Insulated rolling bearing and method for manufacturing an insulated rolling bearing

Abstract

The present invention provides an insulated rolling bearing capable of easily and efficiently forming an insulating layer on the surface of its components, and a method for manufacturing the insulated rolling bearing. [Solution] An insulated rolling bearing comprises an outer ring 1, an inner ring 2 positioned radially inward of the outer ring 1, a plurality of rolling elements 3 incorporated between the outer ring 1 and the inner ring 2, and a resin insulating coating 5 provided on the outer ring 1, wherein the insulating coating 5 is formed of a heat-shrinkable tube 9 that shrinks when heated, and the heat shrinkage start temperature T0 of the heat-shrinkable tube 9 is 80°C or higher.

Description

Technical Field

[0001] This invention relates to a rolling bearing with insulation and a method for manufacturing the rolling bearing with insulation.

Background Art

[0002] In a rolling bearing that supports the rotating shaft of a device that uses electricity, such as an electric motor or an alternator (generator), when an electric current flows inside the bearing, a spark may occur between the outer ring or the inner ring and the rolling elements, and a phenomenon (electrical erosion) may occur in which the surfaces of the outer ring, the inner ring, and the rolling elements are locally melted by the spark. As a rolling bearing capable of preventing this electrical erosion, a rolling bearing with insulation provided with an insulating coating on the outer ring is known (for example, Patent Document 1).

[0003] <000001'2>The rolling bearing with insulation of Patent Document 1 has an outer ring, an inner ring disposed radially inside the outer ring, a plurality of rolling elements incorporated between the outer ring and the inner ring, and a resin insulating coating provided on the outer ring. This insulating coating is formed by insert molding (that is, a method of molding the insulating coating by injecting molten resin into the cavity inside the mold with the outer ring set inside the mold).

[0004] When providing a resin insulating coating on the outer ring, it is mainstream to form the insulating coating by insert molding as in Patent Document 1. However, forming the insulating coating by insert molding requires large-scale equipment and molds, so there is a problem that the manufacturing cost of the rolling bearing with insulation increases.

[0005] Therefore, in order to reduce the manufacturing cost of the rolling bearing with insulation, a rolling bearing with insulation provided with an insulating coating by a method different from insert molding, as disclosed in Patent Document 2, has been proposed.

[0006] The rolling bearing with insulation of Patent Document ʺ forms a resin insulating coating that covers the outer peripheral surface and a pair of axial end faces of the outer ring by disposing a resin heat-shrinkable tube on the radially outer side of the outer ring and heating and shrinking the heat-shrinkable tube. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 3068311 [Patent Document 2] Japanese Patent Publication No. 2001-107974 [Overview of the project] [Problems that the invention aims to solve]

[0008] Incidentally, heat-shrinkable tubing used as insulating coating for rolling bearings begins to shrink when heated to a temperature above its shrinkage start temperature, and has the potential to shrink until it reaches a final shrinkage rate (e.g., 60%) corresponding to that heating temperature. On the other hand, heat-shrinkable tubing installed on rolling bearings is usually heated to a point where it is in close contact with the outer ring, before it reaches its final shrinkage rate, and often leaves room for further shrinkage by reheating.

[0009] For example, when the rotating shafts of electric motors or alternators are supported by rolling bearings, the bearing temperature rises after operation begins due to internal friction in the bearings, and then settles to a steady temperature (bearing operating temperature) after a certain period of time. If this bearing operating temperature is above the heat shrinkage start temperature of the heat shrink tubing, additional heat shrinkage of the heat shrink tubing (insulating coating) may occur during use of the rolling bearing, potentially causing wrinkles or other damage to the insulating coating due to dimensional changes. Generally, this bearing operating temperature is considered to be 80°C or lower for normal use and 120°C or lower for high-temperature use.

[0010] Therefore, the object of the present invention is to provide an insulated rolling bearing that suppresses the occurrence of wrinkles or other defects in the insulating coating during use of the rolling bearing, and a method for manufacturing the insulated rolling bearing. [Means for solving the problem]

[0011] To solve the above problems, the present invention provides: Outer ring and, An inner ring positioned radially inward of the outer ring, A plurality of rolling elements are incorporated between the outer ring and the inner ring, The outer ring has a resin insulating coating provided on it, In an insulated rolling bearing in which the insulating coating is formed of a heat-shrinkable tube that shrinks when heated, The outer ring has a cylindrical outer surface with a constant outer diameter along the axial direction, a pair of chamfered portions with a circular arc cross-section whose outer diameter gradually decreases axially outward from the outer surface, and a pair of axial end faces extending radially inward from the pair of chamfered portions. The insulating coating comprises a cylindrical outer covering portion that covers the outer surface of the outer ring, a pair of chamfered covering portions with a circular arc cross-section that cover the pair of chamfered portions of the outer ring, and a pair of end covering portions that cover the pair of axial end faces of the outer ring. An insulated rolling bearing was constructed (first configuration) characterized in that the heat shrinkage start temperature of the heat shrink tubing is 80°C or higher.

[0012] According to the first configuration, the heat-shrinkable tube is placed radially on the outer ring, and the insulating coating can be formed by heating and deforming the heat-shrinkable tube. This eliminates the need for large-scale equipment, such as when insulating the outer ring by insert molding. Therefore, it is possible to reduce the manufacturing cost of the insulated rolling bearing. Furthermore, by using a heat-shrinkable tube with a heat-shrinkage initiation temperature of 80°C or higher, additional heat shrinkage of the heat-shrinkable tube (insulating coating) during use of the rolling bearing is less likely to occur, thus suppressing wrinkles and other defects in the insulating coating.

[0013] In the first configuration, when a cut is formed in the insulating coating before use, a configuration (second configuration) can be made in which the expansion of the cut is suppressed during use. This second configuration is obtained when a heat shrink tube is used in which the heat shrinkage start temperature is higher than the operating temperature.

[0014] In the first or second configuration, the insulating coating may have a withstand voltage of 200V or more and an insulating resistance of 1MΩ or more (third configuration). According to the third configuration, when used as an insulating rolling bearing to support the rotating shaft of an electric motor for driving an electric vehicle or the reduction gear of that electric motor, it is possible to effectively prevent electrolytic corrosion from occurring on the outer ring, inner ring, and rolling elements.

[0015] Furthermore, as a method for manufacturing the insulated rolling bearing described above, A bearing preparation step for preparing a rolling bearing comprising an outer ring, an inner ring positioned radially inward of the outer ring, and a plurality of rolling elements incorporated between the outer ring and the inner ring, wherein the outer ring has a cylindrical outer surface with a constant outer diameter along the axial direction, a pair of chamfered portions with a circular arc cross-section whose outer diameter gradually decreases axially outward from the outer surface, and a pair of axial end faces extending radially inward from the pair of chamfered portions, A heat shrink tube placement step is to place a heat shrink tube made of resin that shrinks when heated on the radially outer side of the aforementioned rolling bearing, The process includes a heat shrink tube heating step, in which the heat shrink tube is heated and deformed to form an insulating coating having a cylindrical outer peripheral covering portion that covers the outer peripheral surface of the outer ring, a pair of chamfered covering portions with a circular arc cross-section that covers the pair of chamfered portions of the outer ring, and a pair of end covering portions that cover the pair of axial end faces of the outer ring. A method for manufacturing an insulated rolling bearing was constructed (fourth configuration) in which the heat shrinkage start temperature of the heat shrink tube in the heat shrink tube heating step is 80°C or higher. [Effects of the Invention]

[0016] The insulated rolling bearing and the method for manufacturing the insulated rolling bearing according to the present invention use a heat-shrinkable tube with a heat shrinkage initiation temperature of 80°C or higher for forming the insulating coating, so that additional heat shrinkage of the heat-shrinkable tube (insulating coating) is less likely to occur during use of the rolling bearing. Therefore, it is possible to suppress the occurrence of wrinkles and other defects in the insulating coating. [Brief explanation of the drawing]

[0017] [Figure 1] Cross-sectional view showing a rolling bearing with insulation according to an embodiment of the present invention [Figure 2] Cross-sectional view taken along line II-II of FIG. 1 [Figure 3] Flowchart for explaining a method of manufacturing a rolling bearing with insulation according to the present invention [Figure 4] It is a view for explaining the method of manufacturing the rolling bearing with insulation of FIG. 2, and shows a state in which a heat shrinkable tube before shrinkage is arranged on the radially outer side of the outer peripheral surface of the outer ring [Figure 5] It is a view showing a state in which the heat shrinkable tube shown in FIG. 4 is heated and heat shrunk to cover the outer peripheral surface and the chamfered portion of the outer ring [Figure 6] It is a view showing a state of covering up to the axial end face of the outer ring following FIG. 5 [Figure 7] View showing the heat shrinkage characteristics of the heat shrinkable tube [Figure 8] View showing an example of the usage state of the rolling bearing with insulation shown in FIG. 2

Embodiments for Carrying Out the Invention

[0018] FIG. 1 shows a rolling bearing with insulation according to an embodiment of the present invention. This rolling bearing with insulation has an outer ring 1, an inner ring 2 coaxially arranged on the radially inner side of the outer ring 1, a plurality of rolling elements 3 incorporated with a circumferential interval between the outer ring 1 and the inner ring 2, an annular cage 4 for holding the circumferential interval of the plurality of rolling elements 3, and a resin insulation coating 5 provided on the outer ring 1

[0019] The axial direction is a direction parallel to the central axis of the outer ring 1 (the central axis of the bearing), the radial direction is a direction perpendicular to the central axis of the outer ring 1, and the circumferential direction is a direction along the circumference that circulates around the central axis of the outer ring 1. The outer ring 1 and the inner ring 2 are formed symmetrically with respect to the axial center. Also, the inner side in the axial direction is the side approaching the axial center of the outer ring 1 and the inner ring 2 along the axial direction, and the outer side in the axial direction is the side moving away from the axial center of the outer ring 1 and the inner ring 2 along the axial direction

[0020] As shown in Figure 2, the rolling element 3 is radially sandwiched between the outer ring raceway groove 6 formed on the inner circumference of the outer ring 1 and the inner ring raceway groove 7 formed on the outer circumference of the inner ring 2. The rolling element 3 is a ball in this case. The outer ring raceway groove 6 and the inner ring raceway groove 7 are grooves with an arc-shaped cross-section perpendicular to the circumferential direction. The outer ring 1, inner ring 2, and rolling element 3 are each made of steel.

[0021] The outer ring 1 has a cylindrical outer surface 1a with a constant outer diameter that does not change along the axial direction, a pair of chamfered portions 1b with a cross-sectional arc shape whose outer diameter gradually decreases axially outward from the outer surface 1a, and a pair of axial end faces 1c extending radially inward from the pair of chamfered portions 1b. The axial end faces 1c are planes perpendicular to the axial direction.

[0022] Here, the outer diameter φD (see Figure 4) of the outer circumferential surface 1a of the outer ring 1 is set to be between 45 mm and 110 mm, and the axial width dimension of the outer ring 1 is set to be between 9 mm and 30 mm. In addition, the surface roughness of the outer circumferential surface 1a of the outer ring 1 along the axial direction is set to be between 0.05 μm and 1.6 μm. The chamfered portion 1b of the outer ring 1 is an arc-shaped surface whose cross-section perpendicular to the circumferential direction smoothly connects to the outer circumferential surface 1a of the outer ring 1, and its arc radius R (see Figure 4) is set to be 0.3 mm or more.

[0023] The insulating coating 5 has a cylindrical outer circumferential coating portion 5a that covers the outer circumferential surface 1a of the outer ring 1, a pair of chamfered coating portions 5b with a circular arc cross-section that cover a pair of chamfered portions 1b of the outer ring 1, and a pair of end-face coating portions 5c that cover a pair of axial end faces 1c of the outer ring 1. The pair of chamfered coating portions 5b are formed in conjunction with both axial ends of the outer circumferential coating portion 5a, and the pair of end-face coating portions 5c are formed in conjunction with the radially inner ends of the pair of chamfered coating portions 5b. It is preferable that the end-face coating portions 5c are provided in close contact with the axial end faces 1c of the outer ring 1, but they may also be provided in a state where they are lifted away from the axial end faces 1c of the outer ring 1 (a state where there is a gap between the axial end faces 1c of the outer ring 1 and the end-face coating portions 5c). Note that in the figure, the thickness of the insulating coating 5 is greatly exaggerated for clarity.

[0024] The insulating coating 5 is set to have a thickness such that the outer peripheral coating portion 5a (i.e., the thinnest part of the outer peripheral coating portion 5a, the chamfered coating portion 5b, and the end face coating portion 5c) has a withstand voltage of 200V or more and an insulation resistance value of 1MΩ or more. This insulating coating 5 is formed from a heat-shrinkable resin tube 9 that shrinks when heated, and as will be described later, this heat-shrinkable tube 9 is selected to have a heat shrinkage start temperature T0 that is higher than the bearing operating temperature of the insulated rolling bearing.

[0025] An example of a manufacturing method for this insulated rolling bearing will be explained using Figure 3.

[0026] [Bearing preparation process] (Step S1 in Figure 3) Prepare the rolling bearing 8 shown in Figure 4. This rolling bearing 8 incorporates multiple rolling elements 3 between the outer ring 1 and the inner ring 2, and does not have the insulating coating 5 shown in Figure 2.

[0027] [Heat shrink tubing placement process] (Step S2 in Figure 3) After the bearing preparation process described above, a heat-shrinkable resin tube 9 is placed on the radially outer side of the rolling bearing 8, as shown in Figure 4.

[0028] As the heat-shrinkable tube 9, for example, a tube made from a resin material such as polyolefin resin, polyvinyl chloride resin, or fluororesin can be formed, irradiated with an electron beam to crosslink the resin material, and then heated to a predetermined high temperature, stretched radially (or radially and axially), and cooled. In this case, the dimensions of the stretched tube correspond to the dimensions of the heat-shrinkable tube 9 before shrinkage by heating.

[0029] Furthermore, the axial length w (see Figure 4) of the heat shrink tube 9 is set to be sufficiently longer (1.6 times or more, preferably 1.8 times or more) than the axial width dimension of the outer ring 1 (distance between a pair of axial end faces 1c) of the outer ring 1, so that the axial end faces 1c of the outer ring 1 can be reliably covered with the heat shrink tube 9 during the heat shrink tube heating process described later.

[0030] [Heat shrink tubing heating process] (Step S3 in Figure 3) After the heat shrink tubing placement step described above, the heat shrink tubing 9 is heated and deformed to sequentially form an insulating coating 5, as shown in Figures 5 and 6, which has a cylindrical outer peripheral coating portion 5a that covers the outer peripheral surface 1a of the outer ring 1, a pair of chamfered coating portions 5b with a circular arc cross-section that cover a pair of chamfered portions 1b of the outer ring 1, and a pair of end-face coating portions 5c that cover a pair of axial end faces 1c of the outer ring 1. As a method for heating the heat shrink tubing 9, methods such as blowing hot air onto the outer circumference of the heat shrink tubing 9 with a heating gun or the like can be used, or a method of passing the rolling bearing 8 and the heat shrink tubing 9 positioned radially outside it through a heating furnace while being supported by a support.

[0031] As shown in Figure 7, the heat shrink tubing 9 begins to shrink when heated to a temperature above the heat shrinkage start temperature T0, which is determined for each product. Once heated to a predetermined shrinkage temperature T1, it has the potential to shrink to a final shrinkage rate (e.g., 60%) corresponding to that heating temperature. On the other hand, the heat shrink tubing 9 installed on rolling bearings is usually heated to a point where it is in close contact with the outer ring 1, before reaching its final shrinkage rate, often leaving room for further shrinkage by reheating.

[0032] For example, when a rotating shaft 10 (see Figure 8) of an electric motor or alternator is supported by a rolling bearing, the bearing temperature rises after the start of operation due to internal friction in the bearing, and settles to a steady temperature (bearing operating temperature) after a certain period of time. If this bearing operating temperature is above the thermal shrinkage start temperature T0 of the heat shrink tubing 9 (for example, temperature T2 shown in Figure 7), additional thermal shrinkage of the heat shrink tubing 9 (insulating coating 5) may occur during use of the rolling bearing, potentially causing wrinkles or other damage to the insulating coating 5 due to dimensional changes.

[0033] In this insulated rolling bearing, the insulating coating 5 is formed using a heat-shrinkable tube 9 whose thermal shrinkage start temperature T0 is 80°C or higher. Therefore, there is little risk of additional thermal shrinkage of the heat-shrinkable tube 9 (insulating coating 5) occurring during use of the rolling bearing.

[0034] For example, if the bearing operating temperature is not expected to exceed 80°C, additional thermal shrinkage during use of the rolling bearing can be prevented by using a heat shrink tube 9 with a thermal shrinkage start temperature T0 of 80°C or higher (or 90°C or higher to ensure a safety margin).

[0035] As shown in Figure 8, the insulated rolling bearing of this embodiment can be used as a rolling bearing to support the rotating shaft 10 of an electrical device (such as the rotating shaft of an electric motor, the rotating shaft of a speed reducer that reduces the rotation of an electric motor, or the rotating shaft of an alternator). In Figure 8, the insulated rolling bearing is assembled between the cylindrical inner circumference of a housing hole 12 formed in a non-rotating housing 11 and the outer circumference of the rotating shaft 10 located at the center of the housing hole 12. Here, the inner ring 2 is the rotating side and the outer ring 1 is the non-rotating side, so the insulated rolling bearing is assembled so that the inner ring 2 is fitted to the outer circumference of the rotating shaft 10 in an interference fit, and the outer ring 1 is fitted to the inner circumference of the housing hole 12 in a clearance fit.

[0036] As shown in Figure 4, this insulated rolling bearing can be manufactured by placing a heat-shrinkable tube 9 radially outside the outer ring 1 and heating and deforming the heat-shrinkable tube 9 to form the insulating coating 5. This eliminates the need for large-scale equipment, such as when the insulating coating 5 is applied to the outer ring 1 by insert molding. Therefore, it is possible to reduce the manufacturing cost of the insulated rolling bearing.

[0037] Furthermore, since this insulated rolling bearing uses a heat shrink tubing 9 whose heat shrinkage start temperature T0 is higher than the bearing operating temperature when forming the insulating coating 5, additional heat shrinkage of the heat shrink tubing 9 (insulating coating 5) is less likely to occur during use of the rolling bearing, and wrinkles and other defects in the insulating coating 5 can be suppressed.

[0038] Whether a heat shrink tubing 9 with a heat shrinkage start temperature T0 of 80°C or higher (having a heat shrinkage start temperature T0 higher than the bearing operating temperature) is used in this insulated rolling bearing can be easily determined by making a cut in, for example, the end face covering portion 5c of the insulating coating 5 of the insulated rolling bearing and visualizing the change in the insulating coating 5 when additional heat shrinkage occurs.

[0039] In other words, if an insulating rolling bearing with a notch formed in it is assembled, for example, between the housing 11 and the rotating shaft 10 as shown in Figure 8, and then operated under normal conditions (regular operation), and the expansion of the notch is suppressed even when the bearing temperature rises during this normal operation, it can be determined that a heat shrink tubing 9 with a heat shrinkage start temperature T0 of 80°C or higher is being used. If the notch expands, it can be determined that a heat shrink tubing 9 with a heat shrinkage start temperature T0 lower than 80°C is being used.

[0040] Furthermore, since the insulating coating 5 of this insulated rolling bearing has a dielectric strength of 200V or more and an insulation resistance of 1MΩ or more, it is possible to effectively prevent electrolytic corrosion from occurring on the outer ring 1, inner ring 2, and rolling elements 3 when used as an insulated rolling bearing to support the rotating shaft 10 of the electric motor or the reduction gear of the electric motor for driving an electric vehicle. As an evaluation method, the dielectric strength test method described in JIS C 2110-1:2016 can be used, and the insulation resistance test method described in JIS C 2140:2009 can be used. Dielectric strength refers to the applied voltage that does not lead to dielectric breakdown.

[0041] In the above embodiment, as shown in Figure 2, the axial width dimension of the outer ring 1 and the axial width dimension of the inner ring 2 are the same (that is, the axial end face 1c of the outer ring 1 and the axial end face 2c of the inner ring 2 are at the same axial position). However, it is also possible to set the axial width dimension of the outer ring 1 to be smaller than the axial width dimension of the inner ring 2 so that the surface of the end face covering portion 5c of the insulating coating 5 is at the same axial position as the axial end face 2c of the inner ring 2.

[0042] Furthermore, although the above embodiment described an example in which balls are used as the rolling elements 3, other shapes of rolling elements 3, such as cylindrical rollers, may also be used.

[0043] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of symbols]

[0044] 1 Outer ring 1a Outer surface 1b Chamfered section 1c Axial end face 2 Inner ring 3 Rolling element 5. Insulating coating 5a Outer sheathing part 5b Chamfered coating 5c End covering part 8 Rolling bearings 9 Heat shrink tubing T0 is the temperature at which thermal shrinkage begins.

Claims

1. Outer ring (1) and, An inner ring (2) is positioned radially inward of the outer ring (1), A plurality of rolling elements (3) are incorporated between the outer ring (1) and the inner ring (2), The outer ring (1) has a resin insulating coating (5) provided on it, In an insulated rolling bearing in which the insulating coating (5) is formed of a heat-shrinkable tube (9) that shrinks when heated, The outer ring (1) has a cylindrical outer surface (1a) with a constant outer diameter along the axial direction, a pair of chamfered portions (1b) with a circular arc cross-section whose outer diameter gradually decreases axially outward from the outer surface (1a), and a pair of axial end faces (1c) extending radially inward from the pair of chamfered portions (1b). The insulating coating (5) has a cylindrical outer peripheral coating portion (5a) that covers the outer peripheral surface (1a) of the outer ring (1), a pair of chamfered coating portions (5b) with a circular arc cross-section that cover the pair of chamfered portions (1b) of the outer ring (1), and a pair of end face coating portions (5c) that cover the pair of axial end faces (1c) of the outer ring (1), An insulated rolling bearing characterized in that the thermal shrinkage start temperature (T0) of the heat shrink tube (9) is 80°C or higher.

2. The insulating rolling bearing according to claim 1, wherein when a notch is formed in the insulating coating (5) and the bearing is used, the expansion of the notch is suppressed during use.

3. The insulating rolling bearing according to claim 1 or 2, wherein the insulating coating (5) has a withstand voltage of 200V or more and an insulating resistance of 1MΩ or more.

4. A bearing preparation step to prepare a rolling bearing (8) having an outer ring (1), an inner ring (2) arranged radially inward of the outer ring (1), and a plurality of rolling elements (3) incorporated between the outer ring (1) and the inner ring (2), wherein the outer ring (1) has a cylindrical outer surface (1a) with a constant outer diameter along the axial direction, a pair of chamfered portions (1b) with a cross-sectional arc shape whose outer diameter gradually decreases axially outward from the outer surface (1a), and a pair of axial end faces (1c) extending radially inward from the pair of chamfered portions (1b), A heat shrink tube placement step is to place a heat shrink tube (9) made of resin that shrinks when heated on the radially outer side of the rolling bearing (8), The process includes a heat shrink tube heating step, in which the heat shrink tube (9) is heated and deformed to form an insulating coating (5) having a cylindrical outer peripheral covering portion (5a) that covers the outer peripheral surface (1a) of the outer ring (1), a pair of chamfered covering portions (5b) with a circular arc cross-section that cover the pair of chamfered portions (1b) of the outer ring (1), and a pair of end-face covering portions (5c) that cover the pair of axial end faces (1c) of the outer ring (1). A method for manufacturing an insulated rolling bearing, wherein the thermal shrinkage start temperature (T0) of the heat shrink tube (9) in the heat shrink tube heating step is 80°C or higher.

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