JP2007064456A - Rolling bearing for robot - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling bearing for a robot capable of effectively preventing flaking on a rolling surface due to hydrogen brittleness. <P>SOLUTION: In the rolling bearing 1 for a robot for rotatably supporting a rotary section of the industrial robot, the rolling bearing 1 has an inner ring 2 and outer ring 3, and a plurality of rollers 4 interposed between the inner ring 2 and outer ring 3, and also provides a seal member 6 for sealing grease compositions 7 in the vicinity of the rollers 4 on openings 8a and 8b on both ends in an axial direction of the inner ring 2 and outer ring 3. The grease compositions 7 are prepared by combining additives into the base grease made from base oil and thickener, the additives include at least one magnesium additive selected from inorganic magnesium and organic magnesium, and a combining ratio of the magnesium additives is 0.05 to 10 pts.wt. to the base grease of 100 pts.wt. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rolling bearing for a robot, and more particularly to a rolling bearing used for an operating part of an industrial robot.

Various industrial robots such as assembly, welding, and painting are used in automobile production lines. In order to shorten the tact time for the purpose of improving productivity, the movement speed of the robot tends to be increased. Robot operation is not continuous rotation but intermittent operation. Increasing the operation speed is the number of times of switching of stop-start-run-stop operation per unit time for rolling bearings used in rotating parts. As the speed increases, the acceleration and deceleration applied to the rolling bearing increase each time, and the slip generated in the bearing increases accordingly. As the use conditions become severe in this way, there is a problem that specific peeling with a change in white structure occurs on the rolling surface of the rolling bearing, and the bearing life time is shortened.
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 texture change that occurs at an early stage, for example, a method of adding a passivating agent to a grease composition (see Patent Document 1) or a method of adding bismuth dithiocarbamate ( Patent Document 2) is known.
However, as the usage conditions of rolling bearings used in recent industrial robots become severe, sufficient measures cannot be taken with the method of adding a passivating agent or the method of adding bismuth dithiocarbamate.
JP-A-3-210394 JP-A-2005-42102

  The present invention has been made to cope with such problems, and even when used in a rotating part of an industrial robot where acceleration and deceleration are intermittently applied, the rolling bearing rolling surface due to hydrogen embrittlement is used. An object of the present invention is to provide a rolling bearing for a robot that can effectively prevent peeling.

An automotive electrical equipment / auxiliary rolling bearing according to the present invention is an automotive electrical equipment / auxiliary rolling bearing that rotatably supports a rotating shaft driven by engine output on a stationary member, the rolling bearing comprising an inner ring and An outer ring, a plurality of rolling elements interposed between the inner ring and the outer ring, and a seal member provided at both axial openings of the inner ring and the outer ring for sealing the grease composition around the rolling element. The grease composition is a grease composition in which an additive is blended with a base grease composed of a base oil and a thickener, and the additive is inorganic magnesium (hereinafter, magnesium is referred to as Mg). And at least one Mg-based additive selected from organic Mg, and the blending ratio of the Mg-based additive is 0.05 to 10 parts by weight with respect to 100 parts by weight of the base grease. To do.
The inorganic Mg is Mg powder.
The organic Mg is Mg stearate.
The thickener is a urea or lithium soap thickener.

  A rolling bearing for a robot that rotatably supports a rotating part of an industrial robot, wherein the grease composition enclosed in the bearing is combined with iron oxide on a frictional wear surface or a new iron-based metal surface exposed by wear in the bearing portion. It contains at least one Mg-based additive selected from inorganic magnesium (hereinafter referred to as Mg) and organic Mg, which can form a film containing an Mg compound.

  In the rolling bearing for a robot of the present invention, the grease composition enclosed in the bearing contains at least one Mg-based additive selected from inorganic Mg or organic Mg in grease composed of a base oil and a thickener. Therefore, rolling bearings used in robots are caused by a large number of times of switching between stop-start-run-stop operation per unit time, and the acceleration and deceleration applied to the rolling bearing increase each time. The occurrence of peculiar delamination due to hydrogen embrittlement, which is seen in Fig. 1, can be suppressed, and the life of the rolling bearing for robot can be extended.

An example of a rolling bearing for a robot that rotatably supports a rotating part of an industrial robot 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.

  In a rolling bearing for robots, as a result of intensive studies to prevent peeling on the rolling surface due to hydrogen embrittlement, a robot encapsulating a grease composition containing at least one Mg-based additive selected from inorganic Mg and organic Mg Rolling bearings for use were found to extend the bearing life. When this bearing rolling surface was observed, the compounded Mg-based additive decomposes and reacts on the frictional wear surface of the bearing or the new surface of the ferrous metal exposed by wear, and the bearing rolling surface contains Mg compound along with iron oxide. It was found that a film was formed. It is considered that this generated film prevents hydrogen generated by decomposition of the lubricating oil from entering the bearing steel and suppresses peeling due to hydrogen embrittlement. The present invention is based on these findings.

Examples of inorganic Mg that can be used in the rolling bearing for the robot of the present invention include Mg powder, Mg carbonate, Mg chloride, Mg nitrate and hydrates thereof, Mg sulfate, Mg fluoride, Mg bromide, Mg iodide, Mg oxyfluoride , Mg oxychloride, Mg oxybromide, Mg oxyiodide, Mg oxide and its hydrate, Mg hydroxide, Mg selenide, Mg telluride, Mg phosphate, Mg oxyperchlorate, Mg oxysulfate, Mg salicylate Mg titanate, Mg zirconate, Mg molybdate, and the like are particularly preferable in the present invention because of excellent heat resistance and resistance to thermal decomposition, and Mg powder having a high extreme pressure effect.
These inorganic Mg may be added to the grease by mixing one type or two types.

The organic Mg that can be used in the rolling bearing for the robot of the present invention is preferably an organic acid Mg salt. As the organic acid constituting the organic acid Mg salt, any salt such as an aromatic organic acid, an aliphatic organic acid, or an alicyclic organic acid can be used.
Specific examples of organic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, heptanoic acid, 2-ethylhexylic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecylic acid Monovalent saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, arachidic acid, monounsaturated fatty acids such as acrylic acid, crotonic acid, undecylenic acid, oleic acid, gadreic acid, Malonic acid, methylmalonic acid, succinic acid, methylsuccinic acid, dimethylmalonic acid, ethylmalonic acid, glutaric acid, adipic acid, dimethylsuccinic acid, pimelic acid, tetramethylsuccinic acid, suberic acid, azelaic acid, sebacic acid, brassic acid Divalent saturated fatty acids such as fumaric acid, maleic acid, oleic acid, etc. Examples thereof include fatty acid derivatives such as Japanese fatty acid, tartaric acid and citric acid, aromatic organic acids such as benzoic acid, phthalic acid, trimellitic acid and pyromellitic acid, and alicyclic organic acids such as naphthenic acid.
Of these, stearic acid having excellent lubricity is preferably used. These can be used alone or as a mixture.

Base oils that can be used in the present invention include mineral oils such as spindle oil, refrigerating machine oil, turbine oil, machine oil, dynamo oil, highly refined mineral oil, liquid paraffin, GTL oil synthesized by the Fischer-Tropsch process, polybutene, poly- Hydrocarbon synthetic oils such as α-olefin oil, alkylnaphthalene, and alicyclic compounds, or natural oils, polyol ester oils, phosphate ester oils, polymer ester oils, aromatic ester oils, carbonate ester oils, diester oils, etc. Non-hydrocarbon synthetic oils such as ester oils, liglycol oils, silicone oils, polyphenyl ether oils, alkyldiphenyl ether oils, alkylbenzene oils, and fluorinated oils can be used.
Of these, alkyl diphenyl ether oils, poly-α-olefin oils, polyol ester oils, and mineral oils that are excellent in heat resistance and lubricity are preferably 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. Of these, lithium soaps and urea compounds are preferable, and urea compounds are particularly preferable in view of heat resistance, cost, and the like.

The urea compound is obtained by reacting an isocyanate compound with 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.
Base grease for blending various compounding agents by blending a base compound with a base oil can be obtained. The base grease is produced by reacting an isocyanate compound and an amine compound in a base oil.

  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.

  The blending ratio of the thickener in the base grease is 1 to 40 parts by weight, preferably 3 to 25 parts by weight of the thickener in 100 parts by weight of the 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 at least one Mg-based additive selected from inorganic Mg and organic Mg is 0.05 to 10 parts by weight with respect to 100 parts by weight of the base grease. That is, (1) When Mg-based additive is only inorganic Mg, 0.05 to 10 parts by weight of inorganic Mg with respect to 100 parts by weight of base grease, (2) When Mg-based additive is only organic Mg, 0.05 to 10 parts by weight of organic Mg with respect to 100 parts by weight of grease (3) When the Mg-based additive is inorganic Mg and organic Mg, inorganic Mg and organic Mg are added to 100 parts by weight of base grease. Combine 0.05 to 10 parts by weight.
The blending ratio of the Mg-based additive is preferably 0.01 to 5 parts by weight. If the blending amount is less than 0.01 parts by weight, peeling on the rolling surface due to hydrogen embrittlement cannot be effectively prevented. On the other hand, if the blending amount exceeds 10 parts by weight, the delamination-suppressing effect reaches its peak and the cost increases, and it causes poor lubrication and easily causes surface-originating fatigue delamination.

  In addition to the Mg-based additive, a known grease additive may be included as necessary. Examples of the additives include antioxidants such as organic zinc compounds, amines, and phenolic compounds, metal deactivators such as benzotriazole, viscosity index improvers such as polymethacrylate and polystyrene, molybdenum disulfide, and graphite. Examples thereof include solid lubricants, metal sulfonates, antirust agents such as 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.

Examples 1 to 6
In half of the base oil shown in Table 1, 4,4-diphenylmethane diisocyanate (Millionate MT manufactured by Nippon Polyurethane Industry Co., Ltd., hereinafter referred to as MDI) is dissolved in the ratio shown in Table 1, and the remaining half of the base oil is dissolved. A monoamine having a double equivalent of MDI was dissolved in The respective blending ratios and types are shown in Table 1.
A solution in which monoamine was dissolved was added while stirring the solution in which MDI was dissolved, and then the reaction was continued for 30 minutes at 100 to 120 ° C. to produce a diurea compound in the base oil.
To this, an Mg-based additive and an antioxidant were added at the blending ratio shown in Table 1, 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 Table 1, the synthetic hydrocarbon oil used as the base oil has a kinematic viscosity at 40 ° C of 47 mm ² / sec, mm ² / sec, Shinflud 801 manufactured by Nippon Steel Chemical Co., Ltd., and the alkyldiphenyl ether oil has a kinematic viscosity at 40 ° C of 97 mm ² / Molemura High-Lube LB100 manufactured by Matsumura Oil Co., Ltd., and Kaolube 268 manufactured by Kao Co., Ltd. having a kinematic viscosity of 33 mm ² / sec at 40 ° C. was used as the polyol ester oil. As the mineral oil, a paraffinic mineral oil having a kinematic viscosity of 30.7 mm ² / sec (40 ° C.) was used.
As the antioxidant, alkylated diphenylamine was used.

  The resulting grease composition was subjected to a penetration test, a high-temperature high-speed test, and a rapid acceleration / deceleration test. Consistency measurement is performed by a method according to Japanese Industrial Standard JIS K2220. Test methods and test conditions are shown below for a high-temperature high-speed test and a rapid acceleration / deceleration test. The results are shown in Table 1.

High-temperature, high-speed test The rolling bearing for robot (6204) was filled with 1.8 g of the grease composition obtained in each example, and the bearing outer ring outer diameter was 180 ° C, radial load was 67 N, and axial load was 67 N. The sample was rotated at a rotation speed of 10000 rpm, and the time until burn-in was measured.

Rapid acceleration / deceleration test 2.3 g of the grease composition obtained in each example was put in a rolling bearing for robot (6303) and incorporated in a rolling bearing for internal rotation to apply a load. I did it. 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 generator stopped when the vibration of the vibration detector exceeded the set value was measured. In the test, a grease composition in which 1 part by weight of pure water was previously mixed with 100 parts by weight of the grease composition was used. The test was terminated in 100 hours.

Example 7 and Example 8
Li-12-hydroxystearate was added to the base oil shown in Table 1, and dissolved by heating at 200 ° C. while stirring. In addition, each compounding ratio is as Table 1. Thereafter, the mixture was cooled, and a magnesium-based additive and an antioxidant were added at a blending ratio shown in Table 1 and homogenized with a three roll 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. The results are shown in Table 1.

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 1 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 1.

  As shown in Table 1, all the peeling occurrence lifetimes of the rolling bearings for robots of the examples were 100 hours or more. Therefore, it can be seen that the rolling bearing using the grease composition of each example can effectively prevent the specific peeling accompanied with the white texture change occurring on the rolling surface.

  In the rolling bearing for robot of the present invention, the grease composition enclosed in the rolling bearing can effectively prevent the specific peeling accompanied with the white texture change occurring on the rolling surface of the rolling bearing and has excellent bearing life. It can be suitably used as a rolling bearing for use.

It is sectional drawing of a deep groove ball bearing.

Explanation of symbols

1 Grease-filled bearing (rolling bearing)
2 Inner ring 3 Outer ring 4 Rolling element 5 Cage 6 Seal member 7 Grease composition 8a, 8b Opening

Claims (5)

A rolling bearing for a robot that rotatably supports a rotating part of an industrial robot,
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 an additive is blended with a base grease composed of a base oil and a thickener.
The additive contains at least one magnesium-based additive selected from inorganic magnesium and organic magnesium, and the blending ratio of the magnesium-based additive is 0.05 to 10 parts by weight with respect to 100 parts by weight of the base grease. This is a rolling bearing for robots.   The rolling bearing for a robot according to claim 1, wherein the inorganic magnesium is magnesium powder.   The rolling bearing for a robot according to claim 1, wherein the organic magnesium is magnesium stearate.   4. A rolling bearing for a robot according to claim 1, wherein the thickener is a urea-based or lithium soap-based thickener. A rolling bearing for a robot that rotatably supports a rotating part of an industrial robot,
At least selected from inorganic magnesium and organic magnesium, wherein the grease composition sealed in the bearing can form a film containing a magnesium 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 robot characterized by containing one magnesium-based additive.

Images