JP2013166901A - Lubricant, and rolling bearing including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such problems that, when a rolling bearing that supports an axis of rotation runs micro-reciprocation or receives micro-vibration, fretting occurs on the surface of rolling elements or rolling contact surface, causing various troubles such as delamination starting from increased bearing torque or a part of damage.SOLUTION: By adding stearic acid, or stearic acid and a metal stearate, to lubricant, an occurrence of fretting can be suppressed over a long period of time. The bearing including such lubricant can be provided more inexpensively than a bearing employing ceramic balls because steel balls can be used.

Description

  The present invention relates to a lubricant used in various apparatuses and devices, and a rolling bearing in which the lubricant is sealed.

  Rolling bearings are generally used for the parts that support the rotating shaft in rotating equipment such as motors. However, especially when performing reciprocating movements or receiving minute vibrations, the surface of the rolling element or rolling elements are used. Damage called fretting occurs on the running surface, causing various problems such as an increase in bearing torque and separation starting from the damaged part.

  On the other hand, in Patent Document 1, by adopting a ceramic ball having high wear resistance as a rolling element, the oil film is easily cut by a minute reciprocating motion, and even if both are in direct contact, the sliding 2 It prevents adhesion between surfaces and reduces the occurrence of fretting. In Patent Document 2, a lubricant added with iron sulfide fine particles having a high fretting suppression effect is sealed in a bearing. Further, although not intended to suppress fretting, Patent Documents 3 and 4 add inorganic Mg fine particles and Mg stearate to the lubricant to suppress exfoliation due to white texture change caused by hydrogen embrittlement.

JP 2005-188726 A JP 2009-227981 A JP 2007-023105 A JP 2007-045994 A

  However, ceramic balls are more expensive than steel balls that are normally used, and the method of adding fine particles of inorganic compounds is not sufficient in suppressing fretting. For these technologies, there is a strong demand for further improvement of the effect at a low cost.

  Accordingly, an object of the present invention is to provide a lubricant having a high fretting suppression effect. It is another object of the present invention to provide a rolling bearing that is more excellent in fretting resistance and more durable.

The above object is achieved by the following configuration.
(1) A lubricant comprising stearic acid in a lubricating oil.
(2) A lubricant characterized by further containing a metal stearate in the lubricating oil.
(3) A rolling bearing characterized by enclosing the lubricant (1) or (2).

  The lubricant according to the present invention has an effect of suppressing the occurrence of fretting over a long period of time. Further, since a steel ball can be used, a bearing including such a lubricant can be provided at a lower cost than a bearing using a ceramic ball.

It is sectional drawing which shows an example of a ball bearing. It is a schematic diagram which shows the fretting test machine used in the Example. It is a schematic diagram for demonstrating an amplitude ratio. It is a schematic diagram which shows the state which a disk test piece wears in a fretting test. It is a graph which shows the relationship between the heating time of the lubricating oil which added the stearic acid Mg, and damage ratio. It is a graph which shows the relationship between the heating time of lubricating oil, and a total acid value. It is a graph which shows the result of having analyzed the change of the component accompanying heating of lubricating oil using the gas chromatograph mass spectrometer. It is a graph which shows the relationship between the heating time of the lubricating oil which added the stearic acid, and damage ratio. It is a graph which shows the damage ratio of Example 3 and a comparative example.

  Hereinafter, the present invention will be described in detail.

  The lubricant according to the present invention is obtained by adding stearic acid or stearic acid and a stearic acid metal salt to a lubricating oil.

  As the stearic acid metal salt, Mg stearate, Ca stearate, Zn stearate, Li stearate or the like can be used.

  There is no restriction | limiting in lubricating oil, Mineral oil, synthetic oil, etc. can be suitably selected according to the objective or application location. Synthetic oils include aliphatic hydrocarbon oils, aromatic hydrocarbon oils, ester oils, ether oils, tricresyl phosphate, silicone oils, perfluoroalkyl ether oils, and the like. Examples of the aliphatic hydrocarbon oil include normal paraffin, isoparaffin, polybutene, polyisobutylene, 1-decene oligomer, poly-α-olefin (such as a co-oligomer of 1-decene and ethylene), or a hydride thereof. . Examples of the aromatic hydrocarbon oil include alkylbenzene (monoalkylbenzene, dialkylbenzene, polyalkylbenzene, etc.), alkylnaphthalene (monoalkylnaphthalene, dialkylnaphthalene, polyalkylnaphthalene) and the like. Examples of ester oils include aliphatic diesters, aromatic esters, polyol esters, and complex esters (oligoesters of polyhydric alcohols and dibasic acids and mixed fatty acids of monobasic acids). Examples of the aliphatic diester include dibutyl sebacate, di-2-ethylhexyl sebacate, dioctyl adipate, diisodecyl adipate, ditridecyl adipate, ditridecyl glutarate, methylacetyl ricinolate and the like. Examples of the aromatic ester include trioctyl trimellitate, tridecyl trimellitate, tetraoctyl pyromellitate and the like. Examples of the polyol ester include trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, pentaerythritol belargonate, and the like. Ether oils include polyglycols and phenyl ethers. Examples of the polyglycol include polyethylene glycol, polypropylene glycol, polyethylene glycol monoether, and polypropylene glycol monoether. Examples of the phenyl ether include monoalkyl triphenyl ether, alkyl diphenyl ether, dialkyl diphenyl ether, pentaphenyl ether, and dialkyl tetraphenyl ether.

  In addition, there is no limit to the thickener when it is used as grease. For example, metal soap (aluminum soap, barium soap, calcium soap, lithium soap, sodium soap, etc.), composite metal soap (lithium complex soap, calcium complex soap, Aluminum complex soap, etc.), urea compounds (diurea, triurea, tetraurea, polyurea, etc.), silica gel, bentonite, urethane compounds, urea-urethane compounds, sodium terephthalate, etc. can be appropriately selected according to the purpose.

  In addition, various additives used for the lubricant can be added depending on the purpose. For example, amines such as phenyl-1-naphthylamine, phenols such as 2-tert-butylphenol, antioxidants such as sulfur and dithiophosphate, organic sulfonates such as alkali metals and alkaline earth metals, alkyls, Rust preventives such as alkyls such as alkenyl succinic acid esters, alkenyl succinic acid derivatives, partial esters of polyhydric alcohols such as sorbitan monooleate, extreme pressure agents such as phosphorus, zinc dithiophosphate, organic molybdenum, fatty acids, animal and vegetable oils An oiliness improver such as benzotriazole or a metal deactivator such as benzotriazole can be added alone or in appropriate combination.

  Further, there are no restrictions on the characteristics such as the viscosity of the lubricating oil and the characteristics such as the consistency of the grease.

  In the present invention, there are no restrictions on the type of rolling bearing. FIG. 1 illustrates a ball bearing. In the illustrated ball bearing, a plurality of balls 5 as rolling elements are held via a cage 7 between an inner ring 2 having an inner ring raceway 1 and an outer ring 4 having an outer ring raceway 3. The bearing space formed by the outer ring 4 and the ball 5 is filled with the above-described lubricant and sealed with a seal 6.

  In such a ball bearing, the oil film easily breaks due to a minute reciprocating motion, and as a result, fretting wear is likely to occur.By using a lubricant added with stearic acid, the surface of the oil bearing agent of stearic acid has a function. Form a protective film to reduce fretting. Therefore, the ball 5 does not need to be made of ceramic and can be made inexpensive. Further, by adding not only stearic acid but also Mg stearate, since the stearic acid is generated in the course of oxidative degradation of the lubricating oil, fretting can be suppressed over a long period of time.

  In addition, as a kind of rolling bearing, besides a ball bearing, a roller bearing with a cage, a total rolling bearing, a total roller bearing, and the like can be given, and the rolling surface may be a single row or a double row.

  Hereinafter, the present invention will be further described with reference to examples and comparative examples.

Example 1
A test lubricant A was prepared by adding 1.0 mass% of Mg stearate to VG32 (mineral oil, kinematic viscosity at 40 ° C. of 30 mm ² / s).

(Example 2)
A test lubricant B was prepared by adding 1.0 mass% of stearic acid to VG32 (mineral oil, kinematic viscosity at 40 ° C. of 30 mm ² / s).

(Example 3)
Test Lubricant C was prepared by adding 1.0 mass% of Mg stearate and stearic acid to VG32 (mineral oil, kinematic viscosity at 40 ° C. of 30 mm ² / s).

(Comparative example)
Test lubricant D was prepared by adding nothing to VG32 (mineral oil, kinematic viscosity at 40 ° C. of 30 mm ² / s).

(Fretting test)
The test lubricants A to D prepared above were sealed in the same amount in a single type thrust ball bearing (invention number: 51305) having an inner diameter of 25 m, an outer diameter of 52 mm, and a height of 18 mm to produce a test bearing. Then, the test bearing was mounted on a fretting tester manufactured by Nippon Seiko Co., Ltd. shown in FIG. 2, and a fretting test was performed under the following test conditions. In the test bearing, in order to accurately measure the maximum height (Ry) of the damaged portion, a disk test piece in which the lower race is lapped is used.
・ Maximum surface pressure: 3.2 GPa
・ Maximum rocking speed: 20mm / s
-Number of oscillations: 10,000 times-Amplitude ratio: 2.0

  As shown in FIG. 3, the amplitude ratio is a ratio “A / D” between the contact circle diameter (D) and the amplitude (A). As shown in FIG. 4, the disk test piece is worn as the rocking occurs, and wear powder accumulates on the circumference of the contact ellipse, and the portion is greatly damaged. Therefore, fretting is performed by observing the surface of the lower race with an interference microscope before and after the test, measuring the maximum height (Ry) of the damaged portion, and determining the ratio of Ry (Ry after test / Ry before test: damage ratio). Can be evaluated. The less damage, the closer the damage ratio is to 1.

  The graph in FIG. 5 compares the damage ratio between mineral oil added with Mg stearate (Example 1) and additive-free mineral oil (Comparative Example). The horizontal axis of the graph represents the heating time of the lubricating oil. When the lubricating oil of Example 1 was heated at 160 ° C., the damage ratio was smaller as compared with the comparative example as the heating time was longer. 1 was confirmed. The heating is performed in order to accelerate the deterioration of the lubricating oil, and the heating time can be regarded as representing the operating time of the bearing in which the lubricating oil is enclosed. From this result, it can be seen that the lubricating oil to which Mg stearate is added exhibits an effect of suppressing fretting as compared to the case where the lubricating oil is not added as the operating time of the bearing is extended.

  FIG. 6 shows the results of investigation on the relationship between the heating time of the lubricating oil and the total acid value. FIG. 6 shows that the addition of Mg stearate prevents the lubricating oil from being oxidized and deteriorated. This means that Mg stearate is more easily oxidized than lubricating oil. It is considered that the reason why Mg stearate is easily oxidized is that Mg has a large ionization tendency. A large ionization tendency means that the reducing action of depriving oxygen from other substances is strong, and it is considered that the oxidation of the lubricating oil was suppressed.

  In order to investigate what kind of substance the Mg stearate was changed to when oxidized, a component analysis of the lubricating oil was performed using a gas chromatograph mass spectrometer. FIG. 7 shows the result. No difference was found in the waveforms of the additive oil (VG32) and mineral oil added with Mg stearate (VG32 + St-Mg) at 160 ° C. for 24 h, but lubrication with Mg stearate added and heated for 550 h A characteristic peak was confirmed from the oil (indicated by a circle in FIG. 7). As a result of analyzing this part, it was found to be stearic acid. It is considered that stearic acid was produced by heating the lubricating oil to which Mg stearate was added, and this exhibited a fretting suppression effect.

  Therefore, a fretting test was performed using a lubricating oil (Example 2) to which only stearic acid was added. The test results are shown in FIG. From FIG. 8, it was confirmed that fretting can be suppressed by adding only stearic acid without heating the lubricating oil.

  From the above results, it was confirmed that Mg stearate prevents oxidative degradation of the lubricating oil and that the effect of suppressing fretting is exhibited by producing stearic acid little by little during the reaction process. Further, by adding both Mg stearate and stearic acid to the lubricating oil from the beginning (Example 3), the effect of suppressing fretting can be improved over a long period from the initial stage of using the bearing (FIG. 9). reference).

DESCRIPTION OF SYMBOLS 1 Inner ring track 2 Inner ring 3 Outer ring track 4 Outer ring 5 Ball 6 Seal 7 Cage

Claims (3)

  A lubricant comprising stearic acid in a lubricating oil.   The lubricant according to claim 1, further comprising a metal stearate in the lubricating oil.   A rolling bearing comprising the lubricant according to claim 1 or 2.

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