US2237526A - Extreme pressure lubricating composition - Google Patents

Description

1TB E EXTREME PRESSURE LUflRliDdilliliGr COMPOSITION Robert L. Humphreys, Berkeley, Ualiih, assignor to Standard Oil Company of California, San Francisco, Calif., a corporation of Delaware No Drawing. Application December it, laid, Serial No, 257,125

i Claims.

' of certain organic polysulfides.

in general, the primary requirement of such an extreme pressure lubricant is that it shall possess high lubricating film strength; preferably it also has low rates of wear and low coeihcients of friction; and it is an object of the present invention to disclose and provide a novel type of lubricating composition which fulfills these requirements. It is a further object of this invention to disclose and provide extreme pressure lubricants that do not suffer a loss or deterioration of high film strength, low rate of wear, or low coefficients of friction in long continued use under severe conditions, and which have no tendency to cause gumming or fouling of the lubricated metal parts or surfaces under such long continued service.

its now known, one class of compositions designed for use as extreme pressure lubricants comprises mineral lubricating oils to which has been added, preferably in i1so1uble form, sufficient amounts of various active agents discovered to possess the properties of increasing the iilm strength and/or of decreasing wear and/or of decreasing coefficients of friction of the mineral base to which they have been added. lvlineral oil lubricants containing added metallic soaps, notably lead soaps, and/or sulfurized fatty acid or fatty oils, such as sulfurized animal or vegetable oils, are examples of such compositions. il'ertain of the compositions of this type have the very serious defects that they tend to cause gummlng of the metal parts; certain of them tend to separate into their constituent parts upon long continued subjection to severe operating conditions.

iinothcr class of compositions designed for such service, comprises mineral lubricating oils, either alone or in admixture with fatty oils, to which have been added sulfur in elemental or uncombined form. Compositions containin such uncomblned sulfur have the serious defects that they'cause undue corrosion and wear of the metal parts to be lubricated, or the parts adiaccnt thereto, such as bushings, etc. which result not only in deterioration of the said metal parts, but lead directly to a short life of the lubricatinn compositions themselves.

l have now discovered that the addition of small amounts of organic polysulfides, particularly the disulfldes, trisulfides and tetrasulfides, in admixture with hydrocarbon or fatty lubricating oils, provide lubricating compositions which satisfy all of the primary requirements of extreme pressure lubricants, and, in addition, are stable in long continued use, do not separate into their constituent parts and do not tend to form gum, or to foul or corrode metal surfaces.

The amounts of the said organic polysulfides required to be added to hydrocarbon or fatty lubricating oils for the preparation of the compositions of my invention vary somewhat, de pending upon the severity of the service for which they are designed, and, to some extent, upon the character of thehydrocarbon or fatty lubricating stock used as a base; these amounts are in all cases small, however, compared with the amounts of active agents of the prior types, and in general vary between about V2 of 1% and about 5% of the oil base, by weight.

The organic polysulfides to be added to mineral or fatty lubricating oils in preparing the compositions of this invention are compounds in which two organic radicals are linked together by a combination of two or more sulfur atoms, and they may correspond to any of the following type formulae:

the above type formulae that a variety of compounds of the polysulfide type are contemplated to be added to mineral or fatty lubricating oils in preparing therefrom extreme pressure lubricating compositions in accordance with my in" vention, and i have found in general that all such compounds are effective to markedly increase the iilm strength of the lubricating compositions in which they are caused to be present, excepting only, and in general, those polysulfides whose vapor pressures are sufficiently high as to cause their vaporization from the compositions in long continued severe service and likewise those which tend to decompose at temperatures of 300 F. or thereabouts.

In exemplifying the compositions of my invention, and in order to point out the variety of organic polysulfides which I have found suitable in the preparation of compositions of this character, reference is made to the accompanying tabulation setting out the results of the actual practice of the invention, in which various types of sulfur linkage are represented and in which R and R of the above type formulae are shown as represented by various organic radicals:

polysulfides, in suitable amounts, is admixed with a hydrocarbon or fatty mineral oil and the admixture merely agitated mechanically in order to obtain complete and homogeneous solution. I have found in general that the polysulfides are easily soluble in hydrocarbon and fatty oils to the extent required, and that no dificulty is encountered in incorporating them therein.

A particular feature of my invention lies in the s it 1 t in t t li t l u ur menu 4 s reng s cc Emmplc Type formula content added fi g on steel, total load in pounds Percent by Percent by Percent by H weight weight weight I Dibenzyl disulflde R-S-R 26. 2. 0 0. 62 700 II Dicresyl disulflde R-S-S-R 26. 0 2.0 0.52 410 i III Benzothiazol tetrasulflde RS-SSR 32. 4 2.0 0. 65 510 S IV Dithionaphthoic acid disul- II II fide R-C-SS-CR 31. 5 2. 0 0. 63 420 Mineral oil stock, 175 vls. at 7 210 F., Universal Saybolt. N one 150 Excluding sulfur contained in the thiazole ring, found ineffective to increase lubricating film strcngth.

In the respective columns in the above tabulation there are set out: first, typical organic polysulfides, representative of a great number which may suitably be used in the practice of my invention; second, the type formula of the said organic polysulfides, particularly setting out the sulfur linkage therein; third, the amount of combined sulfur in each of the said organic polysulfides, in percentage by weight; fourth, the amount of each of the organic polysulfides added to a mineral hydrocarbon lubricating oil base batch (kept uniform in amount here only for the purposes of exemplificatlon); fifth, the amount of sulfur in each of the finished extreme pressure lubricants, in percentage by weight; sixth; the film strength of the finished lubricating compositions, as measured on the Timken. machine described by O. L. Maag in the National Petroleum News of November 16, 1932, page 52, article entitled Extreme Pressure Lubricants, wherein the O. K. load in pounds, or the load carrying capacity of the lubricant, is directly measured. In the above exemplifying tabulation the same mineral oil stock was used throughout.

Reference has been made hereinabove to the fact that in the organic polysulfides of the present invention, the organic radicals, represented in the type formulas, by R and B, may be those in which elements other than carbon and hydrogen (such as oxygen, sulfur, nitrogen, etc.) may be present. Example III of the above table. particularly illustrates one such compound. The benzothiazol tetrasulfide of this example, which has been shown to have a superior load carrying capacity, has the following general structural formula:

This compound is not only illustrative of organic tetrasulfides, but is also illustrative of organic compounds which may be other than aryl and alkyl tetrasulfides and which may be other than hydrocarbon-substituted polysulfides.

In the preparation of the compositions of my invention, the desired polysulfide or mixture of preparation of bases or concentrates containing relatively large amounts of polysulfides in admixture with hydrocarbon or fatty oils. Such concentrates may be stored or transported in this form and before actual use in extreme pressure lubrication service may be diluted with the same or other lubricating oil to any desired concentration. Admixtures of the polysulfides and lubricating oils containing upward of 50% of the active agents, by weight, may in this way be prepared. In preparing concentrates or bases of this character complete solution of the polysulfides is not in all cases necessary, although most of them are freely oil soluble to this extent. Blending agents, such as amyl or higher alcohols, may be employed as homogenizers in the case of those polysulfides not freely oil soluble to this extent, if desired; incorporation of the less soluble active agents in suspended form, however, is suficient to allow these polysulfides to function in decreasing film strength in actual use.

Obviously the character and viscosity of the lubricating oil in which the polysulfides are added will be dependent to some extent upon the character of service to which the composition is ultimately to be put, and I am not to be limited in the character of the lubricating composition used as a base in the preparation of my compositions. For example, I find that the life of metal cutting tools is very remarkably lengthened by the incorporation of small amounts of organic polysulfides in either the mineral hydrocarbon or fatty oils used ordinarily in this service. Moreover, miscible metal cutting oils may be prepared in which the usual oil component is replaced with an oil containing small amounts of these polysulfides in solution and it will be found that the life of the cutting tools is greatly lengthened and the character of the metal surfaces cut much improved, especially in severe cutting service. Further, semi-solid and solid lubricating greases may be prepared, in the usual manner, wherein small amounts of these polysulfldes may be incorporated in the hydrocarbon and fatty oils ordinarily used therein; the lubricating film strength is in all cases increased to a degree comparable to the increases pointed out in the example tabulated above.

While I have described in detail the character of my invention and given numerous illustrative examples of the preparation and application of the compositions of my invention, 1 have done so by way of illustration and with the intention that no limitation should be imposed upon the invention thereby. It will be obvious to those skilled in the art that numerous modifications and variations of the above illustrative examples may be effected in the practice of my invention, which is of the scope of the claims appended hereto.

I claim:

1. A lubricating composition containing a lubricating oil and at least 0.5% by weight thereof of benzothiazol tetrasuliide.

2. A lubricating composition consisting of a lubricating oil and benzothiazol tetrasulfide.

'3. A composition of matter, comprising a lubricating oil containing between about 0.5 and about 5.0 per cent by weight of benzothiazol tetrasulfide.

a. An extreme pressure lubricant comprising an admixture of a hydrocarbon lubricating oil and a small amount, suflicient to give the mixture increased load-carrying capacity, of benzothiazol tetrasulflde.

5. An extre e pressure lubricant composition comprising a hydrocarbon lubricant and a small amount, suflicient to give the mixture increased load-carrying capacity, of an organic compound having the following general structural formula:

6. An extreme pressure lubricant base comprising an admixture of an oil and benzothiazol tetrasuliide, capableof dilution with a hydrocarbon lubricating oil to produce an extreme pressure lubricant containing between about 0.5 and about 5.0 per cent by weight of said benzothiazol tetrasulflde.

7. An extreme pressure lubricant base containing 50 or more per cent by weight of benzethiazol tetrasulflde in admixture with an oil.

' ROBERT L. HUMPHREYS.