IL27166A - Dry lubricant,articles coated therewith and method of making it - Google Patents

Description

B'SIR ,»a» na»e nam Dry lubricant articles coated therewith, and method of making I ΪΗΕ BUNKER-RAMO CORPORATION Gi 25795 la This Invention relates to a dry lubricant, method of application thereof to the sur oe of an article, and a coated article eo obtained.

Hitherto w en dry lubricants, powders, waxes and liquid lubricants are applied to a surface the particles and liquid. Instead of adhering tenaciously to the surface, are, in moat cases, large&y removed af er tie firirt wipe.

U,3. Paten specsification So, 2,995,462 discloses two embodiments of a bearing material. In one embodiment the metal is coated by plating over a coating of cracked or recessed polytetrafluoroethylene (PTFE) . In the other embodiment a mixture of lead powder and particles of PTFE is roll-impregnated into sintered bronze. Both of these known materials have the disadvantage that they lose their lubricant properties after a relatively short use, owing to the wear-down of their outer layers.

The particles are deposited as a thin layer of discrete particles, for example, of .05 to .5 microns diameter (although 40 microns is operable), and the metal is deposited as a continuous thin layer over and partially around the particles so that the final result of multilayer deposition is a substantially homogeneous dispersion of particles in metal.

In order to prevent removal of one deposition before the other is made, the direct strike or deposition is made at a higher current density and for a longer time than the reverse strike. For example, the direct strike may be at a current density of 10 amperes per square foot while the reverse strike will be at 5 - 80 per cent less current density. Likewise, the control time can be 5 - 30 seconds for the direct deposition on the cathode with only 1 - 5 seconds for deposition when the polarity is reversed.

It should be understood that the current source may be a direct current source such as a battery or rectifier combined with suitable relays, reversing switches and resistances controlled by a timing mechanism to reverse the current at predetermined times and vary its value in accordance with the requirements of the article being coated, and the coating bath, care being taken as above mentioned to have the direct strike or deposition at a current density and time such as to prevent any substantial removal of one deposition before the other is made. The electric potential need not be above, and preferably is below the value at which electrolysis of water occurs. Suitable apparatus and electrical controls are well known in the art, such as, for example, the electrical controls shown in "Electroplating Engineering Handbook" published lubricating properties. Most of such materials in aqueous dispersions normally have or can be made to have a negative charge.

Suitable materials include molybdenum disulphide, copper oxide, oxide sulphides, and other compounds of metals and also plastics and resins known for their lubricating properties. Particularly satisfactory results, however, have been obtained with particles of fluorocarbon polymers. These include polytetrafluoroethylene, polychlorotrifluoro ethylene, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoro-ethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluor propylene copolymer, polyhexafluoropropylene, poly 1, 1, 1-trifluoro-propylmethyldichlorosilane, fluorosilicone elastomers, polyfluor-aniline, and copolymers of tetrafluoroethylene and trifluoronitroso-methane. The preferred fluorocarbons are those that are completely fluorinated, and of these the best, from the point of view of low coefficient of friction, is polytetrafluoroethylene. This material, under the trademark TEFLON, is commercially available as negatively charged particles in an aqueous liquid.

The lubricating compositions can be applied to any surface such as, for example, ceramics and metals.

The treated surfaces can be used for bearings, including clock bearings; electrical contacts, hard-coat die surfaces, and dry lubrication of shells for military and space applications.

The treated parts exhibit low friction and extended wear.

The coatings give constant insertion and withdrawal forces to electrical contacts having low electrical resistance, and the contacts exhibit extended wearability.

The coatings may be of any thickness, but in general the The following example gives a detailed procedure of carrying out the invention, it being understood that modifications of this procedure and the materials can be made and that the example is merely illustrative of a procedure which has been found satisfactory and is not intended to limit the invention thereto.

EXAMPLE I The base or substrate used was polished brass panels (4 inches by 2% inches) having a major surface area of 20 square inches. Steel panels were also used after 0.0002 inch thickness of initial copper plate.

The substrate was made free of foreign materials, dirt, grease and oxides before processing. A water-break free surface is a good indication for adequate cleaning. The following procedure for cleaning the brass panels was used: (a) Degreased in perchloroethylene vapor for two minutes, followed by five minutes ultrasonic cleaning in perchloroethylene. (b) Soaked clean for five minutes at room temperature in a solution of sodium carbonate (6 oz. per gal.), sodium cyanide (0.5 oz. per gal.) and preferably one per cent of a wetting agent, followed by cold running water rinse. (c) Electrocleaned in a solution of sodium carbonate (3 oz. per gal.), trisodium phosphate (2 oz. per gal.), sodium cyanide (1 oz. per gal.), and sodium hydroxide (0.5 oz. per gal.) - 160°F for 40 seconds direct strike and five seconds reverse polarity at ■was moved briskly up and down and in swirling motion manually to rinse thoroughly. (d) Neutralized dip in 5 per cent H2SO4 solution with manual swirling agitation of work for 10 seconds followed by two running rinses, 30 seconds each. (e) Striked in cyanide copper solution of the following composition at 15-20 ASF - 125°F for one minute, maintaining manual agitation of work.

Copper Cyanide 3.5 oz/gal Sodium Cyanide 4.6 oz/gal Sodium Carbonate 4.0 oz/gal Rochelle Salt 6.0 oz/gal Free NaCN 0.75-1.0 oz/gal Followed by two rinses and a neutralized dip in per cent I^SO^, followed by another rinse. The work (copper panel) was then transferred to the plating tank.

The bath for electrophoretic and electrolytic deposition was prepared as follows: 24 ounces of CuSO,,5H_0, and 7.0 ounces of H S0, (CP.) 4 i *- 4 was added to distilled or deionized water to make up two gallons of solution. This was treated with activated carbon at 5 g. per liter for 10 hours at room temperature, the solution filtered, and the filtrate transferred to a water jacketed glass tank of two gallons capacity, having means of heating and maintaining the temperature of the bath between 100° - 130°F. TEFLON aqueous suspension No. 3170 (0.5% by weight negatively charged colloidal the electrolyte at 5 c.c. per liter while stirring to insure uniform dispersion. The bath before and after the TEFLON additive had a o Baume of 10 Be, a specific conductivity without the additive of 96,000 Mhos/cm and with the additive of 94,000 Mhos/cm.

The brass panel was attached to a cathode rod agitator in the bath reciprocating at the rate of 28 strokes per minute.

A direct current of 10 to 40 amperes per square foot was applied for the first two minutes.

The anode on the direct strike consisted of copper slabs.

The power supply was then switched to a periodic reverse system with the following cycles: direct cycle - 16 seconds reverse cycle - 3 seconds The current density of the reverse cycle was adjusted to 50 per cent of the current density in the forward or direct cycle by means of a rheostat connected in series with the reverse cycle.

The process is feasible for rack as well as barrel plating.

The method can be carried out with other fluorocarbon polymers with little or no change in the conditions of the above example, and also with other lubricating particles by minor modifications apparent to those skilled in the art of electrolytic and electrophoretic deposition.

Claims (1)

1. 6. The composition of claim 15 in which the particles of tetrafluoroethylene are .05 to .5 microns in diameter, uniformly dispersed in the metal. 17. A dry lubricant consisting essentially of a mixture of electrolytically plated metal containing electrophoretically deposited solid lubricant particles. 18. A coating composition for electrolytic and electro-phoretic deposition consisting essentially of a solution having metal ions and dispersed therein negatively charged particles of a fluorocarbon polymer. 19. The composition of claim 18 wherein the fluorocarbon polymer is polytetrafluoroethylene. DATED THIS 26TH DAY OF DECEMBER 1966