US3703449A

US3703449A - Formation of lubricant coating by electrolysis

Info

Publication number: US3703449A
Application number: US85107A
Authority: US
Inventors: John Peter George Farr; Geoffrey Whaley Rowe
Original assignee: American Metal Climax Inc
Current assignee: Cyprus Amax Minerals Co
Priority date: 1969-11-13
Filing date: 1970-10-29
Publication date: 1972-11-21
Anticipated expiration: 1989-11-21
Also published as: DE2052977A1; FR2069321A5; GB1313510A; JPS506183B1; CA918595A

Abstract

A METHOD OF PROVIDING A LUBRICANT ON AN ARTICLE HAVING AN ELECTRICALL CONDUCTING SURFACE, SUCH AS A METAL ARTICLE, IN ORDER TO PROVIDE LUBRICATION DURING METAL FORMING OPERATIONS, COMPRISES MAKING THE ARTICLES TO THE COATED THE ANODE IN AN ELECTROLYTIC CELL, THE ELECTROLYTE OF THE CELL CONTAINING A SOLUBLE ORGANIC SULPHUR COMPOUND AND THEN PASSING AN ELECTRIC CURRENT THROUGH THE CELL WHEREBY A SULPHUR CONTAINING CONSTITUENT IS FORMED IN THE ELECTROLYTE FROM WHICH THE LUBRICANT COATING IS PRODUCED ON THE SURFACE OF THE ARTICLE. THE SOLUBLE ORGANIC SULPHUR COMPOUND MAY BE THIOACETAMIDE OR THIOUREA. IF DESIRED A FURTHER CONSTITUENT MAY BE PROVIDED IN THE ELECTROLYTE AND THE LUBRICANT COATING MAY BE PROVIDED AS A RESULT OF REACTION OF THE SULPHUR CONTAINING CONSTITUENT WITH THE FURTHER CONSTITUENT. THE FURTHER CONSTITUENT MAY BE AMMONIUM MOLYBDATE. THE LUBRICANT COATING MAY BE REMOVED AFTER PERFORMANCE OF THE METAL FORMING OPERATION BY PASSING THE ARTICLE THROUGH A FURTHER ELECTROLYTE THROUGH WHICH A CURRENT IS PASSED TO REMOVE THE LUBRICANT COATING.

Description

Nov. 21, 1972 v J. P. G. FARR ETAL 3,103,449

I FORMATION OF LUBRICANT COATING BY ELECTROLYSIS Filed Oct. 29, 1970 3,703,449 FORMATION OF LUBRICANT COATING BY ELECTROLYSIS John Peter George Farr and Geoffrey Whaley Rowe, Birmingham, England, assignors to American Metal Climax Inc., New York, N.Y.

Filed Oct. 29, 1970, Ser. No. 85,107 Claims priority, application Great Britain, Nov. 13, 1969, 55,605/ 69 Int. Cl. C23b 11/02 US. Cl. 204-56 R 18 Claims ABSTRACT OF THE DISCLOSURE A method of providing a lubricant on an article having an electrically conducting surface, such as a metal article, in order to provide lubrication during metal forming operations, comprises making the article to be coated the anode in an electrolytic cell, the electrolyte of the cell containing a soluble organic sulphur compound and then passing an electric current through the cell whereby a sulphur containing constituent is formed in the electrolyte from which the lubricant coating is produced on the surface of the article. The soluble organic sulphur compound may be thioacetamide or thiourea. If desired a further constituent may be provided in the electrolyte and the lubricant coating may be provided as a result of reaction of the sulphur containing constituent with the further constituent. The further constitutent may be ammonium molybdate.

The lubricant coating may be removed after performance of the metal forming operation by passing the article through a further electrolyte through which a current is passed to remove the lubricant coating.

This invention relates to a method of providing a lubricant on an article having an electrically conducting surface, especially, but not exclusively, a metal article, such as wire, to provide lubrication during wire drawing, or strip, to provide lubrication during rolling or pressure.

It is well known that it is desirable, and in certain cases essential, to provide lubrication during metal-working operations such as wire and tube drawing, rolling of strip, forging and deep drawing. The use of a lubricant enables higher working speeds and a greater amount of metal deformation to be obtained than is possible without a lubricant and, of course, the more effective the lubricant, the higher is the speed of working and the greater is the amount of deformation which can be achieved.

A most effective group of lubricants in the art of metal working is those which are commonly referred to in the art as extreme-pressure lubricants. These lubricants can provide a reactive radical such as Clor S"- which, it is thought, enters into chemical reaction with the surface of the metal during the metal working operation to form, for example, metal chloride or metal sulphide which acts as a lubricant. The reactive radical in extreme-pressure lubricants is derived from an organic compound' United States Patent l 3,793,449 Patented Nov. 21, 1972 (2) Description of the prior art By providing the reactive radical from an unreactive organic compound no such corrosive attack on the metal article occurs and the radical reacts with the metal only as a result of being liberated from the organic compound by thermal energy created during the metal working operation.

Extreme-pressure lubricants have been found to be more effective in metal working operations than simple organic lubricants especially when high temperatures and pressures are created during the metal working operation. Extreme-pressure lubricants are especially favoured for drawing stainless steel, titanium and nickel alloys which are otherwise prone to transfer of metal from the workpiece to the metal working tool.

The thermal energy required to liberate the reactive radical from the organic compound to cause the radical to react with the metal surface to provide the lubricant is provided by plastic deformation of the metal during working and in particular by friction and plastic deformation of localised protuberances on the metal article. Usually the temperature rise of the whole articles does not provide sufiicient thermal energy for liberation of the radical and reaction with the metal surface and so the reaction of the radical with the metal surface is confined to the region where localised friction and deformation, of the workpiece has taken place and this has been demonstrated by radioactive tracer techniques.

It is therefore a characteristic feature of conventional extreme-pressure lubrication that very close contact, and perhaps even localised welding, must occur between the metal article and the metal working tools to provide the necessary thermal energy for the above mentioned reactions to take place. Moreover, in many metal working operations, such as wire or tube drawing, the article moves past the metal working tools at very high speeds, for example, in the case of wire drawing, at a speed of 1000 feet per minute through a die the contact length of which is 0.5 inch and thus the time of contact of the wire with the die is 250 micro-seconds. Thus, the release of the reactive radical and its reaction with the metal surface must occur within this very short time if it is to be effective as a lubricant. If the reaction takes longer than this time then the wire will have left the die before the reactive radical can provide a lubricant. Thus, damage to the surface of the metal article being worked and/ or to the metal working tools can occur because of the need for the very close contact, and possibly the need for welding, to provide suflicient thermal energy to cause the reactive radical to act as a lubricant and there is also a possibility of damage in metal working operations performed at a speed so fast that the metal article has moved out of contact with the die before the necessary reactions can occur.

SUMMARY OF THE INVENTION It is accordingly an object of the present invention to provide a new and improved method of providing a lubricant film on an article having an electrically conducting surface whereby the above mentioned disadvantages are overcome or are reduced.

According to the invention a method of providing a lubricant coating on an article having an electrically conducting surface includes the steps of, making the article an anode in an electrolytic cell, the electrolyte of the cell containing a soluble organic sulphur compound, and passing an electric current through the cell whereby a sulphur containing constituent is formed in the electrolyte from which the lubricant coating is produced on the surface of the article.

The lubricant coating may be provided as a result of electrochemical reaction of the sulphur containing constituent with the surface of the article.

Alternatively, the lubricant coating may be provided as a result of reaction of the sulphur containing constituent with a further constituent of the electrolyte.

The article may be a metal article.

At least the surface of the article may be connected in an electric circuit to act as the anode of the electrolytic cell and there being a further electrode provided in contact with the electrolyte of the cell and connected in said electric circuit to provide the cathode of the cell.

The organic sulphur compound may be thioacetamide or thiourea and the organic sulphur compound may be in a solution of sulphuric acid in water at a concentration lying approximately in the range 0.02 N to 0.2 N H 80 Preferably, not more than 5% by weight of the organic sulphur compound may be present in the electrolyte.

Preferably, the organic sulphur compound is thioacetamide.

The additional constituent of the electrolyte may be a molybdenum compound. In this case, molybdenum disulphide is the compound formed as a lubricant coating on the article.

When the additional constituent is not present in the liquid the surface of the article may be made of mild steel, tin, or molybdenum.

When the additional constituent is present in the electrolyte the surface of the article may be made of mild steel, tin, stainless steel, titanium, molybdenum or a nickel alloy.

If desired, subsequent to providing a lubricant coating on a metal article by the method set out hereinbefore a forming operation is performed on the article.

If desired, immediately after the forming operation the article may be contacted with an electrolyte and a relatively high alternating current passed through the liquid adjacent the article to remove the lubricant coating.

The forming operation may be a drawing operation, a pressing operation, a rolling operation or a forging operation.

When the forming operation is a continuous operation such as wire drawing or rolling the electrolyte is provided in a bath through which the article is passed continuously.

When the forming operation is a batch operation, such as forging, the electrolyte is provided in a bath into which the article is placed and from which it is removed prior to the forming operation and, if the lubricant film is to be removed after the metal working operation the article is immersed in a suitable bath and then removed therefrom immediately after the metal working operation.

A still further aspect of the invention is an article produced by a metal working operation as set out above.

The method of the present invention makes it possible to provide a lubricant coating on an article without relying upon thermal energy created during the metal working operation to provide the lubricant coating. In addition, the time taken to provide the lubricant coating is relatively short, so that the method can be applied to continuous production techniques without having to slow down the rate of production to an uneconomical level.

The method of the present invention therefore has the considerable advantage that the formation of the lubricant coating can be closely controlled by means of the applied potential and current density independently of the speed of the metal working operation or upon close proximity or welding between the metal article and the metal working tool thereby avoiding the problem mentioned hereinbefore of possible damage to the metal article or metal working tool as a result of such close contact and possible welding before it is possible for the extreme-pressure lubricants used hereto to provide a lubricating action.

In addition, the amount of lubricant present can be simply and easily controlled merely by adjusting the potential and current density and/or adjusting the period 4 of time for which the liquid is in contact with the metal article. For example, in the case of a continuous metal working operation such as wire drawing the length of the bath through which the wire is passed immediately prior to drawing may be chosen so that it is of an appropriate length for the intended speed of drawing. In the case of a batch process such as forging or deep drawing then the time for which the article is immersed in the bath is adjusted as necessary to give the desired amount of lubricant coating.

Moreover in operation such as deep drawing it is sometimes desirable to produce lubricant films at certain 10- calised positions so as to encourage differential metal flow during drawing and this can be achieved with the method of the present invention, for example, by positioning a further electrode in relatively close proximity to the metal article in the regions where it is desired to produce the local lubricant film so that the majority of the lubricant coating is formed at these regions and relatively little or no lubricant coating is provided at other regions.

With some extreme-pressure lubricants used hitherto the organic compound of the lubricant containing the reactive radicals can decompose especially in the presence of moisture and this leads to corrosion of the metal article and it has therefore been necessary to remove the extremepressure lubricants and their decomposition products after the metal working operation. This has usually been performed by two separate operations using organic solvents and inorganic fluxes. In the method of the present invention the coating can be removed immediately after the metal working operation by contacting the metal article with a liquid of the same composition as the carrier liquid with which the liquid is contacted before the metal working operation and establishing an alternating potential difference in the liquid adjacent the metal article to disrupt the lubricant film and so restore the metal to its original condition.

The apparatus used in the removal operation is similar to that used in the appropriate process for the lubricant coating forming operation.

In those cases where the method is performed with the electrolyte not containing said additional constituent the lubricant coating achieved is a compound of the metal of which the article is made. For example, if the metal is a mild steel then the lubricant coating will be iron sulphide.

If however said further constituent is provided in the liquid then the lubricant formed is not dependent upon the metal of which the article is made. For example, if the further constituent is a molybdenum compound then molybdenum disulphide will be formed in the electrolyte and will deposit on the surface of the article to form a surface layer of molybdenum disulphide irrespective of the metal of which the article is made. Molybdenum disulphide is recognised to give better lubrication than iron sulphide for example.

The precise mechanism which causes the molybdenum disulphide to deposit on the metal wire and the nature of the bonding of the molybdenum disulphide to the metal wire is not fully understood but the molybdenum disulphide is relatively strongly bonded onto the metal article although apparently not so strongly as is the lubricant film formed as a result of reaction with the metal of the wire.

It is therefore possible with the method of the present invention to provide, relatively strongly bonded to the metal article, a lubricant such as molybdenum disulphide (which is well known as an outstandingly good lubricant) irrespective of the nature of the metal of which the article is made whereas with conventional extreme-pressure lubricants this has not been possible and only compounds of the metal of which the article is made have been possible. Five examples of the method according to the present invention will now be described by way of example.

DESCRIPTION OF THE PREFERRED EMBODIMENT Example 1 Annealed 1.2 mm. dia. molybdenum wire was cold drawn to 8% R.A. through a tungsten carbide die at a speed of 9 ft./min. With no lubrication the wire suffered considerable surface damage and the drawing load was in excess of 150 lb. With a liberal application of a graphite-bearing oil normally used for drawing M the load was reduced to 90-110 1b., the wire this time having a satisfactory surface finish. A length of the wire was made the anode in a tank containing N/S H2SO +l0 gm./l. thioacetamide+10 gm./l. ammonium molybdate and a current of 100 ma./cm. was passed for 10 seconds from a 6-volt battery. When this wire was drawn a 90- 120 lb. load was recorded, and scanning electron micrographs showed the surface finish of this wire to be slightly superior to that of the oil-drawn wire.

Example 2 Annealed mild steel wire of 1.0 mm. dia. was cold drawn to 12% R.A. through a tungsten carbide die at 6 ft./min. With no lubricant present the wire surface was heavily scored and the drawing load was 105 lb. With a conventional chlorinated extreme-pressure lubricant the load was 93 lb. and the wire had a satisfactory surface finish. When a metallic soap lubricant was used the surface was also satisfactory but the load was reduced to 75 lb. With a lubricant formed electrolytically as in Example l a load of 70 lb. was recorded and again a good surface finish was achieved.

Example 3 Annealed 18/8 stainless steel wire of 1.0 mm. dia. was cold drawn to 25% R.A. through a tungsten carbide die at 6 ft./min. Without a lubricant there was considerable metallic pick-up and the drawing load was 197 lb. With a metallic soap lubricant the surface was much improved, the drawing load this time being 147 lb. With a lubricant electrolytically formed as in Example 1 the surface finish was again satisfactory and the drawing load was 145 1b.

Example 4 Annealed mild steel wire was drawn to 5% R.A. with no lubricant. There was considerable pick-up and a drawing force of 70 lb. was required. Another sample of the wire was made the anode in a cell containing N/ H SO +10 gm./litre thioacetamide and a current of 300 ma./cm. was passed for 10 secs. The force needed to draw this wire was '63 lb. and the surface finish was satisfactory.

Example 5 Annealed mild steel wire was drawn to 5% R.A. with no lubricant. There was considerable pick-up and a drawing force of 70 lb. was required. Another sample of the wire was made the anode in a tank containing N/10 H SO +10 gm./litre thiourea and a current of 300 ma./ cm. was passed for 10 sec. The force needed to draw this wire was 63 lb. and the surface finish again was satisfactory.

BRIEF DESCRIPTION OF THE DRAWINGS The apparatus used in the examples described hereinbefore is illustrated in the accompanying drawing which is a diagrammatic representation of the apparatus used.

Referring now to the drawing, the apparatus comprises a wire drawing die 10 which can be made of tungsten carbide. The metal working die 10 is mounted in a die block 11 provided with a load cell 12 to enable the drawing load to be measured. The die block 11 is provided on a conventional draw bench, not shown, and the wire 14 under test is drawn through the die 10 by a conventional capstan 15 provided on the draw bench.

0n the input side of the die 10 the wire 14 is passed through an electrolytic bath 16 provided with suitable seals 17 of neoprene rubber and which contains the solution described in the examples. Counter electrodes 18 are also mounted in the bath 16 above and spaced from the wire 14 and the counter electrode 18 is connected through an ammeter 19 to a battery 20 whilst the wire 14 is connected in electric circuit with the positive terminal of the battery 20 through a variable resistance 21. The connection to the moving wire 14 is made through contacts provided at the die 10.

When it is desired to remove the lubricant immediately after drawing a bath 22 similar to the bath 16 is provided on the output side of the die 10 so that the wire 14 is drawn through both baths by the capstan 15 of the draw bench. In this second bath the wire is connected in circuit with an alternating current source 23.

When the method is performed in a rolling operation on strip or sheet a bath of suitable width is provided and is provided with suitable sealing means to prevent leakage of the solution as the sheet or strip enters and leaves the bath.

When the method of the present invention is performed on batch operations, such as forging or deep drawing, a bath of suitable dimensions, open at the top, is provided and the article to be worked is lowered into the bath for an appropriate period of time to form a coating of appropriate thickness or to remove the coating as appropriate.

If a lubricant coating is required only on certain regions of the workpiece the counter electrode is made of appropriate shape so that the coating is deposited only in the regions adjacent the counter electrode.

We claim:

1. A method of providing a lubricant coating on an article having an electrically conducting surface including the steps of, providing an electrolytic cell including a cathode, making the article an anode in said electrolytic cell, providing an aqueous electrolyte for the cell containing a soluble organic sulphur compound, and passing an electric current through the cell whereby a sulphur containing constituent is formed in the electrolyte from which the lubricant coating is produced on the surface of the article.

2. A method according to claim 1 wherein the sulphur containing constituent electrochemically reacts with the surface of the article to provide the lubricant coating.

3. A method according to claim 1 including providing a soluble molybdenum compound as a further constituent of said electrolyte wherein the sulphur containing constituent reacts with said molybdenum compound of the electrolyte to provide the lubricant coating.

4. A method according to claim 3, wherein the molybdenum compound is ammonium molybdate.

5. A method according to claim 1, wherein the article is a metal article.

6. A method according to claim 1, wherein the organic sulphur compound is thioacetamide.

7. A method according to claim 1 wherein the organic sulphur compound is thiourea.

8. A method according to claim 1, wherein the organic sulphur compound is in a solution of sulphuric acid in water at a concentration lying approximately in the range 0.02 N to 0.2 N H 50 9. A method according to claim 1, wherein not more than 5% by weight of the organic sulphur compound is present in the electrolyte.

10. A method according to claim 1, wherein subsequent to providing the lubricant coating a forming operation is performed on the article.

11. A method according to claim 10, wherein the article is a metal article and the forming operation is a drawing operation, a pressing operation, a rolling operation, or a forging operation.

12. A method according to claim 10, wherein the forming operation is performed immediately subsequent to providing the lubricant coating.

13. A method according to claim 10, wherein after the forming operation the metal article is contacted with a further electrolyte and an alternating electrical current is applied in the liquid adjacent the article to remove the lubricant coating.

14. A method according to claim 10 wherein the forming operation is a continuous operation and the electrolyte is provided in a bath through which the metal article is continuously passed.

15. A method according to claim 10 wherein the forming operation is a batch operation and the electrolyte is provided in a bath into which the article is placed and from which the article is removed prior to the forming operation.

16. A method according to claim 13 wherein the forming operation is a continuous operation and the further electrolyte, with which the article is contacted after the forming operation, is provided in a bath through which the article is continuously passed.

17. A method according to claim 13 wherein the forming operation is a batch operation and the further electrolyte with which the article is contacted after the forming operation is contained in a bath into which the article is placed and from which it is removed subsequent to the forming operation.

18. A method according to claim 1, wherein the cathode is positioned in operative relation to the metal article only in those regions where it is desired to produce a lubricant film so that the local thickness of the lubricant film produced on the article may be adjusted.

References Cited UNITED STATES PATENTS 3,591,472 7/ 1971 Amsallem 20456 R 3,438,789 4/1969 Weiss et al 204-56 R 2,512,141 6/1950 Ma et a1. 204--56 R FOREIGN PATENTS 201,345 8/1967 U.S.S.R 204-92 JOHN H. MACK, Primary Examiner R. L. ANDREWS, Assistant Examiner