US2991247A

US2991247A - Process for forming a semifluid grease involving cooling to a subzero temperature

Info

Publication number: US2991247A
Application number: US703710A
Authority: US
Inventors: Kurt R Fisch
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-12-18
Filing date: 1957-12-18
Publication date: 1961-07-04
Anticipated expiration: 1978-07-04

Description

United States Patent PROCESS FOR FORMING 'A SEMIFLUID GREASE INVOLVING COOLING TO A SUBZERO TEM- PERATURE Kurt R. Fisch, Philadelphia, Pa., assignor to the United States of America as represented by the Secretary of the Army No Drawing. Filed Dec. 18, 1957, Ser. No. 703,710

3 Claims. (or. 252- 333) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purpose without the payment of any royalty thereon.

This invention relates to a semifluid grease composition for use as an extreme pressure lubricant and to a method for its preparation.

An important object of this invention is to provide a lubricating compound for the rotating and elevating mechanisms of a gun able to withstand (extremely high) pressures of the order of 60,000 p.s.i., thought to be from gases escaping from the gun, without decomposing or evaporating.

Another object of this invention is to provide a composition which retains its lubricating properties when subjected to severe cold working conditions.

With the advent of modern firearms capable of firing at rapid speeds causing pressures to mount to 57,000 lbs. per square inch and temperatures to reach well above 260 F., the problem of proper lubrication of these mechanisms became very acute. The lubricants known to the prior art were inadequate in that they either broke down or evaporated at the extremely high pressures, or else when subjected to a temperature well below the freezing point of water, they gelled and became very stiff.

The lubricant made in accordance with this invention has an advantage over the prior lubricants in that it is stable at temperatures of 260 F. and pressures of 60,000 lbs. per square inch, furthermore, when the firing mechanisms are subjected to temperatures as low as -65 F., permitting satisfactory operation of the gun.

The invention consists of mixing 80-89% by weight of at least one material from a group consisting of esters of adipic, pimelic, suberic, azelaic, sebacic acids, a particularly preferred ester being di-2-ethyl hexyl sebacate, having a centistoke viscosity at 100 F. in the range from nine to fourteen and a centistoke viscosity at 65 F. of not more than 12 thousand with about 1.5 by weight of any rust inhibitor, such as barium petroleum sulfonate, 1.0% by weight of di isopropyl acid phosphite to enhance extreme pressure stability, about 0.5% of any oxidation inhibitor from the group having a phenolic derivation, such as 2,6-di-tertiary butyl para cresol, to preclude any reaction with the di isopropyl acid phosphite, and from 17.0% to 8% of a thickening agent such as lithium stearate. The weight of the thickening agent is controlled by the polarity of the other components. The higher their polarity the more thickening agent will have to be added to insure stability of the suspension which is formed. The suspension of lithium stearate is homogeneously dispersed throughout the mixture. The mixture is heated to 185 C. to 195 C. The temperature must be kept below 195 C. to prevent the formation of a grease which results if the heating is prolonged or if the temperature is too high. The character of the solution changes above 195 C. resulting in a different crystalline structure. If

2,991,241. Patented Ju i/4i 1961 2 the temperature is below 185 C. a slurry will result. it has been found empirically that the proper fiber structure is obtained by keeping the temperature within the prescribed range.

The mixture is rapidly chilled at a rate of 25 C./minute to a final temperature about 30 C. This cooling rate is important to obtain the proper fiber structure. If the rate is any slower by a substantial amount a slurry will result. Proper chilling produces a thixotropic mixture which when worked changes its viscosity and flow characteristics and becomes a semifluid grease. The resulting compound is then worked in a grease worker to give it the proper mechanical treatment. The size and shape of the fibers in which the liquid is enclosed will determine the properties of the final composition. After the semifluid grease has been thoroughly worked by 100 strokes of a grease worker, it is placed in a vacuum of about 2 mm. pressure. The air bubbles are then exhausted from the composition in a period of two hours.

A specific example which has proved successful within the pressure and temperature requirements has been pro duced in the following manner: Mixing 89% by weight of di-Z-ethyl hexyl sebacate with 1.5% barium petroleum sulfonate, 1% di-isopropyl acid phosphite, and 0.5 2,6- di-tertiary butyl para cresol; adding 8% lithium stearate; homogeneously dispersing the lithium stearate throughout the mixture; heating the mixture to a temperature range from 185 C. to 195 C.; immediately chilling the mixture at a rate of 25 C./rninute to a final temperature of -30 C.; homogenizing the mixture and exhausting the air from the mixture. Other examples which have been successfully tested have been produced by substituting iso amyl adipate and di-Z-ethyl hexyl azelate for di-2- ethyl hexyl sebacate.

I claim:

1. A method for producing an extreme pressure semifluid grease lubricating composition capable of use at temperatures between about 300 F. to -76 F. comprising the steps of forming a mixture of 80 to 89% by weight of an ester selected from the group consisting of esters of adipic, pimelic, suberic, azelaic and sebacic acids having a centistoke viscosity at F. in the range of 10 to 14 and below about 12,000 at -65 F., about 1% by weight of di-isopropyl acid phosphite for imparting extreme pressure stability to said composition, about 1.5% by weight of barium petroleum sulfonate for imparting rust inhibiting properties to said composition and about 0.5% by weight of 2,6-di-tertiary butyl para cresol for imparting oxidation inhibiting properties to said composition, admixing a thickening agent to said mixture within the range of about 8 to 17% by weight, homogeneously dispersing the thickening agent throughout the mixture, heating the mixture to about l95 C. to prevent the thickened mixture fromforming a grease, immediately chilling the heated mixture to about 30 C. at a rate approximating 25 C. per minute to prevent slurry formation and yet resulting in a thixotropic mixture, and mechanically working the thixotropic mixture to form a semifluid grease.

2. The process of claim 1 wherein said thickening agent is lithium stearate.

3. The process of claim 1 including the step of exhausting the air from the mechanically worked semifluid grease to inhibit separation of components therefrom.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Bergstrom et a1 J an. 20, 1942 Ricketts Sept. 1, 1942 Wasson et a1 Mar. 11, 1947 Zisman et a1 Sept. 7, 1948 Ashburn et a1 Sept. 28, 1948 Bondi Oct. 31, 1950 Davies et a1. Sept. 4, 1951 Eckert Sept. 16, 1952 '4 OTHER REFERENCES Development of Schematic Analytical Procedures for Synthetic Lubricants and Their Additives, Schmidt et al., WADC Technical Report 54-464, Denver Research Inst., April 1955, pages 6 and 7.

Manufacture and Application of Lubricating Greases, Boner, Reinhold Pub. Corp., N.Y., 1954, pages 227, 228, 278 and 279.

Concise Chemical and Technical Dictionary, Bennett, Chemical Pub. 00., N.Y., 1947, page 363.

Claims

1. A METHOD FOR PRODUCING AN EXTREME PRESSURE SEMIFLUID GREASE LUBRICATING COMPOSITION CAPABLE OF USE AT TEMPERATURES BETWEEN ABOUT 300*F. TO -76*F. COMPRISING THE STEPS OF FORMING A MIXTURE OF 80 TO 89% BY WEIGHT OF AN ESTER SELECTED FROM THE GROUP CONSISTING OF ESTERS OF ADIPIC, PIMELIC, SUBERIC, AZELAIC AND SEBACIC ACIDS HAVING A CENTISTOKE VISCOSITY AT 100*F. IN THE RANGE OF 10 TO 14 AND BELOW ABOUT 12,000 AT -65*F., ABOUT 1% BY WEIGHT OF DI-ISOPROPYL ACID PHOSPHITE FOR IMPARTING EXTREME PRESSURE STABILITY TO SAID COMPOSITION, ABOUT 1.5% BY WEIGHT OF BARIUM PETROLEUM SULFONATE FOR IMPARTING RUST INHIBITING PROPERTIES TO SAID COMPOSITION ABOUT 0.5% BY WEIGHT OF 2,6-DI-TERTIARY BUTYL PARA CRESOL FOR IMPARTING OXIDATION INHIBITING PROPERTIES TO SAID COMPOSITION, ADMIXING A THICKENING AGENT TO SAID MIXTURE WITHIN THE RANGE OF ABOUT 8 TO 17% BY WEIGHT, HOMOGENEOUSLY DISPERSING THE THICKENING AGENT THROUGHOUT THE MIXTURE, HEATING THE MIXTURE TO ABOUT 185-195*C. AT A RATE APPROXIMATING MIXTURE FROM FORMING A GREASE, IMMEDIATELY CHILING THE HEATED MIXTURE TO ABOUT -30*C. AT A RATE APPROXIMATING 25*C. PER MINUTE TO PREVENT SLURRY FORMATION AND YET RESULTING IN A THIXOTROPIC MIXTURE, AND MECHANICALLY WORKING THE THIXOTROPIC MIXTURE TO FORM A SEMIFLUID GREASE.