JP2006242330A - Rolling bearing for fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing for a fuel cell system, effectively preventing exfoliation on a rolling surface due to hydrogen brittleness. <P>SOLUTION: In the rolling bearing for the fuel cell system, a grease composition is filled which is formed by incorporating thickening agent and additive in base oil. The additive contains at least molybdate or molybdate and organic acid salt. The molybdate is alkali metal salt of molybdic acid, and the organic acid salt is alkali metal salt of organic acid having a carbon number of 1 to 20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a rolling bearing for a fuel cell system, and more particularly to a rolling bearing for a fuel cell system used in a pressure feeder that pumps various fluids in the fuel cell system.

In recent years, a fuel cell system has attracted attention as a new power source or a distributed power generator for automobiles. A fuel cell has a high power density, operates at a low temperature, has little deterioration of battery constituent materials, and is easy to start, a solid polymer electrolyte fuel cell is considered to be effective as a power source for a transport body such as an automobile. .
In a fuel cell system, it is necessary to pump hydrogen, hydrogen-rich reformed gas, and air as an oxidant to a fuel cell, and a supercharger, impeller pump, scroll pump, swash plate pump Various pumping machines such as a machine and a screw type pumping machine are used.
Also, in solid polymer electrolyte fuel cells, hydrogen is generated by a chemical reaction for power generation and air as an oxidant reacts, and the polymer membrane can function as a solid electrolyte. In addition, since it is humidified by the humidifier and is always maintained in a state containing moisture, moisture is mixed in the gas pumped by the pressure feeder. When this moisture enters the bearing, metal contact may occur due to poor lubrication, and premature peeling with a change in white structure may occur on the rolling surface of the rolling bearing.
This specific exfoliation is different from the exfoliation from the inside of the rolling contact surface caused by normal metal fatigue, and is a fracture phenomenon that occurs from a relatively shallow portion of the surface of the rolling contact surface and is considered to be hydrogen embrittlement caused by hydrogen. As a method for preventing such an unusual peeling phenomenon accompanied by a white tissue change that occurs at an early stage, for example, a method of adding a passivating agent to a grease composition is known (Patent Document 1).

However, with the recent increase in the usage conditions of rolling bearings, sufficient measures cannot be taken with the method of adding a passivating agent.
In response to the demand for increased power generation, pumping machines are required to have higher speed and higher performance. Rolling bearings also rotate at higher speeds and loads, so the bearings can reach a high temperature of about 180 ° C. Therefore, it is also required to have excellent heat resistance.
JP-A-3-210394

  The present invention has been made to cope with such a problem, and an object of the present invention is to provide a rolling bearing for a fuel cell system that can effectively prevent separation on a rolling surface due to hydrogen embrittlement.

A rolling bearing for a fuel cell system according to the present invention is a rolling bearing for a fuel cell system that rotatably supports a rotating portion provided in a pressure feeder for pumping a fluid used in the fuel cell system,
The rolling bearing includes an inner ring and an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, and a seal member for sealing a grease composition around the rolling elements is provided for the shafts of the inner ring and the outer ring. The grease composition is a grease composition in which a thickener and an additive are blended with a base oil, and the additive contains at least molybdate. Features.
The molybdate is an alkali metal salt of molybdic acid.
The alkali metal salt of molybdic acid is at least one alkali metal salt of molybdic acid selected from sodium molybdate, potassium molybdate, and lithium molybdate.
The molybdate is characterized by being blended in an amount of 0.01 to 10 parts by weight with respect to 100 parts by weight of the total amount of base oil and thickener.

  The additive includes an organic acid salt. The organic acid salt is an alkali metal salt of an organic acid having 1 to 20 carbon atoms.

The molybdate is 0.01 to 5 parts by weight with respect to 100 parts by weight of the total amount of the base oil and the thickener, and the organic acid salt is 5 to 70 parts by weight with respect to 100 parts by weight of the molybdate added. It is characterized by being partly blended.
The thickener is a urea-based thickener.

A rolling bearing for a fuel cell system according to the present invention is a rolling bearing for a fuel cell system that rotatably supports a rotating portion provided in a pressure feeder for pumping a fluid used in the fuel cell system,
The grease composition enclosed in the bearing promotes the formation of the molybdate and the film capable of forming a film containing a molybdenum compound together with iron oxide on the frictional wear surface or the new ferrous metal surface exposed by wear in the bearing portion. It contains an organic acid salt.

  In the rolling bearing for a fuel cell system according to the present invention, the grease composition enclosed in the bearing comprises a molybdate or a molybdate and an organic acid salt mixed with a grease composition comprising a base oil and a thickener. Therefore, in the fuel cell system in which the start-rapid acceleration operation-high-speed operation-sudden deceleration operation-sudden stop is frequently performed, the occurrence of peculiar delamination due to hydrogen embrittlement seen in the rolling bearing used is suppressed. The life of the rolling bearing for the fuel cell system can be extended.

As a result of intensive studies on a method for effectively preventing separation on the rolling surface due to hydrogen embrittlement, a rolling bearing for a fuel cell system in which a grease composition containing molybdate is encapsulated is used. As a result of the life test, it was found that the bearing life can be extended.
It was found that by adding molybdate, the molybdate decomposes and reacts on the frictional wear surface or the newly formed metal surface exposed by wear, and a molybdenum compound film is formed on the bearing rolling surface along with iron oxide. This iron oxide and molybdenum compound coating formed on the rolling surface of the bearing suppresses the generation of hydrogen due to the decomposition of the grease composition and prevents unique peeling due to hydrogen embrittlement, thus extending the life of the rolling bearing. Conceivable.
It was also found that the bearing life can be further extended by using a grease composition in which the molybdate and the organic acid salt are used in combination. As a result of surface analysis of the transfer surface of the rolling bearing, compared to the case where only molybdate is blended, when molybdate and organic acid salt are used in combination, the oxide film is thicker and the molybdenum content is higher. I understood. From this, it is considered that the organic acid salt has an action of promoting the formation of the iron oxide and molybdenum compound coating on the bearing rolling surface. For this reason, the iron oxide and molybdenum compound coating formed on the rolling surface of the bearing suppresses the generation of hydrogen due to the decomposition of the grease composition and prevents unique peeling due to hydrogen embrittlement, thus extending the life of the rolling bearing. it is conceivable that. The present invention is based on these findings.

An example of the rolling bearing for the fuel cell system of the present invention is shown in FIG. FIG. 1 is a cross-sectional view of a deep groove ball bearing in which a grease composition is enclosed.
In the deep groove ball bearing 1, an inner ring 2 having an inner ring rolling surface 2a on the outer peripheral surface and an outer ring 3 having an outer ring rolling surface 3a on the inner peripheral surface are arranged concentrically, and the inner ring rolling surface 2a and the outer ring rolling surface 3a. A plurality of rolling elements 4 are arranged between the two. Sealers 6 that are fixed to the cage 5, the outer ring 3, and the like that hold the plurality of rolling elements 4 are provided in the axially opposite end openings 8a, 8b of the inner ring 2 and the outer ring 3, respectively. A grease composition 7 is enclosed at least around the rolling element 4.

An example of a pressure feeder in which the rolling bearing for the fuel cell system of the present invention is used is shown in FIG. FIG. 2 is a cross-sectional view of an impeller type pressure feeder used in a fuel cell vehicle. In FIG. 2, an arrow surrounded by a dotted line represents a gas. As shown in FIG. 2, the impeller type pressure feeder is configured such that a rotating shaft 10 to which an impeller 9 is fixed is supported on a casing 11 by a plurality of rolling bearings 1 arranged at intervals in the axial direction. . When the rotating shaft 10 that rotates by receiving power from a motor or the like rotates at high speed, the impeller 9 also rotates at high speed, and the gas sucked from the gas suction port 12 is pressurized by the centrifugal force of the impeller 9, and the casing 11, the back plate 13, The gas is delivered from the gas discharge port 15 through the pressurizing volute 14 formed in the above.
The back plate 13 and the rotary shaft 10 are sealed by a seal ring 17 disposed therebetween so that gas does not leak from the pressure volute 14 to the rolling bearing 1. However, in this impeller type pressure feeder, when the sealing performance of the seal ring 17 is reduced as the rotary shaft 10 rotates at high speed, the gas is transferred from the back space 16 on the back surface of the impeller 9 to the rotary shaft 10 and the seal ring 17. To the rolling bearing 1 through the gap 18. In order to prevent this, a mechanical seal 19 is provided. Regarding the sealing performance of the mechanical seal 19, the sliding surface between the mechanical seal 19 and the rotary shaft 10 is in a water-lubricated state with water vapor contained in the gas. As a result, water vapor or the like may enter the bearing 1 and the bearing 1 may deteriorate.
For this reason, in the rolling bearing for the fuel cell system of the present invention, in order to prevent the intrusion of water vapor from the impeller 9 side and the leakage of the grease composition 7 (see FIG. 1) enclosed in the bearing 1, The bearing 1 is provided with a seal member 6 (see FIG. 1) having hydrogen embrittlement resistance.

In the rolling bearing for a fuel cell system according to the present invention, the molybdenum compound coating formed on the bearing rolling surface is a frictional wear surface or a newly formed metal surface exposed by wear due to the molybdate contained in the grease composition sealed in the bearing. Decomposes and reacts to form a molybdenum compound film with iron oxide.
Furthermore, the formation of the film is promoted by using a molybdate and an organic acid salt in combination, and compared with the case where only molybdate is blended, the oxide film is thicker and the molybdenum content in the oxide film is reduced. Can do a lot. 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 grease composition and can prevent peculiar peeling due to hydrogen embrittlement.

The molybdate that can be used in the present invention is preferably a metal salt. Examples of the metal constituting the metal salt include lithium, sodium, potassium, 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 chemical structure having 1 to 20 carbon atoms is particularly preferable because it promotes 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, undecylic 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 an alkali metal salt such as a lithium salt, a sodium salt, or a potassium salt, and a sodium salt is more preferable among the alkali metal salts. Preferred sodium salts of organic acids include sodium benzoate, monosodium sebacate, disodium sebacate, monosodium succinate, and disodium succinate.

  Base oils that can be used in the present invention are mineral oils such as spindle oil, refrigerator oil, turbine oil, machine oil, dynamo oil, highly refined mineral oil, liquid paraffin, GTL oil synthesized by the Fischer-Tropsch method, polybutene, poly- Hydrocarbon synthetic oils such as α-olefins, alkylnaphthalenes and alicyclic compounds, or natural oils, polyol ester oils, phosphate ester oils, polymer ester oils, aromatic ester oils, carbonate ester oils, diester oils, poly Non-hydrocarbon synthetic oils such as glycol oil, silicone oil, polyphenyl ether oil, alkyldiphenyl ether oil, alkylbenzene oil, and fluorinated oil can be used.

  Thickeners that can be used in the present invention include benton, silica gel, fluorine compounds, lithium soap, lithium complex soap, strong lucium soap, calcium complex soap, aluminum soap, aluminum complex soap, and other soaps, diurea compounds, polyurea compounds, etc. These urea compounds are mentioned. In consideration of heat resistance, cost, and the like, a urea compound is desirable.

  Examples of the urea compound include a diurea compound and a polyurea compound. A diurea compound is obtained by reaction of a diisocyanate and a monoamine, for example. Examples of the diisocyanate include phenylene diisocyanate, tolylene diisocyanate, diphenyl diisocyanate, diphenylmethane diisocyanate, octadecane diisocyanate, decane diisocyanate, hexane diisocyanate, etc., and monoamines include octylamine, dodecylamine, hexadecylamine, stearylamine, Examples include oleylamine, aniline, p-toluidine, cyclohexylamine and the like. The polyurea compound can be obtained, for example, by reacting diisocyanate with a monoamine or diamine. Examples of the diisocyanate and monoamine include those similar to those used for the production of the diurea compound. Examples of the diamine include ethylenediamine, propanediamine, butanediamine, hexanediamine, octanediamine, phenylenediamine, tolylenediamine, xylenediamine, And diaminodiphenylmethane.

A urea compound is obtained by reacting an isocyanate compound and an amine compound. In order not to leave a reactive free radical, the isocyanate group of the isocyanate compound and the amino group of the amine compound are preferably blended so as to be approximately equivalent.
A base grease composition for blending a urea compound with a base oil and blending various compounding agents can be obtained. The base grease is produced by reacting an isocyanate compound and an amine compound in a base oil.

  The blending ratio of the thickener in the base grease is 1 to 40 parts by weight, preferably 3 to 25 parts by weight, based on 100 parts by weight of the whole base grease. If the content of the thickener is less than 1 part by weight, the thickening effect will be reduced, making it difficult to make grease, and if it exceeds 40 parts by weight, the resulting base grease will be too hard and the desired effect will not be obtained. Become.

  The blending ratio of molybdate is 0.01 to 10 parts by weight with respect to 100 parts by weight of the total amount of base oil and thickener. When molybdate is used together with organic acid salt, 0.01 to 5 parts by weight of the molybdate and 100% by weight of molybdate are added to 100 parts by weight of the total amount of base oil and thickener. The organic acid salt is blended in an amount of 5 to 70 parts by weight per part. 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.

  In addition to a mixed compounding agent of molybdate and organic acid salt, a known additive for grease can be contained as necessary. As this additive, for example, antioxidants such as organic zinc compounds, amine-based, phenol-based and sulfur-based compounds, metal deactivators such as benzotriazole, viscosity index improvers such as polymethacrylate and polystyrene, molybdenum disulfide, Examples thereof include solid lubricants such as graphite, rust preventives such as metal sulfonates and polyhydric alcohol esters, friction reducing agents such as organic molybdenum, oily agents such as esters and alcohols, and antiwear agents such as phosphorus compounds. These can be added alone or in combination of two or more.

  Since the grease composition that can be used in the present invention can suppress the occurrence of peculiar peeling due to hydrogen embrittlement, the life of the grease-sealed bearing can be improved. For this reason, ball bearings, cylindrical roller bearings, tapered roller bearings, spherical roller bearings, needle roller bearings, thrust cylindrical roller bearings, thrust tapered roller bearings, thrust needle roller bearings, thrust spherical roller bearings, etc. Can be used as grease.

Examples 1 to 13 and Example 16
4,4-Diphenylmethane diisocyanate (MDI) is dissolved in half of the base oil shown in Table 1 and Table 2 in the proportions shown in Table 1 and Table 2, and 4,4-diphenylmethane is dissolved in the remaining half of the base oil. A monoamine that was twice the equivalent of diisocyanate was dissolved. The respective blending ratios and types are as shown in Table 1 and Table 2.
A solution in which monoamine is dissolved is added while stirring the solution in which 4,4-diphenylmethane diisocyanate is dissolved, and then the reaction is continued at 100 to 120 ° C. for 30 minutes to form a diurea compound in the base oil. It was.
To this, molybdate, organic acid salt and antioxidant were added at the blending ratios shown in Tables 1 and 2, and the mixture was further stirred at 100 to 120 ° C. for 10 minutes. Thereafter, the mixture was cooled and homogenized with three rolls to obtain a grease composition.

In Tables 1 and 2, the alkyl diphenyl ether oil used as the base oil is LB100 under the trade name of Matsumura Oil Co., Ltd., synthetic hydrocarbon oil is Shinflud 601 under the trade name of Nippon Steel Chemical Co., and polyol ester is the trade name of Kao Corporation. Kaolube 268 was used respectively. The mineral oil used was a paraffinic mineral oil with a kinematic viscosity of 30.7 mm ² / s (40 ° C).
As the antioxidant, alkylated diphenylamine was used.

  The obtained grease composition was subjected to a high-temperature high-speed test, a rapid acceleration / deceleration test, and a blending penetration measurement according to Japanese Industrial Standards. Test methods and test conditions are shown below. The results are shown in Tables 1 and 2.

High temperature high speed test:
The grease composition obtained in each example was sealed in a rolling bearing for a motor (6204) of 1.8 g, and the bearing outer ring outer diameter temperature was 180 ° C., a radial load of 67 N, and an axial load of 67 N. It was rotated at the number of revolutions, and the time to burn-in was measured.

Rapid acceleration / deceleration test:
1.8 g of the grease composition obtained in each example was sealed in a rolling bearing for motor (6204), and incorporated in a rolling bearing for internal rotation, and a rapid acceleration / deceleration test was performed. The rapid acceleration / deceleration test conditions were set such that the load applied to the pulley attached to the tip of the rotating shaft was 3234 N and the rotation speed was 0 to 18000 rpm. Then, abnormal peeling occurred in the bearing, and the time when the vibration of the vibration detector exceeded the set value and the tester stopped was measured. In the test, a grease composition in which 1% by weight of pure water was mixed in advance was used. The test was terminated in 100 hours.

Example 14 and Example 15
Li-12-hydroxystearate was added to the base oil shown in Table 2, and dissolved by heating at 200 ° C. with stirring. In addition, each compounding ratio is as Table 2. Thereafter, the mixture was cooled, molybdate, organic acid salt and antioxidant were added at the blending ratio shown in Table 2, and homogenized with three rolls to obtain a grease composition. The grease composition was subjected to a high-temperature high-speed test and a rapid acceleration / deceleration test in the same manner as in Example 1. However, considering the heat resistance of Li soap grease, the high-temperature high-speed test was conducted at 150 ° C.

Comparative Examples 1 to 5
By the method according to Example 1, the thickener and base oil were selected at the blending ratios shown in Table 2 to adjust the base grease, and further additives were blended to obtain a grease composition. The obtained grease composition was evaluated by performing the same test as in Example 1. The results are shown in Table 2.

  As shown in Tables 1 and 2, each example can effectively prevent specific delamination accompanied by a white structure change occurring on the rolling surface of a rolling bearing for a motor, so a high-temperature high-speed test and a rapid acceleration / deceleration test Is excellent. All of the rapid acceleration / deceleration tests in each example showed 100 hours or more.

  In the rolling bearing for fuel cell system of the present invention, since the grease composition enclosed in the rolling bearing can effectively prevent specific peeling accompanied with white structure change occurring on the bearing rolling surface, the bearing life is excellent. In addition to the fuel cell system, it can be used as a rolling bearing used in a pumping machine for pumping various fluids at a high pressure in factories such as petroleum, petrochemicals, gas, and steel.

It is sectional drawing of a deep groove ball bearing. It is sectional drawing of an impeller type pressure feeder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Deep groove ball bearing 2 Inner ring 3 Outer ring 4 Rolling element 5 Cage 6 Seal member 7 Grease composition 8 Opening part 9 Impeller 10 Rotating shaft 11 Casing 12 Gas inlet 13 Back plate 14 Pressure volute 15 Gas outlet 16 Back space 17 Seal ring 18 Gap 19 Mechanical seal

Claims (9)

A rolling bearing for a fuel cell system that rotatably supports a rotating part provided in a pressure feeder for pumping fluid used in a fuel cell system,
The rolling bearing includes an inner ring and an outer ring, and a plurality of rolling elements interposed between the inner ring and the outer ring, and a seal member for sealing a grease composition around the rolling elements is provided on the shafts of the inner ring and the outer ring. The grease composition is a grease composition in which a thickener and an additive are blended with a base oil, and the additive contains at least molybdate. A rolling bearing for a fuel cell system.   The rolling bearing for a fuel cell system according to claim 1, wherein the molybdate is an alkali metal salt of molybdic acid.   3. The rolling for a fuel cell system according to claim 2, wherein the alkali metal salt of molybdic acid is at least one alkali metal salt of molybdic acid selected from sodium molybdate, potassium molybdate and lithium molybdate. bearing.   4. The fuel according to claim 1, wherein the molybdate is blended in an amount of 0.01 to 10 parts by weight with respect to 100 parts by weight of the total amount of base oil and thickener. Rolling bearing for battery system.   The rolling additive for a fuel cell system according to any one of claims 1 to 4, wherein the additive contains an organic acid salt.   6. The rolling bearing for a fuel cell system according to claim 5, wherein the organic acid salt is an alkali metal salt of an organic acid having 1 to 20 carbon atoms.   The molybdate is 0.01 to 5 parts by weight with respect to 100 parts by weight of the total amount of base oil and thickener, and the organic acid salt is 5 to 70 parts by weight with respect to 100 parts by weight of the molybdate added. The rolling bearing for a fuel cell system according to claim 5 or 6, characterized in that it is partially blended.   The rolling bearing for a fuel cell system according to any one of claims 1 to 7, wherein the thickener is a urea thickener. A rolling bearing for a fuel cell system that rotatably supports a rotating portion provided in a pump for pumping fluid used in a fuel cell system,
The grease composition enclosed in the bearing promotes the formation of the molybdate and the film capable of forming a film containing a molybdenum compound together with iron oxide on the frictional wear surface or the new ferrous metal surface exposed by wear in the bearing portion. A rolling bearing for a fuel cell system comprising an organic acid salt.

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