KR20120042743A - Grease composition and machine component - Google Patents

Abstract

A grease composition containing a base oil, a thickener and an additive,
40 degreeC dynamic viscosity of base oil is 50-200mm <2> / s,
The thickener contains a diurea compound represented by the following general formula (I),
Formula (I): R ¹ -NHCONH-R ² -NHCONH-R ³
(Wherein R ² is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R ¹ and R ³ are the same or different groups and represent a cyclohexyl group, a straight or branched alkyl group having 8 to 22 carbon atoms)
The additive is at least one selected from the group consisting of metal salts of naphthenic acid, salts of fatty acids having 6 to 10 carbon atoms and aliphatic amines having 6 to 10 carbon atoms, and organic sulfonic acid metal salts. The composition of this invention is excellent in fritting resistance from normal temperature to low temperature (for example, about -50 degreeC, Preferably about -40 degreeC).

Description

Grease composition and machine component

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to grease compositions and mechanical parts, and more particularly, to lubricating grease compositions having excellent fretting resistance under normal temperatures to low temperatures, and mechanical parts such as bearings enclosed therein.

Automobiles, electrical appliances, various mechanical parts and products are often transported by rail or truck. During this conveyance, fretting occurs in grease-coated lubrication parts due to vibration caused by seams or rough roads of the rails. Fretting is a surface damage that occurs under a small amplitude, and it is known that oxidative wear is generated in the air, and that the abrasive action causes severe abrasion. (Yamamoto Yuji et al .: Tribolage, Science and Engineering, 1999 201--20 pages published November 25).

The countermeasures include (1) reducing the relative sliding amount, (2) separating both sides, preventing direct contact, and (3) coating the contact surface such as phosphate coating or preventing adhesion between surfaces by supplying lubricant / grease. Yamamoto Yuji, et al .: Tribolage, Science and Engineering, published on November 25, 1999, pages 201 to 203.

In practice, greases with excellent fretting resistance are often developed and reviewed in the field of grease technology for automotive wheel bearings. For example, the use of aromatic diurea as a thickener to soften the roughness has been reported to significantly improve the fretting resistance compared to grease using lithium soap as a conventional thickener (T. Endo). Eurogrease, November / December (1997) pages 25-40).

In this way, there has been a countermeasure such as changing the type of thickening agent or softening the roughness to improve the inflow of grease.

However, aromatic diurea is inferior in fluidity, and when used in a bearing, for example, has a long life in deep groove bearings, but in angular contact ball bearings, there is a drawback in that the lubrication life is short due to insufficient inflow into the lubrication portion. The bearing is limited. Thus, the improvement by the change of a thickener has a problem that the grease obtained is inferior in versatility.

In addition, if the roughness is softened, there is a problem of leakage. Therefore, this is also less versatile as grease.

However, these are all reported as a countermeasure against fretting occurring at room temperature, and there are few reports that fretting occurring at low temperature can be prevented.

In addition, under low temperature, as the viscosity of the base oil increases, the inflow of grease decreases, so that (3) the ability to prevent adhesion between surfaces by the supply of grease decreases. Therefore, a countermeasure to use a base oil mainly composed of expensive synthetic oil in order not to cause an increase in viscosity of the base oil under low temperature is conceivable. However, there is no sufficient inhibitory effect on the increase of base oil viscosity, resulting in an increase in raw material costs. have.

An object of the present invention is to provide a grease composition excellent in fritting resistance.

It is another object of the present invention to provide an oil-resistant coating at room temperature to low temperature (e.g., -50 ° C, preferably about -40 ° C) without leaning on a base oil mainly composed of expensive synthetic oils. It is to provide a grease composition having excellent ting property.

Another object of the present invention is to provide a mechanical part using the grease composition.

The present invention provides a grease composition and a mechanical part shown below.

1.A grease composition containing a base oil, a thickener and an additive,

40 degreeC dynamic viscosity of base oil is 50-200mm <2> / s,

The thickener contains a diurea compound represented by the following general formula (I),

Formula (I): R ¹ -NHCONH-R ² -NHCONH-R ³

(Wherein R ² is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R ¹ and R ³ are the same or different groups and represent a cyclohexyl group, a straight or branched alkyl group having 8 to 22 carbon atoms)

The additive is at least one selected from the group consisting of naphthenic acid metal salts, salts of fatty acids having 6 to 10 carbon atoms and aliphatic amines having 6 to 10 carbon atoms, and organic sulfonic acid metal salts.

2. The metal naphthenic acid salt is at least one member selected from the group consisting of zinc cyclopentanoate and zinc cyclohexanoate, and the amine salt is a salt of a linear fatty acid having 6 to 10 carbon atoms and a linear aliphatic amine having 6 to 10 carbon atoms. And the organic sulfonate is at least one selected from the group consisting of dinonylnaphthalenesulfonate calcium salt, dinonylnaphthalenesulfonate zinc salt and dinonylnaphthalenesulfonate barium salt.

3. Content of the said naphthenic acid metal salt is 0.5-5.0 mass%, the content of the said amine salt is 1.5-5.0 mass%, and content of the said organic sulfonic acid metal salt is 1.5-5.0 mass% in grease composition, The said 1 or The grease composition of 2.

4. A mechanical part formed by encapsulating a grease composition according to any one of 1 to 3 above.

The grease composition of the present invention is excellent in fretting resistance. Therefore, the grease composition of the present invention can be used for lubrication of various mechanical parts. The target mechanical parts are not particularly limited, but for example, rolling bearings, ball screws, linear guide bearings, various gears, cams and constant velocity joints, journal bearings (sliding bearings), pistons, screws, ropes, chains, etc. Can be. It is particularly suitable for rolling bearings.

The base oil used in the grease composition of the present invention is not particularly limited as long as the kinematic viscosity at 40 ° C is 50 to 200 mm 2 / s. If the kinematic viscosity at 40 ° C. is less than 50 mm 2 / s, the oil film tends to be thin, and a sufficient oil film thickness may not be secured. If it exceeds 200 mm 2 / s, the viscosity resistance tends to increase.

Mineral oil is most preferred in terms of cost and performance. It is possible to mix and use mineral oil or synthetic oil as needed.

Examples of the synthetic oils include ester-based synthetic oils represented by diesters and polyol esters, synthetic hydrocarbon oils represented by polyαolefins and polybutenes, ether-based synthetic oils represented by alkyldiphenyl ethers and polypropylene glycols, and silicone oils. Various synthetic oils can be used, and these may be used alone or in combination of two or more thereof.

However, from the viewpoint of cost and performance, the content of mineral oil in the base oil is preferably 70% by mass or more, more preferably 80 to 100% by mass, most preferably 100% by mass.

The thickener used in the grease composition of this invention contains the specific diurea compound represented by general formula (I).

The content of the diurea compound in the grease composition of the present invention is preferably such that the roughness of the grease composition is 235 to 325, more preferably 280 to 325. Specifically, it is preferably 5-15 mass%, more preferably 8-12 mass% with respect to the whole grease composition.

If the shear is applied to the grease at less than 5 mass%, the grease will soften, and the grease will easily leak from the mechanical parts.

On the other hand, in grease using a metal soap such as lithium soap as a thickener, it is impossible to impart sufficient fretting resistance.

The additive used in the grease composition of the present invention contains at least one member selected from the group consisting of naphthenic acid metal salts, salts of fatty acids having 6 to 10 carbon atoms and aliphatic amines having 6 to 10 carbon atoms, and organic sulfonic acid metal salts.

Zinc, magnesium, calcium, aluminum etc. are mentioned as a metal of a naphthenic acid metal salt. Among them, zinc salts are particularly excellent.

The fatty acid having 6 to 10 carbon atoms constituting the amine salt may be a straight or branched chain fatty acid.

Moreover, the C6-C10 aliphatic amine which comprises the said amine salt should just be a linear or branched aliphatic amine. Preferably it is a salt of a C6-C10 straight chain fatty acid and a C6-C10 linear aliphatic amine, More preferably, it is a salt of C8-C straight fatty acid and C8-C straight aliphatic amine.

As organic sulfonic acid which comprises the said organic sulfonic-acid metal salt, synthetic sulfonic acids, such as petroleum sulfonate obtained by sulfonation of the aromatic hydrocarbon component in lubricating oil fraction, dinonyl naphthalene sulfonic acid, and heavy alkylbenzene sulfonic acid, are mentioned.

Examples of the metal of the organic sulfonic acid metal salt include calcium, zinc, barium and sodium. The organic sulfonic acid calcium salt may be neutral or high basic salt. For example, a calcium salt having a base of 50 to 500 mgKOH / g is used.

Preferably it is a metal salt of dinonyl naphthalene sulfonic acid, Especially preferably, it is a calcium salt, zinc salt, and barium salt of dinonyl naphthalene sulfonic acid.

In the grease composition of this invention, content of the naphthenic acid metal salt becomes like this. Preferably it is 0.5-5.0 mass%, Especially preferably, it is 1.0-5.0 mass%.

Content of the salt of a C6-C10 fatty acid and C6-C10 aliphatic amine becomes like this. Preferably it is 1.5-5.0 mass%, Especially preferably, it is 2.0-5.0 mass%.

The content of the organic sulfonic acid metal salt is preferably 1.5 to 5.0 mass%, particularly preferably 2.0 to 5.0 mass%.

What is necessary is just to adjust content suitably when using 2 or more types together.

If the content is less than the above, there is an effect as a rust preventive agent, but the fretting prevention effect occurring from normal temperature to low temperature is insufficient, and even if it is added 5.0 mass% or more, further addition effect is not recognized and it is uneconomical.

Naphthenic acid metal salts, fatty acid amine salts and organic sulfonates used as additives in the grease composition of the present invention are generally used for a wide range of applications as rust inhibitors for lubricating oils, and are also used as rust inhibitors for greases as well.

However, there are no reports or disclosures that the naphthenic acid metal salts, amine salts, and organic sulfonic acid metal salts have an effect on preventing fretting occurring from room temperature to low temperature.

To the grease composition of the present invention, other general purpose additives other than the naphthenic acid metal salts, amine salts and organic sulfonic acid metal salts may be added as necessary. For example, the additive shown below is mentioned.

Antioxidant

 Amines: phenyl α naphthylamine, alkylated phenyl α naphthylamine, alkylated diphenylamine, etc.

 Phenols: 2, 6-di-tert-butyl-p-cresol, pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl- Hindered phenols, such as 3- (3, 5-di-t- butyl- 4-hydroxyphenyl) propionate, etc.

 Quinoline series: 2, 2, 4-trimethyl-1, 2 dihydroquinoline polymer, etc.

Antirust

 Carbonic acid and its derivatives: alkenyl amber acid anhydride, alkenyl amber acid ester, alkenyl amber acid ester

 Carbonates: metal salts (Ca, Ba, Mg, Al, Zn, Na, etc.) or amine salts such as fatty acids, dibasic acids, lanolin fatty acids, alkenyl succinic acids

 Passivating agent: Na nitrite, Na molybdate

 Ester: sorbitan trioleate, sorbitan monooleate, etc.

 Metal corrosion inhibitors: benzotriazole or its derivatives, zinc oxide, etc.

Extreme pressure agent

 Phosphorus compound: Tricredyl phosphate, tri-2-ethylhexyl phosphate, etc.

 Sulfur compounds: dibenzyl disulfide, various polysulfides, etc.

 Sulfur-phosphorus compounds: triphenylphosphoronate

 Organometallic extreme pressure agents: salts such as Zn, Mo, Sb, Bi of dialkyldithiophosphoric acid, salts such as Zn, Mo, Sb, Ni, Cu, Bi of dialkyldithiocarbamic acid, etc.

 In addition, ashless dithiocarbamate, ashless dithiophosphate carbamate

Solid lubricants: molybdenum disulfide, graphite, PTFE, MCA and the like.

Prevention of fretting at room temperature can be handled by changing the type of thickener (effect of (2) by the aromatic urea coating), or by softening the roughness (making grease inflow good) (Comparative Example described later). 6-10, Comparative Examples 19 and 20).

However, under low temperature, the fretting prevention effect by supply of grease cannot be expected by the fall of grease inflow property.

The grease composition of the present invention contains a specific additive (a naphthenic acid metal salt, a salt of a fatty acid having 6 to 10 carbon atoms and an aliphatic amine having 6 to 10 carbon atoms, or an organic sulfonic acid metal salt). For this reason, when this is used, for example, in a bearing, the strong adsorption force on the surface of the member of this additive exerts an adhesive action at the interface between the diurea grease and the ball and the inner and outer races, resulting in a decrease in grease inflow. It is thought that the fretting under low temperature can be prevented by fully isolate | separating both surfaces and preventing direct contact also under under.

The effect of the present invention that the fretting resistance from normal temperature to low temperature can be improved by the addition of a specific additive is not easily predicted by those skilled in the art.

(Examples 1-14, Comparative Examples 1-17)

A predetermined amount was reacted with 1 mol of the raw material isocyanate at a ratio of 2 mol of the raw amine in the base oil, and a predetermined amount was added to the additive to adjust the roughness to a prescribed level with a three-stage roll mill.

(Comparative Example 18)

After mixing, dissolving, cooling a predetermined amount of lithium hydroxystearate in a predetermined amount of base, and cooling it, a predetermined amount was added to the additive, and adjusted to a prescribed roughness with a three-stage roll mill.

(Test Methods)

Miscibility: JIS K 2220.7

-Fafnir friction oxidation test (according to ADTM D 4170)

-Standard test to evaluate fretting resistance

Test grease is applied to the following two test thrust bearings, and the prescribed swinging operation is performed to determine the amount of wear (weight loss due to fretting wear).

[Exam conditions]

Bearing: ANDREWS W 5/8

Load: 2450 N (5501bf) (surface pressure: 1861 MPa)

Rotation angle: 0.21 rad (12 °)

Oscillating cycle: 25 Hz

Time: 22h

Temperature: 25 ℃, -30 ℃

Grease loading: 1.0 g per bearing

Abrasion: Reduction of race mass per bearing (total mass reduction of test bearing race / 2)

[Judgment]

◎: Abrasion amount 2.0 mg or less (fretting resistance: considerably large)

○: Abrasion amount greater than 2.0 and less than 5.0 mg (fretting resistance: large)

(Triangle | delta): More than 5.0 amount of abrasions less than 15.0 mg (fretting resistance: there exists some)

X: Abrasion amount 15.0 mg or more (fretting resistance: no)

Antirust Test: ASTM D1743-73 Bearing Antirust Test

[Judgment]

○: no rust

×: rust

The results are shown in Tables 1-5.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Isocyanate MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} Amine
(Molar ratio) ODA (1) ODA (1) ODA (1) ODA (1) ODA (1) ODA (1) ODA (1) CHA (7) CHA (7) CHA (7) CHA (7) CHA (7) CHA (7) CHA (7) Thickener (mass%) 11 11 11 11 11 11 11 Base oil
(Mixed mass ratio) Mineral oil (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Base oil (mass%) 88.3 88.0 87.0 87.0 87.0 87.0 87.0 Base oil kinematic viscosity (40 ℃) ㎠ / s 100 100 100 100 100 100 100 Zinc naphthenate ^{* 2} 0.7 1.0 2.0 Fatty acid amine salt ^{* 3} 2.0 Ca sulfonate ^{※ 4} 2.0 Zn sulfonate ^{* 5} 2.0 Ba sulfonate ^{※ 6} 2.0 Mixed illumination 300 300 300 300 300 300 300 Abrasion 25 ℃ ○ ◎ ◎ ◎ ◎ ◎ ◎ Abrasion -30 ℃ ○ ◎ ◎ ◎ ◎ ◎ ◎ Antirust test ○ ○ ○ ○ ○ ○ ○

Example 8 Example 9 Example 10 Example 11 Example 12 Example 13 Example 14 Isocyanate MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} Amine
(Molar ratio) OA OA OA OA OA OA OA Thickener (mass%) 9 9 9 9 9 9 9 Base oil
(Mixed mass ratio) Mineral oil (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Base oil (mass%) 90.3 90.0 89.0 89.0 89.0 89.0 89.0 Base oil kinematic viscosity (40 ℃) ㎠ / s 100 100 100 100 100 100 100 Zinc naphthenate ^{* 2} 0.7 1.0 2.0 Fatty acid amine salt ^{* 3} 2.0 Ca sulfonate ^{※ 4} 2.0 Zn sulfonate ^{* 5} 2.0 Ba sulfonate ^{※ 6} 2.0 Mixed illumination 300 300 300 300 300 300 300 Abrasion 25 ℃ ○ ◎ ◎ ◎ ◎ ◎ ◎ Abrasion -30 ℃ ○ ◎ ◎ ◎ ◎ ◎ ◎ Antirust test ○ ○ ○ ○ ○ ○ ○

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Isocyanate MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} Amine
(Molar ratio) ODA (1) ODA (1) ODA (1) ODA (1) ODA (1) ODA (1) CHA (7) CHA (7) CHA (7) CHA (7) CHA (7) CHA (7) Thickener (mass%) 11 11 11 11 11 11 Base oil
(Mixed mass ratio) Mineral oil (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Base oil (mass%) 89.0 87.0 87.0 87.0 87.0 87.0 Base oil kinematic viscosity (40 ℃) ㎠ / s 100 100 100 100 100 100 Phosphorothionate ^{※ 7} 2.0 Calcium Carbonate ^{※ 8} 2.0 Zinc Stearate ^{※ 9} 2.0 MoDTC ^{※ 10} 2.0 ZnDTP ^{※ 11} 2.0 Mixed illumination 300 300 300 300 300 300 Abrasion 25 ℃ × ○ × ○ × × Abrasion -30 ℃ × × × × × × Antirust test × × × × × ×

Comparative Example 7 Comparative Example 8 Comparative Example 9 Comparative Example 10 Comparative Example 11 Comparative Example 12 Isocyanate MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} Amine
(Molar ratio) ODA (1) ODA (1) ODA (1) OA OA OA CHA (7) CHA (7) CHA (7) Thickener (mass%) 11 8 11 9 9 9 Base oil
(Mixed mass ratio) Mineral oil (100) Mineral oil (100) PAO (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Base oil (mass%) 89 92 89 91 89 89 Base oil kinematic viscosity (40 ℃) ㎠ / s 40 100 100 100 100 100 Phosphorothionate ^{※ 7} 2.0 Calcium Carbonate ^{※ 8} 2.0 Mixed illumination 300 340 300 300 300 300 Abrasion 25 ℃ △ △ × × ○ × Abrasion -30 ℃ × × × × × × Antirust test × × × × × ×

Comparative Example 13 Comparative Example 14 Comparative Example 15 Comparative Example 16 Comparative Example 17 Comparative Example 18 Isocyanate MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} MDI ^{* 1} Li soap Amine OA OA OA OA OA Thickener (mass%) 9 9 9 9 7 8 Base oil
(Mixed mass ratio) Mineral oil (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Mineral oil (100) Base oil (mass%) 89 89 89 91 93 90 Base oil kinematic viscosity (40 ℃) ㎠ / s 100 100 100 40 100 100 Zinc naphthenate ^{* 2} 2.0 Zinc Stearate ^{※ 9} 2.0 MoDTC ^{※ 10} 2.0 ZnDTP ^{※ 11} 2.0 Mixed illumination 300 300 300 300 340 300 Abrasion 25 ℃ ○ × × △ △ × Abrasion -30 ℃ × × × × × × Antirust test × × × × × ○

※One; Diphenylmethane diisocyanate

※2; Naphthenic acid metal salt mainly containing zinc cyclopentanoate

* 3; Salts of straight-chain fatty acids having 8 carbon atoms and straight-chain aliphatic amines having 8 carbon atoms

※4; Dinonyl naphthalene sulfonate calcium

* 5; Zinc dinonyl phthalene sulfonate

※ 6; Dinonyl naphthalene sulfonate barium

※ 7; Mixtures of Alkylphosphoronate Compounds and Amine Compounds

     HITEC 833 (product made by Apton Chemical Corporation)

※8; Calcium carbonate

※ 9; Zinc stearate

※ 10; MOLYVAN A (product made in R.T.VANDERBILT company)

※ 11; LUBRIZOL 1395 (product made in Japan Lubrizol company)

ODA: Octadecylamine

CHA: cyclohexylamine

OA: octylamine

PAO: Poly-α-olefin

In addition, the addition amount in the total amount of grease in (2) of * 2-* 6, * 8, * 9 in a table | surface: The mass% shows the active ingredient concentration of an additive.

In addition, in the table, the addition amount in the total amount of grease in () of (7), (10), and (11): the mass% indicates the concentration of the product added.

The grease compositions of Examples 1 to 14 to which naphthenic acid metal salts, salts of 6 to 10 carbon atoms and aliphatic amines of 6 to 10 carbon atoms, or organic sulfonic acid metal salts are added as additives, are prepared at room temperature and low temperature without softening roughness. Less wear, excellent fretting resistance and excellent rust resistance.

The grease compositions of Comparative Examples 1, 9 and 10 that do not contain the specific additive of the present invention have a large amount of abrasion under normal temperature and low temperature, resulting in poor fretting resistance and poor rust resistance.

The grease compositions of Comparative Examples 2, 4, 11 and 13, which contain additives different from the specific additives of the present invention, have a small amount of abrasion at room temperature, but a large amount of abrasion at low temperature, resulting in poor fretting resistance and poor rust resistance.

The grease compositions of Comparative Examples 3, 5, 6, 12, 14, and 15, which contain additives different from the specific additives of the present invention, have a large amount of abrasion under normal temperature and low temperature, resulting in poor fretting resistance and poor rust resistance.

The grease compositions of Comparative Examples 7 and 16 using a base oil having a low kinematic viscosity have a small amount of abrasion at room temperature, but a large amount of abrasion at low temperature results in poor fretting resistance and rust resistance.

The grease compositions of Comparative Examples 8 and 17 having a small content of a thickener have a high degree of miscibility and a little wear at normal temperature, but a large amount of wear at low temperature results in poor fretting resistance and rust resistance.

The grease composition of Comparative Example 18 using lithium soap as a thickener is excellent in rust resistance, but has a large amount of abrasion under normal temperature and low temperature, resulting in inferior fretting resistance.

Claims (4)

A grease composition containing a base oil, a thickener and an additive,
40 degreeC dynamic viscosity of base oil is 50-200mm <2> / s,
The thickener contains a diurea compound represented by the following general formula (I),
Formula (I): R ¹ -NHCONH-R ² -NHCONH-R ³
(Wherein R ² is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R ¹ and R ³ are the same or different groups and represent a cyclohexyl group, a straight or branched alkyl group having 8 to 22 carbon atoms)
The additive is at least one selected from the group consisting of naphthenic acid metal salts, salts of fatty acids having 6 to 10 carbon atoms and aliphatic amines having 6 to 10 carbon atoms, and organic sulfonic acid metal salts. The method of claim 1,
The naphthenic acid metal salt is at least one selected from the group consisting of zinc cyclopentanoate and zinc cyclohexanoate, wherein the amine salt is a salt of a linear fatty acid having 6 to 10 carbon atoms and a linear aliphatic amine having 6 to 10 carbon atoms, An organic sulfonate is at least one member selected from the group consisting of dinonylnaphthalenesulfonate calcium salt, dinonylnaphthalenesulfonate zinc salt and dinonylnaphthalenesulfonate barium salt. 3. The method according to claim 1 or 2,
The grease composition, wherein the content of the naphthenic acid metal salt is 0.5 to 5.0 mass%, the content of the amine salt is 1.5 to 5.0 mass%, and the content of the organic sulfonic acid metal salt is 1.5 to 5.0 mass%. A mechanical part formed by enclosing the grease composition according to any one of claims 1 to 3.