JPH10102083A - Lubricant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a long-life lubricant, not only excellent in abrasion resistance but also low in friction coefficient and usable in various machines and apparatuses by using an oil or a grease containing boron nitride. SOLUTION: This lubricant comprises a base oil and boron nitride and is used for a sliding member in which at least one surface of opposite sliding surfaces is composed of cast iron (preferably spherical graphite cast iron). Hexagonal boron nitride is preferably used as the boron nitride and the grain diameter size thereof is >=1 and <=30μm expressed in terms of average grain diameter. The grain diameter of secondary grains is <=30μm at the maximum and preferably <=20μm. A boron nitride having <=4 graphitization index for the hexagonal boron nitride is preferably selected for use. The content of the boron nitride is preferably 0.5-20wt.% in the total amount of the composition. Thereby, the resultant lubricant is effectively used for automobiles, ships, iron-manufacturing equipment and construction machines, high-temperature and high-speed bearings, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an automobile, a ship,
The present invention relates to a lubricant used for steelmaking equipment, construction machinery, high-temperature / high-speed bearings, and the like.

[0002]

2. Description of the Related Art Oils and greases are widely used as lubricants for various sliding parts in the fields of transportation machines such as automobiles, machinery for steel making, construction machines, and the like. For higher efficiency, there is an increasing demand for lubricants having higher performance characteristics. Conventionally, lubricants with improved lubrication properties by dispersing graphite and molybdenum disulfide in oil and grease lubricants have been used. Drugs are eagerly needed.

Recently, it has been studied to improve the lubricating properties by adding hexagonal boron nitride powder to a lubricant (Guo, Okada, Kimura: Production Research, Vol. 242, No. 4).
No. 6, page 4 (1994)). However, although it has been reported that hexagonal boron nitride powder is a solid lubricant having a layered crystal structure and can be improved in wear resistance by dispersing in a lubricant, the reduction of friction coefficient is insufficient. .

[0004]

That is, an object of the present invention is to provide not only excellent wear resistance but also a low coefficient of friction.
An object of the present invention is to provide a long-life lubricant for use in various machines and devices.

[0005]

Means for Solving the Problems The present inventors have conducted various studies experimentally in view of the above circumstances, and as a result, it has been found that an oil or grease lubricant containing boron nitride precipitates graphite in the structure. The present inventors have found that the coefficient of friction is remarkably reduced when used for a sliding member having cast iron as a sliding surface, and the present invention has been accomplished.

That is, the present invention provides a lubricant for a sliding member in which at least one of the opposed sliding surfaces is made of cast iron,
A lubricant characterized by containing a base oil and boron nitride, preferably the lubricant characterized in that the cast iron is spheroidal graphite cast iron; The lubricant is characterized by containing a lubricant.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS When a lubricant containing hexagonal boron nitride in a base oil is applied to a sliding member made of two bearing steels facing each other, boron nitride powder enters the sliding surface and slides. It is known that boron nitride causes interlayer slip on the moving surface, thereby preventing metal contact between sliding members and improving wear resistance. However, the coefficient of friction is still high, and there is no indication for reducing the coefficient. The present inventors have experimentally studied the combination of various sliding materials with a lubricant containing boron nitride, but the reason is unknown, but at least one of the opposed sliding surfaces is made of cast iron. Only when using a lubricant containing boron nitride in the sliding member, without impairing the wear resistance improvement effect, the knowledge that the friction coefficient can be reduced,
This has led to the present invention.

[0008] Boron nitride belongs to various crystal systems such as cubic, rhombohedral, hexagonal, etc.
Various materials such as N and t-BN are known, but hexagonal boron nitride is used in the present invention. This is because only hexagonal boron nitride has sliding performance due to its crystal structure.

With respect to the size of the hexagonal boron nitride particles, a method for evaluating the particle size using a microtrack is known, and the average particle size of the present invention is also measured by the above method.

By the way, boron nitride having a small average particle diameter often forms secondary particles by aggregating some of the particles, similarly to powder containing general fine particles. In the present invention, it is important to measure the size of the secondary particles, particularly the maximum diameter of the secondary particles, together with the measurement of the average particle size. The maximum diameter of the secondary particles can be facilitated using an optical microscope. That is, when a small amount of grease containing boron nitride is sandwiched between two slide glasses and observed with an optical microscope at a magnification of 200 to 400 times while transmitting light, secondary particles in which fine particles are aggregated are particles. Inside is dark. At this time, those having a bright color inside of the particles are not secondary particles, but are primary particles without aggregation of the particles. The major axis and minor axis (diameter in the direction perpendicular to the major axis) of the secondary particles in the visual field are measured, and the maximum value of the minor axis is defined as the maximum diameter of the secondary particles.

The present inventors have studied experimentally and found that the hexagonal boron nitride exhibits stable lubricant properties because no aggregation of boron nitride particles occurs in a lubricant composition such as oil or grease. Was found to be particularly important for.

That is, when hexagonal boron nitride is contained in a lubricant composition and actually used as a lubricant, in order to exhibit the above-described sliding performance inherent to boron nitride, the larger the particles, the larger the size of the particles. Good, but on the other hand the smaller the particles are, the easier it gets into between the two sliding surfaces. Furthermore, although the primary particles of boron nitride are generally flat,
Some may aggregate to form secondary particles. Since the secondary particles are not flat compared to the primary particles,
Since it is difficult to enter between the sliding surfaces, the friction characteristics of the lubricant deteriorate as a result. In addition, there is a problem that the base oil and the thickener in the lubricant hardly penetrate into the gaps between the primary particles constituting the secondary particles, and air tends to remain inside the secondary particles. If air remains, the amount of base oil and thickener around the boron nitride will be insufficient at the local area of the lubrication surface, and as a result, a sufficient amount of lubricant will not be supplied to the sliding surface, and the friction coefficient will decrease. A fluctuating phenomenon occurs.

As described above, with respect to the hexagonal boron nitride particles in the lubricant composition, there are appropriate sizes for the particle size and the secondary particle size of the powder aggregate, and
According to the results of the experimental studies by the present inventors, the average particle diameter of the particle diameter is 1 μm or more and 30 μm or less,
For secondary particles, the maximum is 30 μm or less, preferably 2 μm or less.
0 μm or less. When the average particle diameter is less than 1 μm or more than 30 μm, the particles are too small to exhibit sufficient boron nitride-specific sliding properties, or boron nitride particles are not supplied between sliding surfaces. For this reason, there may be a problem that the friction coefficient of the lubricant is not sufficiently reduced or stably, and the low friction coefficient cannot be maintained for a long period of time. As for the maximum diameter of the secondary particles, the smaller this is, the more the fluctuation of the coefficient of friction is suppressed, and if the maximum diameter of the secondary particles is 30 μm or less, preferably 20 μm or less, the stability of the frictional resistance further increases, and This is favorable because stable sliding characteristics can be achieved over the entire range. It is apparent that the lower limit of the maximum diameter of the secondary particles does not need to be specified from the gist of the present invention.

It is desirable that the hexagonal boron nitride has developed crystals in terms of slip forming ability. As an index for knowing the degree of development of the hexagonal boron nitride crystal, a graphitization index represented by Formula 1 is known.

[0015]

Where Ia is the peak area in X-ray diffraction of (100), Ib is (101), and Ic is (102). The smaller the graphitization index, the more the crystallinity The properties are good.

In the present invention, when boron nitride having a graphitization index of 4 or less is selected, the stability of the friction coefficient is good, and
A lubricant composition having more favorable lubricant properties is obtained.

Further, the content of boron nitride is in the range of 0.5 to 20% by weight, preferably 1 to 10% by weight, based on the total amount of the lubricant composition. If the amount is less than 0.5% by weight, a sufficient amount of boron nitride will not be supplied to the sliding surface. If the amount exceeds 20% by weight, the viscosity of the lubricant composition will be too high to exhibit sufficient lubricating performance. Since the required sliding characteristics are different depending on the application, it is selected for each application within the above range. In particular, in the range of 1 to 10% by weight, it is used for a wide range of applications, and a low friction coefficient is stably achieved. It is suitable.

In the present invention, the cast iron contains C:
2.5-4.0%, Si: 0.5-3.5%, Mn:
0.2 to 1.0%, P: 0.03 to 0.8%, and the feature is that graphite is dispersed and precipitated in the structure. The reason why the friction coefficient is reduced when such a cast iron is used is not well understood, but the interaction between the graphite precipitated on the sliding surface of the cast iron and the above-described boron nitride causes a stable formation of graphite and boron nitride. It is considered that a boundary lubrication layer is formed.

The cast iron is divided into (1) gray cast iron, (2) white cast iron, (3) chill cast iron,
It is classified into (4) mottled cast iron, (5) spheroidal graphite cast iron, (6) malleable cast iron, and (7) alloy cast iron, and at least one of two surfaces on which members made of these materials slide. The above phenomenon is found in which the coefficient of friction is reduced when used in any of the above methods, and any of them can be used in the present invention. In particular, according to the findings obtained by the present inventors experimentally studied, spherical graphite having a structure in which graphite is precipitated in a spherical form by adding an appropriate amount of a spheroidizing agent such as Mg, Si, Ca and Ce. Cast iron is preferred. Note that if cast iron is used for one surface of the sliding member in the opposing slide, bearing steel, mechanical steel, or the like may be used for the other surface of the slide member. Is more preferably achieved because the phenomenon of reduction of the above is further achieved.

As the base oil used in the present invention, various lubricating oils such as petroleum-based lubricating oils and synthetic oils can be used. As the petroleum-based lubricating oil, for example, a lubricating oil such as a paraffinic or naphthenic oil obtained by combining various refining treatments with a lubricating oil fraction obtained by distilling crude oil at normal pressure or reduced pressure is preferable. Examples of the synthetic oil include α-olefins such as polybutene and alkylbenzene. Examples include diesters such as alkyl naphthalene and ditridecyl glutarate, silicone oils, and perfluoroalkyl ethers. The base oil can be used alone or as a mixture when used. In addition, in the classification according to the application in which the lubricating oil is used, the lubricating oil can be applied to gear oil, bearing oil, turbine oil, engine oil and the like.

Another invention according to the present invention is a lubricant for a sliding member in which at least one of the opposed sliding surfaces is made of cast iron, characterized in that it contains a base oil, boron nitride and a thickener. Lubricant. As the thickener, a compound having a urea group (so-called urea-based thickener), metal soap, or the like can be used, and the amount of addition is 2 to 25 in the total amount of the base lubricant composed of the base oil and the thickener. weight%
Is common. As the urea-based thickener, for example, aliphatic diurea such as 4,4'bis (3-octylureido) diphenylmethane, and other various types such as alicyclic diurea, aromatic diurea, triurea, and tetraurea are known. Can also be used. As the metal soap, for example, sodium soap, calcium soap, aluminum soap, and lithium soap such as lithium-12 hydroxystearate can be used. Further, these urea-based thickeners and metal soaps can be used alone or in combination of urea-based thickeners and metal soaps. Further, the compound having a urea group is prepared by mixing a diisocyanate with a compound of a primary amine or a secondary amine, and adding
It can also be obtained by reacting at 200 ° C. Also,
The classification according to the use in which the lubricant containing the thickener is used can be applied to wheel bearing grease, constant velocity joint grease, bearing grease, and the like.

In the present invention, other components can be added as long as the lubricant does not deteriorate. Examples of the components include graphite, fluorocarbon, molybdenum disulfide, polytetrafluoroethylene, antimony sulfide, solid lubricants such as borates of alkali metals and alkaline earth metals, and sulfur compounds and phosphorus compounds. Various extreme pressure agents,
Various antioxidants represented by phenol compounds and amine compounds, rust inhibitors and the like can be mentioned.

Hereinafter, the present invention will be described more specifically based on Examples and Comparative Examples.

[0024]

【Example】

[Examples 1 to 3] V which is a paraffinic mineral oil as a base oil
Using G15, 1.5% by volume or 3% by volume of boron nitride was added to the total amount of the composition to prepare a lubricant. For the sliding test, a 3-roller / ring type tester shown in FIG. 1 was used. FIG. 2 is a cross-sectional view taken along line AA ′ of FIG. In this tester, although not shown, the upper ring-shaped test piece in the oil tank rotates and performs sliding friction with the three lower roller-shaped test pieces also fixed in the oil tank. . The ring-shaped test piece was made of bearing steel (SUJ2), and the three roller-shaped test pieces were made of spheroidal graphite cast iron (FCD4
50-10). After heating the lubricant to 40 ° C., a sliding test was carried out under the following conditions while stirring so that boron nitride did not precipitate, and the friction coefficient and the specific wear amount were measured. Table 1 shows the results.

<Sliding test conditions> Test load: 784 N Sliding speed: 157 mm / sec Test time: 60 min

[0026]

[Table 1]

Example 4 Boron nitride having an average diameter of 8.5 μm was added to grease using Li soap as a thickening agent in an amount of 1.5% by volume with respect to the total amount of the composition, and the mixture was subjected to three-stage roll mill By mixing, a lubricant was prepared. In this example, the lubricant was applied to a roller-shaped test piece in an appropriate amount, and
An evaluation test was performed under the same conditions as in Example 3. Table 1 shows the results.
Shown in

Comparative Examples 1 and 2 As Comparative Example 1, an evaluation test was performed under the same conditions as in Example 1 except that three roller-shaped test pieces were made of bearing steel (SUJ2). Further, as Comparative Example 2, an evaluation test was performed under the same conditions as in Example 1 except that graphite was used as the solid lubricant. Table 1 shows the results.

[0029]

Industrial Applicability The lubricant of the present invention has a low coefficient of friction, a low specific wear amount, and good wear resistance, so that the service life of the machine / apparatus using the lubricant can be prolonged. Above is useful.

[Brief description of the drawings]

FIG. 1 shows a three-roller / ring type friction tester used in Examples and Comparative Examples.

FIG. 2 is a cross-sectional view taken along line A-A ′ of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ring-shaped test piece 2 Roller-shaped test piece 3 Holding plate 4 Mounting screw 5 Base

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C10N 40:02 40:06 50:10

Claims (3)

[Claims] 1. A lubricant for a sliding member, wherein at least one of the opposed sliding surfaces is made of cast iron, wherein the lubricant contains a base oil and boron nitride. 2. The lubricant according to claim 1, wherein said cast iron is spheroidal graphite cast iron. 3. The lubricant according to claim 1, further comprising a base oil, boron nitride and a thickener.