Claims:Claims:
1. A method for preparing a conductive seal, comprising:
depositing a metal layer wherein the metal is selected from gold, palladium, copper, aluminum and combinations thereof on a seal by a physical vapor deposition process at a temperature in a range from about 40 degrees centigrade to about 80 degrees centigrade; wherein the thickness of the layer of metal on the seal is less than at least about 250 nanometres to obtain the conductive seal.
2. The method of claim 1, wherein the physical vapour deposition process is radio frequency (RF) sputtering, direct current (DC) sputtering, or thermal evaporation.
3. The method of claim 1, wherein the physical vapor deposition process is carried out at a temperature below about 60 degrees centigrade
4. The method of claim 1, wherein the metal is gold, palladium or combinations thereof.
5. The method of claim 1, wherein the conductive seal is used in a motor or a generator.
6. The method of claim 1, wherein the thickness of the layer of metal on the seal is in a range from about 10 nanometres to about 250 nanometres.
7. The method of claim 1, wherein the conductive seal is a contact-type seal.
8. A bearing comprising a conductive seal, wherein the conductive seal comprises a metal layer having a thickness of the layer of metal on the seal is less than at least about 250 nanometres.
9. The bearing of claim 8, wherein the bearing comprises an outer race, a retainer, a plurality of balls, an inner race, and a conductive seal.
10. The bearing of claim 8, wherein the thickness of the layer of metal on the seal is in a range from about 10 nanometres to about 250 nanometres.
, Description:1. Title of the Invention: Conductive Seal for Bearings

2. Technical Field:
[0001] The present invention generally relates to the field of seals for bearings. More particularly, the invention relates to a seal for motor or generator bearings.
3. BACKGROUND
[0002] Seals are used to protect bearings from excess grease loss and contamination from the bearing. In electric motors and generators, the bearings are typically positioned in between the shaft and the body of the motor. However, during the operation of a motor or a generator, a voltage is developed between the shaft or the rotor and the housing. Once the voltage reaches a level sufficient to cause dielectric breakdown of the grease used for lubrication, the voltage arcs through the bearing. This arcing results in electrical discharge machining of the bearing, thus causing wear and damage to the bearing, and reducing the life of the device. In order to mitigate this problem, it is desired that these voltages are grounded, and not allowed to build up on the rotor or the shaft.
[0003] Conductive seals are known in the art. For example, German patent applications DE102015224042A1 and DE102010004853A1, both assigned to Schaellfler Technologies, describe metal coatings on elastomeric seals to provide a conductive property to the seals. The thickness of the coating is between 0.5 microns to 900 microns. Japanese patent JP6372306B2 assigned to NSK Ltd. describes a rolling bearing with a metallic coating on the seal. However, in all these cases, the thickness of the metal deposited is in the range of hundreds of microns, which results in an increase in temperature of the seal during the coating process. This in turn can degrade the seal material. Also, the thickness of the metal coating makes the process both time-consuming and expensive.
[0004] Accordingly, there remains a need for a bearing for a motor or a generator, which obviates the aforesaid drawbacks.
4. OBJECTS OF THE INVENTION / SUMMARY OF THE INVENTION
[0005] An object of the present invention is to provide a method for preparing a conductive seal. The method includes the steps of depositing a metal layer wherein the metal is selected from gold, palladium, copper, aluminum and combinations thereof on a seal by a physical vapor deposition process at a temperature in a range from about 40 degrees centigrade to about 80 degrees centigrade; to obtain the conductive seal. The thickness of the layer of metal on the seal is less than at least about 250 nanometres.
[0006] Another object of the present invention is to provide a bearing comprising a conductive seal, wherein the conductive seal includes a metal layer. The thickness of the layer of metal on the seal is less than at least about 250 nanometres.
[0007] These and other objects of the invention herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however that the following descriptions, while indicating embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing the spirit thereof, and the embodiments herein include all such modifications.
5. Brief Description of Drawings
[0008] The embodiments of the invention are illustrated in the accompanying drawings, throughout which the reference letters indicate corresponding part in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:
[0009] FIG. 1 illustrates a conductive seal in accordance with an embodiment of the invention.
[0010] FIG. 2 illustrates a bearing comprising a conductive seal in accordance with an embodiment of the invention.
[0011] FIG. 3 illustrates a graph showing the change in conductivity as a function of time of a conductive seal in accordance with an embodiment of the invention.
[0012] FIG 4 illustrates electron micrographs showing wear of the surface of a conductive seal as a function of time in accordance with an embodiment of the invention, and a prior art uncoated seal.
6. DETAILED DESCRIPTION OF THE INVENTION
[0013] While various embodiments of the invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions may occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed.
[0014] In the specification and the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings:
[0015] The singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. “Substantially” means a range of values that is known in the art to refer to a range of values that are close to, but not necessarily equal to a certain value.
[0016] Other than in the examples or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, and the like, used in the specification and claims are to be understood as modified in all instances by the term “about.” In some aspects of the current disclosure, the terms “about” or “approximately” are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the terms are defined to be within 10%, alternatively within 5%, alternatively within 1%, or alternatively within 0.5%.
[0017] As used herein, the term “substantially” and its variations are defined as being largely but not necessarily wholly what is specified as understood by one of ordinary skill in the art, and in one non-limiting aspect substantially refers to ranges within 10%, within 5%, within 1%, or within 0.5%.
[0018] Various numerical ranges are disclosed herein. Because these ranges are continuous, they include every value between the minimum and maximum values. The endpoints of all ranges reciting the same characteristic or component are independently combinable and inclusive of the recited endpoint. Unless expressly indicated otherwise, the various numerical ranges specified in this application are approximations. The endpoints of all ranges directed to the same component or property are inclusive of the endpoint and independently combinable. The term “from more than 0 to an amount” means that the named component is present in some amount more than 0, and up to and including the higher named amount.
[0019] As used herein, “combinations thereof” is inclusive of one or more of the recited elements, optionally together with a like element not recited, e.g., inclusive of a combination of one or more of the named components, optionally with one or more other components not specifically named that have essentially the same function. As used herein, the term “combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.
[0020] As used herein, the term “bearing” refers to a device that is used to support the rotating shaft of a motor or a generator. The bearing is composed of a seal, an inner race, a plurality of balls, a retainer ring, and an outer race. The shaft is supported on the inner race, while the outer race is in contact with the body of the motor or the generator.
[0021] As used herein, the term “seal” refers to a seal that is used to cover the sides of a bearing, to prevent loss of grease from and contamination of the bearing.
[0022] As used herein, the term “conductive seal” refers to a seal that allows the flow of current through it.
[0023] As used herein, the term “surface roughness” refers to the average roughness value of the surface.
[0024] As used herein, the term “contact type seal” refers to a seal wherein the inner race of the bearing is in contact with the seal lip.
[0025] As used herein, the term “electrical discharge machining (EDM)” refers to the removal of material or machining of a material by an electrical discharge current.
[0026] One embodiment of the present invention is a method for preparing a conductive seal. The method includes the steps of depositing a metal layer wherein the metal is selected from gold, palladium, copper, aluminum and combinations thereof on a seal by a physical vapor deposition process at a temperature in a range from about 40 degrees centigrade to about 80 degrees centigrade; to obtain the conductive seal. The thickness of the layer of metal on the seal is less than at least about 200 nanometres.
[0027] In an embodiment of the present invention, the conductive seal may be a seal with a metal layer deposited thereon. In one embodiment of the present invention, the metal is selected from gold, palladium, copper, aluminum and combinations thereof. Typically, the metal may be deposited on the seal using various deposition techniques known in the art, non-limiting examples include a physical vapor deposition process, or a chemical vapour deposition process. In one embodiment of the present invention, the deposition process can be a physical vapor deposition process. In an embodiment of the present invention, the physical vapour deposition process may be a radio frequency (RF) sputtering, a direct current (DC) sputtering, or a thermal evaporation.
[0028] In an embodiment of the present invention, the temperature of the process may be below about 80 degrees centigrade. In another embodiment of the present invention, the physical vapor deposition may be carried out at a temperature in a range from about 40 degrees centigrade to about 80 degrees centigrade. In yet another embodiment of the present invention, the physical vapour deposition may be carried out at a temperature in a range from about 60 degrees centigrade to about 80 degrees centigrade.
[0029] In one embodiment of the present invention the thickness of the layer of metal on the seal is at least less than about 250 nanometres. In an embodiment of the present invention, the thickness of the layer of metal on the seal may be less than about 200 nanometres. In another embodiment of the present invention, the thickness of the layer of metal on the seal may be in a range from about 10 nanometres to about 250 nanometres. In an embodiment of the present invention, the thickness of the layer of metal on the seal may be in a range from about 10 nanometres to about 100 nanometres. In an embodiment of the present invention, the thickness of the layer of metal on the seal may be about 1/10th of the surface roughness of the seal.
[0030] In an embodiment of the present invention, the conductive seal is used in a motor or a generator. In an embodiment of the present invention, the conductive seal is used in a DC motor or an AC motor. In an embodiment of the present invention, the conductive seal is used in a DC generator or an AC generator. In an embodiment of the present invention, the conductive seal may be used in an electric vehicle motor, a railway traction motor, an equipment drive motor, or a fan motor.
[0031] In one embodiment of the present invention the conductive seal may be a contact type seal.
[0032] In an embodiment of the present invention, the seal may be made of a non-conducting material. In an embodiment of the present invention, the seal may be made of an elastomer. In another embodiment of the present invention, the seal may be made of nitrile butadiene rubber (NBR).
[0033] Another embodiment of the present invention is a bearing comprising a conductive seal, wherein the conductive seal comprises a metal layer having thickness of the layer of metal on the seal is at least less than about 250 nanometres.
[0034] A conductive seal in accordance with one embodiment of the present invention will now be described with reference to the drawings.
[0035] In an example embodiment of the present invention, as shown in Fig. 1, the conductive seal 100 includes a seal 102 coated with a metal layer 104. The metal layer 104 is in contact with the seal edge 106. At the point where the meal coating 104 contacts the seal edge 106, a coating wear region 108 is seen. The coating wear region indicates the position where the metal later contacts the seal edge, and wear is observed due to the metal layer 104 moving past the seal edge 106, during operation. The contact between the metal layer 104 and the seal edge 106 ensures that there is no voltage developed between the shaft and the rotor and the housing of the motor or generator where the seal is used.
[0036] Referring now to Fig. 2 a bearing 200 in accordance with an embodiment of the present invention is shown. The bearing includes conductive seals 202a and 202b, an outer race 204, a plurality of balls 206, a retainer 208, and an inner race 210. The plurality of balls 206 are placed inside the retainer 208, which is placed between the outer race 204 and the inner race 210, to form the bearing 200. The conductive seals 202a and 202b are disposed on neither side of the bearing 200.
[0037] Fig. 3 depicts graph 300 showing the variation in resistivity of the conductive seal as a function of operation time, for two different coating thicknesses is shown in according to an embodiment of the present invention. The graph 300 shows a curve 302 which indicates a change in resistivity of a conductive seal with a metal layer having a thickness of about 15 nanometres. While the curve 304 shows the change in resistivity of a conductive seal with a metal layer having a thickness of about 50 nanometres. The thickness of the metallic coating was measured using optical profilometry. It is observed in both cases, that after an initial decrease in conductivity, which can be attributed to wear, the resistivity remains almost constant.
[0038] Referring to Fig. 4, the image 400 shows micrographs showing the wear on the surface of a conductive seal according to an embodiment of the present invention. Figures 402, 404, 406a and 406b show images of the wear of a prior art non-conductive seal. Figures 402 and 404 refer to ear of a conductive seal that has been operated for 25 and 90 hours respectively, while figures 406a and 406b show the wear of a conductive seal that has been operated for 128 hours. Figures 408, 410, 412a and 412b show images of the wear of a conductive seal according to an embodiment of the present invention. Figures 408 and 410 refer to ear of a conductive seal that has been operated for 25 and 90 hours respectively, while figures 412a and 412b show the wear of a conductive seal that has been operated for 128 hours. in comparison with a prior art non-conductive seal, for different operation times of 25 hours, 90 hours and 128 hours. It is observed that the wear of the conductive seal is similar to that of the prior art seal. Since the wear of the seal does not change the wear properties of the seal, the conductive coating does not adversely affect the seal life.
[0039] Examples:
[0040] Example 1: A rubber seal bearing part number 6309 LU manufactured by Kaili Rubber Co. was first washed with soap water to remove any dirt and oil from the surface of the seal. The seal was then dipped in n-hexane and ultrasonically cleaned. The cleaned seal was placed inside the sputtering chamber and the chamber evacuated to about 10 Pascal. The sputtering current was set to 20 milliAmperes and the seal coated for 60 seconds with gold. The seal was allowed to cool for 30 seconds, and again sputtered for 60 seconds. The chamber was vented, and the seal removed. The temperature of the seal was measured using thermal imaging. It was observed that the temperature did not go beyond 56°C. The conductivity of the seal was measured using an electric resistance meter, by installing the coated seal on a ceramic bearing.
[0041] Advantages
[0042] The technical advantages brought in by the present invention are as follows;
1. Wear and damage to the bearings is reduced due to the conductive seal preventing build-up of voltage on the motor parts, thus preventing electrical discharge machining.
2. The conductive seals are inexpensive to manufacture.
3. The method of the present invention may be used on an existing seal, to produce a conducting seal.
4. The use of these conductive seals do not require any modifications to the electrical machinery.
5. The coating does not adversely affect the life of the seal.
[0043] While considerable emphasis has been placed herein on the components and component parts of the various embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the embodiments without departing from the scope and spirit of the invention. These and other changes in the various embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.