Electrical insulating bearing

Abstract: A bearing (1) is provided with a rolling element (6) interposed between an outer ring (3) and an inner ring (5) thereof. The outer ring (3) of the bearing (1) is formed by integrating three elements of: a metallic outer ring body (11) having a path of rotation of said rolling element (6); an insulating thin film (12), being made of polymer elastic material having an electrical insulating property, and covering a portion where said outer ring body(11) is mounted to a housing (2); and a thin metallic plate (13) provided on an outer surface of the insulating thin film (12).

Description: This invention relates to an electrical insulating bearing of the kind as referred to by the preamble of the claim. A conventional bearing having a rolling element interposed between an outer ring and an inner ring has been known in the art. In a rotary electrical equipment, shaft voltage is usually generated between both ends of a rotary shaft, between the rotary shaft and each bearing, or in engaging sections of the rotary shaft with each bearing. This shaft voltage is generated due to various reasons, such as, magnetic unbalance, static storage, direct application of an external power source to the rotary shaft, and an induced electricity generated in the shaft with the use of a rectifier power source. Excessive generation of this shaft voltage causes shaft current to flow through each bearing portion, resulting in wear in the bearings, damage to the rotary shaft, and blackening of lubricating oil, or in some cases, damage to or scorch of bearing. Various approaches have been taken to avoid the above-mentioned problems. For example, Japanese Utility Model Registration Application Laying-open Gazette No. 60-161721 discloses a technique of insulating a bearing with a ceramic layer. In this application, the bearing is treated with a ceramic surface finishing process to form a ceramic layer thereon. Synthetic plastic resin having elasticity and viscosity is then poured into porous portions of the ceramics in order to reinforce the ceramic layer. Japanese Patent Application Laying-open Gazette No. 59-103023 discloses a technique of forming an insulating coating of inorganic compounds with a thermal spraying method. Japanese Patent Application No. 53-81459 discloses a technique of forming an insulating coating with a baking or a coating method. Japanese Utility Model Registration Application Laying-open Gazette No. 59-173467 discloses an insulating technique using a ceramic coating formed by a thermal spraying method. Various techniques for insulating an axle bearing portion have been known in the art. For example, Japanese Utility Model Registration Application Laying-open Gazette No. 54-105408 discloses a technique of forming an insulating polymer member to cover an outer peripheral surface and a side surface of an outer ring. Japanese Utility Model Registration Application Laying-open Gazette No. 58-33820 discloses a technique of interposing an electrical insulating member between an outer ring and a saddle. In this application, this electrical insulating member is formed in such a manner that a coating member of a polymer elastic material is sandwiched between thin metallic plates. The generic CH-A- 322 744 discloses a roller bearing having an outer metallic ring of which at least the circumferential surface is covered with a relatively thick rubber layer for clamping any inherent vibrations and noises of the bearing. The rubber layer could be provided with an outer steel ring for its contact with a supporting structure. When rotary bearings used in main electric motors for rolling stocks are not electrically insulated, shaft current flows between a main electric motor frame and an armature shaft through a metallic bearing. As a result, the bearing is subject to damage or scorch. The aforementioned prior art techniques attempted to interrupt shaft current in order to protect bearing portions in main electric motors from damage. Bearings used in main electric motors for rolling stocks are generally installed onto end covers (mounting portions of bearings) of main electric motors. Accordingly, an installation work of a bearing to this cover is necessary. In this sense, higher dimensional accuracy is required for bearings. However, this higher dimensional accuracy cannot be obtained easily when it comes to bearings having insulating members. As a result, overall dimensional accuracy in installation lowers when installing these bearings with lower dimensional accuracy. A ceramic-treated bearing has succeeded in improving its dimensional accuracy, but not in overcoming brittleness of ceramic itself. In addition, insulating capacity of the bearing from the cover of the main electric motors can be evaluated only after installation. In terms of improving dimensional accuracy, a technique using the polymer insulating materials alone is disadvantageous since it is impossible to raise the dimensional accuracy of the polymer member itself. Furthermore, an insulating material is made into a form of a thin layer in order to lessen the amount of distortion when load acts upon the bearing. But this tends to cause damages to the polymer member or ceramic materials upon installation or removal of the bearing. It is an object of the invention to provide an electrical insulating bearing which can satisfy the requirement for dimensional accuracy and also for easy and accurate installation, and which can, at the same time, facilitate an evaluation of insulating capacity. In accordance with the present invention as outlined by the appended claims an electrical insulating property of a bearing itself can be evaluated even before installation, and at the same time, requirement for dimensional accuracy and also for easy and accurate installation can be satisfied. Since the outer ring is formed by integrating the outer ring body, the insulating thin film and the thin metallic plate, the outer ring itself has insulating property for electrically insulating the bearing from a housing portion. Accordingly, an electrical resistance between the outer ring body and the thin metallic plate can be measured before installation to the housing to evaluate insulating property of the bearing. Thus, it is unnecessary to provide any additional elements between the bearing and the housing in order to electrically insulate the bearing. As a result, installation of the bearing can be facilitated and dimensional accuracy in the bearing portion can be easily improved. Distortion in the insulating thin film due to load can be kept minimum because of thinness thereof. Therefore, any negative effect on dimensional accuracy can be disregarded. In addition, dimension of the outer ring can be adjusted by machining the thin metallic plate. Since the insulating film and the metallic plate are thin in thickness, an outer diameter of the outer ring can be similar to those of conventional outer rings. Thus, modification on the part of the housing is not required. Furthermore, the insulating thin film being made of polymer elastic materials also provides for toughness and resistance against fracture caused by heavy load during operation. The thin metallic plate protects the insulating thin film from scratch or damage upon installation of the bearing onto the housing as well as from breakage due to heavy load during operation. Other and further features and advantages of the invention will more fully appear from the following description with reference to the accompanying drawings, in which: Fig.1 is a sectional view showing a bearing; Fig.2 is a sectional view showing an outer ring; Fig.3 is a sectional view showing a device for manufacturing the outer ring; Figs.4 and 5 are sectional views showing modified examples of an outer ring. Fig.1 shows an insulating bearing 1 installed onto an end cover of a main electric motor. This bearing 1 is made up by interposing a plurality of rolling elements (balls or rollers) 6 between an outer ring 3 and an inner ring 5. The outer ring 3 is fixed onto the cover of the main electric motor (hereinafter called a housing 2). An armature shaft 4 is inserted in the inner ring 5. As shown in the enlarged drawing of Fig.2, the outer ring 3 is made up by integrating the following three elements into a solid one-piece body: an outer ring body 11; an insulating thin film 12 which covers an outer periphery of the outer ring body 11; and a thin metallic plate 13 which is provided on an outer surface of the insulating thin film 12. The outer ring body 11 is made of metal, and accordingly has conductivity. The outer ring body 11 has a path 11a of the rolling element 6 in an inner periphery thereof. The insulating thin film 12 is made of a polymer elastic material. This insulating thin film 12 is provided on a portion extending from an outer peripheral surface 11b to a side surface 11c of the outer ring body 11 so as to electrically insulate the outer ring body 11 from the housing 2. The thin metallic plate 13 is adhered to the insulating thin film 12 on a portion corresponding to the outer peripheral surface 11b of the outer ring body 11. However, the thin metallic plate 13 is provided on the insulating thin film 12 while leaving an exposed portion in the periphery of the insulating thin film 12 so as not to make direct contact with the outer ring body 11. Desirable thickness and property of the insulating thin film 12, and desirable thickness of the thin metallic plate 13 when an outer diameter of the outer ring 3 is approximately 170 mm are as follows. insulating thin film thickness from 0.1 to 2.0 mm shore hardness from 80A to 60D electrical resistance not less than 100MΩ thickness of thin metallic plate 1.0 mm Thickness of the insulating thin film 12 and the thin metallic plate 13 in the above table is shown by thickness in the superposed portions thereof. The inner ring 5 has a path 5a of the rolling element 6 in the outer periphery thereof. Each rolling element 6 is supported by a cage 7. The inner ring 5, rolling element 6, and cage 7 are made of metal, and therefore, have conductivity. The manufacturing method of the outer ring 3 will be now described. A metal mold shown in Fig.3 is utilized in this method of manufacturing the outer ring 3. In Fig.3, reference numeral 15 designates a lower die wherein the outer ring body 11 is inserted. Reference numeral 16 designates an upper die which covers the outer ring body 11, and reference numeral 17 designates an outer die for positioning a thin metallic plate member 13A onto the outer ring body 11 as well as for molding a cavity 19 to form the insulating thin film 12 in association with the lower die 15, and reference numeral 18 designates an outer frame for fixing the outer die 17. The outer die 17 is split in the circumferential direction. The method of manufacturing the outer ring 3 comprises the following steps: 1. Processing the outer peripheral surface 11b and the side surface 11c of the outer ring body 11 (namely portions thereof on which the insulating thin film 12 is coated) with sand blasting treatment. Then, applying adhesives to the outer peripheral surface 11b and the side surface 11c. After drying the outer peripheral surface 11b and the side surface 11c at room temperature, pre-heating them at 50°C for 120 minutes. To take an example, CHEMLOK #218 manufactured by Hughson Chemicals, Load Co. can be used as adhesives. 2. Pre-heating the lower die 15, upper die 16, outer die 17, and outer frame 18 to 95°C. Then, incorporating the outer ring body 11 and the thin metallic plate member 13A into the mold as shown in Fig. 3. 3. Pouring polymer elastic material 20 into the cavity 19 in the mold. 4. After vulcanizing (mold cure) the polymer elastic material 20 inside the mold for 30 minutes, releasing it from the mold and carrying out re-vulcanization at 110°C for 24 hours. 5. Installing the rolling elements 6 between the inner ring 5 and the outer ring 3 obtained through the above-mentioned process (or by further performing a finishing treatment on the outer surface of the thin metallic plate member 13A with grinding machining if necessary). Thus, the bearing 1 is obtained. One example of a composition of the polymer elastic material is as follows. PTMEG (polytetramethyleneglycol manufactured by Mitsui-toatsu Co., L-100) 100 weight part (60°C) CURAMINE MT (3,3-dichloro-4,4-diaminodiphenylmethane) 19 weight part (120°C) In this way, the insulating thin film 12 of the outer ring 3 is made of polyurethane. In the bearing of the present invention, therefore, with this insulating thin film 12, the outer ring 3 possesses capacity of insulating the bearing 1 from the housing 2. As a result, insulation property of the outer ring 3 can be evaluated by measuring electrical resistance between the outer ring body 11 and the thin metallic plate 13 at the time when the production of the outer ring 3 is completed. In this embodiment, the superposed portion of the insulating thin film 12 and the thin metallic plate 13 were 0.5 mm and 1.0 mm, respectively in thickness, and electrical resistance was not less than 100 MΩ. Then, the bearing 1 is installed onto the housing 2 and the armature 4. While the bearing 1 is installed on the housing 2 and the armature 4, no discharge occurs from the housing 2 to the armature 4 since not less than 100 MΩ electrical resistance exists in the insulating thin film 12 of the bearing 1. Accordingly, the bearing 1 will never wear excessively. The thin metallic plate 13 is provided inside the periphery portion of the insulating thin film 12 so as not to make contact with the outer ring body 11. This means that the thin metallic plate 13 does not adversely affect electrical insulating property of the bearing 1. In addition, with the insulating thin film 12 covering not only the outer peripheral surface 11b but also the side surface 11c of the outer ring body 11, electrical insulating property can be reliably obtained. As described earlier, the outer ring 3 has insulating capacity. Accordingly, when installing the bearing 1, it is not required to insert any additional element between the bearing 1 and the housing 2 in order to form an electrical insulating state therebetween. This will promote easy installation of the bearing 1. Further, dimensional accuracy in the bearing portion (that is a positional accuracy between the housing 2 and the armature 4 while the bearing 1 is installed on the housing 2) is basically determined by an outside diameter of the bearing 1, namely, an outside diameter of the outer ring 3. This means that higher dimensional accuracy of the bearing portion can be achieved by adjusting the dimension of the outer ring 3 at the time when the outer ring 3 is produced. When an additional element is necessary, dimensional accuracy of the bearing portion proportionally decreases. In contrast, when an additional element is unnecessary, as in the present invention, dimensional accuracy of the bearing portion increases. Due to its thinness, the insulating thin film 12 is not easily subject to deformation caused by load during operation. Thus, any effect on the dimensional accuracy because of deformation can be disregarded. More specifically, the insulating thin film 12 is designed to have a thickness of not less than 0.1 mm in the thinnest part thereof in order to acquire desired electrical insulating property, and as well as a thickness of not more than 2.0 mm on account of deformation caused by load during operation. The insulating thin film 12 is designed to have a shore hardness of not less than 80A so as to possess enough strength to withstand load generated during operation even with a thickness of only 0.1 mm and also to reduce the amount of deformation caused by load. The insulating thin film 12 is further designed to have a shore hardness of not more than 60D. A shore hardness of over 60D results in lower toughness, increasing susceptibility to damage caused by load during operation. Since the insulating thin film 12 and the thin metallic plate 13 are thin in their thickness, an outside diameter of the outer ring 3 can be almost similar to that of a conventional ring. Accordingly, no modification is necessary in the housing 2. The thin metallic plate 13 protects the insulating thin film 12 from damage or scratch when assembling or incorporating the bearing 1 to the housing 2. This plate 13 also protects the insulating thin film 12 from breakage caused by excessive load during operation while the bearing 1 is incorporated in the housing 2. Therefore, it is desirable that the thin metallic plate 13 has a thickness larger than that of the insulating thin film 12. Figs.4 and 5 show modified examples of an outer ring. An outer ring 21 shown in Fig.4 is provided with an insulating thin film 23 and a thin metallic plate 24, each having the equal width, so as to expose overall portion of the side surface of an outer ring body 22. On the other hand, an outer ring 25 shown in Fig.5 exposes an insulating thin film 27 from the both sides of a thin metallic plate 28 so as to cover a side surface of an outer ring body 26 with the insulating thin film 27. Thus, thickness of the insulating thin film 27 is consistent both in an outer peripheral surface and in the side surface of the outer ring body 26. The modified example illustrated in Fig.5 is provided with the insulating thin film and the thin metallic plate which are formed only in a portion where the outer ring body is incorporated to the housing. As in this example, the insulating thin film and the thin metallic plate in the other aforementioned examples of the invention can be formed only in a portion where the outer ring body is incorporated to the housing. The aforementioned examples apply to a rotary bearing of a main electric motor for railroad vehicles. It is also applicable to bearings of various equipments, such as electrical welding equipment, or to chassis bearings for vehicles.

Claims: An electrical insulating bearing having a rolling element (6) interposed between an outer ring (3; 21; 25) and an inner ring (5), said outer ring comprising a metallic outer ring body (11; 22; 26) having a path of rotation (11a) of said rolling element (6); a layer (12; 23; 27) of a polymer elastic material having an electrical insulating property which covers at least the circumferential surface of said metallic outer ring body; and a thin metallic plate (13; 24; 28) provided on an outer surface of said insulating layer; characterized by said outer ring (3; 21; 25) being integrally formed as a one-piece body of said metallic outer ring body, said insulating layer and said thin metallic plate, said insulating layer comprising an insulating thin film (12; 23; 27) having a thickness form 0.1 to 2.0 mm, a shore hardness from 80A to 60D and an electrical resistance of not less than 100MΩ.

Inventors: FUSE YOSHIYA C O BANDO CHEMICA, KINOSHITA KOJI C O BANDO CHEMI, NITTA YUKIO C O RAILWAY TECHNI, SATO KOUICHI C O RAILWAY TECHN, WATANABE TOMOKI C O RAILWAY TE, FUSE, YOSHIYA, C/O BANDO CHEMICAL INDUSTRIES, LTD., KINOSHITA, KOJI, C/O BANDO CHEMICAL INDUSTRIES LTD, NITTA, YUKIO, C/O RAILWAY TECHNICAL, SATO, KOUICHI, C/O RAILWAY TECHNICAL, WATANABE, TOMOKI, C/O RAILWAY TECHNICAL
Applicants: BANDO CHEMICAL IND, RAILWAY TECHNICAL RES INST, BANDO CHEMICAL INDUSTRIES, LIMITED, RAILWAY TECHNICAL RESEARCH INSTITUTE
Application year: 1990
Main classification: F16C27
IPC codes: F16C27, F16C35, F16C19