JP5122730B2 - Solid lubricant and rolling bearing with solid lubricant - Google Patents

Description

  The present invention relates to a solid lubricant used under conditions in which the fluidity of the lubricant itself hinders lubrication, and a rolling bearing enclosing the solid lubricant, and more particularly, a stranded wire machine, an electric device, or an automobile part. The present invention relates to a solid lubricant-enclosed rolling bearing that is used as various bearings.

  In general, a rolling bearing lubricated with grease needs to be sealed by providing a sealing device such as a seal member in order to cope with the fluidity of grease during rotation of the bearing. Therefore, this grease lubrication method cannot be adopted for a special bearing with a small width that cannot be sealed. Further, in a stranded wire machine in which the bearing itself is centrifugally moved, the grease in the bearing is scattered by the action of centrifugal force and seized in a short period of time, so the grease has to be frequently replaced.

  Therefore, the bearing is reduced in size without the need for a seal member, etc., and a lubricating composition for preventing the lubricant from scattering even by the centrifugal motion of the bearing itself, for example, a liquid obtained by mixing ultrahigh molecular weight polyethylene and lubricating oil such as mineral oil.・ After filling the semi-solid mixture into the bearing space, a lubricating composition has been developed that solidifies by heat treatment with the bearing, and the above special bearing has been successful.

  However, even in such a lubricating composition, the entire lubricating composition or only the lubricating oil naturally flows before the heat treatment. Therefore, when filling the bearing, it is necessary to artificially hold the mixture in the inner space between the inner and outer rings of the bearing until it hardens, and the metal lid or the like prevents the mixture from flowing out. Moreover, since it has high fluidity, it is easy to fill the bearing internal space, and it is difficult to keep it partially filled. As a result, the bearing torque tends to increase. Further, when a synthetic oil such as a diester is used as the lubricating oil, there has been a problem that the oil is released during heating, that is, the oil oozes out from the solid lubricant.

  In order to cope with the above-mentioned various problems, the present inventors heated a mixture containing ultrahigh molecular weight polyethylene and grease having a dropping point higher than the melting point of the polyethylene to the melting point, and solidified the bearing. A lubricating composition is disclosed (see Patent Document 1 and Patent Document 2).

However, if the ratio of the grease and oil lubricant components is increased in order to improve the lubricity, the mechanical strength of the solidified lubricating composition for bearings is significantly reduced, and the solid state is affected by centrifugal force under high speed rotation. There are problems such as destruction.
Japanese Patent Publication No. 63-23239 Japanese Patent No. 2912733

  The present invention has been made to address such problems, and is a solid lubricant composed of a lubricant and an ultra-high molecular weight polyolefin, and even if the ratio of the lubricant component is increased, It is an object of the present invention to provide a solid lubricant capable of maintaining sufficient lubrication performance and mechanical strength in a bearing application such as a stranded wire machine, an electric device, or an automobile part, and a rolling bearing in which the solid lubricant is sealed.

The solid lubricant of the present invention comprises a mixture containing at least a lubricant and an ultrahigh molecular weight polyolefin powder having an average molecular weight of 1 × 10 ^{6 to} 5 × 10 ⁶ , at a temperature equal to or higher than the gel point of the ultrahigh molecular weight polyolefin powder. A solid lubricant formed by heating and cooling to solid, wherein the lubricant is a grease containing an oil composed of at least one mineral oil as a base oil, and the oil is subjected to ndM ring analysis. It is characterized in that the ratio of naphthene carbon number to total carbon number obtained by law is 30% or more. In the following, the ratio of naphthene carbon number is expressed as naphthene carbon amount (%).

A mixture containing at least a lubricant and an ultrahigh molecular weight polyolefin powder having an average molecular weight of 1 × 10 ^{6 to} 5 × 10 ⁶ is heated to a temperature equal to or higher than the gel point of the ultrahigh molecular weight polyolefin powder, and then cooled and solidified. The lubricant is a solid lubricant, and the lubricant is an oil composed of at least one mineral oil, and the oil has the number of naphthene carbon in the total number of carbons determined by the ndM ring analysis method. Is characterized by a ratio of 30% or more.

Here, the gel point of the ultrahigh molecular weight polyolefin powder refers to a temperature at which the viscosity of the mixture rapidly increases when the mixture with grease or mineral oil is stirred while being heated.
In addition, the ndM ring analysis method is an empirical formula based on n (refractive index), d (density), M (average molecular weight), and sulfur content of aromatic components, naphthene components, and paraffin components in oil. This is an estimation method (ASTM D 3238-80). The naphthene carbon number in the present invention is the base oil when grease is used as a lubricant, and the number of carbons constituting the naphthene component contained in the oil when oil is used as a lubricant, that is, the naphthene hydrocarbon. It is.

The mixture is characterized by comprising 60 to 90% by weight of the lubricant and 40 to 10% by weight of the ultrahigh molecular weight polyolefin powder.
The mixture comprises 50 to 89% by weight of the lubricant, 40 to 10% by weight of the ultrahigh molecular weight polyolefin powder, and 10 to 1% by weight of solid wax.

  The solid lubricant encapsulated rolling bearing of the present invention is an inner ring and an outer ring, a rolling element interposed between the inner ring and the outer ring, and a rolling bearing formed by enclosing a solid lubricant around the rolling element. The lubricant is the solid lubricant described above.

The solid lubricant of the present invention comprises an oil comprising at least one mineral oil, or a grease based on the oil, an ultrahigh molecular weight polyolefin powder having an average molecular weight of 1 × 10 ^{6 to} 5 × 10 ⁶ , a solid wax, Is a mixture obtained by heating to a temperature equal to or higher than the gel point of the ultra-high molecular weight polyolefin powder and then solidifying by cooling. The above oil is an oil having a naphthene carbon content of 30% or more. Therefore, even if the amount of lubricant is increased, sufficient mechanical strength and hardness as a solid lubricant can be maintained.

  Since the solid lubricant encapsulated rolling bearing of the present invention is formed by encapsulating the solid lubricant of the present invention, sufficient mechanical strength and hardness as a solid lubricant can be maintained even if the amount of the lubricant is increased, Solid lubricant for bearings used under conditions that impede the fluidity of the solid lubricant itself, such as stranding machines, electric equipment, printers, automobile parts, electrical accessories, construction machinery, etc. It can be suitably used as a solid lubricant used for bearings of various industrial machines.

The ultrahigh molecular weight polyolefin powder used in the present invention may be a powder composed of polyethylene, polypropylene, polybutene or a copolymer thereof, or a mixed powder obtained by blending individual powders, and is measured by the viscosity method of each powder. The average molecular weight is 1 × 10 ^{6 to} 5 × 10 ⁶ . A polyolefin having such a molecular weight range is superior to a low molecular weight polyolefin in rigidity and oil retention, and hardly flows even when heated to a high temperature.

The oil used in the present invention is an oil comprising at least one mineral oil and having a naphthene carbon content of 30% or more. A naphthenic mineral oil whose mineral oil has a naphthene carbon content of 30% or more can be used alone as an oil used in the present invention. Also, even if paraffinic mineral oil with low naphthenic carbon content is used, the mixing ratio is adjusted so that the naphthenic carbon content of the mixed oil obtained by mixing with naphthenic mineral oil with high naphthenic carbon content is 30% or more. can do.
When the naphthene carbon content of the oil used in the present invention is less than 30%, the durometer A hardness (JIS K6253 A type) of the solid lubricant becomes small (for example, 59 or less) and is scattered by the action of centrifugal force. Or the solid state cannot be maintained.
Examples of the mineral oil having a naphthene carbon content of 30% or more include naphthenic mineral oils having a high naphthene carbon content such as Krysef F150 and Krysef F68 manufactured by Nippon Oil Corporation.

  The mineral oil-based grease used in the present invention is not particularly limited, and is a grease using the above oil having a naphthene carbon content of 30% or more as a base oil and soap or non-soap as a thickener. Examples of the soap include lithium soap, sodium soap, aluminum soap, calcium soap, barium soap and the like, or a composite soap and a mixed soap of these soaps. Examples of non-soap include urea, sodium terephthalate, polytetrafluoroethylene, bentonite, and silica gel.

The solid lubricant of the present invention is prepared by uniformly mixing a predetermined amount of lubricant (the above oil or grease) and a predetermined amount of ultrahigh molecular weight polyolefin powder, and pouring the mixture into a mold having a predetermined shape. Heat above the gel point and then cool to solidify to give a solid lubricant having an oily surface, that is, a surface from which oil oozes. In the case where grease is used as the lubricant, it is preferable to heat it above the gel point and below the dropping point of the grease.
The preferable blending ratio of the solid lubricant is 60 to 90% by weight for the lubricant and 40 to 10% by weight for the ultrahigh molecular weight polyolefin powder. The amount of each depends on the degree of oil separation, tenacity and hardness required for the solid lubricant. Therefore, the greater the amount of ultrahigh molecular weight polyolefin powder, the greater the hardness of the gel after being dispersed and held at a predetermined temperature. Various organic or inorganic fillers can be blended in order to increase rigidity while maintaining a high oil content.

The melting point of the ultrahigh molecular weight polyolefin powder according to the present invention is not constant because it changes in accordance with the average molecular weight, but for example, the melting point of the one having an average molecular weight of 2 × 10 ⁶ by the viscosity method is about 136 ° C. Commercially available products with the same average molecular weight include Mipperon XM-220 (manufactured by Mitsui Chemicals).
Therefore, in order to disperse and hold the ultrahigh molecular weight polyolefin powder in the grease, after mixing the two, the temperature is higher than the temperature at which the ultra high molecular weight polyolefin powder causes gelation, and if grease is used, it is less than the dropping point. It is preferable to heat at a temperature of, for example, 150 to 200 ° C. Thereby, a solid solid lubricant can be obtained.

Further, the solid wax used in the present invention is an additive for suppressing oil oozing, and moderately suppresses the separation rate of oil oozing on the oily surface of the solid lubricant. Among them, it may be a compound such as a solid wax or a low-molecular polyolefin containing the same. Examples of the solid wax include plant waxes such as carnauba wax and candelina wax, animal waxes such as beeswax and insect wax, and petroleum waxes such as paraffin wax.
The blending ratio of the solid wax is 1 to 10% by weight based on the whole solid lubricant. As the blending ratio increases, the oil separation rate can be suppressed, and the speed at which the oil oozes out decreases. However, if it exceeds 10% by weight, the mechanical strength of the solid lubricant is lowered, which is not preferable.
In the case of blending the solid wax, the preferred blending ratio of the whole solid lubricant is 50 to 89% by weight for the lubricant, 40 to 10% by weight for the ultrahigh molecular weight polyolefin powder, and 10 to 1% by weight for the solid wax. %.

An example of the solid lubricant-enclosed rolling bearing of the present invention is shown in FIGS. FIG. 1 is a cross-sectional view of a rolling bearing that encloses a solid lubricant in a spot pack shape, and FIG. 2 is a cross-sectional view of the rolling bearing that encloses a solid lubricant in a full pack shape.
A solid lubricant encapsulated rolling bearing 1 of the present invention includes an inner ring 2 and an outer ring 3, and a rolling element 4 interposed between the inner ring 2 and the outer ring 3, and a solid lubricant 5 is provided around the rolling element 4. It is obtained by encapsulating.
The following method is mentioned as an example of the sealing method of the solid lubricant 5. A predetermined amount of lubricant (the above oil or grease) and a predetermined amount of ultra-high molecular weight polyolefin powder are uniformly mixed and then heated to 90 to 120 ° C. to obtain a semi-solid state. Next, the bearing 1 is sealed while maintaining this state. As shown in FIGS. 1 (a) and 1 (b), the sealing method is such that a cage 6 made of two strips is overlapped and fixed by a rivet 7 between an inner ring 2 and an outer ring 3. As shown in FIG. 2 (a) and FIG. 2 (b), the entire portion between the inner ring 2 and the outer ring 3 is filled in a so-called full pack shape. Things. In the sealed state as described above, the entire bearing is heated above the gel point of the ultra-high molecular weight polyolefin powder, and then cooled and solidified, so that the semi-solid material is solidified to become a solid lubricant. The solid lubricant-filled rolling bearing 1 is manufactured. In addition, when using grease as a lubricant as mentioned above, it is preferable to heat above the gel point and below the dropping point of the grease.

Examples 1 to 8 and Comparative Examples 1 to 4
Urea-mineral oil grease or mineral oil and ultra-high molecular weight polyolefin powder are mixed in the proportions shown in Table 1, and this mixture is put into a φ10 × 8 mm mold, heated to 160 ° C., cooled and solidified. A solid lubricant was used. In addition, about Example 4 and the comparative example 2, it mixed also including the solid wax.
The durometer A hardness was measured as a measure of the strength of the resulting solid lubricant. The results are shown in Table 1. The durometer A hardness was measured based on JIS K6253.
Also, urea-mineral oil grease or mineral oil and ultra-high molecular weight polyolefin powder are mixed in the proportions shown in Table 1, and this mixture is sealed in a bearing 6204, heated to 160 ° C., cooled, and this mixture is solidified. Thus, a bearing in which a solid lubricant was enclosed was obtained. In addition, about Example 4 and the comparative example 2, it mixed also including the solid wax.
The bearing was set at 100 ° C, and a radial load of 67 N and an axial load of 67 N were applied. The bearing was rotated at a rotational speed of 5000 rpm for 1 hour, and the solid lubricant in the bearing was examined for damage. The results are also shown in Table 1.
Details of the paraffinic mineral oil A, paraffinic mineral oil B, and naphthenic mineral oil in Table 1 are shown in Table 2.

Comprehensive evaluation:
A solid lubricant that has a durometer A hardness of 60 or more and that is sealed in a bearing and that does not break the solid state even when subjected to centrifugal force due to high-speed rotation. Evaluate it as “○”, and evaluate the solid lubricant that has a durometer A hardness of less than 60 and breaks in the solid state due to the centrifugal force of high-speed rotation enclosed in the bearing. “×” is also shown in Table 1.

  As is clear from Table 1, in the examples using oils having a naphthene carbon content of 30% or more or greases containing the oils, oils having a naphthene carbon content of less than 30% or greases containing the oils were used. From the comparative example, the durometer A hardness of the solid lubricant was increased, and the solid lubricant sealed in the bearing did not scatter or break even when subjected to the centrifugal force due to the high-speed rotation of the bearing.

  Since the solid lubricant of the present invention has excellent hardness and mechanical strength, the solid lubricant for bearings used under conditions that hinder the fluidity of the solid lubricant itself, specifically, stranded wire It can be suitably used as a solid lubricant used for bearings of various industrial machines such as machines, electric devices, printing machines, automobile parts, electrical accessories, construction machines and the like.

1 is a cross-sectional view of a solid lubricant-enclosed rolling bearing according to an embodiment of the present invention. It is sectional drawing of the solid lubricant enclosure rolling bearing which concerns on the other Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling bearing enclosed with solid lubricant 2 Inner ring 3 Outer ring 4 Rolling element 5 Solid lubricant 6 Cage 7 Rivet

Claims (5)

A mixture containing at least a lubricant and an ultrahigh molecular weight polyolefin powder having an average molecular weight of 1 × 10 ^{6 to} 5 × 10 ⁶ is heated to a temperature equal to or higher than the gel point of the ultrahigh molecular weight polyolefin powder, and then cooled and solidified. A solid lubricant, which is used by being enclosed in a rolling bearing,
The lubricant is a grease containing at least one mineral oil as a base oil, and the base oil has a naphthene carbon number ratio of 30 in the total carbon number determined by the ndM ring analysis method. %, A solid lubricant characterized by being at least%. The solid lubricant according to claim 1, wherein the solid lubricant has a durometer A hardness of 60 or more.   3. The solid lubricant according to claim 1, wherein the mixture comprises 60 to 90% by weight of the lubricant and 40 to 10% by weight of the ultrahigh molecular weight polyolefin powder.   3. The mixture according to claim 1, wherein the mixture comprises 50 to 89% by weight of the lubricant, 40 to 10% by weight of the ultra high molecular weight polyolefin powder, and 10 to 1% by weight of solid wax. Solid lubricant. An inner ring and an outer ring, a rolling element interposed between the inner ring and the outer ring, and a rolling bearing in which a solid lubricant is sealed around the rolling element,
The solid lubricant encapsulated rolling bearing, wherein the solid lubricant is the solid lubricant according to any one of claims 1 to 4.

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