JP2019157082A - Solid lubricant and solid lubricant-sealed roll bearing - Google Patents

Abstract

To provide a solid lubricant capable of long-term use by suppressing initial oil separation ratio and subsequent oil separation, and a solid lubricant-sealed roll bearing in which the solid lubricant is sealed.SOLUTION: A solid lubricant 17 is a solid body of a blend containing a grease composed of a base oil and a thickener, an ultra-high molecular weight polyolefin, and an additive. The ultra-high molecular weight polyolefin is contained by 30-40 mass% to the whole solid lubricant, and the additive is a cellulose powder or a cellulose fiber and is contained by 5-10 mass% to the whole solid lubricant.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a solid lubricant and a rolling bearing in which the solid lubricant is enclosed, and more particularly to a solid lubricant containing ultrahigh molecular weight polyethylene as a resin component and the solid lubricant-enclosed rolling bearing.

  Conventionally, lubrication grease is enclosed in a rolling bearing for the purpose of reducing rolling friction and sliding friction. Rolling bearings filled with grease have a long life, do not require an external lubrication device, and are inexpensive, so they are widely used for general purposes such as automobiles and industrial machines.

  However, when a semi-solid lubricant such as grease is used, the rotational torque increases due to the stirring resistance by the lubricant. In order to solve this problem, a solid lubricant has been proposed in which a mixture of ultrahigh molecular weight polyethylene and a grease having a dropping point having a melting point higher than that of the ultrahigh molecular weight polyethylene is heated above the melting point to be solidified. (Patent Document 1).

Japanese Patent Publication No. 63-23239

  However, in the solid lubricant, the initial oil separation rate may increase. In that case, it is considered that the lubricating oil leaks out from the bearing, contaminates other parts, or the lubricating oil is not effectively used and the bearing life is shortened. From the viewpoint of bearing life, it is desirable that the lubricating oil contained in the solid lubricant exudes little by little and over a long period of time.

  The present invention has been made in view of the above circumstances, a solid lubricant that can be used for a longer time by suppressing the initial oil separation rate and subsequent oil separation, and a solid lubricant in which the solid lubricant is enclosed An object is to provide an encapsulated rolling bearing.

  The solid lubricant of the present invention is a solid lubricant that is a solid body of a mixture comprising a grease comprising a base oil and a thickener, an ultrahigh molecular weight polyolefin, and an additive, wherein the ultrahigh molecular weight polyolefin is, 30-40 mass% is contained with respect to the whole said solid lubricant, The said additive is a cellulose powder or a cellulose fiber, and 5-10 mass% is contained with respect to the said whole solid lubricant, It is characterized by the above-mentioned.

  The grease is contained in an amount of 50 to 65% by mass with respect to the entire solid lubricant.

The ultra high molecular weight polyolefin has an average molecular weight of 1 × 10 ^{6 to} 3 × 10 ⁶ .

  A solid lubricant-enclosed rolling bearing in which a solid lubricant is enclosed in a rolling bearing, wherein the solid lubricant is the solid lubricant of the present invention.

  The solid lubricant of the present invention is a solid lubricant containing grease, ultrahigh molecular weight polyolefin, and cellulose powder or cellulose fiber, and ultrahigh molecular weight polyolefin and cellulose material (hereinafter referred to as cellulose) with respect to the entire solid lubricant. A predetermined amount of each of the cellulose material including powder and cellulose fiber) is contained, so that the initial oil separation rate can be suppressed. Further, the base oil oozes out little by little from this solid lubricant, and can ooze out in a large amount and can be used for a long time.

  Since the solid lubricant encapsulated rolling bearing of the present invention encapsulates the solid lubricant of the present invention, the bearing life is excellent.

It is sectional drawing which shows an example of the solid lubricant enclosure rolling bearing of this invention. It is sectional drawing which shows the other example of the solid lubricant enclosure rolling bearing of this invention.

  The solid lubricant of the present invention is a lubricant obtained by solidifying a mixture of grease as a lubricating component, ultrahigh molecular weight polyolefin as a resin component, and an additive. Lubricity is imparted by the base oil contained in the grease exuding from the solid lubricant. The present inventors have found that by using cellulose powder or cellulose fiber as an additive, the initial oil separation rate can be suppressed and the subsequent oil separation can be suppressed. The present invention is based on such knowledge.

  The grease used in the present invention comprises a base oil and a thickener. The base oil is not particularly limited, and those commonly used in the field of grease can be used. For example, highly refined oils, mineral oils, ester synthetic oils, ether synthetic oils, synthetic hydrocarbon oils (PAO oils), silicone oils, fluorine oils, and mixed oils thereof can be used.

  Further, the thickening agent is not particularly limited, and a common one that is usually used in the field of grease can be used. For example, soap-type thickeners such as metal soaps and composite metal soaps, and non-soap-type thickeners such as benton, silica gel, urea compounds and urea / urethane compounds can be used. Examples of the metal soap include sodium soap, calcium soap, aluminum soap, and lithium soap. Examples of the urea compound and urea / urethane compound include diurea compounds, triurea compounds, tetraurea compounds, other polyurea compounds, and diurethane compounds. Among these, it is preferable to use a urea compound having excellent heat durability.

  The blending degree of grease (JIS K 2220) composed of the base oil and the thickener is preferably NLGI consistency number of 2 to 3. This range is suitable for suppressing oil separation.

Examples of the ultrahigh molecular weight polyolefin used in the present invention include a powder composed of polyethylene, polypropylene, polybutene or a copolymer thereof, or a mixed powder obtained by blending individual powders. Here, the average molecular weight of each powder measured by the viscosity method is preferably 1 × 10 ^{6 to} 3 × 10 ⁶ . This is because a polyolefin having such a molecular weight range is superior to a low molecular weight polyolefin in rigidity and oil retention. Of the ultra high molecular weight polyolefins, it is preferable to use ultra high molecular weight polyethylene.

  The content of the ultra-high molecular weight polyolefin in the solid lubricant of the present invention is 30 to 40% by mass, preferably 32 to 40% by mass, and more preferably 35 to 40% by mass with respect to the entire solid lubricant. . Oil content can be moderately suppressed by making this content into 30-40 mass%.

  Cellulose materials used in the present invention include softwood kraft pulp, hardwood kraft pulp, manila hemp pulp, sisal hemp pulp, bamboo pulp, esparto pulp, cotton pulp, etc., plant-derived cellulose, high polymerization degree by low acid melt spinning Regenerated cellulose (polynosic rayon), regenerated cellulose such as solvent-spun rayon using an amine-oxide organic solvent, bacteria-derived cellulose, animal-derived cellulose such as sea squirt, and nanocellulose by electrospinning. In the present invention, the cellulose powder is particulate cellulose having an aspect ratio (major axis / minor axis) of less than 3, and the cellulose fiber is fibrous cellulose having an aspect ratio of 3 or more.

  When cellulose powder is used as the cellulose material, it is preferable to use a cellulose powder having an average particle size of 50 μm or less by a particle size distribution analyzer (laser diffraction method), and an average particle size of 12 μm or less. Is more preferable. In terms of sieving, it is preferable to use particles that pass through a sieve having a sieve opening of 38 μm (US ASTM standard 400 mesh sieve).

  When cellulose fibers are used as the cellulose material, it is preferable to use cellulose fibers having a fiber size that is somewhat small. Specifically, cellulose fibers having an average fiber diameter of 20 μm or less and an average length of 100 μm or less are preferably used, and those having an average fiber diameter of 10 μm or less and an average length of 30 μm or less are used. It is more preferable.

  Moreover, you may use the cellulose nanofiber manufactured by a physical method or a chemical method from a plant origin cellulose as a cellulose fiber used for this invention. Examples of physical methods (defibration) include a high-pressure homogenizer method, a microfluidizer method, a ball mill pulverization method, and a grind mill pulverization method. Examples of the chemical method include a TEMPO oxidation method.

  When cellulose nanofibers are used, for example, those having an average fiber diameter of 4 to 500 nm and an average fiber length of 1 μm or more can be used. Further, those having an average fiber length / average fiber diameter aspect ratio of 10 or more can be used. In addition, the fiber diameter and fiber length in this invention can be measured with the electron microscope, atomic force microscope, etc. which are normally used in this field | area. The average fiber diameter and the average fiber length can be calculated as a number average fiber diameter and a number average fiber length based on the above measurement.

  In the solid lubricant of the present invention, the cellulosic material is an additive that suppresses oil seepage, and moderately suppresses the separation rate of oil that exudes to the oily surface of the solid lubricant. Content of a cellulose material is 5-10 mass% with respect to the whole solid lubricant, Preferably it is 7-10 mass%. By using a cellulose material of 5% by mass or more based on the entire solid lubricant, the oil separation rate can be suppressed, and the speed at which the oil oozes can be reduced. On the other hand, when the content of the cellulose material exceeds 10% by mass, the mechanical strength of the solid lubricant may be lowered.

  In the solid lubricant, the mass ratio of the ultra-high molecular weight polyolefin to the cellulose material is 3: 1 to 8: 1, preferably 3: 1 to 5: 1, more preferably 3.5: 1 to 4. .5: 1. In addition to the cellulose material, various organic or inorganic additives can be added to the solid lubricant of the present invention.

  In view of the above, as a more preferable form of the solid lubricant of the present invention, grease comprising a base oil and a thickener is 50 to 65% by mass, ultrahigh molecular weight polyolefin is 30 to 40% by mass, and cellulose material is 5%. 10 mass%, and the mass ratio of ultrahigh molecular weight polyolefin to cellulose material is 3: 1 to 5: 1. In this case, it is more preferable not to include other additives.

The solid lubricant of the present invention is a mixture of grease, a predetermined amount of ultrahigh molecular weight polyolefin, and a predetermined amount of cellulose material, and the mixture is directly enclosed in a mold or bearing having a predetermined shape. It is obtained by heating to a temperature equal to or higher than the gel point (melting temperature) and then cooling to solidify. A method of mixing the grease, the ultrahigh molecular weight olefin, and the cellulose material is not particularly limited, and a generally used stirrer such as a Henschel mixer or a ribbon mixer can be used. The heating (firing) condition is preferably higher than the gel point and lower than the dropping point of the grease. For example, when the average molecular weight of the ultrahigh molecular weight polyolefin is 1 × 10 ^{6 to} 3 × 10 ⁶ , it is preferable to heat at a temperature of 150 to 200 ° C.

  An example of a rolling bearing in which the solid lubricant of the present invention is enclosed will be described with reference to FIG. FIG. 1 is a cross-sectional view of a rolling bearing that encapsulates a solidified solid lubricant in a spot pack shape. In the rolling bearing 11, an inner ring 12 having an inner ring rolling surface on the outer peripheral surface and an outer ring 13 having an outer ring rolling surface on the inner peripheral surface are arranged concentrically, and a plurality of rolling bearings 11 are provided between the inner ring rolling surface and the outer ring rolling surface. A number of rolling elements 14 are arranged. A cage 15 holds the plurality of rolling elements 14. In the rolling bearing 11, a solid lubricant 17 is enclosed around the rolling element 14.

  FIG. 2 shows another example of a rolling bearing in which the solid lubricant of the present invention is enclosed. FIG. 2 is a cross-sectional view of a rolling bearing that is solidified and encloses a solid lubricant in a full pack shape. As in the case of FIG. 1, the rolling bearing 11 in the form of FIG. 2 includes an inner ring 12, an outer ring 13, a rolling element 14, and a cage 15, and the solid lubricant 17 is placed around the rolling element 14. It is obtained by encapsulating.

  The following method is mentioned as an example of the sealing method of the solid lubricant 17. A semi-solid product obtained by uniformly mixing a predetermined amount of the above grease, a predetermined amount of ultra-high molecular weight polyolefin, and a predetermined amount of cellulose material is sealed in the rolling bearing 11. As shown in FIGS. 1 (a) and 1 (b), the sealing method is such that a cage 15 made of two strips is overlapped and fixed by a rivet 16 between an inner ring 12 and an outer ring 13. What is enclosed in a so-called spot pack shape, or what is filled in a so-called full pack shape between the inner ring 12 and the outer ring 13 as shown in FIGS. 2 (a) and 2 (b). Can be mentioned. In such a sealed state, the entire bearing is heated to a temperature equal to or higher than the gel point of the ultra-high molecular weight polyolefin and equal to or lower than the dropping point of the grease, and then cooled and solidified, whereby the semi-solid material is obtained. Is solidified into a solid lubricant, and the solid lubricant-enclosed rolling bearing of the present invention is obtained.

  The type of the rolling bearing of the present invention is not limited, and may be an angular ball bearing, a cylindrical roller bearing, a needle roller bearing, a tapered roller bearing or the like in addition to the deep groove ball bearing shown in each drawing. Moreover, any of the form which has a sealing member, and the form which does not have a sealing member may be sufficient.

  About Example 1 and Comparative Examples 1 and 2, each component was mixed by the compounding composition (mass%) shown in Table 1, respectively. The obtained mixture was sealed in a ring-shaped mold so as to be a test piece of Φ10 mm × 8 mm, and the mass was measured (mass before heating). The encapsulated mixture was heated at 160 ° C. for 30 minutes together with the mold and then cooled to obtain a solid lubricant test piece. At this time, the oil which exuded was wiped off and the mass was measured (0 h mass after heating). Furthermore, the oil which exudes after standing at room temperature for 36 hours was wiped off and the mass was measured (36 hours after heating). Then, oil was extracted from the solid lubricant after standing for 36 h using a solvent, and the mass of the extracted oil was measured (oil extraction amount).

Based on the measured mass before heating, the oil separation rate (% by mass) was calculated by the following formula. The oil separation rate (0h) is the initial oil separation rate.
Oil separation rate (0h) = {(mass before heating−0h mass after heating) / mass before heating} × 100
Oil separation rate (36h) = {(mass before heating−36h mass after heating) / mass before heating} × 100
Moreover, durometer A hardness (based on JISK6253) was measured using the obtained solid lubricant test piece. The measurement results are shown in Table 1.

  As shown in Table 1, Example 1, which is the solid lubricant of the present invention, was superior to Comparative Examples 1 and 2 in the initial oil separation rate, the oil separation rate with time, and the oil extraction amount. . Specifically, the amount of oil extracted was the largest while the initial oil separation rate was 7% by mass or less and the change in oil separation rate until standing for 36 hours was 1% by mass or less. From this, the solid lubricant of Example 1 can be used for a long time because it can suppress the initial oil leakage and can slowly exude a large amount of oil. Further, the solid lubricant of Example 1 has a durometer A hardness of 80 or more, and the mechanical strength is maintained.

  Since the solid lubricant of Comparative Example 1 has a durometer A hardness of 80 or less, it may be damaged by centrifugal force during use. Moreover, although the comparative example 2 is excellent in mechanical strength, there are many initial oil separation rates of 9 mass% or more, and there exists a possibility of an oil leak. Moreover, since the amount of extracted oil is the smallest, the oil is not effectively used, and there is a possibility that the service life cannot be extended.

  As described above, since the solid lubricant of the present invention contains a predetermined amount of cellulose material, the initial and time-dependent oil separation rate is suppressed and a large amount of oil can be oozed while maintaining the mechanical strength. Because there is, it can exude oil for a long time little by little.

  Since the solid lubricant of the present invention can be used for a longer time by suppressing the initial oil separation rate and subsequent oil separation, it can be widely used as a solid lubricant for rolling bearings in which the solid lubricant is enclosed.

DESCRIPTION OF SYMBOLS 11 Rolling bearing 12 Inner ring 13 Outer ring 14 Rolling element 15 Cage 16 Rivet 17 Solid lubricant

Claims (4)

A solid lubricant which is a solid body of a mixture comprising a grease comprising a base oil and a thickener, an ultrahigh molecular weight polyolefin, and an additive,
The ultra high molecular weight polyolefin is contained in an amount of 30 to 40% by mass with respect to the whole solid lubricant,
The said additive is a cellulose powder or a cellulose fiber, and 5-10 mass% is contained with respect to the said solid lubricant whole, The solid lubricant characterized by the above-mentioned.   2. The solid lubricant according to claim 1, wherein the grease is contained in an amount of 50 to 65 mass% with respect to the entire solid lubricant. 3. The solid lubricant according to claim 1, wherein the ultra-high molecular weight polyolefin has an average molecular weight of 1 × 10 ^{6 to} 3 × 10 ⁶ . A solid lubricant encapsulated rolling bearing in which a solid lubricant is enclosed in a rolling bearing,
A solid lubricant-enclosed rolling bearing, wherein the solid lubricant is the solid lubricant according to any one of claims 1 to 3.

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