Oil-repellent treatment method for thrust ball bearings

Abstract

To retain an oil amount even in an environment where only a small amount of a lubrication oil is provided to prevent seizure in a thrust ball bearing.SOLUTION: A thrust ball bearing has: multiple balls: a bearing ring 31 having an annular raceway surface 31a on which the balls roll; and a retainer which holds the balls in a rollable manner. An oil repellent film 41a is provided on a portion, excluding a portion which contacts with the balls, of the raceway surface 31a by oleophobic processing.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a thrust ball bearing. [Background technology]

[0002] In the automotive field, automobiles are becoming more electric, smaller, and faster in order to improve fuel efficiency. Accordingly, bearings are being filled with lubricating oil instead of grease, or lubricating oil is applied to the rolling elements and raceway surfaces to reduce torque. Furthermore, the amount of lubricating oil used is being reduced to reduce loss due to lubricating oil.

[0003] However, there is concern that a reduction in the amount of oil will result in a lack of lubricating oil, which can cause damage such as seizure. When a bearing rotates at high speed, the lubricating oil that lubricates the rolling elements and raceway surfaces is moved to the outside by centrifugal force. Therefore, if the supply is cut off or the amount of oil supplied is small, the lubricating oil will gradually decrease, and eventually seizure will occur.

[0004] Therefore, for example, Patent Document 1 discloses a technology relating to a bearing device in which an oil-repellent coating is formed on the outer peripheral surface of the inner ring and the inner peripheral surface of the outer ring in a first region P1 and a second region P2 excluding the rotating raceway groove and the fixed raceway groove. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-125550 A Summary of the Invention [Problem to be solved by the invention]

[0006] Incidentally, thrust ball bearings are used in transmissions for automobiles and industrial construction machinery, and are also widely used in other rotating equipment, and are preferably used for high-speed rotation applications. However, thrust ball bearings have a problem that they are prone to seizure, particularly in environments with a small amount of lubricating oil, because structural constraints make it impossible to use sealing members such as seals, and lubricating oil is prone to leak outside the bearing due to centrifugal force.

[0007] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a thrust ball bearing that can retain an amount of lubricating oil and prevent seizure even in an environment where the amount of lubricating oil is small. [Means for solving the problem]

[0008] The object of the present invention is achieved by the following thrust ball bearing configuration (1). (1) A thrust ball bearing comprising a plurality of balls, a raceway having an annular raceway surface on which the balls roll, and a cage that holds the balls so that they can roll, a thrust ball bearing, wherein the raceway surface is subjected to an oil repellent treatment except for a portion that comes into contact with the balls.

[0009] Further, preferred embodiments of the present invention relating to the thrust ball bearing relate to the following (2) and (3). (2) A thrust ball bearing as described in (1) above, wherein a portion of the raceway surface radially outward from the portion that comes into contact with the balls is subjected to an oil repellent treatment. (3) A thrust ball bearing as described in (1) or (2) above, wherein a portion of the raceway surface that is radially inward of the portion that comes into contact with the balls is subjected to an oil repellent treatment. Effect of the Invention

[0010] According to the thrust ball bearing of the present invention, the annular raceway surface of the raceway ring is treated with an oil repellent treatment on the portion other than the portion that comes into contact with the balls, so that even if the lubricating oil held between the raceway surface and the balls attempts to move out of the bearing due to centrifugal force, it is blocked by the oil repellent treated portion and is prevented from moving any further. Therefore, even in a thrust ball bearing with a particularly low oil volume, a sufficient amount of oil is held, and seizure can be effectively prevented. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a partially cutaway perspective view showing a thrust ball bearing. [Diagram 2] FIG. 2 is a diagram for explaining a method of applying an oil repellent treatment to the raceway surface of the raceway ring. [Diagram 3] FIG. 3 is a diagram for explaining another method of applying an oil repellent treatment to the raceway surface of the raceway ring. [Figure 4] FIG. 4 is a graph showing the results of plotting the cumulative probability of breakage (%) against the life (hours) for the products of the examples and the products of the comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will now be described in detail with reference to the drawings.

[0013] 1 is a partially cutaway perspective view showing the structure of a thrust ball bearing. As shown in the figure, a thrust ball bearing 30 includes a fixed raceway 31 and a rotating raceway 32 that are opposed to each other, a plurality of balls 33 that are disposed between the fixed raceway 31 and the rotating raceway 32 so as to be able to roll therebetween, and a cage 34 that holds the balls 33 so as to be able to roll.

[0014] The multiple balls 33 are held at regular intervals in the circumferential direction of the fixed raceway 31 and the rotating raceway 32 by a cage 34. The cage 34 is formed by pressing a steel plate of a uniform thickness, and has ball pockets 34a that hold the balls 33, and outer flanges 34b and inner flanges 34c that are bent in the axial direction from both radial ends of the surface having the ball pockets 34a to hold the balls. The outer flanges 34b and inner flanges 34c are pressed into a corrugated shape.

[0015] In this embodiment, at least one, and preferably both, of the raceway surface 31a of the fixed raceway ring 31 and the raceway surface 32a of the rotating raceway ring 32 are subjected to an oil-repellent treatment (not shown) on the raceway surfaces 31a, 32a other than the portions that come into contact with the balls 33. More specifically, in this embodiment, of the raceway surfaces 31a, 32a, both the radially outer and radially inner portions of the portions that come into contact with the balls 33 are subjected to an oil-repellent treatment.

[0016] The oil repellent treatment is carried out, for example, by the steps shown in Figs. 2(a) to (d).

[0017] First, as shown in FIG. 2(a), annular masking tape 40 is adhered to each of raceway surface 31a of fixed raceway ring 31 and raceway surface 32a of rotating raceway ring 32. For convenience of explanation, FIG. 2 shows only raceway surface 31a of fixed raceway ring 31. The width of masking tape 40 is preferably equal to or slightly longer than the radial length of the concave surface with which balls 33 come into contact. By adhering masking tape 40, only the outer peripheral portion of raceway surface 31a (radially outward from the portion of raceway surface 31a that comes into contact with balls 33) and the inner peripheral portion (radially inward from the portion of raceway surface 31a that comes into contact with balls 33) are exposed.

[0018] 2(b), an oil-repellent liquid 41 is evenly applied to the entire surface of the raceway surface 31a including the portion covered with the masking tape 40. Examples of a method for applying the oil-repellent liquid 41 include spray coating using a spray 42 and roller coating.

[0019] The oil repellent liquid 41 contains an oil repellent, a solvent, a binder, etc. As described below, this oil repellent liquid 41 becomes an oil repellent film 41a on the raceway surfaces 31a, 32a after drying. Suitable oil repellents include fluorine-based surfactants, fluorine-based silane coupling agents, fluorine-based polymers, etc. To improve the applicability, these may be dissolved in a solvent, or a binder may be used in combination.

[0020] 2(c), the oil-repellent liquid 41 is dried to form an oil-repellent film 41a on the raceway surface 31a. The drying may be performed at room temperature, but may be heated if necessary.

[0021] After drying, as shown in FIG. 2(d), the adhered masking tape 40 is peeled off, leaving an oil-repellent film 41a on each of the outer and inner peripheral portions of the raceway surface 31a, and a fixed raceway ring 31 is obtained in which the raceway surface 31a is exposed in the radial center portion corresponding to the width of the masking tape 40 sandwiched between the two portions.

[0022] Another method for the oil repellent treatment is, for example, performed through the steps shown in Figs. 3(a) to (d).

[0023] First, as shown in FIGS. 3(a) and 3(b), the fixed race 31 is prepared, and the oil repellent liquid 41 is uniformly applied to the entire raceway surface 31a using, for example, a spray .

[0024] Next, as shown in FIG. 3(c), the applied oil-repellent liquid 41 is dried to form an oil-repellent film 41a on the entire surface of the raceway surface 31a. As described below, the oil-repellent film 41a formed on the entire raceway surface 31a is peeled off from the portion of the raceway surface 31a that is in contact with the balls 33 by rotating the bearing, but it is sufficient that the peeled-off oil repellent does not act as a foreign matter, and that the hardness of the components (oil repellent, etc.) of the oil repellent liquid 41 is sufficiently small compared to the hardness of the raceways 31, 32 and balls 33. Suitable oil repellents for achieving the above purpose include the above-mentioned fluorine-based surfactants, fluorine-based silane coupling agents, fluorine-based polymers, etc.

[0025] Next, although not shown, the thrust ball bearing 30 is assembled using a cage incorporating the balls 33, the fixed raceway 31 on which the oil repellent film 41a is formed as described above, and the rotating raceway 32 on which the oil repellent film 41a is formed in a similar manner. A predetermined lubricant is then applied to the balls 33, and the bearing is rotated with a predetermined load applied.

[0026] After the rotation is stopped after a predetermined time has elapsed, the bearing is washed with oil, whereby, as shown in Figure 3(d), there is no oil-repellent film 41a on the portion of the raceway surface (in Figure 3, the raceway surface 31a of the fixed raceway 31) that is in contact with the balls 33, and a raceway surface having oil-repellent films 41a formed on both the outer and inner portions of the raceway surface is obtained.

[0027] The above describes an example of the oil repellent treatment method.

[0028] In the thrust ball bearing 30 obtained in this manner, the annular raceway surfaces 31a, 32a of the raceways 31, 32 are treated with an oil repellent coating on the portions other than those in contact with the balls 33, and have an oil repellent coating 41a, so that even if the lubricating oil held between the raceway surfaces 31a, 32a and the balls 33 attempts to move outside the bearing due to centrifugal force, for example, it is blocked by the oil repellent coating (i.e., the portion on which the oil repellent coating 41a is formed) and is prevented from moving any further. Therefore, even in the thrust ball bearing 30 with a particularly low oil volume, a sufficient amount of oil is held, and seizure can be effectively prevented.

[0029] In the above embodiment, the raceway surfaces 31a, 32a are shown to have an oil-repellent treatment applied to both the radially outer and inner portions of the raceway surfaces 31a, 32a relative to the points of contact with the balls 33, but the oil-repellent treatment may also be applied to at least one of the radially outer and radially inner portions.

[0030] Furthermore, as the thrust ball bearing 30 rotates, the lubricating oil held between the raceway surfaces 31a, 32a and the balls 33 is more likely to move radially outward than radially inward due to centrifugal force, so in order to effectively prevent the lubricating oil from leaking out of the bearing, it is preferable that at least the radially outward portion be treated to be oil-repellent. However, in order to also effectively prevent the lubricating oil from leaking out radially inward, it is even more preferable that the oil-repellent treatment be applied to both the radially outward and radially inward portions.

[0031] Incidentally, there is no limitation to the configuration of the thrust ball bearing 30 itself, and it may be, for example, a single type that receives an axial load in one direction, or a double type that receives an axial load in both directions. Also, the outer diameter side of the raceways 31 and 32 may be provided with a flange (rib) extending in an axial direction perpendicular to the raceway surfaces 31a and 32a. In particular, by providing a flange on the radially outer side of the rotating raceway 32, the movement of lubricating oil to the outside due to centrifugal force can be more effectively suppressed.

[0032] Also, the cage 34 may be formed by molding two plates, combining them and crimping them to hold the balls 33. Furthermore, the cage 34 may be made of a pressed steel plate, a synthetic resin, or a copper alloy. There are no particular limitations on the lubricating oil, and any commonly used lubricating oil may be used. EXAMPLES

[0033] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

[0034] (Preparation of test bearings) The following thrust ball bearings were prepared. Ball bearing type: Single thrust ball bearing, model number 51305 (manufactured by NSK Ltd.) -Ring material: SUJ2 (high carbon chromium bearing steel specified in JIS G 4805) · Cage material: 66 nylon Ball material: SUJ2 (high carbon chromium bearing steel material specified in JIS G 4805) Number of balls: 6

[0035] Following the process shown in FIG. 3, the raceway surface of the raceway ring was subjected to a predetermined oil repellent treatment. First, the raceway 31 was degreased with an organic solvent, and then an oil-repellent liquid 41 containing PTFE (polytetrafluoroethylene) and a cellulose-based binder was sprayed evenly over the entire surface of the raceway 31 (Fig. 3(b)). It was then dried at room temperature (25°C) for two hours (Fig. 3(c)). Next, the oil-repellent film formed over the entire raceway surface of the raceway was removed from the areas that came into contact with the balls by the following procedure (Fig. 3(d)).

[0036] First, a test bearing was made using a cage incorporating raceways and balls, and this test bearing was placed in a test machine housing, and 1 ml of additive-free turbine oil, ISO-VG32, was applied to the test bearing. Next, the test machine housing with the test bearing placed in it was placed in the test machine. Next, a load of 600 kgf was applied, and the bearing was rotated at a rotation speed of 2000 rpm for 10 seconds. After the rotation was stopped, the test bearing was taken out and washed with heptane.

[0037] (Seizure test) For the example, a thrust ball bearing was prepared incorporating a raceway ring with an oil-repellent film formed on the raceway surface by the above-mentioned method, and for the comparative example, a thrust ball bearing was prepared incorporating a raceway ring with no oil-repellent treatment on the raceway surface. Each thrust ball bearing was degreased and cleaned with heptane, and after being installed in a housing, a load was applied and rotation was started. The test conditions were as follows, reproducing an environment in which the supply of lubricating oil was cut off. After rotation began, the point at which the bearing torque exceeded five times the initial value was determined to be "seizure" and the test was discontinued. [Test conditions] Lubricant type: ISO-VG32 additive-free turbine oil Lubricant quantity: 1ml (initial supply only) Load capacity: 600kgf Rotational speed: 2000 rpm ·Temperature: Room temperature (25℃)

[0038] The test results of the thrust ball bearings according to the embodiment and comparative examples are shown in Fig. 4. Fig. 4 is a plot (Weibull plot) of the cumulative probability of failure (%) against the life (hours) for each of the embodiment and comparative examples. In FIG. 4, data indicated by "●" indicates the case where the oil-repellent treatment was applied (Example), and data indicated by "□" indicates the case where the oil-repellent treatment was not applied (Comparative Example).

[0039] The meanings of "e", "L10" and "L50" in FIG. 4 are as follows: "e": An index that represents the variability of the lifespan. The smaller the variability of the lifespan data, the larger this value. "L10": This indicates the time (or total number of revolutions, etc.) that 90% of bearings can rotate without suffering damage due to rolling fatigue, and the ISO has stipulated that L10 is the "rated life of a rolling bearing." "L50": Indicates the time (or total number of revolutions, etc.) that 50% of bearings can rotate without suffering damage due to rolling fatigue. When there is a small amount of life data or the life data varies greatly, the accuracy of L10 may decrease. In such cases, lifespans may be compared using L50 data.

[0040] As shown in FIG. 4, the value of "e" in the case of the oil-repellent treatment (Example) is 0.72, and the value of "e" in the case of the oil-repellent treatment (Comparative Example) is 1.40. This means that there is a large difference in the degree of variation in the lifespan data, i.e., there is a difference in the magnitude of the Weibull slope. Therefore, in this test example, a comparison of lifespans was made using the L50 data. Furthermore, when comparing the "L50" value of the product with oil repellent treatment (Example), i.e., 5.3, with the "L50" value of the product without oil repellent treatment (Comparative Example), i.e., 0.7, the Example product with the specified oil repellent treatment showed a lifespan more than 7 times longer than the Comparative Example product without the oil repellent treatment. [Explanation of symbols]

[0041] 30 Thrust ball bearing 31 Fixed bearing ring 31a Raceway surface 32 Rotating raceway 32a Raceway surface 33 balls 34 Cage 40 Masking Tape 41 Oil repellent liquid 41a Oil repellent film 42 Spray

Claims

1. A method for oil repellent treatment of a thrust ball bearing having a plurality of balls, a raceway having an annular raceway surface on which the balls roll, and a cage that holds the balls so that they can roll, comprising the steps of: an oil-repellent treatment step is performed in which an oil-repellent liquid is applied to at least a portion of the raceway surface other than the portion that comes into contact with the balls, and the applied oil-repellent liquid is dried; The oil repellent treatment step includes: applying the oil repellent liquid to the entire surface of the raceway surface; a step of drying the applied oil-repellent liquid to form an oil-repellent film on the entire surface of the raceway surface; a step of assembling a thrust ball bearing using a raceway having a raceway surface on which the oil repellent film is formed and the balls; rotating the thrust ball bearing and peeling off the oil repellent film from the portion of the raceway surface that is in contact with the balls.

2. 2. The method for oil-repellent treatment of a thrust ball bearing according to claim 1, further comprising the step of: subjecting a portion of said raceway surface radially outward of a portion that comes into contact with said balls to the oil-repellent treatment.

3. 3. The method for oil-repellent treatment of a thrust ball bearing according to claim 1, further comprising the step of: subjecting the raceway surface to an area radially inward of a portion that comes into contact with the balls.

4. An oil-repellent treatment method for a thrust ball bearing as described in any one of claims 1 to 3, wherein the outer diameter side of the raceway is provided with a flange extending in an axial direction perpendicular to the raceway surface.

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