US2339715A - Low temperature grease - Google Patents

Description

Patented Jan. 18, 1944 LOW TEMPERATURE GREASE Rulon Wells McOmie and Harold A. Woods, Martinez, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application July 13, 1942, Serial No. 450,792

Claims.

This invention relates to a low temperature grease which has an efiective lubricating temperature range of between about -80 F. and +175 F. More particularly, it deals with a calcium soap grease comprising a low pour point mineral oil and a small amount of an aqueous solution containing both glycerin and a lower glycol.

It is the purpose of this invention to widen the effective lubricating range of calcium soap greases so that they are usable at extremely low temperatures. It is another purpose of this invention to'produce a grease which is capable of giving efiective lubrication over the range of most extreme atmospheric temperature changes. A further purpose is to produce a grease which has a minimum change in its consistency over such a wide temperature range. A still further purpose is to produce a grease which has a low shearing stress at temperatures of 60 F. and

below. v

The low temperature grease of this invention has a consistency between about 200 and 390, and preferably between about 330 and 370, at 77 F., as determined by A. S. T. M. Cone Penetration Test D217-38T. It consists essentially of: between about and by weight ofa calcium soap; not over about 5%, preferably between 1.5% and 3.5%, by weight of an aqueous solution of glycerin and a glycol; and the remainder a low pour point and low viscosity mineral lubricating oil. The grease may also contain small amounts of other ingredients which are added to the mineral oil, such as var- .iousinhibitors, extreme pressure additives, stabilizers, etc.

The several constituents of the grease will now be discussed.

The soap The particular type of soap employed comprises predominantly a calcium soap.- Calcium soaps are prepared by saponifying fats or fatty acids with calcium hydroxide alone or together with minor amounts of other alkali and/or alkalinemetal hydroxides. The fats which may be employed in making the soaps may be of either animal or vegetable origin, such as mutton fat, lard oil, tallow, fish oils, rosin, degras, olive oil, rape seed oil, cotton seed oil, castor oil, perilla oil, sunflower seed oil, ground-nut oil, palm oil, and the like, or mixtures of two or more of these fats. 'Fats comprise mostly glycerides of fatty acids and usually contain some free fatty acids, -the most common, of which are lauric, palmitic, stearic, and oleic acids. In addition to calcium soap minor amounts of other soaps may be employed, particularly alkali and alkaline earth (other than calcium) soaps, such as lithium, sodium, potassium, and barium soaps. Aluminum soap may also be used.

The aqueous solution The proper composition of the aqueous solution is of the greatest importance. It consists predominantly of three essential ingredients, i. e. water, glycerin and a glycol, the amounts of which are limited to definite ratios. The weight Water, 28 to 61%, preferably about 38% Glycerin, 28 to 61%, preferably about 50% Suitable glycols are those which are water- 'soluble and have not more than four carbon atoms per molecule, e. g. ethylene glycol, propylene glycols, butylene glycols, or diethylene glycol.

The ingredients may be added to the soap mixture before final dilution with the mineral oil or a. portion thereof may be present in the soap mixture, such as water retained by the soap during saponification for stabilization, and glycerine produced during the saponification of fats amounting to approximately 10% by weight of the fats. However, if the amounts of these ingredients are not within the above limits the a correct amount of each is added to bring the composition of the aqueous solution within said limits.

- The mineral oil I The temperature at which a grease becomes solid and loses its plasticity to the point of be- I coming rigid under low shearing stresses depends directly upon the fluidity of the oil which it contains. Fluidity'at low temperature depends in turn on the pour, point and the viscosity. Below the pour point the oil ceases to be fluid and above the pour point the viscosity of the oil determines its fluidity. Accordingly, the

particular mineral oil employed in the greasetemperatures.

below about 50 F. and preferably below'about -'I5 F.; and has as low a viscosity as is consistent with proper lubricating power and stability of the grease. Too low a viscosity causes both loss of lubrication and separation of the oil from the soap in the grease at relatively high Thus there are limits to the viscosity of the oil suitable for use in this grease, which limits are: Saybolt Universal Viscosities at 100 F. between-about 40 and 75 seconds and at 60 F. below 250,000 and preferably not more than about 200,000 seconds. Inasmuch as viscosities at 60 F. are difiicult to measure directly they may be determined by extrapolation from viscosities at higher temperatures with the aid of an extended A. S. T. M. Viscosity Temperature Chart D341-32T.

Other ingredients It may be desirable to add various inhibitors, extreme pressure additives, and the like to the grease of this invention, provided they do not in-' terfere with the low temperature operation of the grease. Usually not over 1% by weight of any such ingredient is added, although, depending on the nature of the additive, quantities up to 10% by weight of the mineral oil may be added.

Some extreme pressure additives comprise: esters of phosphorus acids. such as triaryl, alkyl or aralkyl phosphates or phosphites, alkyl phenol phosphates or phosphites, etc.; neutral aromatic sulfur compounds of relatively high boiling temperatures such as diaryl sulfides, diaryl disulfides, alkyl aryl disulfides, e. g. diphenyl sulfide, diphenol sulfide, dicresol sulfide, dixylenol sulfide, methyl butyl diphenol sulfide, dibenzyl sulfide, correspondin diand trisulfides, etc.; sulfurized fatty acids or esters of fatty acids and alcohols, e. g. fatty oils, sperm oil, etc., in which the sulfur is strongly bonded; sulfurized longchain olefins such as may be obtained by dehydrogenation or cracking of wax; sulfurized phosphorized fatty oils or acids, phosphorus acid esters having sulfurized organic radicals, such as esters of phosphoric or phosphorus acids with sulfurized hydroxy fatty acids; chlorinated hydrocarbons as chlorinated parafiins, aromatic hydrocarbons, terpenes, mineral lubricating oils, etc.; or chlorinated fatty acids containing the chlorine in position other than alpha position.

Additional ingredients other than extreme pressure additives may comprise anti-wear agents,

such as oil-soluble urea or thiourea derivatives,

Example A low temperature grease was prepared by first saponifying a mixture of three parts tallow and one part lard oil with about 14% by weight of hydrated lime containing about .15% by weight of sodium hydroxide in a pressure vessel in the presence of a small amount of water and a minor portion of a mineral oil to keep the mixture in a of this invention is one which has a pour point liquid state after the saponification. The saponification was carried out at a temperature of about 260 F. for a period of about 35 minutes and then the saponified mixture was slowly run into a steam-jacketed open continuously agitated kettle containing another minor portion of the mineral oil. The mineral oil consisted of a mineral pale lubricating oil having a Saybolt Uni- I versal Viscosity of 60 seconds at F., an extrapolated Saybolt Universal Viscosity of 150,000 seconds at 60 F., and a pour point of 60 F., and contained dissolved 5.0% by weight of a sulfurized sperm oil as an extreme pressure addi tive. The blended oil had a Saybolt Universal Viscosity at 100 F. of 72.4, and of 200,000 sec-- onds at 60 F. To this soap mixture was added a small percentage of ethylene glycol and then it was mixed and diluted with the remainder of the blended oil until a grease having an A. S. T. M. consistency of about 330 at 77 F. was obtained. The final composition of this grease was as follows:

This grease was tested in an airplane bomb door retracting screw comprising two bevel gears, two double row ball bearings and a screw with an Acme thread, all of which was enclosed in a wooden box serving as a refrigerator. The drive for the screw was run at 154 R. P. M. through a reduction gear by a 5 horsepower electric motor. This motor was cradled in ball bearings and the torque taken on a one-foot lever arm by a spring scale. A tension load of 1070 pounds was applied to the screw by means of a 10-inch diameter piston in an air cylinder. Thermocouples were placed at various intervals in the box containing the screw mechanism to record the temperature of the grease and mechanism and then the screw mechanism in the box was packed with dry ice (solid CO2). At -78 F. the mechanism could still be operated'efiectively. The measured torque on the mechanism lubricated by the grease at this temperature was not over 12.5 foot-pounds compared with 11 foot-pounds at 60 F., andabout 9 foot pounds at about +60 F. and above, up to about F. Thus, change in torque over the entire temperature range from -78 F. to +150 F. was only of the order of about 30%, which is remarkably low. The torque determined by this test is proportional to the shear resistance of the grease at the temperatures tested.

The low temperature greases of this invention are particularly applicable for lubricating mechanisms that are used in climates having severe temperature changes, as well as in mechanisms of transportation, including aircraft, which operate within short periods of time between tropical temperatures at sea level and sub-zero tem-' peratures of high altitudes.

We claim as our invention:

1. A low temperature grease, having an A. S. T. M. consistency ranging between about 200 and 390 at 77 F. comprising from 10% to 20% by weight of a calcium soap, between about 1.5%

and by weight of an aqueous solution containing glycerin and a water-soluble glycol of not more than 4 carbon atoms, and the remainder a mineral oil having a pour point below about --50 F. and Saybolt Universal viscosities at 100 F. of between about 40 and 75 seconds, and at -60 F. of less than about 250,000 seconds, the ratio of glycerin to water in said aqueous solution ranging between about 1:2 and 2:1 and the ratio of the aqueous glycerin to the glycol ranging be tween about :1 and 5:1.

2. The grease of claim 1 wherein the content of the aqueous solution is between about 1.5 and 3.5% by weight of the grease.

3. A low temperature grease. having an effec- V tive lubricating range between about 80 F, and j +175 F. comprising from 10% to by weight of a calcium soap, between about 1.5% and 5% by weight of an aqueous solution containing glycerin 1nd a water-soluble glycol of not more than 4 carbon atoms, and the remainder a mineral oil 15 proximately:

having a'pour-point below about -50 F. and 1 Saybolt Universal viscosities at 100 Roi? between about and '75 seconds, and at 60 F. of less than about 250,000 seconds. said aqueous solution 5 comprising in percentages byweight:

Percent Water 28-61 Glycerin 28-61 Glycol 9-17 m x 4. The grease of claim 3 wherein the glycol is ethylene glycol.

5. The grease of claim 3 wherein the aqueous solution comprises in percentages by weight ap- Percent Water 38 Glycerin Glycol 12 RULON WELLS McOMIE. HAROLD A. woons.