 190"C. At this temperature layers of the insulating coating are applied using an electrostatic spray. The casting is then allowed to cool, for example by dipping in water, and the blanking apparatus removed.

It will be appreciated that the housing 10 is machined oversize at the face 26 and shoulder 20 prior to coating such that the coated faces can then be machined to the bearing diameter.

Alternatively, the insulating material used may be a ceramic material, for example alumina or zirconia. The surfaces to be treated are shot or grit blasted prior to the coating being applied and particles of the ceramic material projected on to the surfaces by a high temperature flame gun.

The housing 10 is provided with a cap 22 to close the other end thereof. An internal surface 23 of the cap which engages the bearing is provided with an insulating coating 23a corresponding to the layer 28.

The bearing housing is thus compact with no requirement for any additional components to provide the necessary insulation, the insulating layer being preformed to be an intergral part of the housing.

Various modifications may be made without departing from the invention. For example, it will be appreciated that the invention can be applied to housings for various types of bearings including ball and roller bearings.

WHAT I CLAIM IS- 1. A method of electrically insulating a bearing housing from its bearing, comprising blasting internal seating surfaces for the bearing with abrasive media before applying a coating of an electrically insulating material to the mternal seating surfaces.

2. A method according to claim 1, wherein the internal seating surfaces are degreased prior to the coating being applied.

3. A method according to claim 1 or 2, wherein the internal seating surfaces are machined oversize prior to the coating being applied, and the coated faces are then machined to the bearing diameter.

4. A method according to any of claims 1 to 3, wherein the internal seating surfaces are primed with adhesive prior to the coating being applied.

5. A method according to any of the preceding claims, wherein the housing is heated to a predetermined temperature prior to the coating being applied, and at said predetermined temperature the coating of a synthetic material is applied by means of an electrostatic spray, and forms an integral part of the housing.

6. A method according to any of claims 1 to 3, wherein the coating is applied by projecting particles of a ceramic material at a predetermined temperature on to the internal seating surfaces and forms an integral part of the housing.

7. A housing for a bearing which can rotatably support a shaft in an electric machine, said housing having a coating of an electrically insulating material on internal seating surfaces for the bearing and formed in accordance with the method of any of claims 1 to 3.

8. A housing according to claim 7, including a cap, the latter having a coating of said electrically insulating material on its internal seating surface for the bearing.

9. A housing according to claim 7 or 8, wherein said electrically insulating material is a synthetic material.

10. A housing according to claim 9 wherein said synthetic material is a polyamide material.

11. A housing according to claim 10, wherein said polyamide material is nylon.

12. A housing according to claim 7 or 8, wherein said electrically insulating material is a ceramic material.

13. A housing according to claim 12, wherein said ceramic material is alumina or zirconia.

14. A method of electrically insulating a bearing housing from its bearing substantially as hereinbefore described with reference to the accompanying drawing.

15. A housing for a bearing substantially as hereinbefore described with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. bearing 12 is located, and a central circular opening through which the shaft 14 extends into the housing 10 and the bearing 12. The inner periphery of the housing 10 provides a seating face 26 for the bearing 12 and the surfaces of the face 26 and the shoulder 20 are provided with a coating 28 of electrically insulating material so as to insulate the housing 10 from the bearing 12, and thus the shaft 14, preventing shaft voltages from causing deterioration of the bearing due to the breakdown of the bearing oil film, and pitting of the bearing. The insulating material used is preferably a plastics coating of a polyamide material, for example nylon. This material has all the necessary qualities to withstand expected working stresses and temperatures. Before applying the coating, the casting is degreased and the surfaces to be coated are lightly shot blasted, the area not to be coated being blanked off. A primer adhesive is then applied to the surfaces which are to be coated and the casting is heated up to a temperature of 190"C. At this temperature layers of the insulating coating are applied using an electrostatic spray. The casting is then allowed to cool, for example by dipping in water, and the blanking apparatus removed. It will be appreciated that the housing 10 is machined oversize at the face 26 and shoulder 20 prior to coating such that the coated faces can then be machined to the bearing diameter. Alternatively, the insulating material used may be a ceramic material, for example alumina or zirconia. The surfaces to be treated are shot or grit blasted prior to the coating being applied and particles of the ceramic material projected on to the surfaces by a high temperature flame gun. The housing 10 is provided with a cap 22 to close the other end thereof. An internal surface 23 of the cap which engages the bearing is provided with an insulating coating 23a corresponding to the layer 28. The bearing housing is thus compact with no requirement for any additional components to provide the necessary insulation, the insulating layer being preformed to be an intergral part of the housing. Various modifications may be made without departing from the invention. For example, it will be appreciated that the invention can be applied to housings for various types of bearings including ball and roller bearings. WHAT I CLAIM IS-

1. A method of electrically insulating a bearing housing from its bearing, comprising blasting internal seating surfaces for the bearing with abrasive media before applying a coating of an electrically insulating material to the mternal seating surfaces.

11. A housing according to claim 10, wherein said polyamide material is nylon.