JPS6132357B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to improving fatigue life and elastohydrodynamic (EHD) lubrication of antifriction bearings, such as roller and ball bearings. More particularly, the present invention relates to the use of certain fluids that provide increased elastohydrodynamic film thickness, thus avoiding critical lubrication and reliability while providing increased bearing fatigue life. In properly made, properly assembled and lubricated rolling contact bearings, the life of the bearing is generally determined by the fatigue of the materials of the raceways and rotating elements in contact with each other. be done. The time at which fatigue occurs depends on the magnitude of the stress and the actual number of stress cycles at the stress application or failure site. Fatigue testing using a large number of bearings operated under carefully controlled conditions provides the basis for load evaluation provided by various bearing manufacturers. These ratings are always based on some expected life expectancy. A widely used evaluation expression is "B ₁₀ life" for rotating contact (friction resistant) bearings. This B ₁₀ life is usually expressed in hours (hr.), and this is the 90
% exceeds stated life under specified speed, lubrication, temperature and load or stress conditions. It is well known that the lubricant itself can have a significant effect on the fatigue life of rolling contact bearings. Current lubricants for high performance ball and roller bearings often utilize highly refined mineral oil based stocks with multi-purpose additive packages incorporated therein. Certain synthetic fluid based stocks, usually esters, are also known as bearing lubricants. However, there remains a need for new classes of lubricants that extend bearing fatigue life beyond that provided by most modern formulated mineral oils or synthetic lubricants. If the rotating elements of a ball or roller bearing are actually separated by an elastohydrodynamic lubricant film, this bearing can be expected to have a very long operating life. In practice, however, many EHD films are hydrodynamically deficient and therefore
It has been discovered that it is thinner than could be expected from EHD theory. Hydrodynamic deficiencies result in metal-to-metal contact between the raceway of the bearing and the opposing surface roughness of the rotating element. In many cases, thin EHD films can reduce normal bearing life. In other cases, however, such films may be acceptable even if those of the surface roughness are actually exposed. This is because some lubricants use additives that react with metals to form metal-organic protective films. However, lubricant oxidative stability is usually reduced by such additives. Additionally, certain antiwear additives useful in lubricants include
Although it may initially reduce bearing wear, long-term use can cause corrosive wear of the rolling contact bearing metal. Insufficient EHD film thickness is encountered, for example, in ball bearings of the type used in inertia gyros. Low speed operation of gyrospin shaft bearings can result in bearing failure conditions and a concomitant reduction in fatigue life. Such bearings are for example 20000rpm
It is characterized by a high rotation speed exceeding . but
If the EHD film is not fully developed, fatal defects often occur at very low rotation speeds. In certain special bearing applications, a premium is placed on extended fatigue life at the expense of higher drag torque produced by the lubricant itself, if necessary. i.e., certain lubricants are subject to agitation, fluid shear,
Although it may cause slightly higher rolling drag losses due to dynamic friction and the like, it may nevertheless be a desirable lubricant if bearing life is increased due to other properties.
High speed gyro bearings are typical of such special applications. Other examples are found in bearings used in spin stabilized communications satellites. However, it has been discovered that even the most modernly formulated mineral oil or synthetic lubricants can exhibit limited EHD film thickness in special applications. It is therefore an object of the present invention to provide means and methods for increasing the EHD film thickness and fatigue life of rolling contact bearings by selecting lubricants. Another object of the invention is to
The objective is to provide a synthetic fluid that provides increased bearing fatigue life compared to typical mineral oil lubricants. Yet another object of the present invention is to provide a specific class of synthetic fluids that provide increased bearing fatigue life compared to commonly used synthetic lubricants. Yet another object is to provide a stable synthetic lubricant having a viscosity similar to mineral oil, but with improved bearing fatigue properties. Another object of the present invention is to provide a synthetic fluid that provides greater EHD film thickness at low operating speeds, thus preventing chipping and minimizing raceway wear. Yet another object of the invention is to provide a larger amount of lubricant for a given amount of lubricant in the bearing recess.
The idea is to provide a synthetic fluid that gives the EHD thickness at the start of operation. Yet another object of the present invention is to provide a synthetic fluid that maintains a unique EHD film thickness at zero bearing speed during rotational direction changes. Yet another object is to provide a stable synthetic lubricant having a viscosity similar to mineral oils containing antiwear additives, but with thicker EHD film forming properties. These and other objects of the invention will become apparent from the following description. It has been discovered that synthetic fluids of the type defined in the present invention unexpectedly provide excellent lubricants for anti-friction bearings due to improved EHD film thickness and fatigue life properties.
These synthetic fluids exhibit superior fatigue life and EHD film thickness over those of conventional mineral oil and synthetic fluid base stocks. The preferred lubricants of this invention include compounds having from 10 to about 70 carbon atoms and containing at least two cyclohexyl groups. Compounds of the invention that are generally useful as superior base stocks for anti-friction bearing lubricants include fused, chained or one or more C _1-16 alkylene, carboxy or ether. Includes one or more cyclohexyl compounds having two or more cyclohexyl rings joined by a bond, each containing a total of 10 to about 70 carbon atoms. Preferred compounds are those having 2 to about 6 cyclohexyl rings, and more preferably 2 to 4 such rings. Particularly preferred compounds for use in the present invention are hydrogenated dimers and/or trimers of alpha-alkylstyrenes. Generally, it is preferred that the hydrogenated material contain no more than about 20% by weight of cyclic compounds, and more preferably no more than 10% or less. Although the alkyl group of the alpha-alkylstyrene can be of 1 to 4 carbon atoms, it is generally preferred that the alkyl group is ethyl or methyl. Preferred dimers and trimers are therefore hydrogenated linear or cyclic dimers or trimers of alpha-methylstyrene and alpha-ethylstyrene, hydrogen of alpha-methylstyrene and alpha-ethylstyrene. linearized codimers and mixtures thereof. Examples of representative continuous or linked cyclohexyl compounds other than the aforementioned alpha-alkylstyrene dimers and trimers include dicyclohexyl, 4-(1-methyl-ethyl)dicyclohexyl, 4,4'-bis(1 -methylethyl)dicyclohexyl, x-isohexyl-4'-isopropyldicyclohexyl, x-cyclopentyldicyclohexyl, dicyclohexylmethane, (x-ethylcyclohexylcyclohexylmethane, [x-
Cyclohexyl(1-methylethyl)]-cyclohexylmethane, bis(2,4,6-trimethylcyclohexyl)methane, 1,1-dicyclohexylethane, 1,1,3-tricyclohexylpropane, 1,2,3-tricyclohexyl Propane, trimethylolpropane tricyclohexane carboxylate, 1,2-tercyclohexyl, 1,3-tercyclohexyl, x-(1,1
-dimethylbutyl)-1,3-tercyclohexyl, x-(1,1-dimethylbutyl)-1,2-tercyclohexyl, 1,2-isopropyltercyclohexyl, 1,3-isopropyltercyclohexyl, bis(1, 3-cyclohexyloxy)cyclohexane, 1.x-bis(methylcyclohexyl)cyclohexane, dicyclohexylcyclohexane-1.3-dicarboxylate,
x・x'-quartercyclohexyl, tricyclohexylmethane, bis, cis- and trans-
1,3-cyclohexylcyclohexanedicarboxylate, 1,1-dicyclohexyl-2-methylpropane, 1,1-dicyclohexyl-2-
Methylbutane, 1,1-dicyclohexyl-2,
5-dimethylhexane, 1,1-dicyclohexylpentane, 1,2-dicyclohexylpentane, 1,2-di(x-ethylcyclohexyl)propane, 2,2-dicyclohexylpropane,
Mention may be made of 2,3-dicyclohexyl-2,3-dimethylbutane, 1,3-dicyclohexyl-2-methylbutane and 1,3-dicyclohexylbutane. A particularly preferred group of such compounds are dicyclohexyl, alkyldicyclohexyl, tercyclohexyl, alkyltercyclohexyl, quartercyclohexyl, quinoxyclohexyl, 2,3-dicyclohexyl-2.
3-dimethylbutane and mixtures thereof, where alkyl contains from 1 to about 18 carbon atoms. Examples of fused ring cyclohexyl compounds and compounds having structures containing combinations of fused, continuous and/or linked cyclohexyl groups include cis-decalin, trans-decalin, 2,3-dimethyldecalin, isopropyldecalin, tertiary-butyldecalin, per Hydrofluorene, perhydrophenanthrene, perhydromethylcyclopentadiene trimer, perhydrocyclopentadiene trimer, perhydrofluoranthene, 1-cyclohexyl-1,3,3-trimethylhydroindane,
x-hexyl perhydrofluoranthene, x-cyclohexyl perhydrofluoranthene, poly(ethyl-1-methyl) perhydrofluoranthene, x-isopropyl perhydrofluoranthene, x-cyclohexyl perhydrofluoranthene,
x-Isododecylperhydrofluorene, 1-cyclohexyldecalin, 2-(cyclohexyl-
x-methyl)bicyclo(2.2.1)heptane,
Perhydropyrene, ethylperhydrofluorene, perhydroanthracene, bis-2-decalin, 1-cyclohexyldecalin, 2-cyclohexyldecalin, dimethylcyclohexyldecalin, 4,5-methyleneperhydrophenansin, 1,3-dicyclohexyloxy Mention may be made of cyclohexane and cyclohexyldecahydronaphthyl ether. A particularly preferred group of such compounds are those selected from the group consisting of decalin, cyclohexyldecalin, alkyl-substituted decalin, alkyl-substituted cyclohexyldecalin, and mixtures thereof, where the alkyl has 1 to about 18 carbon atoms. shall contain. In addition to the cyclohexyl type base stocks cited above, base stocks used in the present invention may include, for example, paraffinic and naphthenic petroleum,
It may contain small amounts of other lubricant compositions including _C2-5 polyolefins and synthetic lubricants (e.g. mono- and dicarboxylic acid esters). The utility and operability of the present invention is not negated by the incorporation of small amounts of such non-critical base stock components in combination with the essential cyclohexyl compound. In this regard, hydrogenated polyisobutylene has been found to be an excellent formulation component. Preparation of Unsaturated Dimers Alpha-alkylstyrene linear dimers can be prepared by polymerizing alpha-alkylstyrene monomers by known techniques. Particularly preferred monomers include alpha-methylstyrene and alpha-ethylstyrene and ring-substituted monomers thereof such as methyl-alpha-methylstyrene, methyl-alpha-ethylstyrene, ethyl-alpha-methylstyrene,
Ethyl-alpha-ethylstyrene, isopropyl-alpha-methylstyrene, isopropyl-
Examples include alpha-ethylstyrene and others. Alpha-alkylstyrenes are easily polymerized by contacting alpha-alkylstyrene monomers with small amounts, e.g. 5% by weight or less, of catalyst materials such as phosphorous oxyhalides and a mixture of small amounts of strong mineral acids. It is forced to form the corresponding unsaturated dimer. The catalytic material is a mixture of phosphorous oxychloride or phosphorus oxybromide and a strong mineral acid (e.g. hydrochloric acid, hydrobromic acid, orthophosphoric acid, nitric acid or sulfuric acid) or 80 to 98% by weight of phosphorous oxyhalide and 20 to 20% of the acid. 2% by weight
an aqueous solution of any of these acids in an amount corresponding to . Other catalysts are also useful in the polymerization of alpha-alkylstyrenes, including acid clays such as activated montmorillonite and Lewis acid catalysts. The polymerization can be carried out by mixing a small amount of catalyst material with the monomer and then holding or heating the mixture at a reaction temperature of 0 to 130°C, preferably 10° to 80°C, and atmospheric pressure. can. However, higher pressures can also be used. The unsaturated linear dimer produced is composed of a mixture of the corresponding isomeric 1-pentene and 2-pentene derivatives. For example, the unsaturated dimers of alpha-methylstyrene are 2,4-diphenyl-4-methyl-1-pentene and 2,4-diphenyl-4-methyl-1-pentene, respectively.
It is an isomeric compound that is 4-diphenyl-4-methyl-2-pentene. 1-pentene and 2-
The relative proportion of pentene isomer derivatives produced is
Much seems to depend on the temperature at which the polymerization reaction is carried out. At temperatures of approximately 0° to 80°C,
Polymerization reactions tend to produce the unsaturated compound 2,4-diphenyl-4-methyl-1-pentene as the main component, whereas at higher temperatures of about 90° to 130°C, 2,4-diphenyl-4-pentene is usually produced. 4-Methyl-2-pentene is produced in an amount equal to or greater than the 1-pentene isomer. However, the particular isomer produced is of little importance to the invention. The reason is that both isomers produce the same hydrogenation products. This dimerization reaction is preferably carried out at a temperature of about 130° C. or less so as to promote the production of linear dimers preferentially over cyclic dimers. Dimerization of alpha-methylstyrene at 100 °C in the presence of 0.50% montmorillotonite catalyst gives about 80 mol% conversion to unsaturated dimer, which is about 97% by weight.
It is composed of 3% linear dimer and 3% cyclic dimer. These unsaturated dimerization products are recovered from unreacted monomers by distillation. Of course,
The scope of the present invention is not intended to exclude alpha-methylstyrene dimers and trimers in which cyclic moieties predominate over linear moieties. Certain applications make such fluids desirable. Hydrogenation of Unsaturated Dimers Unsaturated dimers of alpha-alkylstyrenes may be hydrogenated using conventional techniques. This hydrogenation is preferably carried out using molecular hydrogen-generating catalysts capable of promoting the hydrogenation, such as metals, in particular those from groups 1 to 3 of the periodic table, or compounds thereof, in particular oxides, alone or in various mixtures with each other; It is carried out in the presence of a support material such as silica, zinc oxide, alumina, charcoal, diatomaceous earth, etc. The reaction can be carried out at a temperature of about 20 DEG to 250 DEG C. and a pressure of about atmospheric pressure to 2500 psig. Preferred operating conditions are generally about 50°C to 200°C and about 500 to 1500 psig. The hydrogenation of the unsaturated dimer is substantially complete such that less than about 2% and preferably less than 0.5% unsaturation remains in the hydrogenated product. This hydrogenation can be carried out in the presence of a suitable organic solvent, most often inert to the hydrogenation conditions, such as paraffins, naphthenes and sterically hindered unsaturated hydrocarbons. The preparation and hydrogenation of alpha-alkylstyrene dimers described above can be applied to the preparation of alpha-alkylstyrene trimers and automatically give this result. This latter is particularly useful in certain bearing applications where specific viscosity requirements must be met or high EHD film thicknesses are required in low speed bearing operations. In such cases, dimeric and trimeric blends are useful. In addition to the cyclohexyl type base stock materials, the lubricants of the present invention contain conventional additives including, for example, viscosity index improvers, antioxidants, antiwear agents, corrosion inhibitors, dispersants, dyes, antifoam agents, etc. It can contain substances. Several methods and techniques have been devised for laboratory measurements of rolling contact bearing fatigue life. One widely used maneuver is U.S. Patent No.
This is the "RC" (Rotating Contact) fatigue tester described in the specification of No. 3053073. This RC fatigue tester, a laboratory-type device, has shown good correlation with full-scale bearing fatigue data. this is
CRC Report No. 413, “The, Development of
Equipment and Techniques for Evaluating
"Effects of Oils on Bearing Fatigue Life" (Development of equipment and techniques for evaluating the effect of oil on bearing fatigue life)
Research Council, Inc.]. The use of Weibull distribution plots provides accurate predictions of bearing fatigue life from RC rig data, as described in US Pat. No. 3,053,073 (Karamchi). The following Examples 1-3 illustrate the significantly superior bearing fatigue life that can be achieved using the synthetic fluids of the present invention when compared to prior art bearing lubricants. In Examples 1 and 2, the fatigue test equipment was similar to that of US Pat. No. 3,053,073. Bearing life is expressed in "B ₁₀ " and "B ₅₀ " in units of stress cycles. Stress cycles are easily converted to operating time by considering the estimated bearing speed. B ₁₀ lifetime is defined above. B ₅₀ means that 50% of a given quantity of bearings of the type being tested will exceed the indicated life under specified operating conditions. Example 1 The relative performance of two lubricants was compared on a fatigue life tester. One is a control or reference fluid;
The other was a synthetic fluid within the scope of this invention. The control fluid was an ester-based stock commonly used in turbine engine lubricants meeting Military Specification MIL-L-23699. The rolling contact fatigue life for this control fluid is the highest quality assured and commercially available MIL-L
-23699 fluid was known to be comparable to that of fluid. More specifically, the control fluid was a pentaerythritol ester of short chain fatty acids. In contrast, the synthesis fluid of the present invention consisted essentially of linear dimers and trimers of fully hydrogenated alpha-methylstyrene.
More specifically, this synthetic test fluid contains 75.5% by weight
of hydrogenated alpha-methylstyrene linear dimer, 23.5% by weight of hydrogenated alpha-methylstyrene linear trimer and 1.0% by weight of 2,6-di-tert-butyl-p. -Contained cresol. Both the control fluid and the hydrogenated alpha-methylstyrene fluid were evaluated using the same test sample. The test sample is in the form of a cylindrical rod and is identified by reference number 20 in US Pat. No. 3,053,073. Hertz stress is 700000
pounds per square inch (492.2×10 ⁶ Kg/m ² ), the test sample speed was 12500 rpm, the fluid temperature was 200〓 (93.3℃), and the test sample temperature was 600〓 (315℃). Ta. The following table shows the fluid of the invention (hydrogenated alpha-methylstyrene) compared to that of the control fluid.
The significantly higher fatigue life numbers obtained using Five tests were performed on the inventive fluid and eight tests were performed on the control fluid. Data in the table represent average results.

[Table] Styrene formulation
In the following examples, the relative performance of several additional fluids was compared on a fatigue life tester. Example 2 An ester-based synthetic fluid meeting Military Specification MIL-L-7808 was used as a control fluid. Two synthetic fluids within the scope of the present invention were used for comparison. The test sample temperature is 300〓, and the Hertzian stress is
700,000 pounds per square inch (492.2×10 ⁶ Kg/m ² )
, the test sample speed is 12500rpm, and the test sample material is standard bearing alloy steel
is SAE52100 steel, and the fluid temperature is approx.
The temperature was 100〓(37.8℃). The following table provides significantly higher fatigue life data obtained using the fluid of the present invention when compared to the control fluid. All percentages are by weight.

[Table] Hydrogenated linear dimer of tyrene 99.0% and 2,
6〓Ditertiary butyl〓p〓Cresol 1.0%
To further illustrate the superior bearing fatigue life achievable through the use of the synthetic fluid of the present invention:
Fatigue tests were conducted according to Example 3 and using actual roller bearings in place of the fatigue test equipment previously described. Example 3 As a control fluid, 115 at 100〓 (37.8℃)
A paraffinic mineral oil with a nominal viscosity of ~120 Saybolt Universal seconds was used. This fluid was representative of current mineral oils useful for lubricating rolling contact bearings. For comparison, a synthetic fluid within the scope of the present invention was used. This synthetic test fluid contains 94.0% by weight hydrogenated linear dimer of alpha-methylstyrene;
5.0% by weight hydrogenated linear trimer of alpha-methylstyrene and 1.0% by weight 2,6-ditertiary
Contains butyl-p-cresol. Fatigue testing was conducted on tapered roller bearings with an average cone diameter of 2.4 inches. This bearing has a maximum Hertzian stress of 272,000 pounds per square inch (191 x ¹⁰⁶ Kg/ ^m2 ) and 2700
It was operated at a cone speed of revolutions/min. Fluid flow to the test bearings was maintained at a rate of 0.25 gallons per minute (0.95 per minute), while the bearing temperature (measured on the outside diameter) was 150°C (65.6°C) for the first experiment. And for the second experiment it was kept at 240㎓ (115.6℃). The following table gives the fatigue results for Example 3, where the fluid of the invention has 1.7 times more fatigue resistance at 150〓 and 3.5 times more resistance at 250〓 than that of the mineral-based control fluid. of fatigue resistance to the bearing.

[Table] When a mixture of hydrogenated linear dimers and trimers of alpha-methylstyrene is used,
The relative proportions can be varied within very wide limits. However, the examples show that even better fatigue results can be achieved with a predominant presence of dimer. Thus, a preferred dimer-trimer mixture comprises about 60% to about 95% hydrogenated linear dimer of alpha-methylstyrene and about 5% to about 40% hydrogenated linear trimer of alpha-methylstyrene. Contains %. Several methods and techniques have been devised to measure EHD thickness in antifriction bearings under dynamic conditions. One of these is known as the contact resistance method. Examples 4 and 5 below describe details of laboratory experiments in which the surprising results experienced using the fluids of the present invention when compared to typical mineral oil lubricants of the prior art. This contact resistance method is then used to demonstrate unexpected EHD film thickness increases. Example 4 A test bearing designed for relatively low rotational speeds was an angular contact ball bearing with a bore diameter of 2.36 inches (6 cm) on the inner race and an outside diameter of 3.74 inches (9.5 cm) on the outer race. .
The ball retainer has been intentionally removed;
and there each 0.406 inches (1.03cm)
There were 19 balls of diameter. The test bearing was assembled on an electric motor with a vertical axis of rotation and the inner race was driven at speeds from 0 to 100 revolutions per minute (rpm). The outer race was restrained from rotation. . A 35 lb (15.9 Kg) weight on the outer race gave an axial bearing preload of 35 lb. The electrical circuit was connected to a bearing with a liquid metal slip ring capable of carrying 100 microamps, with an open circuit voltage in the bearing of 10 millivolts. The voltage drop in the bearing was read on a recorder along with the rpm. The test bearings were cleaned with xylene, acetone and fluorocarbons after which a thick film of test oil was liberally applied to the bearing surface. The bearing was then operated between 0 and 100 rpm under a 35 pound axial load, and the voltage drop within the bearing was reduced from zero to zero for each 10 rpm increment.
Measured up to 100 rpm. A decimal resistance box was used in place of the bearing to calibrate the recorder before testing. The natural frequency response of this recorder made it possible to read the average bearing resistance. Two test operations were conducted, one of which was
one using a mineral oil of a typical formulation of the prior art having a viscosity of 100° (37.8°C) of 114 centistokes, and another using a fluid within the scope of the present invention having a viscosity of 100° of 120 centistokes. It was the one I used. The latter fluid is alpha
It consisted essentially of fully hydrogenated linear dimers and trimers of methylstyrene. More specifically, this synthesis fluid contains 57.4% by weight hydrogenated linear dimer of alpha-methylstyrene and 35.18% by weight hydrogenated linear dimer of alpha-methylstyrene.
% by weight of hydrogenated linear trimer of alpha-methylstyrene. Also included were 4.63 weight percent acrylate viscosity index improver, 1.85 weight percent zinc phosphorodithioate wear inhibitor, and up to 1 weight percent each of other typical additives (eg, antifoam agents, etc.). That is, the two fluids being compared each had approximately the same viscosity, and each was formulated using a typical additive package. The results of Example 4 are shown in the following table.

[Table] The table describes various operating characteristics of fluids for EHD lubrication, where complete EHD lubrication is indicated in the table by the symbol "∞" (infinity). That is, perfect EHD lubrication is achieved when the measured (transverse) resistance (in ohms) within the bearing is infinitely large. If the resistance is a finite value, e.g. 1100 ohms, this lubricant film will still be in the hybrid region, i.e. somewhere between a partial EHD film with high metal-to-metal contact and a full EHD thickness without coarse partial contact. It is in the middle. At 100 rpm on the test bearing, the mineral oil was still in the mixed region, while the alpha
Methystyrene-based fluids are complete at 40 rpm
Achieved EHD lubrication. The superiority of the inventive fluid for low speed bearing operations is very clear from the results in the table. To further illustrate the superior EHD lubrication provided by the fluid of the present invention, another test was carried out using a smaller bearing than that of Example 4, but one designed for much higher operating speeds. A comparative test was conducted. Details and results of the second test are described in Example 5. Example 5 Two new Model R-2 equipment ball bearings with 12 1/26 inch diameter balls were assembled without a conventional ball retainer. It has been discovered that the desired amount of free oil in the ball race weight track is most easily controlled in retainerless bearings. Furthermore, bearings without retainers are much easier to control to stable torque levels than conventional bearings with retainers. Each bearing in this Example 5 was operated with a full complement of balls using 96 micrograms of synthetic fluid within the scope of the present invention. The synthesis fluid contained an 80%:20% mixture by weight of hydrogenated linear trimer and hydrogenated linear dimer of alpha-methylstyrene. This fluid is
160 centistokes at 137〓 (53.8℃), 100〓
(37.8℃) 1.418 centistokes, and 210
It had a viscosity of 18.4 centistokes at (98.9°C). These two test bearings were assembled into a housing and supported each end of a shaft supporting a gyromotor rotor. Apply an axial preload of 1.5 lbs, and reduce its operating temperature to 137 〓
The desired maximum speed was set to 2400 rpm. Film thickness was measured using a mechanical system adapted to detect changes in film thickness in relation to bearing axis displacement. This mechanical displacement was then coupled to an electrical measuring device sensitive enough to measure film thickness to less than 1 microinch. Several starts from 0 rpm were made and in each case the bearing was rapidly accelerated to an rated speed of 2400 rpm and the fluid film thickness was recorded during the start. The first start produced an unexpected 32 microinch fluid film.
This decreased to 11.7 microinches within 5 minutes as the bearing reached equilibrium with the lubricant held within the bearing. Restarting resulted in the initial 25 microinch film being reduced to 21 microinches. Such high film thickness is highly unusual at most speeds. When compared to experience on the same type of bearing using a prior art highly refined lubricant having a viscosity of 160 centistokes at Had half. The substantial film thicknesses experienced using the synthetic fluids of the present invention occurred at approximately 100 to 1000 times lower bearing speeds than for prior art fluids. Thus, the surprising ability of the fluids of the present invention to produce substantial EHD films at very low bearing speeds provides an advance in lubrication technology unknown to the prior art. That is, the alpha used in Example 5
The methylstyrene trimer/dimer mixture gave EHD film production of over 5 microinches at very low rpm, such as 15 rpm and 137° fluid temperature. Repeated operation at 110°C (43.3°C) gave a film thickness of 10 microinches at 7 rpm. These unusually high initial films
Observed on each start-up after a rest period, regardless of whether the direction of bearing rotation was reversed or not. This abnormally high initial film was not observed if the bearing was left stationary for several seconds after rotational reversal. Nevertheless, low speed film thicknesses using the synthetic fluids of the present invention were significantly higher than those observed using mineral-based lubricants. Bearing torque was higher at all speeds using the alpha-methylstyrene fluid than using the mineral oil control fluid. At room temperature, on a low speed dynamometer, the trick was approximately twice as large at 1 rpm and 3-4 times as large at 20 rpm. At 2400 rpm and 137°, the torque was approximately four times greater for alpha-methylstyrene trimer/dimer than for a typical highly refined mineral oil control fluid. Since friction losses in anti-friction bearings are orders of magnitude lower than other losses in mechanical power transmission systems, such torque build-up is typically difficult with substantially higher EHD film thicknesses, especially under troublesome low-speed operating conditions. It is acceptable in exchange. Although the invention has been described herein with respect to particular embodiments, it is to be understood that the invention is not limited thereto and that various embodiments are possible within the scope of the claims. The novel technical matters disclosed by the present invention will be summarized below. 1 fused or chained or 1
2 linked by one or more _C1 - _C16 alkylene, carboxy or ether bonds
Elasticity of a rolling contact bearing consisting of introducing into the rolling contact surface a fluid containing one or more cyclohexyl compounds having one or more cyclohexyl rings and each containing from 10 to 70 carbon atoms. A method of improving hydrodynamic film thickness and increasing its fatigue life. 2. The method according to item 1, wherein the fluid contains a compound having 2 to 6 cyclohexyl rings. 3. The method of claim 2, wherein the fluid contains a hydrogenated dimer or trimer of alpha-alkylstyrene or a mixture thereof. 4. The method according to item 3 above, wherein the alpha-alkylstyrene is alpha-methylstyrene. 5 Alpha-methylstyrene cyclic dimer is 20
said fourth being present in an amount not exceeding % by weight.
The method described in section. 6, wherein the hydrogenated dimer consists essentially of about 90-100% by weight of a hydrogenated linear dimer of alpha-methylstyrene and 0-10% by weight of a hydrogenated cyclic dimer of alpha-methylstyrene. The method described in Section 4. 7. The fluid mixture contains from about 60 to about 95% by weight hydrogenated linear dimer of alpha-methylstyrene and from about 5 to about 40% by weight hydrogenated linear trimer of alpha-methylstyrene. The method described in Section 3.

Claims (1)

[Claims] 1 fused or chained or 1
A type of cyclohexyl compound having two or more cyclohexyl rings connected by one or more C1 to _C16 alkylene, carboxy or ether bonds and each containing 10 to ₇₀ carbon atoms A method for improving the elastohydrodynamic film thickness of a rolling contact bearing and increasing its fatigue life, characterized in that a fluid containing 100% or more is introduced into the rolling contact surface.