Rolling bearing and manufacturing method thereof

Abstract

The present invention provides a rolling bearing which achieves a long service life without increasing the cost. In this rolling bearing, a plurality of rolling bodies (3) are held between an outer ring (2) and an inner ring (1) at regular intervals in a rollable manner by means of a retainer (4), and this rolling bearing is filled with a lubricant G. The retainer (4) is a resin retainer, and at least one of the outer ring (2), the inner ring (1), and each of the rolling bodies (3) has a coating film that is derived from a constituent material of the resin retainer. It is preferable that the resin retainer is formed of a polyamide resin composition that contains glass fibers, and that the coating film is formed of a nitrogen compound that contains SiO2.

Description

[Technical Field]

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

[0002] A rolling bearing is generally constructed by holding a plurality of rolling elements between an outer ring and an inner ring at equal intervals by a cage so that they can roll freely, and filling a bearing space formed by the outer ring, inner ring, and rolling elements with a lubricant. Metal cages made of iron or other metals are often used as the cage, as in Patent Document 1, for example. Metal cages have advantages such as being strong and being easily manufactured by machining, such as press working.

[0003] Furthermore, in rolling bearings, if the outer and inner rings and rolling elements are all made of metal, there is a problem that the outer and inner rings come into metallic contact with the rolling elements, causing wear and seizure. For this reason, measures have been taken such as making the rolling elements out of ceramic as in Patent Document 2, or applying a hardening treatment to the outer ring raceway surface, inner ring raceway surface, and rolling element surfaces as in Patent Document 3. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2014-224608 [Patent Document 2] Japanese Patent Application Publication No. 2015-209936 [Patent Document 3] Japanese Patent Publication No. 2022-189424 Summary of the Invention [Problem to be solved by the invention]

[0005] However, as shown in Test 1 described later, rolling bearings using iron cages have a shorter lifespan than rolling bearings using plastic cages.

[0006] Furthermore, ceramic rolling elements are expensive, and if they are subjected to hardening treatment, a separate process is required, which increases the manufacturing cost.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a rolling bearing having a long life without increasing costs. [Means for solving the problem]

[0008] The inventors discovered that when a resin cage is used, a coating derived from the constituent material of the cage is formed on the inner ring, outer ring, and rolling elements, and this led to the completion of the present invention. That is, the above-mentioned object of the present invention is achieved by the following rolling bearing configuration [1].

[0009] [1] A rolling bearing comprising a plurality of rolling elements held by a cage between an outer ring and an inner ring so as to be freely rollable at equal intervals, and filled with a lubricant, The cage is a resin cage, A rolling bearing characterized in that at least one of the outer ring, the inner ring, and the rolling elements has a coating derived from the constituent material of the resin cage.

[0010] Further, preferred embodiments of the present invention relating to the rolling bearing relate to the following [2] to [5].

[0011] [2] The rolling bearing according to [1], wherein the coating contains SiO2. [3] The rolling bearing according to [1] or [2], wherein the resin cage is made of a resin composition containing glass fibers. [4] The rolling bearing according to [3], wherein the base resin of the resin composition is polyamide, and the coating is a nitrogen compound containing SiO2. [5] The rolling bearing according to any one of [1] to [4], wherein the lubricant is an additive-free lubricating oil or a grease composition based on an additive-free lubricating oil.

[0012] The above object of the present invention is achieved by the following configuration [6] relating to a method for manufacturing a rolling bearing.

[0013] [6] A method for manufacturing a rolling bearing in which a plurality of rolling elements are held by a cage between an outer ring and an inner ring so as to be freely rollable at equal intervals and filled with a lubricant, A resin cage is used as the cage, a coating derived from a constituent material of the resin cage formed on at least one of the outer ring, the inner ring, and the rolling elements by rotating the rolling bearing.

[0014] Furthermore, preferred embodiments of the present invention relating to a method for manufacturing a rolling bearing relate to the following [6] to

[10] .

[0015] [7] The method for manufacturing a rolling bearing according to [6], wherein a coating containing SiO2 is formed as the coating. [8] A method for manufacturing a rolling bearing according to [6] or [7], in which the resin cage contains glass fiber. [9] The method for manufacturing a rolling bearing according to any one of [6] to [8], wherein the base resin of the resin cage is polyamide, and the coating film is formed of a nitrogen compound containing SiO2.

[10] The method for producing a rolling bearing according to any one of [6] to [9], wherein the lubricant used is an additive-free lubricating oil or a grease composition based on an additive-free lubricating oil. [Effects of the Invention]

[0016] According to the present invention, a resin cage is used and a coating derived from the constituent material of the resin cage is formed on at least one of the outer ring, inner ring, and rolling elements, thereby preventing direct contact between the inner and outer rings and the rolling elements, suppressing seizure and providing a rolling bearing with a long life. Furthermore, simply by incorporating the resin cage, a coating can be formed as the bearing rotates, eliminating the need for hardening processes and the like, and there is no increase in manufacturing costs. [Brief explanation of the drawings]

[0017] [Figure 1]FIG. 1 is a cross-sectional view that schematically shows a ball bearing, which is an example of the rolling bearing of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing a measuring device used to measure the thickness of the oil film on the rolling surface in the examples. [Figure 3] Figure 3 is a graph showing the test results of the test bearing using an iron cage in Test 1, where (A) shows the change in outer ring temperature per rotation time, (B) shows the change in lubricating film thickness in the gap between the inner ring raceway surface and the ball rolling surface per rotation time, and (C) shows the change in impedance per rotation time. [Figure 4] FIG. 4 is a graph showing the test results of the test bearing using a resin cage in Test 1, where (A) shows the change in outer ring temperature per rotation time, (B) shows the change in lubricating film thickness in the gap between the inner ring raceway surface and the ball rolling surface per rotation time, and (C) shows the change in impedance per rotation time. [Figure 5] FIG. 5 is a graph showing the results of Test 2. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and can be implemented with any modifications within the scope of the gist of the present invention.

[0019] [Rolling bearings] In the present invention, there is no limitation on the type of rolling bearing, and an example is the ball bearing shown in Fig. 1. Note that Fig. 1 is a cross-sectional view showing a ball bearing in schematic form. The ball bearing shown in the figure is roughly configured such that a plurality of rolling elements, i.e., balls 3, are held by a cage 4 between an inner ring raceway surface 1a formed on the outer peripheral surface of an inner ring 1 and an outer ring raceway surface 2a formed on the inner peripheral surface of an outer ring 2, and a seal 5 seals in lubricant G filled in a bearing space 6 formed by the inner ring 1, the outer ring 2, and the balls 3. Note that reference numeral 2b denotes a seal fitting groove provided in the outer ring 2.

[0020] Furthermore, the inner ring 1, outer ring 2 and balls 3 may all be made of metal, and there is no need to use ceramic balls or to apply hardening treatment.

[0021] In the present invention, a resin cage is used as the cage 4, and a coating (hereinafter referred to as the "specific coating") derived from the constituent material of the resin cage is formed on at least one of the inner ring 1, outer ring 2, and balls 3; more specifically, at least one of the inner ring raceway surface 1a, outer ring raceway surface 2a, and rolling surfaces of the balls 3. This specific coating is formed when the resin cage wears as the bearing rotates, and wear powder made from the constituent material rolls onto the inner ring raceway surface 1a, outer ring raceway surface 2a, and rolling surfaces of the balls 3. As a result, the inner ring 1 and outer ring 2 do not come into direct contact with the balls 3, preventing seizure even though the inner ring 1, outer ring 2, and balls 3 are all made of metal, thereby extending the life of the rolling bearing. In other words, the specific coating acts like a protective film to prevent seizure.

[0022] The resin cage is preferably made of a resin composition containing glass fiber for reinforcement, and therefore, SiO2 is present in the specific coating.

[0023] Considering the heat resistance and strength of the resin cage, polyamide, polyphenylene sulfide, polyether ether ketone, polyamide imide, polyether imide, etc. are suitable as the base resin of the resin composition, but polyamide is preferred because of its versatility and low cost. When polyamide is used as the base resin, the specific coating contains a nitrogen compound as well as SiO2.

[0024] There are no limitations on the thickness of the specific coating, but it is preferably 1 nm or more, and more preferably 10 nm or more. If the thickness is less than 1 nm, there is a risk that the effect of preventing seizure will not be sufficient.

[0025] The lubricant G is not limited and may be either a lubricating oil or a grease composition, although additive-free base oils for the lubricating oil and grease composition are preferred. By additive-free, we mean lubricating oils or base oils that do not contain the various additives typically used in lubricating oils filled into bearings or base oils for grease compositions, such as antioxidants (e.g., amine-based, phenol-based, sulfur-based, zinc dithiophosphate, zinc dithiocarbamate), rust inhibitors (e.g., metal sulfonates, ester-based, amine-based, metal naphthenate, succinic acid derivatives), extreme-pressure agents (e.g., phosphorus-based, zinc dithiophosphate, organic molybdenum), oiliness improvers (e.g., fatty acids, animal and vegetable oils), and metal deactivators (e.g., benzotriazole). In the present invention, a specific coating is formed on the inner ring 1, outer ring 2, and ball 3, but if the lubricating oil or base oil contains additives, the additives are likely to adversely affect the formation of the specific coating.

[0026] There are no limitations on the type of lubricating oil itself and the base oil itself, and any of mineral oil, synthetic oil, and natural oil may be used. Mineral oils can be those refined by an appropriate combination of vacuum distillation, oil deasphalting, solvent extraction, hydrocracking, solvent dewaxing, sulfuric acid washing, clay refining, hydrorefining, etc. Synthetic oils include hydrocarbon oils, aromatic oils, ester oils, ether oils, etc. Natural oils include beef tallow, lard, soybean oil, rapeseed oil, rice bran oil, coconut oil, palm oil, palm kernel oil, and other oils, as well as hydrogenated versions of these. There are also no limitations on viscosity, but considering the lubrication of rolling bearings, a kinematic viscosity of 5 to 400 mm at 40°C is preferred. 2 / s is preferred.

[0027] [Manufacturing method] As described above, by using a resin cage, the specific coating is formed as the bearing rotates on at least one of the inner ring raceway surface 1a, the outer ring raceway surface 2a, and the rolling surfaces of the balls 3. At this time, the rotation conditions of the bearing, such as the rotation speed, temperature, preload, and rotation time, are controlled to achieve the desired film thickness, preferably 1 nm or more.

[0028] Furthermore, as shown in Test 1 in the Examples section below, when a resin cage is used, the impedance remains high even when the bearing rotation is stopped at a certain point. This is thought to be because the specific coating remains even after the bearing has stopped, giving the cage a longer life than an iron cage.

[0029] Taking these factors into consideration, in the manufacturing method of a rolling bearing, a resin cage is used as the cage 4, and after the bearing is assembled, the rotation conditions of the bearing are controlled so that rotation is stopped when a predetermined film thickness is reached. Also, it is preferable that the base resin of the resin cage is polyamide, and that it is filled with additive-free lubricating oil or a grease composition whose base oil is additive-free lubricating oil.

[0030] Therefore, according to the present invention, there are no restrictions on the materials of the inner ring 1, outer ring 2, and balls (rolling elements) 3, and no additional steps such as hardening treatment are required, which does not increase manufacturing costs. [Example]

[0031] The present invention will be further clarified by the following test examples.

[0032] (Test 1) The test bearing was assembled using a resin cage made of polyamide 66 and an iron cage for the bearing number "608". The lubricant was additive-free poly-α-olefin oil (kinematic viscosity: 130 mm 2 / s, 40°C) was used. A life test was carried out on both test bearings using a test device 200 shown in FIG.

[0033] In the testing apparatus 200, a test bearing 210 rotatably supports a rotating shaft 220. The rotating shaft 220 is rotated by a motor 230. The rotating shaft 220 is also connected to an LCR meter 250 via a rotary connector 240. The rotary connector 240 is configured using, for example, carbon brushes, and the test bearing 210 is electrically connected to the LCR meter 250. The angular frequency ω and AC voltage V of an AC power source are input to the LCR meter 250, and in response, the LCR meter 250 outputs the impedance of the test bearing 210. The thickness of the lubricating coating is then determined using information on the AC voltage V of the angular frequency ω and the relative permittivity at the high frequency limit.

[0034] The test involved applying an alternating current of 0.2 V and 1 MHz frequency to testing equipment 200, and continuously rotating test bearing 210 at 6,000 rpm under conditions of an axial load of 32 N, a radial load of 0 N, and a maximum contact load of 1.0 GPa, to determine the relationship between rotation time and lubricant coating thickness. The outer ring temperature of the test bearing was set to 150°C, and rotation was stopped when the temperature rose by 10°C, indicating that seizure had occurred.

[0035] Figure 3 shows the test results for a test bearing using an iron cage. (A) shows the change in outer ring temperature per rotation time t (min), (B) shows the change in lubricant film thickness in the gap between the inner ring raceway surface and the ball rolling surface per rotation time t (min), and (C) shows the change in impedance per rotation time t (min). Figure 4 shows the test results for a test bearing using a resin cage, where (A) is the change in outer ring temperature per rotation time t (min), (B) is the change in lubricant film thickness in the gap between the inner ring raceway surface and the ball rolling surface per rotation time t (min), and (C) is the change in impedance per rotation time t (min).

[0036] As shown in Figure 3(A), in the test bearing using an iron cage, after 300 minutes of rotation, the outer ring temperature of the test bearing began to rise more rapidly than initially, which was thought to be causing seizure, so the rotation was stopped. Also, as shown in Figure 3(B), the thickness of the lubricating film had decreased significantly at the time of stopping, and as shown in Figure 3(C), the impedance also decreased significantly. The decrease in impedance means that the amount of oil film was small and that the amount of metal-to-metal contact between the inner and outer rings and the balls was relatively large.

[0037] In contrast, in the test bearings using a resin cage, as shown in Figure 4(A), the rise in outer ring temperature was kept to within 10°C even after 3,500 minutes of rotation, and no seizure occurred. Furthermore, as shown in Figure 4(B), there is a tendency for the amount of coating to increase with rotation, and as shown in Figure 4(C), the impedance also increases. Furthermore, although rotation was stopped after 3,500 minutes, the result of continuing to measure the impedance, as shown in Figure 4(C), shows that the impedance remained high, indicating that a sufficient amount of coating remained even after rotation was stopped.

[0038] Furthermore, when the inner ring raceway surfaces of both test bearings were observed with an SEM after the rotation had stopped, spotty deposits were found on the rolling surface of the test bearing with a plastic cage, whereas no deposits were found on the test bearing with an iron cage. Component analysis of the deposits detected components derived from the polyamide 66 in the plastic cage. This suggests that the presence of components derived from the polyamide 66 in the deposits acts like a protective film, preventing seizure and contributing to extending the lubrication life.

[0039] (Test 2) A ball bearing with the bearing number "608" was assembled using a resin cage made of glass fiber-containing polyamide 66. The lubricant was additive-free poly-α-olefin oil (kinematic viscosity: 130 mm 21 mg of a ball bearing (1000 rpm, 40°C) was used. Using the test apparatus 200 shown in Figure 2, an alternating current of 0.2 V and 1 MHz frequency was applied to the test apparatus 200, and an axial load of 32 N, a radial load of 0 N, and a maximum contact load of 1.0 GPa were applied to the assembled ball bearing. The ball bearing was then rotated continuously at 6000 rpm for 3500 minutes with the outer ring temperature at 150°C.

[0040] After stopping the rotation, the inner ring raceway surface was observed with an SEM, and the location where the deposits were present was selected and subjected to ESCA analysis (Electron Spectroscopy for Chemical Analysis) in the depth direction. The results are shown in Figure 5(A), and a clear peak due to SiO2 was detected down to a depth of 10 nm. This peak due to SiO2 is thought to be caused by glass fibers in the resin cage.

[0041] In addition, a similar ESCA analysis was performed on a ball bearing that was not rotating immediately after assembly, but no peaks derived from SiO2 were detected, as shown in Figure 5(B).

[0042] Tests 1 and 2 show that using a plastic cage results in a longer life than a metal cage, and that a specific coating derived from the constituent components of the plastic cage is formed as the bearing rotates.

[0043] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0044] This application is based on a Japanese patent application (Patent Application No. 2023-088743) filed on May 30, 2023, the contents of which are incorporated herein by reference. [Explanation of symbols]

[0045] 1. Inner circle 2 outer ring 3 balls (rolling elements) 4 Cage 5 Seals 6 Bearing space G. Lubricant

Claims

1. A rolling bearing comprising a plurality of rolling elements held by a cage between an outer ring and an inner ring so as to be freely rollable at equal intervals, and filled with a lubricant, The cage is a resin cage, a coating derived from a constituent material of the resin cage is provided on at least one of the outer ring, the inner ring, and the rolling elements; A rolling bearing characterized in that SiO 2 is present in the coating.

2. 2. The rolling bearing according to claim 1, wherein the resin cage is made of a resin composition containing glass fibers.

3. The base resin of the resin composition is polyamide, and the coating is SiO ２ 3. The rolling bearing according to claim 2, wherein the nitrogen compound contains:

4. 2. The rolling bearing according to claim 1, wherein the lubricant is an additive-free lubricating oil or a grease composition containing an additive-free lubricating oil as a base oil.

5. A method for manufacturing a rolling bearing comprising a plurality of rolling elements held by a cage between an outer ring and an inner ring so as to be freely rollable at equal intervals, and filled with a lubricant, comprising: A resin cage is used as the cage, A method for manufacturing a rolling bearing, characterized in that a coating containing SiO 2 derived from a constituent material of the resin cage is formed on at least one of the outer ring, the inner ring, and the rolling elements by rotating the rolling bearing.

6. 6. The method for manufacturing a rolling bearing according to claim 5, wherein the resin cage contains glass fiber.

7. The base resin of the resin cage is polyamide, and SiO ２ The method for producing a rolling bearing according to claim 6, wherein the coating is formed using a nitrogen compound containing

8. 6. The method for producing a rolling bearing according to claim 5, wherein the lubricant is an additive-free lubricating oil or a grease composition based on an additive-free lubricating oil.

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