Process for producing a metal-lubricant
US 2964476 A
Description (OCR text may contain errors)
Dec. 13, 1960 B. c. coAD 2,964,476
PROCESS FOR PRODUCING A METAL-LUBRICANT BEARING. ELECTRICAL CONTACT, AND
THE LIKE Filed Sept. 28. 1956 Sintered Body Made From Metallic Powder And A Lubricant Comprising Solid Polymerised Halogenated Hydrocarbon.
5 BMW- 54% United States Patent PROCESS FOR PRODUCING A METAL-LUBRI- CANT BEARING, ELECTRICAL CONTACT,
AND THE LH(E Brian-Colliver Coad, Hammersmith, London, England, assignor to Morganite Incorporated, Long Island City, N.Y., a corporation of New York Filed Sept. 28, 1956, Ser. No. 612,795 Claims priority, application Great Britain Oct. 3, 1955 9 Claims. (Cl. 252-26) This invention relates to bearings, which term includes any machine element subject to sliding movement relative to another element, and to. electrical contacts such as current collectors, brushes, commutator segments, terminal elements, and the like which may or may not be subject to relative sliding movement;
One object of the invention is to provide an improved bearing material particularly suitable for use under conditions where no lubrication is possible.
- 'A second object of the invention is to provide an improved electrical contact material characterized by very low electrical resistance and rate of wear.
In the achievement of both objects it is sought to provide material of high transverse breaking strength, and high thermal and electrical conductivity.
It is known'that valuable properties can be obtained in bearings and brushes by incorporating polytetrafluoroethylene (hereinafter called P.T.F.E.) as one of the components of the material. The other essential component may be a conducting material (a metal), which will remove heat generated by friction in a hearing, or which will carry the electric current in a brush. It is further known that the presence of a second solid lubricant (e.g. graphite or molybdenum disulphide) is beneficial.
There are difficulties in making a satisfactory mixture .Of metal, P.T.F.E., and such other type of solid lubricant.
P.T.F.E. begins to decompose without melting at about 400 C., consequently, any material containing P.T.F.E. cannot be heated above that temperature. On the other hand the metals which are normally used to make bearings and brushes do not sinter appreciably below about 700 C.
.Hence, a simple mixture of metal, P.T.F.E. and the other solid lubricant, when pressed, must derive its strength from the sintering of the P.T.F.E. For such a mixture, hot pressing at about 350 C. has generally been found to give a stronger product than cold pressing and sintering, but it has commonly been found necessary to incorporate a thermosetting resin into the material in order to obtain adequate strength.
P.T.F.E. is available in the form of a fine powder, but the powder is subject to severe agglomeration. Materials made by blending other powders with P.T.F.E. therefore tend to lack uniformity and to be relatively weak. Thus a material made by blending 50% fine copper powder with 25% fine graphite powder and 25% fine, but agglomerated, P.T.F.E. powder, after hot pressing at 14 tons per square inch and 330 C. had a transverse breaking strength of 1,790 lbs/sq. inch. After cold pressing at 14 tons per square inch, sintering for two hours at 380 C., the material had a transverse breaking strength of 1,410 lbs./sq. inch.
dispersion, and this may be blended with the other components of the mixing, then dried, or precipitated and filtered. Such a material is uniform, but the metal powder is liable to become oxidised during drying. Moreover the metallic particles are liable to become completely coated with P.T.F.E., which is an excellent insulating ma- P.T.F.E. is also available in the form of an aqueous Patented Dec. 13,1960
terial, so that, after forming, the material has very poor electrical and thermal conductivity.
The aqueous dispersion of P.T.F.E. may be put into preformed bodies by impregnation. This method, while satisfactory for some purposes, involves control of poresize in the preform, and further, the quantity of P.T.F.E. introduced is limited by the porosityof the. preform. In order to incorporate substantial amounts of P.T.F.E. similarto those described herein, very high porosity is re- .quired, and this results in poor strength. Thus a preform whose composition after impregnation was 60% copper, 20% graphite and 20% P.T.F.E. had a transverse breaking strength after impregnation of only 1280 lbs./ sq. inch. The present invention is a process for producing a relatively strong and otherwise most suitable material of a bearing or of an electrical contact from metallic powder, P.T.F.E. or other solid lubricant which is a solid polymerized halogenated hydrocarbon, and one or more solid lubricants of another type such as, for example, graphite or molybdenum disulphide (M08 The process of the invention is characterized by making a preliminary mix of an aqueous dispersion of the solid polymerized halogenated hydrocarbon with the other type of solid lubricant, drying and disintegrating the mix, blending it with the metallic powder, and then bringing the mix to shape by pressure accompanied or followed by heating to sinter the body. If P.T.F.E. is thesolid polymerized halogenated hydrocarbon, as is preferred, the shaping of the mix may be accomplished by cold pressing or extrusion followed by sintering in the temperature range of 350 to 450 C. or by hot pressing or extrusion at temperatures ranging from 200 to 400 C. The same applies if chlorotrifiuoroethylene polymers (P.T.F.C.E.)
"are used as the solid polymerized halogenated. hydrocarbon. 1
The metallic powder need not be that of a metal or alloy of a low sintering temperature. It may be, for example, iron, copper or bronze, so that it will be seen that the heating temperatures mentioned above are well below those at which such metals or alloys normally sinter. There is, however, some reason to believe that a certain degree of sintering of the metal does take place despite the relatively low temperature. This could be due to .traces of fluorine being released, from the P.T.F.E. or P.T.F.C.E., and serving to activate some sintering of the metal. I
The metal content of the body is preferably between 40% and by weight of the body.
- Bearings and electrical contacts made according to the invention have a very low coefiicient of friction and possess high strength comparable with that of a cold pressed metal compact sintered at high temperature. Moreover they are characterized by relatively high elec trical and thermal conductivities. v
The invention is illustrated by the following examples:
Example 1 I Finely divided M08 powder was intimately mixed e.g.
in a paddle mixer, with "an aqueous dispersion of P.T.F.E.,
in the ratio of 80% to 20% by weight of the solid content of the P.T.F.E. dispersion. This mixture was dried in an oven at about C. and then pulverized in a hammermill. The pulverized material was then mixed in a pan mixer with a finely divided copper powder in the ratio of 25% by weight of MoS -P.T.F.E. mixture to 75% copper. The resulting three component mixture was thenhot pressed in a die at a pressure of 14 tons per sq. in. and at a temperature of 300 C.
The resulting product was found to have a transverse breaking strength of 9600 lbs./sq. in., and an electrical resistance of 0.04 10- ohm inches. When tested as an unlubricated bearing, this material ran successfully at a P.V. of 10,000 whereas bronze-graphite bearings are satisfactory only up to 2,500 P.V.
These properties may becompared with those of a cold pressed copper compact sintered at high tempera ture, namely:
Electrical resistance of 0.034 l" ohm inches.
Transverse breaking strength of 12,000 lbs./ sq. in.
Example 2 Finely divided natural graphite was intimately mixed, e.g. in a paddle mixer, with an aqueous dispersion of P.T.F.E., in the ratio of 4 'parts by weight of graphite to 1 part by weight of P.T.F.E. This 'materialwas'dried in an oven at 130 C. and thendisintegrated in ahammer mill. The disintegrated material was then mixed in a pan mixer with an equal weight of finely 'divided copper powder. The resultant three component mixture was then hot pressed in a die at a pressure of six tons per sq. in. andat a temperature of 250 C.
The resulting product was found to have a transverse breaking strength of 3200 lbs/sq. in. and an electrical resistance of 0.2 l0 'ohm inches. Further it showed excellent current collecting properties and remarkably low wear when testedasa brush.
Example 3 Finely divided natural graphite was intimately mixed, e.g. in a paddle mixer, with'an aqueous dispersion of P.T.F.E. in the ratio of 3 parts by weight of graphite to 2 parts by weight of P.T.F.E. This material was dried in an oven at 250 C., then disintegrated in a hammer mill. The disintegrated material was then sieved and mixed in a cubical blender with an equal weight of finely divided silver powder. The resultant three component mixture was then cold pressed at 10 tons per sq. in.and sintered for two hours at 380 C.
The resulting product had a transverse breaking strength of 3200 lbs/sq. in. and an electrical resistance of 0.5 10 ohm ins. Moreover, when tested as a brush the material gave an extremely good result under conditions of very difiicult commutation.
Example 4 Finely divided graphite was intimately mixed with an aqueous dispersion of P.T.F.E. in the ratio of 3 parts by weight of graphite to 4 parts by weight of P.T.F.E. This material was dried in an oven at 250 C., then disintegrated in a hammer mill. The disintegrated material was sieved and blended in a cubical blender With'finely divided copper powder in the ratio of 3 parts by weight of copper to two parts by weight of the material. The resultant three component mixture was then cold pressed at 10 tons per sq. in., and sintered for 2 hours at 380 C.
The resulting product had a transverse breaking strength of 6400 lbs. per sq. in. and a resistance of 0.15 10" ohm ins. Moreover when tested as a brush under conditions likely to be encountered at an altitude of 70,000 feet the material gave negligible wear.
Example 5 ing strength of 9000 lbs. sq. in. and a resistance of Thus it will be seen that the invention provides an excellent bearing material or current collector of 'high strength, electrical and thermal conductivity and very low coefficient of friction, in which the lubricating eifects of a solid lubricant and P.T.F.E. are uniformly distributed throughout the body.
The single figure of the drawing is a perspective view depicting a sintered body made from a metallic powder and a solid lubricant including a solid polymerised halogenated hydrocarbon, according to the invention. Such a body may be used as a machine'element subject to sliding movement relative to another element and as an electrical contact member, and may be varied in shape for particular uses or applications.
What is claimed is:
1. Process for producing a material for uses as a bearing and an electric contact from metallic powder, a first solid lubricant selected from the group consisting of polytetrafluoroethylene and chlorotrifluoroethylene polymer, and a second solid lubricane selected from the group consisting of graphite, molybdenum sulphide and mixtures of graphite and molybdenum sulphide, the metallic powder'being present inan amount of 40 to by weight of the material and the balance being made up of substantial proportions of the first and second solid lubricants, characterized by making a preliminary mix of an aqueous dispersion of said first and second solid lubricants, drying and disintegrating the mix, blending it with the metallic powder, and then bringing the mix to shape by pressure and'byheating to a temperature of-200 to 450 C. to sinter the body.
2. Process according to claim 1 in which the second solid lubricant is graphite.
3. Process according to claim 1 in which the second solid lubricant ismolybdenum disulphide.
4. Process according to claim lin which the first solid lubricant is polytetrafluoroethylene.
5. Process according'to claim 1 in which the first solid lubricant is a chlorotrifluoroethylene polymer.
6; Process according-to claim l inwhich the second solid lubricant is graphite and then bringing the mix to shape by cold pressing and thereafter sintering at a temperature within the range of 350 to 450 C.
7. Process according to claim l-inwhichthe second solid lubricant is graphite, and then bringing the mix to shape by pressure accompanied by heat at a temperature within the range of 200 to 400 C.
8. Process according to claim 1 in which the-second solid lubricant is molybdenum disulphide and then bringing the mix to shape by cold pressing and thereafter sintering at a temperature within the range'of 350 to 450 C.
9. Process according to claim 1 in which the second solid lubricant is molybdenum disulphide, and then bringing the mix to shape by pressure accompanied by heat at a temperature within the'range of 200 to 400 C.
References Cited in the file of this patent UNITED STATES PATENTS 1,884,298 Seabury et al Oct. 25, 1932 2,120,549 Dike June 14, 1938 2,400,091 Alfthan May 14, 1946 2,400,099 Brubaker et al May 14, 1946 2,470,264 Richardson May l7, 1 949 2,656,475 Diehl et al. Oct. 20, 1953 2,691,814 Tait Oct. 19, 1954 FOREIGN PATENTS 1,080,017 France Apr. 28, 1953 700,256 Great Britain Nov. 25, 1953