JP2005112901A - Lubricant composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lubricant composition which can effectively prevent the rolling surface of a bearing from peeling due to hydrogen embrittlement. <P>SOLUTION: This lubricant composition used for bearing portions is characterized in that the lubricant composition comprises a molybdate and an organic acid salt. The molybdate is at least one molybdate selected from sodium molybdate, potassium molybdate and lithium molybdate. The organic acid is a 1 to 20C organic acid sodium salt. A film comprising iron oxides and a molybdenum compound is formed on the frictionally worn surface of a bearing portion or an iron-based metal newly-born surface exposed by the wearing. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a lubricating oil used for a bearing portion of a hydraulic motor, a hydraulic pump, or the like, and more particularly to a lubricating oil composition that suppresses an early peeling phenomenon accompanied by a white structure change occurring on a rolling surface of the bearing.

Bearings lubricated with gear oil or hydraulic fluid are generally used in hydraulic motors, hydraulic pumps, and axle planetary parts. As these oils, mineral oils and water-glycol hydraulic fluids are generally used.
In recent years, as the operating conditions of bearings lubricated with gear oil or hydraulic fluid have become harsh, such as high speed and high load, peeling with white structure change has occurred early on the rolling surface of the bearing, which has become a problem. Yes.

  Unlike the exfoliation from the inside of the rolling surface caused by normal metal fatigue, the peculiar delamination with the white structure change that occurs early is a destruction phenomenon that occurs from a relatively shallow part of the rolling surface, It is thought to be hydrogen embrittlement caused by hydrogen. Hydrogen that causes this separation is generated by the decomposition of the lubricating oil. The generation of hydrogen from the lubricating oil can be attributed to two causes: (1) decomposition due to heat and shear, and (2) decomposition reaction using a new metal surface generated by abrasion as a catalyst. The hydrogen thus generated easily penetrates into the bearing steel and causes peeling due to hydrogen embrittlement. It is thought that which of (1) and (2) has a greater influence on the hydrogen generation depends on the use conditions of the bearing, but when (2) is the main cause, the exposure time of the new metal surface generated by wear is reduced. Additives that can be shortened, i.e., can immediately turn the generated new metal surface into an inactive state, are desirable to suppress hydrogen generation.

Conventionally, as a measure to prevent hydrogen embrittlement peeling based on such knowledge, an oxide film is formed on the rolling surface using a black dyeing method (see Patent Document 1). In order to form an oxide film on the resulting new surface, grease is added to a passivating agent (see Patent Document 2) or the bearing ring material itself contains Cr or the like on the rolling surface. There is one that forms an oxide film to prevent peeling (see Patent Document 3).
However, if it peels off due to frictional wear with the rolling elements, the effect is lost and it cannot be said that it is a sufficient countermeasure. In addition, effective countermeasures have not been clarified for lubricating oil, and it has hardly been carried out until now.
Japanese Utility Model Publication No. 6-43349 (paragraph [0008]) JP-A-3-210394 (page 2, upper right column, lines 6 to 15) Japanese Patent No. 3009254 (paragraph [0007])

  The present invention has been made to cope with such a problem, and an object of the present invention is to provide a lubricating oil composition capable of effectively preventing separation on a rolling surface due to hydrogen embrittlement in a bearing.

The lubricating oil composition of the present invention is a lubricating oil composition used for bearing parts, and the lubricating oil composition contains a molybdate and an organic acid salt.
The molybdate is at least one molybdate selected from sodium molybdate, potassium molybdate and lithium molybdate.
The organic acid salt is a sodium salt of an organic acid having 1 to 20 carbon atoms.

  The lubricating oil composition of the present invention is a lubricating oil composition used for a bearing portion, and the lubricating oil composition contains a molybdenum compound together with iron oxide on a friction wear surface or a new ferrous metal surface exposed by wear in the bearing portion. It is characterized by containing a molybdate and an organic acid salt that can form a containing film.

    Another lubricating oil composition of the present invention is a lubricating oil composition used for a bearing portion, and the lubricating oil composition contains a permanganate, particularly potassium permanganate.

  Since the lubricating oil composition used for the bearing portion contains molybdate and an organic acid, or contains potassium permanganate, it is possible to effectively prevent peeling on the rolling surface due to hydrogen embrittlement in the bearing portion. In particular, it is possible to more effectively prevent peeling at the rolling surface due to hydrogen embrittlement in the bearing portion using the water-based lubricant.

  By blending molybdate and organic acid salt, the molybdate decomposes and reacts on the frictional wear surface or the new metal surface exposed by wear, and a molybdenum compound film is formed on the bearing rolling surface along with iron oxide. Furthermore, by using both molybdate and organic acid salt, as a result of surface analysis, it was found that the oxide film was thicker and the molybdenum content was higher than when only molybdate was blended. Therefore, it is considered that the organic acid salt has an effect of promoting the generation of the iron oxide and molybdenum compound coating on the bearing rolling surface. The iron oxide and molybdenum compound coating formed on the rolling surface of the bearing can suppress the generation of hydrogen due to the decomposition of the lubricating oil by the catalytic action, and can prevent peculiar peeling due to hydrogen embrittlement.

  Further, when the lubricating oil composition contains permanganate, the frictional wear surface or the newly formed metal surface exposed by wear becomes an inactive and non-catalytic oxide film state. The oxide film formed on the rolling contact surface of the bearing can suppress the generation of hydrogen due to the decomposition of the lubricating oil by the catalytic action, and can prevent the specific peeling due to hydrogen embrittlement.

  The base oil of the lubricating oil composition that can be used in the present invention may be either an aqueous lubricating oil or a non-aqueous lubricating oil, and any oil that is widely used as a lubricating oil can be used. Specific examples include hydrocarbon oils such as spindle oil, refrigerating machine oil, turbine oil, machine oil, dynamo oil, and other mineral oils, highly refined mineral oil, liquid paraffin, polybutene, polyalphaolefin, alkylnaphthalene, and alicyclic compounds. Oil or natural oil, polyol ester oil, phosphate ester oil, polymer ester oil, aromatic ester oil, carbonate ester oil, diester oil, polyglycol oil, silicone oil, polyphenyl ether oil, alkyl diphenyl ether oil, alkyl benzene oil, Non-hydrocarbon synthetic oils such as fluorinated oils and water-based lubricating oils such as water-glycol hydraulic oils can be used.

In particular, when low friction is required, preferable results can be obtained by using ester oil, silicone oil or the like.
In addition, since molybdate is water-soluble, the effect of suppressing exfoliation due to hydrogen embrittlement can be further exerted by blending with a water-based lubricating oil that can be blended uniformly.
Moreover, when using a non-aqueous lubricating oil, it is preferable to pulverize the molybdate in advance or to add a dispersant.

The molybdate that can be used in the present invention is preferably a metal salt. Examples of the metal constituting the metal salt include sodium, potassium, lithium, magnesium, calcium, copper, zinc, barium and the like.
In the present invention, the metal that easily forms a film containing a molybdenum compound together with iron oxide reacts on the frictional wear surface or the newly formed iron-based metal surface exposed by wear in the bearing portion. Alkali metal salts of the salts are preferred. Suitable alkali metal molybdates include lithium molybdate, sodium molybdate or potassium molybdate, which can be used alone or as a mixture.

  The organic acid salt that can be used in the present invention can be any salt such as an aromatic organic acid, an aliphatic organic acid, or an alicyclic organic acid. As the organic acid, monobasic or polybasic organic acids can be used. Among these, an organic acid having a carboxyl group residue having 1 to 20 carbon atoms is particularly preferable because it facilitates the formation of a film containing a molybdenum compound.

  Specific examples of organic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, heptanoic acid, caprylic acid, pelargonic acid, capric acid, undecyl acid, lauric acid, tridecylic acid, myristic acid, pentadecyl Monovalent saturated fatty acids such as acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid and arachidic acid, monounsaturated fatty acids such as acrylic acid, crotonic acid, undecylenic acid, oleic acid and gadoleic acid, malonic acid and methylmalon Divalent saturation such as acid, succinic acid, methyl succinic acid, dimethyl malonic acid, ethyl malonic acid, glutaric acid, adipic acid, dimethyl succinic acid, pimelic acid, tetramethyl succinic acid, suberic acid, azelaic acid, sebacic acid, brassic acid Divalent unsaturated fatty acids such as fatty acids, fumaric acid, maleic acid, oleic acid, tartaric acid, Fatty acid derivatives such as phosphate, benzoic acid, phthalic acid, trimellitic acid, and aromatic organic acids such as pyromellitic acid.

  The organic acid is preferably a metal salt, and a sodium salt is preferable among the metal salts. Preferred metal salts of organic acids include sodium benzoate, monosodium sebacate, disodium sebacate, monosodium succinate, and disodium succinate.

  Examples of permanganate that can be used in the present invention include sodium, potassium, lithium, magnesium, calcium, copper, zinc, and barium. Of these, potassium permanganate is preferred because it is easily available industrially.

  The blending ratio of molybdate and organic acid salt is 0.01 to 5% by weight of molybdate based on the whole lubricating oil composition, and 5 to 5% of organic acid salt relative to the amount of molybdate added. It is preferable to add 70% by weight. If the blending ratio of molybdate and organic acid salt is less than the above blending range, peeling on the rolling surface due to hydrogen embrittlement cannot be effectively prevented. Moreover, even if it exceeds the said range, the peeling prevention effect does not improve any more.

  When permanganate is used in place of molybdate and organic acid salt, the permanganate content is preferably 0.01 to 5% by weight based on the entire lubricating oil composition. If it is less than 0.01% by weight, peeling on the rolling surface due to hydrogen embrittlement cannot be effectively prevented. Further, if the amount exceeds 5% by weight, not only the anti-separation effect will not be improved but also a lubrication failure will occur, and surface-origin type fatigue delamination will easily occur early.

When adding a mixed compound of molybdate and organic acid salt, oxidation is prevented if necessary as long as it does not impair the formation of a film containing molybdenum compound formed on the new ferrous metal surface exposed on the frictional wear surface. Known compounding agents such as an agent, a rust preventive agent, an oily agent, a viscosity index improver, a pour point depressant, an antifoaming agent, an emulsifier, a metal deactivator, and a cleaning dispersant can be blended.
In particular, when an aqueous lubricant is used, it is preferable to add an appropriate amount of a rust preventive agent in order to prevent rusting of the bearing steel.

When adding permanganate, antioxidants, rust inhibitors, oiliness agents, viscosity index improvers, pour point depressants, antifoaming agents, emulsifiers, metal deactivators, detergent dispersants, etc., as necessary These known compounding agents can be blended.
In particular, when an aqueous lubricant is used, it is preferable to add an appropriate amount of a rust preventive agent in order to prevent rusting of the bearing steel.

An example of a rolling bearing in which the lubricating oil composition of the present invention is used is shown in FIG. FIG. 1 is a perspective view showing an example of a shell needle roller bearing.
In the needle roller bearing 1, a needle roller 3 with a cage 4 is incorporated in an outer ring 2 manufactured from a steel plate by precision deep drawing or the like. The needle roller bearing 1 can have a shaft directly on the raceway and is often lubricated with a lubricating oil composition.

Examples 1-9, Comparative Examples 1-7
Needle roller bearings (inner ring outer diameter φ 24 mm, outer ring inner diameter φ 32 mm, width 20 mm, rollers φ 4 x 16.8 mm x 14) are lubricated with a lubricating oil composition having the composition shown in Table 1 and Table 2. The life test was conducted.
The life test is a rapid load acceleration / deceleration in which the radial load is 6.76 kN and the rotational speed is 3000 rpm → 500 rpm → 3000 rpm → 500 rpm. ) Was measured. The peeling occurrence time was defined as the peeling occurrence time by stopping the testing machine when the vibration of the vibration detector exceeded the set value. Thereafter, it was visually confirmed that peeling occurred on the rolling surface. The results are shown in Tables 1 and 2.

After the life test, discoloration was observed on the rolling surface of the bearing in each example, but no discoloration was observed on the rolling surface after the test in each comparative example. The discoloration of the rolling surface was considered to suppress the occurrence of peculiar delamination due to hydrogen embrittlement, and the discoloration part (formed film) was analyzed. As a result of XPS (ESCA) analyzing the composition of the formed film on the extreme surface, Mo was detected in addition to Fe, O, and C. When the detected Mo was examined in more detail, it was a molybdenum-based composite coating containing molybdenum oxide.
As is clear from the above analysis results, the film is decomposed and reacted on the friction wear surface or the new metal surface exposed by wear to form a film containing a molybdenum compound together with iron oxide. As a result of preventing the hydrogen generated by the decomposition of steel from entering the steel and suppressing the occurrence of peeling, the life characteristics evaluated by the peeling occurrence time were improved.

Examples 10-14, Comparative Examples 8-10
Instead of the lubricating oil composition having the composition shown in Table 1 and Table 2, the same life test as in Example 1 was conducted except that the lubricating oil composition having the composition shown in Table 3 was used. The results are shown in Table 3.

表３に示すように、各実施例は剥離発生時間で評価された寿命特性が向上した。

As shown in Table 3, each example improved the life characteristics evaluated by the peeling occurrence time.

  Since the lubricating oil composition of the present invention can effectively prevent peeling at the rolling surface due to hydrogen embrittlement in the bearing portion, it can be used for a bearing lubricated with gear oil or hydraulic fluid.

It is a perspective view of a needle roller bearing.

Explanation of symbols

1 Needle roller bearing 2 Outer ring 3 Roller 4 Cage

Claims (6)

A lubricating oil composition used for a bearing portion, wherein the lubricating oil composition contains a molybdate and an organic acid salt. The lubricating oil composition according to claim 1, wherein the molybdate is at least one molybdate selected from sodium molybdate, potassium molybdate, and lithium molybdate. The lubricating oil composition according to claim 1 or 2, wherein the organic acid salt is a sodium salt of an organic acid having 1 to 20 carbon atoms. Lubricating oil composition used for a bearing part, the lubricating oil composition being capable of forming a film containing a molybdenum compound together with iron oxide on a frictional wear surface or a new ferrous metal surface exposed by wear in the bearing portion A lubricating oil composition comprising a salt. A lubricating oil composition used for a bearing portion, wherein the lubricating oil composition contains a permanganate. The lubricating oil composition according to claim 5, wherein the permanganate is potassium permanganate.

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