US1959775A - Low friction composition - Google Patents

Description

Patented May 22, 1934 PATENT OFFICE LOW FRICTION COMPOSITION William C. Wllharm, Edgewood, Pa., assignor to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania No Drawing. Application April 23, 1930 Serial No. 446,793

15 Claims.

My invention relates to compressed compositions of matter or alloys and, more particularly, to compositions of this type containing an organic lubricant.

The principal object of my invention is to provide a compressed material comprising a metal, an alloy, or a partial mixture and alloy, of two or more metals, such as those known in the art as bearing metals. which has self-lubricating properties.

A still further object of my invention is to provide a process of preparing compressed materials, such as bearing metals, which comprises mixing together one or more metallic powders, such as copper, zinc, iron, lead, tin, antimony or aluminum, with a small quantity of one or more free fatty acids, or one or more salts of such acids, and subjecting the mixture to heat and pressure in a suitable mold.

Various attempts have heretofore been made to produce anti-friction materials having self-lubricating properties. The usual methods have been to produce either a porous structure which is ca,- pable of absorbing lubricating oil or to add an inorganic lubricating substance, such as graphite, soapstone or tale, to the metals during the alloying process. The former practice, however, has not been entirely satisfactory because bearing metals having a porous structure permit dissipation of the oil, and inorganic substances, such as those specified, do not have sufficient lubricating properties when the requirements are severe.

After numerous experiments and static-fric tion measurements of different materials for oiliness on various substances, Ihave found that soaps are superior to all other materials tested. It was found diilicult, however, to incorporate soap in a lubricating system in which it could be utilized to the best advantage. Attempts were first made to incorporate a small quantity of soap in the usual mineral oils, but lubricating systems embodying such oils are not entirely satisfactory, although some of them are being utilized at the present time.

I have made the discovery that anti-friction material, such as bearing metals, having highly satisfactory lubricating properties, may be produced by incorporating soap in the bearing metal itself. In practicing my invention, one or more metals, which are known in the art as bearing metals, such as copper, zinc, iron, lead, tin, antimony or aluminum, are uniformly mixed, in a powdered form, with a small quantity of one or more fatty acids having at least one carboxyl group, and which are capable of reacting with one or more of the metals to form a soap, such as stearic, palmitic, oleic or dihydroxystearic, and the mixture placed in a steel mold and subjected to a high pressure at an elevated temperature. I preferably first subject the mixture to a pressure of between 30,000 to 50,000 pounds per square inch while the mold is cold. The temperature of the mold is then gradually raised while the pressure is being maintained until it reaches a temperature of approximately 150 to 250 C. The mold is maintained at this pressure and temperature for about one-half hour to allow the fatty acid to distribute itself uniformly through the powdered metal or metals, after which the pressure is raised to from about 100,000 to 200,000 pounds per square inch. The pressure is then released, and after allowing the mold to cool, the bearing is removed.

Another method which I found desirable is to mix a soap, such as sodium or lead oleate or zinc stearate with powdered metals and subject the mixture to heat and pressure in the manner specified in the foregoing example.

The following specifleexample will serve to illustrate my process, although it will be understood that I do'not desire to limit my invention to any particular metal or combination of metals.

50 parts, by weight, of powdered copper and 5 parts, by weight, of powdered lead were mixed with 2.8 parts, by weight, of stearic acid and subjected to a pressure of 40,000 pounds per square inch in a steel mold. The temperature of the mold was gradually increased to 200 C. and maintained at that temperature for about onehalf hour. The pressure was then raised to 140,000 pounds per square inch. After releasing the pressure and allowing the product to cool, the compressed material was removed. The bearing was analyzed and contained 1.34% lead stearate and .28% free stearic acid. A very good bearing may'also be produced when zinc is substituted for the copper in the foregoing example.

A bearing metal prepared by subjecting a mixture, containing 50 parts, by weight, of powdered copper, 5 parts, by weight, of powdered lead, 10 parts, by weight, of powdered zinc and 2 parts, by weight, of stearic acid, to heat, in the manner specified, was tested in service as a bearing for a chromium-plated shaft carrying a load of 15 pounds'per square inch of its projected area, and it was found that the wear on the bearing after one hour was only .00016 of a centimeter. As a comparative test, a bearing free from soap and containing approximately 85% copper, 8% tin and 5% of graphite, when subjected to the same load under the same conditions, was worn approximately .0011 of a centimeter during the same time, which indicates that the wear upon a bearing containing a soap is only about onetenth thatof a bearing containing an inorganic lubricating material.

I prefer to utilize metals containing a high proportion of iron or copper when bearings of high strength are required, to which may be added a minor proportion of zinc and lead, although the cheaper lead-bearing metals may also be produced by my process. For example, a bearing metal suitable for some uses may be prepared by mixing together 50 parts, by weight, of powdered copper, 30 parts, by weight, of powdered lead and 5 parts, by weight, of oleic acid and subjecting the mixture to heat and pressure in the manner specified.

In addition to soap, inorganic materials having lubricating properties may be added, such as graphite, mica, soapstone ortalc. For example, the following ingredients were mixed together in the proportions indicated:

Parts Copper 48 Zinc 10 Lead 5 Stearic acid 2.5 Graphite 2 tween the fatty acid and one or more of the metals and at least a partial alloying efiect between the metals when two or more alloyable metals are employed. Instead of adding the fatty acid to. the mixture of powdered metals and relying upon the heat and pressure to cause a reaction between the fatty acid and either one or more of the metals, it is also within the scope of my invention to mix a suitable soap with the powdered metals. The mixture is then subjected to pressure, with the application of heat, in the manner specified, to cause a compression and at least a partial alloying of the metals.

The amount of free fatty acid or soap may be varied considerably, although, as a rule, I preferably maintain the amount below 10%. When a free fatty acid is employed, it will be understood that oneor more metals must be present which will replace the hydrogen in the carboxyl group of the fatty acid. The degree of pressure and heat during the forming operations may also be widely varied. High pressures are desirable, but the temperature should not be increased to such an extent that it will cause decomposition of -the fatty acid or the soap.

Alloy or compressed structures produced according to my invention are sufficiently ductile to permit die shaping and sizing without surface breaks, and are also sufficiently strong to resist considerable stress without permanent deformation. In addition, they also have the very desirable property that they may be employed in some structures without the employment of a lubricating material, or if the supply of lubricant should become inadequate or be discontinued for some reason, the bearing metal would be capable of resisting the heating action of friction for a considerable length of time by means of its own lubricating properties.

In the above description, my improved material has been described particularly with respect to use as a bearing metal. I do not desire, however, to limit myself in this respect as the material may be employed for other purposes, such as for brushes on direct current generators.

While I have described my invention in considerable detail and have given numerous illustrations, it will be understood that they should be construed as illustrative and not by way of limitation, and in view of the numerous modifications which may be effected therein without departing from the spirit and. scope of my invention, it is desired'that only such limitations shall be imposed as are indicated in the appended claims.

I claim as my invention:

1. A self lubricating material comprising a plurality of solid powdered bodies, one at least of which is a metal, compressed together and having soap of such metal distributed therethrough.

2. A compressed composition having self-lubricating properties comprising a plurality of metals compressed together and having soaps of such metals uniformly distributed therethrough.

3. A compressed composition having self-lubricating properties comprising a major proportion of a metal having high strength, a minor proportion of zinc and lead, and having soaps of such metals uniformly distributed therethrough.

4. A material for shaft or other bearings comprising a structure containing two or more compressed metals at least partially alloyed together and having soaps of such metals distributed therethrough.

5. A compressed composition having self-lubricating properties comprising a major proportion of copper, a minor proportion of lead and zinc and having soaps of such metals distributed therethrough.

6. A compressed composition comprising a plurality of powdered bearing metals compressed under heat and pressure and the reaction product of one or more of the metals with a fatty acid, said fatty acid being of such a composition that the reaction product shall have lubricating properties.

'7. A material comprising compressed powdered bearing metal, free fatty acid and soap produced by the reaction of a portion of the free fatty acid with such metal.

8. A material comprising a plurality of compressed bearing metals at least partially alloyed together, a free fatty acid and a soap produced by the reaction of a portion of the free fatty acid with at least one of the metals.

9. A material comprising a plurality of compressed powdered metals, an inorganic lubricating material and soaps of such metals.

10. The process of producing a self lubricating material which comprises mixing together one or more powdered bearing metals and an organic tion of the soap.

13. The process of producing self-lubricating materials which comprises mixing together one or more powdered bearing metals and a free fatty acid, subjecting the mixture to a pressure of from 30,000 to 50,000 pounds per square inch, raising the temperature of the mold to 150 to 250 centigrade to permit the fatty acid to distribute unli'ormly itself throughout the powdered metal and then raising the pressure to from 100,000 to alloying of the metals, the temperature being insufllcient to cause a decomposi- 200,000 pounds per square inch to form a consolidated structure.

14. A self lubricating body comprising a composite compressed mixture of powdered solid body materials and a bearing metal compound having lubricating properties containing the radicle of a fatty acid, said powdered body materials having considerably less lubricating properties than the compound containing the acid radicle.

15. The process of producing self-lubricating materials which comprises mixing together two or more alloyable powdered bearing metals and a free fatty acid which is capable of reacting with one of the metals to form a soap and compressing the mixture together at an elevated temperature under suillclent pressure to cause a partial alloying of the metals, the temperature being insuiiicient to cause a decomposition of the fatty acid.

WILLIAM C. WEHARM.