US2456496A - Lubricants - Google Patents

Description

Dec. 14, 1948. J, G, FORD ET AL l 2,456,496

lLJJBRICANTS Filed April 15, 1942 fam/f, Pff/wwf?? mf',

Patented Dec. 14, 1948 LUBRICANTS James G. Ford, Sharon, and Robert N. Wenzel,

Swissvale, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 15, 1942, Serial No. 439,066

Claims. (Cl. 25249.6)

This invention relates to lubricants, and more particularly to synthetic compositions characterized by a relatively fiat viscosity-temperature curve.

The object of this invention is to provide a lubricant composed essentially of liquid polymers of dimethyl silicone.

A further object of this invention is to provide for polymerizing essentially dimethyl silicols in producing lubricants characterized by an extremely flat temperature viscosity curve.

Other objects of the invention will, in part, be obvious, and will, in part, appear hereinafter.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description in which the single figure of the drawing is a graph of the temperature viscosity curves of the lubricants prepared according to this invention and prior art type of lubricants.

In the application of lubricating substances to bearings or surfaces to be separated during relative movement, it is desirable that the lubricating substance remain present at the applied surfaces without evaporating or creeping away therefrom. Changes in the lubricating substance due to the presence of atmospheric gases in combination with the temperatures to which it is subjected should not cause sludging or gumming of the lubricant. In addition, a satisfactory lubricant is characterized by relative non-reactivity with the surfaces to which itis applied. Usually lubrication fails when any one of these three changes takes place in an applied lubricant.

Heretofore petroleum oils, vegetable oils and animal oils have been employed as lubricants for bearing surfaces. However, owing to the nature of these materials they have been subject to re action with moisture and atmospheric oxygen. The reaction products are sludges, gums and emulsions which are unsatisfactory .lubricating media. In some cases additions have been made to lubricating materials in the form of stabilizers or inhibitors which have decreased the rate of sludge and gum formation. Lubricants so treated have exhibited some increase in eillciency and a greater effective life.

l Under certain severe conditions which occur in practice, even lubricants containing inhibitors and other additives have not been satisfactory as lubricants over a prolonged period of time. For example, electrical meters attached vto the exterior of buildings and exposed to the hot' sun in tropical climates often reach temperatures of 859 C. vThe lubricants of the most highly developed type have been able to last for only a month before requiring cleaning of the meters and application of new lubricant.

A further unsatisfactory characteristic of prior art lubricants is the rapid change in viscosity with temperature change.

A lubricant which has been selected because it is satisfactory in viscosity at a mean temperature in a given mechanism may become thin and considerably less effective as a lubricant at high temperature conditions. On the other hand, when the mechanism is at its lowest temperature, the lubricant may become extremely thick and viscous. In this state the lubricant not only causes an increased power loss, but frequently surfaces may run bare for a period of time before the lubricant penetrates to all parts of the bearing surfaces and is eliective. The problem of a satisfactory lubricant for many types of apparatus, therefore, is not successfully met by employing the usual types of materials, with or without the addition of inhibitors and other additives.

It may be stated that for most purposes the requirements for a satisfactory liquid lubricant are:

1. Low vapor pressure 2. High resistance to oxidation or reaction with moisture at all operating temperatures 3. No corrosive action upon bearing members 4. Flat viscosity curve within operating range temperature 30 F. to +185 F.

5. Noncreeping 6. Nonpolymerizlng or condensing 7. Nontoxicity It has been discovered that a lubricant meeting all of the above seven requirements as well as or better than any known lubricant may be prepared from silicones. In particular, it has been found that dimethyl silicone polymers which have been treated to remove low boiling constituents meet the above requirements for a lubricant more successfully than any material heretofore known.

Several general processes for preparing silicone polymers are known to the art. The following illustrative examples are given:

Example 1 As disclosed by Kipping and his colleagues,

- silicon tetrachloride in cold ether solution may be casacca Cl SiCliCH: l Cl-gl-Cl CHsMgBr BiClz(CHs)z MSBrCl l SiCl(CHx)| The individual components of this mixture have different boiling points and can be separated by fractional distillation. Dimethyi silicon dichloride may thus be isolated. Its subsequent reaction with water yields dimethyl silicol and the silicol then polymerizes, spontaneously or through the agency of applied heat or catalysts which may be employed to control, within limits. the degree of polymerization and the physical properties of the resulting polymeric product.

Example 2 K. A. Andrianov, J. General Chemistry U. S. S. R. 8, 1255, 1263 (1938) and other workers have disclosed the preparation of silicols and silicones from ethyl silicate. Ethyl silicate may be treated with methyl magnesium bromide in a Grignard reaction to produce the following products:

' casio suoimtcn.

CaHsO-Si-OCsHt CHtMgBr o S(CIH5O)|(CH|)1 C, to summononu.

The methyl ethoxysilanes are readily separable by distillation into monomethyl, dimethyl and trimethyl ethoxysilanes. As mentioned previously, it is desirable to work with only the dimethyl compound. The isolated dimethyl diproduct is unsatisfactory as a lubricant, since the monomethyl silicones present permit the formation of solids and thermosetting types of compounds due to cross linkages between chains of polymer. If liquid polymers from such mixtures are subjected to heat when exposed to oxygen and moisture, they are not stable and will poiymerize further to form more viscous liquids and plastic or rigid solid bodies. l

If on the other hand the dimethyl derivative which is substantially free of the monoand trimethyl silicon compounds, is hydrolyzed and polymerized, the product is a liquid characterized by extreme stability. It is believed that chains or closed rings having the following general form occur:

0H. on.

-o i-oi-o'- Bl El There is always obtained a mixture of polymers. theiraverage molecular size, size distribution, complexity of structure and resulting properties depending upon the conditions, including temperature, agitation and catalysts, under which the reaction with water is carried out.

Polymeric dimethyl silicones which may be produced by practicing any of the processes above disclosed, or other possible methods, so as to isolate essentially the dimethyl fraction consist of a mixture of polymers of different molecular weight. The viscosity depends to a great extent upon the nature of the polymers present. The followingtable is indicative of the range of physical properties obtainable when mixtures prepared under diiferent conditicas were fractionated,

ample, to produce the polymers of predetermined characteristics.

Example 3 Stock and Somieski, Ber, Deuts. Chem. Ges. 52, 695 (1919), disclose that silane may be reacted with hydrogen chloride to produce monochlorosilane and dichlorosilane. Exhaustive methylation of the dichlorosilane with zinc methyl vapor produced dimethylsilane.

The dialkylsilane produced is hydrolyzed with sodium hydroxide to produce a soiution'which when acidiiled precipitates silicones. Stock and Somieski have shown that dimethyl silicone is conveniently prepared by this method. They further disclose that polymers obtained by this process are of a nature similar to those secured by the practice of the Kipping process.

Silicone polymers are built up through chains of alternating silicon and oxygen atoms. It an unseparated mixture of mono. di, and trimethyl silicon derivatives is hydrolyzed, the polymerized u The column headed fraction" refers to the volatile and non-volatile fractions which separate on distilling at 200 C. at an absolute pressure of 5 millimeters of mercury. The volatile fraction in the table in each instance 'is liquid at room temperature.

It will be noted from the above table that the viscosity of a silicone polymer fraction having an approximate average molecular weight of 1500 and produced with a HC1A catalyst is considerably less than the viscosity of a polymer of approximately the same average molecular weight when produced with the relatively more active H2804 catalyst. A relatively unexpected characteristic is the substantially uniform surface tension for the liquid polymers of all molecular weights.

According to this invention a satisfactory lubricant can be secured only if essentially dimethyl silicol molecules are condensed and polymerized. The product produced by condensing essentially dimethyl siliool will be radically different from the polymerized product resulting when a mixture of mono, diand trimethyl silicols having an average of 2 methyl groups .physical or chemical characteristics.

per silicon atom is used. For example, in the art there is described the product consisting of substantially two methyl groups per silicon atom but containing monoand trimethyl silicols in addition to dimethyl silicols. This product is stated to be essentially an oily liquid which. when heated for four hours at 120 C., sets to a soft, somewhat robbery gel. Obviously a gel is an unsatisfactory lubricant. Other properties of these mixtures have been described by those working in the art as forming solids upon being polymerized by exposure to temperatures of 200 C. These solids are not stable at elevated temperatures, since heating for several days at 200 C. causes any increasing embrittlement. They have been described further as oxidizing in air at 300 C. with disintegration taking place when this heating is prolonged for 24 hours.

On the contrary. the product produced from essentially dimethyl silicol polymerized at any temperature with or without a catalyst is a liquid. No solid products have been encountered when this material has been polymerized in numerous ways. When heated at 200 C. for prolonged periods of time, there is no observable chemical change. By heating at this temperature in vacuo light fractions may be removed as a vapor, but the major portion of the liquid does not distill even at 5 mm. of Hg and 200 C.

Among the exceptional properties of polymeric dimethyl silicone is its resistance to oxidation at elevated temperatures. In one test dimethyl silicone polymer has been heated at 200 C. while agitated by a stream of pure oxygen for 17 hours and longer Without any observable change in The liquid was as mobile and as clear after the test as be-4 fore. No sludging or gumming occurred.

cosity index) and one oil of a .zero V. I. It will be noted that the petroleum oils have much steeper viscosity-temperature curves than the synthetic dimethyl silicone lubricants. Considering that the viscosity is plotted on a logarithmic scale, the relative change of viscosity with temperature for the silicones is exceptional.

The slope m in the table is calculated from the viscosities at 210 F. and 100 F. according to the following formula:

where v=viscosity at the indicated temperature.

The following table indicates the slopes of the viscosities of a number of oils which are in commercial use today. The viscosity data were secured from the "A, B. T. M. Standards for Peiroleum -Products and Lubricants, September llIlD 100 V. I. O11 Zero V. I. 011 100 V. I. Oil Zero V. Oil

It will be noted on comparing the viscosity slope' columns of the tables for the dimethyl silicone` polymers and the petroleum oils that the slope of the former is relatively constant from the thinnest liquid to the most viscous liquid. On the "Various atmospheric gases have been applied The data in the above table have been plotted and shown as a graph in Fig. 1. Referring to the viigure, the four relatively straight lines drawn for each of the silicones are substantially parallel to one another. Furthermore, the relative slope of the lines is believed to be the nearest to a zero slope that is obtainable for any known types of material.

For comparison there have been plotted the values of three petroleum oils of 100 V. I. (viscontrary, the table for petroleum oils shows that `the slope changes rapidly from the thinner oils to the heavier oils. The change for petroleum is approximately three times from the thinnest to the heaviest oil in the table. v

rI'he silicone polymers have been subjected to extensive tests on various types of apparatus. In

4one test electrical watt-hour meters have been lubricated with suitable dimethyl silicone polymer and operated in ovens maintained at C. These watt-hour meters have been subjected to atmospheric gases such as oxygen, Water vapor and the normal constituents of air. The best obtainable petroleum lubricants prepared from high grade petroleum products and containing antioxidants and inhibitors failed under these conditions in one month. Ordinary untreated petroleum oils would fail in a day or two. An original supply of dimethyl silicone lubricant has been operating satisfactorily under these conditions for over a year without any observable failure or change in properties. On examination of a meter all the metal parts of the bearings were found to be clean and bright with no signs of gumrning. The lubricant appeared to be as good as when it was originally introduced into the apparatus with no apparent discoloration.

The dimethyl silicone polymer lubricant appears to meet all of the seven requirements herein set forth for an exceptionally satisfactory lubricant. Every test to which the material has been subjected has been successfully met.

It will be appreciated that a lubricant having the extremely :dat viscosity temperature curve exhibited by the dimethyl silicone polymers is highly advantageous for use in apparatus subjected to a wide lrange of temperatures. Precision instruments such. as Watches, clocks me I ters, scientific apparatus and the like willoperate with less power being required at temperatures below 0 l1'. with the silicone lubricant retaining-sumcient body and film forming characteristics to lubricate the bearings adequately at temperatures as high as the boilins point of wa. ter and even higher. The lubricant has been found not to freeze or harden until considerably below -70 E'.

Dimethyl silicones have been found to be satisfactory lubricante since they are stable at high temperatures even when exposed to engen. However, other dia'lkyl silicones, such. for exampie. as diethyl silicone, may be utilized asilibricants dependina on the conditions met.

Since certain obvious changes may be made in the above procedures and diiferent embodiments of the invention could be made' without distinguishing from the scope thereof. it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. A lubricant composed of a mixture of liqi uid polymers of diallwl silicones in which the al.

kyl groups each have at least two carbon atoms u substantially free of the monoalkyl and trialkyi silicone derivatives, the iubricantbeing characterized by resistance to deterioration at high temperatures.

2. In a method oi' lubricating the bearing surso faces oi' moving parts, the step of applying to said surfaces a fluid composition composed of a'mixture of liquid polymeric dimethyl silicones 'laging an average molecular weight greater than 3. In the method of lubricating the bearing surfaces oi' moving parts, the steps of applying to said surfaces a nuid composition composed of a mixture o1' liquid polymeric dialkyl silicones substantially free of the monoalkyl silicone derivatives and substantially free of components which distill at 200 C. and at a pressure of 5 mm. of mercury.

4. In the method of lubricating the bearing surfaces of moving parts, the steps of applying to said surfaces a iluid composition composed of a mixture o! a liquid polymeric dimethyl silicone fraction substantially free of components which distill at 200 C. and at a pressure of 5 mm. of mercury.

5. A lubricant composed of a mixture of liquid polymers of dialkyl silicones, the dialkyl silicones each having a substantial number of alkyl groups with at least two carbon atoms to provide an average of more than two carbon atoms per silicon atom, the silicones being substantially free of the monoalkyl and trialkyl silicone derivatives, the lubricant being characterized by resistance to deterioration at high temperatures.

JAMES G. FORD. ROBERT N. WENZEL.

REFERENCES CITED Tl'ie following references are of record in the ille of this patent: Y

UNITED STATES PATENTS

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