Insulated rolling bearing and method for manufacturing insulated rolling bearing

Abstract

An insulating cover (5) includes: a cylindrical outer peripheral cover section (5a) that covers an outer peripheral surface (1a) of an outer ring (1); a pair of chamfer cover sections (5b) that have an arc-shaped cross section and cover a pair of chamfer sections (1b) of the outer ring (1); and a pair of end surface cover sections (5c) that cover a pair of axial end surfaces (1c) of the outer ring (1). Thick sections (8) that circumferentially extend in an annular shape and have a thickness greater than the thickness of the outer peripheral cover section (5a) at an axially central position are formed at both axial ends of the outer peripheral cover section (5a).

Description

Insulated rolling bearing and method for manufacturing the insulated rolling bearing

[0001] The present invention relates to an insulating rolling bearing and a method for manufacturing the same.

[0002] In rolling bearings that support the rotating shaft of electrical devices such as electric motors and alternators (generators), when an electric current flows inside the bearing, sparks can occur between the outer or inner ring and the rolling elements, causing localized melting of the surfaces of the outer or inner ring or the rolling elements (galvanic corrosion).Insulated rolling bearings in which an insulating coating is provided on the outer ring are known as rolling bearings that can prevent this galvanic corrosion (see, for example, Patent Document 1).

[0003] The insulating rolling bearing of Patent Document 1 has an outer ring, an inner ring arranged radially inward of the outer ring, a plurality of rolling elements installed 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 (i.e., a method of molding the insulating coating by injecting molten resin into a cavity inside a mold with the outer ring set inside the mold).

[0004] When providing an insulating resin coating on an outer ring, the insulating coating is typically formed by insert molding, as in Patent Document 1. However, forming an insulating coating by insert molding requires large-scale equipment and molds, which increases the manufacturing costs of the insulated rolling bearing.

[0005] Therefore, in order to reduce the manufacturing costs of insulating rolling bearings, Patent Document 2 proposes an insulating rolling bearing in which an insulating coating is provided by a method other than insert molding.

[0006] The insulating rolling bearing of Patent Document 2 has a resin heat-shrinkable tube disposed radially outside the outer ring, and the heat-shrinkable tube is heated to shrink it, thereby forming a resin insulating coating that covers the outer peripheral surface and a pair of axial end faces of the outer ring.

[0007] Japanese Patent No. 3068311 Japanese Patent Laid-Open No. 2001-107974

[0008] By the way, when the rotating shaft of an electric motor or alternator is supported by a rolling bearing, a phenomenon called creep can occur where the outer ring of the rolling bearing gradually rotates relative to the housing.

[0009] That is, rolling bearings that support the rotating shaft of electric motors, alternators, etc. have an inner ring that rotates and an outer ring that non-rotates, and are therefore used with the inner ring fitted tightly around the outer periphery of the rotating shaft and the outer ring fitted loosely around the inner periphery of the housing. In this case, when the bearing rotates, minute circumferential slippage accumulates between the housing and outer ring, which are fitted loosely, and this can cause a creep phenomenon in which the outer ring gradually rotates relative to the housing.

[0010] The inventors of the present application have considered using heat-shrinkable tubing to suppress the above-mentioned creep phenomenon, and more specifically, have considered whether the above-mentioned creep phenomenon can be suppressed by using heat-shrinkable tubing when the rotating shaft of an electric motor, alternator, or the like is supported by an insulating rolling bearing having an insulating coating formed with heat-shrinkable tubing, as in Patent Document 2.

[0011] As a result of this investigation, the researchers came up with the idea that, rather than using a heat-shrinkable tube that has unidirectional heat-shrinkability (i.e., a tube that shrinks only in the radial direction when heated, with very little axial shrinkage), which is the most common and for which dimensional control during heat shrinking is easy, using a tube that has bidirectional heat-shrinkability (i.e., a tube that shrinks in both the radial and axial directions simultaneously when heated), it would be possible to form thick-walled sections that extend annularly in the circumferential direction and have a thickness greater than that of the axial centre of the portion of the insulating coating covering the outer peripheral surface of the outer ring, at both axial ends of the portion of the insulating coating covering the outer peripheral surface of the outer ring, and that the sections between these thick-walled sections would function as escape grooves to suppress creep, making it possible to suppress creep of the outer ring.

[0012] The problem this invention aims to solve is to provide an insulated rolling bearing that has low manufacturing costs and can suppress creep.

[0013] In order to solve the above problems, the present invention provides an insulating rolling bearing having the following configuration. and a resin insulating coating on the outer ring, wherein the insulating coating is formed of heat-shrinkable tubing that shrinks when heated; wherein the outer ring has a cylindrical outer peripheral surface with a constant outer diameter along the axial direction, a pair of chamfered portions with an arc-shaped cross section that gradually reduces in outer diameter from the outer peripheral surface to the axially outward, and a pair of axial end faces extending radially inward from the pair of chamfered portions; the insulating coating has a cylindrical outer peripheral covering portion that covers the outer peripheral surface of the outer ring, a pair of chamfered covering portions with an arc-shaped cross section that cover the pair of chamfered portions of the outer ring, and a pair of end face covering portions that cover the pair of axial end faces of the outer ring; and wherein thick-wall portions are formed at both axial ends of the outer peripheral covering portion and extend annularly in the circumferential direction with a thickness greater than the thickness of the outer peripheral covering portion at the axial center.

[0014] This configuration allows the insulating coating to be formed by placing a heat-shrinkable tube radially outside the outer ring and heating and deforming the heat-shrinkable tube, eliminating the need for large-scale equipment as is required when applying an insulating coating to the outer ring by insert molding. This reduces the manufacturing costs of the insulated rolling bearing. Furthermore, thick-walled sections are formed at both axial ends of the outer covering portion, extending annularly in the circumferential direction with a thickness greater than the thickness of the outer covering portion at its axial center. Therefore, the area between these thick-walled sections (the axial center of the outer covering portion) functions as a relief groove to suppress creep caused by contact between the housing and the elastically deformed portion of the outer ring due to forces from the rolling elements, thereby suppressing creep of the outer ring.

[0015] [Configuration 2] The insulating rolling bearing according to Configuration 1, wherein the outer peripheral covering portion has bidirectional thermal shrinkage properties, shrinking simultaneously in both the axial and radial directions when removed from the outer peripheral surface of the outer ring and heated.

[0016] The above configuration is obtained by placing a heat-shrinkable resin tube, which has bidirectional heat shrinkage properties that cause it to shrink simultaneously in both the radial and axial directions when heated, on the radially outer side of the outer ring, and then heating and deforming the heat-shrinkable tube to form an insulating coating.

[0017] Furthermore, this invention also provides the following configuration as a method for manufacturing the insulated rolling bearing described above. [Configuration 3] A bearing preparation step to prepare a rolling bearing having an outer ring, an inner ring disposed 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 to place a heat shrink tube having bidirectional heat shrinkability that shrinks simultaneously in both the axial and radial directions when heated on the radially outward side of the rolling bearing; and a heat shrink tube heating step after the heat shrink tube placement step, in which the heat shrink tube is heated and deformed to form a resin insulating coating having a cylindrical outer surface covering portion that covers the outer 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 face covering portions that cover the pair of axial end faces of the outer ring. A method for manufacturing an insulated rolling bearing, wherein in the heat shrink tube heating step, the inner circumference of the heat shrink tube comes into contact with the outer surface of the outer ring, thereby limiting the axial shrinkage of the portion of the heat shrink tube corresponding to the outer peripheral covering portion. Subsequently, the portions of the heat shrink tube corresponding to the chamfered covering portion and the end face covering portion are heated to shrink them in the axial and radial directions, thereby forming thickened portions extending in annular shape in the circumferential direction at both axial ends of the outer peripheral covering portion, with a thickness greater than the thickness at the axial center of the outer peripheral covering portion.

[0018] [Configuration 4] The method for manufacturing an insulated rolling bearing according to Configuration 3, wherein in the heat shrink tube heating step, end face heaters are arranged axially opposite to a pair of axial end faces of the outer ring, and the portion of the heat shrink tube corresponding to the end face covering is heated with the end face heaters.

[0019] By adopting this configuration, end face heaters are used that are positioned axially opposite to a pair of axial end faces of the outer ring. This allows for focused heating and shrinkage of the chamfered and end face coatings of the heat shrink tubing, thereby increasing the thickness of the chamfered and end face coatings. As a result, it becomes possible to effectively increase the thickness of the thickened sections at both axial ends of the outer periphery coating.

[0020] [Configuration 5] A method for manufacturing an insulating rolling bearing according to Configuration 3 or 4, wherein the heat-shrinkable tube arranging step uses a heat-shrinkable tube having an inner diameter that is 103% or less of the outer diameter of the outer ring.

[0021] By adopting this configuration, the heat shrink tubing is used in the heat shrink tubing placement process with an inner diameter of 103% or less of the outer diameter of the outer ring (i.e., a heat shrink tubing with an inner diameter the same as or close to the outer diameter of the outer ring). This makes it possible to minimize the amount of axial shrinkage that occurs in the heat shrink tubing from the start of heating until the inner circumference of the heat shrink tubing contacts the outer surface of the outer ring. As a result, it is possible to ensure sufficient axial shrinkage in the parts of the heat shrink tubing corresponding to the chamfered and end face coatings after the inner circumference of the heat shrink tubing contacts the outer surface of the outer ring, thereby increasing the thickness of the chamfered and end face coatings. Consequently, it becomes possible to effectively increase the thickness of the walled portions at both axial ends of the outer coating.

[0022] [Configuration 6] The method for manufacturing an insulating rolling bearing according to any one of Configurations 3 to 5, wherein the heat-shrinkable tube arrangement step uses a heat-shrinkable tube (10) having an axial length that is 1.6 times or more the axial width dimension of the outer ring (1).

[0023] When this configuration is adopted, the axial length of the heat-shrinkable tube is long, so that when the heat-shrinkable tube is shrunk in the axial direction by heating, the heat-shrinkable tube can reliably cover the axial end face of the outer ring.

[0024] The insulated rolling bearing of this invention can form an insulating coating by placing a heat-shrinkable tube radially outside the outer ring and heating and deforming the heat-shrinkable tube, thus eliminating the need for large-scale equipment such as insert molding to provide an insulating coating to the outer ring. Therefore, it is possible to reduce the manufacturing cost of the insulated rolling bearing. Furthermore, since thickened sections are formed at both axial ends of the outer circumferential coating, extending in an annular shape in the circumferential direction with a thickness greater than the thickness at the axial center of the outer circumferential coating, the portion between these thickened sections (the axial center portion of the outer circumferential coating) functions as a relief groove to suppress creep caused by the elastic deformation of the outer ring due to the force received from the rolling elements contacting the housing, thereby suppressing creep of the outer ring.

[0025] Figure 1 shows a cross-sectional view of an insulated rolling bearing according to an embodiment of this invention. Figure 2 shows a cross-sectional view along line II-II in Figure 1, and an enlarged view of the vicinity of the chamfered portion of the outer ring in Figure 2. Figure 1 shows a cross-sectional view of an insulated rolling bearing according to an embodiment of this invention. Figure 2 shows a flow diagram illustrating the manufacturing method of the insulated rolling bearing shown in Figure 1. Figure 5 shows a state in which the heat shrink tube is placed radially outward on the outer circumference of the outer ring before shrinkage. Figure 6 shows a state in which the heat shrink tube is further heated and shrunk when the inner circumference of the heat shrink tube is in contact with the outer circumference of the outer ring. Figure 7 shows a state in which the chamfered portion and axial end face of the outer ring are covered with the heat shrink tube. Figure 8 shows another example of the end face heaters, and Figure 2 shows an example of the insulated rolling bearing shown in Figure 2 being incorporated into an electrical device.

[0026] Figure 1 shows an insulated rolling bearing according to an embodiment of the present invention. This insulated rolling bearing comprises an outer ring 1, an inner ring 2 coaxially arranged radially inward of the outer ring 1, a plurality of rolling elements 3 spaced circumferentially between the outer ring 1 and the inner ring 2, an annular cage 4 that maintains the circumferential spacing of the plurality of rolling elements 3, and a resin insulating coating 5 provided on the outer ring 1.

[0027] The axial direction is the direction parallel to the central axis of the outer ring 1 (the central axis of the bearing), the radial direction is the direction perpendicular to the central axis of the outer ring 1, and the circumferential direction is the direction along the circumference that goes around the central axis of the outer ring 1. The outer ring 1 and inner ring 2 are formed symmetrically with respect to the axial center. Furthermore, the axially inner side is the side that approaches the axial center of the outer ring 1 and inner ring 2 along the axial direction, and the axially outer side is the side that moves away from the axial center of the outer ring 1 and inner ring 2 along the axial direction.

[0028] As shown in Figure 2, the rolling elements 3 are sandwiched radially between an outer ring raceway groove 6 formed on the inner circumference of the outer ring 1 and an inner ring raceway groove 7 formed on the outer circumference of the inner ring 2. In this example, the rolling elements 3 are balls. The outer ring raceway groove 6 and the inner ring raceway groove 7 are grooves whose cross sections perpendicular to the circumferential direction are arc-shaped. The outer ring 1, inner ring 2, and rolling elements 3 are each made of steel.

[0029] The outer ring 1 has a cylindrical outer peripheral surface 1a with a constant outer diameter along the axial direction, a pair of chamfered portions 1b with an arc-shaped cross section whose outer diameter gradually decreases axially outward from the outer peripheral 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 flat surfaces perpendicular to the axial direction.

[0030] The outer diameter of the outer peripheral surface 1a of the outer ring 1 is set to be at least 45 mm and not more than 110 mm, and the width dimension of a pair of axial end faces 1c of the outer ring 1 is set to be at least 9 mm and not more than 30 mm. The surface roughness along the axial direction of the outer peripheral surface 1a of the outer ring 1 is set to be at least Ra 0.05 μm and not more than 1.6 μm (preferably at least Ra 0.25 μm and not more than 1.0 μm). The chamfered portion 1b of the outer ring 1 has an arc-shaped surface in a cross section perpendicular to the circumferential direction that smoothly connects to the outer peripheral surface 1a of the outer ring 1, and the arc radius is set to be at least 0.3 mm (preferably at least 0.5 mm).

[0031] 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).

[0032] At both axial ends of the outer peripheral covering portion 5 a, thick-walled portions 8 are formed, which extend annularly in the circumferential direction and have a thickness greater than the thickness of the outer peripheral covering portion 5 a at the axial center. Note that in the drawing, the thickness of the insulating covering 5 is greatly exaggerated for ease of understanding.

[0033] As shown in Figure 3, the thickened portion 8 is adjacent to the chamfered coating portion 5b of the outer peripheral coating portion 5a, and has a shape in which the thickness gradually decreases toward the axially inward direction (left side in the figure). Preferably, the thickness of the thickened portion 8 is 10 μm or more greater than the thickness of the outer peripheral coating portion 5a at the axial center position. The thickness of the insulating coating 5 is set so that it has a withstand voltage of 200 V or more and an insulation resistance of 1 MΩ or more at the axial center position of the outer peripheral coating portion 5a (i.e., the thinnest position). This insulating coating 5 is formed of a heat-shrinkable resin tube that shrinks when heated, as will be described later.

[0034] An example of the manufacturing method for this insulated rolling bearing will be explained following the flow chart shown in Figure 4.

[0035] [Bearing Preparation Step] A rolling bearing 9 shown in Fig. 5 is prepared. This rolling bearing 9 has a plurality of rolling elements 3 assembled between an outer ring 1 and an inner ring 2 (see Fig. 2), and is not provided with the insulating coating 5 shown in Fig. 2.

[0036] [Heat-shrink tube arrangement process] After the above-mentioned bearing preparation process, a resin heat-shrink tube 10 is arranged radially outward of the rolling bearing 9, as shown in Figure 5. Heat-shrink tubes 10 are generally classified into two types: those that have unidirectional heat-shrinkability (those that shrink only in the radial direction when heated, out of the radial and axial directions, and shrink very little in the axial direction; specifically, those with an axial shrinkage rate of 10% or less, as described below) and those that have bidirectional heat-shrinkability (those that shrink simultaneously in both the radial and axial directions when heated). The former type of heat-shrink tube is the most common and allows for easy dimensional control during heat shrinkage, but in this embodiment, the latter type of heat-shrink tube 10 is used.

[0037] The heat-shrinkable tube 10 used has an axial shrinkage rate (the ratio of the amount of reduction in the axial length of the heat-shrinkable tube 10 when the heat-shrinkable tube 10 is completely shrunk to the axial length of the heat-shrinkable tube 10 before shrinkage) of 15% or more (preferably 20% or more, more preferably 25% or more). The heat-shrinkable tube 10 used has a radial shrinkage rate (the ratio of the amount of reduction in the inner diameter of the heat-shrinkable tube 10 when the heat-shrinkable tube 10 is completely shrunk to the inner diameter of the heat-shrinkable tube 10 before shrinkage) of 40% or more. The axial length of the heat-shrinkable tube 10 before shrinkage is set to 1.6 times or more (preferably 1.8 times or more) the axial width dimension (the distance between a pair of axial end faces 1 c) of the outer ring 1 so that the heat-shrinkable tube 10 can reliably cover the axial end faces 1 c of the outer ring 1 when the heat-shrinkable tube 10 is shrunk in the axial direction by heating in the heat-shrinkable tube heating step described below.

[0038] The heat-shrinkable tube 10 can be made by irradiating a resin material such as polyolefin resin, polyvinyl chloride resin, or fluororesin into a tube shape with an electron beam to crosslink the resin material, then stretching the tube in two directions, axially and radially, while heating it to a predetermined high temperature, and then cooling it. In this case, the dimensions of the tube after stretching correspond to the dimensions of the heat-shrinkable tube 10 before shrinkage, and the dimensions of the tube before stretching correspond to the dimensions of the heat-shrinkable tube 10 when it has been completely shrunk by heating.

[0039] Additionally, heat-shrinkable tubing 10 is used having an inner diameter that is 100% or more and 103% or less of the outer diameter of the outer peripheral surface 1a of outer ring 1. Here, to facilitate the task of positioning heat-shrinkable tubing 10 on the outside of outer ring 1, heat-shrinkable tubing 10 is used with an inner diameter that is 100% or more of the outer diameter of the outer peripheral surface 1a of outer ring 1, but it is also possible to use heat-shrinkable tubing 10 with an inner diameter that is less than 100% of the outer diameter of the outer peripheral surface 1a of outer ring 1, and fit that heat-shrinkable tubing 10 onto the outer peripheral surface 1a of outer ring 1 with an interference.

[0040] [Heat-Shrink Tube Heating Step] After the heat-shrink tube placement step described above, the heat-shrink tube 10 is heated and deformed as shown in Figures 6 and 7 to form an insulating coating 5 having a cylindrical outer peripheral covering portion 5a covering the outer peripheral surface 1a of the outer ring 1, a pair of chamfer covering portions 5b with an arc-shaped cross section covering the pair of chamfered portions 1b of the outer ring 1, and a pair of end surface covering portions 5c covering the pair of axial end surfaces 1c of the outer ring 1, as shown in Figure 2. Methods that can be used to heat the heat-shrink tube 10 include blowing hot air onto the outer periphery of the heat-shrink tube 10 using a heating gun or the like, or passing the rolling bearing 9 and the heat-shrink tube 10 positioned radially outward through a heating furnace while supported by a support. The heating temperature for the heat-shrink tube 10 can be set within a range of 70°C to 180°C (preferably 150°C or less).

[0041] Here, when heat-shrinkable tube 10 is heated and shrunk, first, as shown in FIG. 6 , the inner circumference of the portion of heat-shrinkable tube 10 facing the radially outward side of outer ring 1 comes into contact with the outer peripheral surface 1 a of outer ring 1, and the frictional force acting on the contact portion between heat-shrinkable tube 10 and outer ring 1 restricts axial shrinkage of the portion of heat-shrinkable tube 10 corresponding to outer peripheral covering portion 5 a.

[0042] Thereafter, as heating of the heat-shrinkable tube 10 continues, the portion of the heat-shrinkable tube 10 protruding in the axial direction from the contact point with the outer ring 1 (the portion corresponding to the chamfered covering portion 5b and end face covering portion 5c shown in Figure 2) shrinks further in the axial and radial directions due to the heat, covering the chamfered portion 1b and axial end face 1c of the outer ring 1, as shown in Figures 6 and 7. At this time, the portion corresponding to the chamfered covering portion 5b shown in Figure 2 shrinks in the axial direction, increasing the thickness of the chamfered covering portion 5b, and the thickness of both axial end portions of the outer peripheral covering portion 5a connected to the chamfered covering portion 5b also increases, with the result that thick-walled portions 8 are formed at both axial ends of the outer peripheral covering portion 5a, extending annularly in the circumferential direction, with a thickness greater than the thickness of the outer peripheral covering portion 5a at its axial center.

[0043] As shown in FIG. 8 , end heaters 11 are arranged axially opposite a pair of axial end faces 1 c (see FIG. 2 ) of the outer ring 1. The end heaters 11 heat the portions of the heat-shrinkable tubing 10 corresponding to the end-surface covering portions 5 c. This heat-shrinkable tubing 10 is then selectively heated and shrunk in the chamfered and end-surface covering portions 5 b and 5 c, thereby increasing the thickness of the chamfered and end-surface covering portions 5 b and 5 c. This effectively increases the thickness of the thick-walled portions 8 at both axial ends of the outer peripheral covering portion 5 a shown in FIG. 2 . The end heaters 11 shown in FIG. 8 can be hot air heaters that blow hot air in the axial direction or far-infrared heaters that radiate far-infrared rays in the axial direction. Alternatively, the end heaters 11 can be contact heaters (e.g., high-temperature jigs movable in the axial direction) that directly contact and heat the portions of the heat-shrinkable tubing 10 corresponding to the end-surface covering portions 5 c, as shown in FIG. 9 .

[0044] Furthermore, if a heat-shrinkable tube 10 having an inner diameter equal to or less than 103% of the outer diameter of the outer ring 1 (i.e., a heat-shrinkable tube 10 having an inner diameter equal to or close to the outer diameter of the outer ring 1) is used as the heat-shrinkable tube 10 before heating shown in Fig. 5 , the amount of axial shrinkage that occurs in the heat-shrinkable tube 10 from the start of heating until the inner circumference of the heat-shrinkable tube 10 comes into contact with the outer peripheral surface 1a of the outer ring 1 can be kept small. Therefore, as shown in Figs. 6 and 7 , the amount of axial shrinkage that occurs in the portions of the heat-shrinkable tube 10 corresponding to the chamfered covering portion 5b and the end face covering portion 5c after the inner circumference of the heat-shrinkable tube 10 comes into contact with the outer peripheral surface 1a of the outer ring 1 can be ensured, and the thicknesses of the chamfered covering portion 5b and the end face covering portion 5c can be increased. As a result, it is possible to effectively increase the thickness of the thick-walled portions 8 at both axial ends of the outer peripheral covering portion 5a.

[0045] As shown in Figure 10, the insulating rolling bearing of this embodiment can be used as a rolling bearing that supports a rotating shaft 12 of an electrical device (such as the rotating shaft of an electric motor, the rotating shaft of a reducer that reduces the rotation of the electric motor, or the rotating shaft of an alternator). In Figure 10, the insulating rolling bearing is mounted between the cylindrical inner periphery of a housing bore 14 formed in a non-rotating housing 13 and the outer periphery of a rotating shaft 12 located at the center of the housing bore 14. Here, the inner ring 2 is on the rotating side and the outer ring 1 is on the non-rotating side, so the insulating rolling bearing is assembled in such a manner that the inner ring 2 is fitted onto the outer periphery of the rotating shaft 12 with an interference fit, and the outer ring 1 is fitted onto the inner periphery of the housing bore 14 with a loose fit. In this case, there is a problem in that, when the bearing rotates, minute circumferential slippage accumulates between the housing 13 and outer ring 1, which are fitted together with a loose fit, and this can cause creep, in which the outer ring 1 gradually rotates relative to the housing 13.

[0046] To address this issue, the insulated rolling bearing of this embodiment has thick-walled portions 8 formed at both axial ends of the outer peripheral covering portion 5a. These thick-walled portions 8 extend annularly in the circumferential direction and have a thickness greater than the thickness of the outer peripheral covering portion 5a at its axial center. Therefore, the portions between these thick-walled portions 8 (the axial center portions of the outer peripheral covering portion 5a) function as relief grooves to suppress creep caused by contact between the housing 13 and the elastically deformed portion of the outer ring 1 due to the force applied by the rolling elements 3. This makes it possible to suppress creep of the outer ring 1. To ensure this relief groove, it is preferable to apply lubricating oil to the outer periphery of the outer peripheral covering portion 5a before assembling the insulated rolling bearing into the housing 13. In this way, the lubricating oil present between the thick-walled portions 8 of the outer peripheral covering portion 5a forms an oil film between the housing 13 and the outer ring 1. The squeeze effect of this oil film effectively suppresses creep of the outer ring 1.

[0047] 5 to 7 , this insulating rolling bearing can form the insulating coating 5 by placing heat-shrinkable tubing 10 radially outside of the outer ring 1 and heating and deforming the heat-shrinkable tubing 10, eliminating the need for large-scale equipment as is required when providing the insulating coating 5 on the outer ring 1 by insert molding. This makes it possible to reduce the manufacturing costs of the insulating rolling bearing.

[0048] Here, as shown in FIGS. 5 to 7 , when resin heat-shrinkable tubing 10, which has bidirectional heat-shrinkability, shrinking simultaneously in both the radial and axial directions when heated, is positioned radially outside of outer ring 1 and insulating coating 5 is formed by heating and deforming heat-shrinkable tubing 10, outer peripheral coating portion 5 a of insulating coating 5 will have bidirectional heat-shrinkability, shrinking simultaneously in both the axial and radial directions when removed from the outer peripheral surface 1 a of outer ring 1 and heated.

[0049] 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 in 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 in the same axial position as the axial end face 2c of the inner ring 2.

[0050] 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.

[0051] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0052] REFERENCE SIGNS LIST 1 outer ring 1a outer peripheral surface 1b chamfered portion 1c axial end face 2 inner ring 2c axial end face 3 rolling element 5 insulating coating 5a outer peripheral coating portion 5b chamfered coating portion 5c end face coating portion 8 thick portion 9 rolling bearing 10 heat shrinkable tube 11 end face heater

Claims

1. An insulated rolling bearing comprising an outer ring (1), an inner ring (2) disposed 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 (10) that shrinks when heated, wherein the outer ring (1) has a cylindrical outer peripheral surface (1a) having a constant outer diameter along the axial direction, a pair of chamfered portions (1b) with an arc-shaped cross section whose outer diameter gradually decreases from the outer peripheral surface (1a) toward the axially outward direction, 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) that have an arc-shaped cross section and cover the pair of chamfered portions (1b) of the outer ring (1), and a pair of end surface coating portions (5c) that cover the pair of axial end surfaces (1c) of the outer ring (1), and thick-walled portions (8) are formed at both axial ends of the outer peripheral coating portion (5a) and extend annularly in the circumferential direction with a thickness greater than the thickness of the outer peripheral coating portion (5a) at the axial center.

2. An insulating rolling bearing as described in claim 1, wherein the outer peripheral covering portion (5a) has bidirectional heat shrinkability, shrinking simultaneously in both the axial and radial directions when removed from the outer peripheral surface (1a) of the outer ring (1) and heated.

3. A bearing preparation step of preparing a rolling bearing (9) having an outer ring (1), an inner ring (2) arranged radially inside the outer ring (1), and a plurality of rolling elements (3) assembled between the outer ring (1) and the inner ring (2), wherein the outer ring (1) has a cylindrical outer peripheral surface (1a) with a constant outer diameter along the axial direction, a pair of chamfered portions (1b) with an arc-shaped cross section whose outer diameter gradually decreases from the outer peripheral surface (1a) toward the axially outer side, and a pair of axial end surfaces (1c) extending radially inward from the pair of chamfered portions (1b); and a heat-shrinkable tube arrangement step of arranging a resin heat-shrinkable tube (10) radially outside the rolling bearing (9), the heat-shrinkable tube having bidirectional heat-shrinkability that shrinks simultaneously in both the axial and radial directions when heated. a heat-shrinkable tube heating step of heating and deforming the heat-shrinkable tube (10) after the heat-shrinkable tube arrangement step to form an insulating coating (5) having a cylindrical outer peripheral covering portion (5a) covering the outer peripheral surface (1a) of the outer ring (1), a pair of chamfered covering portions (5b) having an arc-shaped cross section covering the pair of chamfered portions (1b) of the outer ring (1), and a pair of end face covering portions (5c) covering the pair of axial end faces (1c) of the outer ring (1), In the heat-shrinkable tube heating step, the inner circumference of the heat-shrinkable tube (10) comes into contact with the outer peripheral surface (1 a) of the outer ring (1), thereby restricting axial shrinkage of the portion of the heat-shrinkable tube (10) corresponding to the outer peripheral covering portion (5 a), and then the portions of the heat-shrinkable tube (10) corresponding to the chamfered covering portion (5 b) and the end face covering portion (5 c) are heated to shrink them in the axial and radial directions, thereby forming thick-walled portions (8) at both axial ends of the outer peripheral covering portion (5 a) that extend annularly in the circumferential direction and have a thickness greater than the thickness of the outer peripheral covering portion (5 a) at the axial center.

4. A method for manufacturing an insulated rolling bearing as set forth in claim 3, wherein the heat-shrinkable tube heating step uses end surface heaters (11) arranged axially opposite a pair of axial end surfaces (1c) of the outer ring (1), and the end surface heaters (11) heat the portions of the heat-shrinkable tube (10) corresponding to the end surface covering portions (5c).

5. A method for manufacturing an insulating rolling bearing as described in claim 3 or 4, wherein in the heat shrink tube placement process, the heat shrink tube (10) has an inner diameter that is 103% or less of the outer diameter of the outer ring (1).

6. A method for manufacturing an insulating rolling bearing as described in claim 3 or 4, wherein the heat shrink tube arrangement step uses a heat shrink tube (10) having an axial length that is 1.6 times or more the axial width dimension of the outer ring (1).

Images