US 2999798 A
Description (OCR text may contain errors)
United States Patent 2,999,798 METHOD OF PRODUCING A WEAR-RESISTING SURFACE ON A METAL ELEMENT Max Eitel, Eslingen (Neckar), and Franz J. Eisele, Stuttgart-'Unterturkheim, Germany, assignors to Daimler- Benz Aktiengesellscl aft, Stuttgart-Unterturkheim, Ger- No Drawing. Filed Dec. 9, 1955, Ser. No. 551,979
6 Claims. (Cl. 204-34) Our invention relates to a method of producing wearresistive surfaces, particularly surfaces of metal parts, subject to impacts such as oscillating levers etc. consisting of steel.
It has been proposed already to increase the resistance to wear of machine parts subject to friction by coating such parts with graphite, the latter being anchored to the surface of the metal part by means of a binding medium such as a lacquer.
It is also known to use natural sulfide of molybdenum in pulverized condition or as a paste as a lubricant to thereby reduce wear. Moreover, it has been found that other sulfides having the same or a similar crystal structure, such as zinc sulfide, have likewise wear-reducing properties. Furthermore, it is common practice to chromium-plate parts subject to friction, such as oscillating levers, for the purpose of reducing the wear. Where the machine part is subjected to a high load, however, such chromium plating will not always sutfice to protect the surface from undue wear where the surface is subjected to impacts.
It is the object of the invention to remedy the situation. According to our invention one or more dry lubricating agents, such as metal sulfides or a metal sulfide of the aforestated kind, preferably zinc sulfide, is applied to the surface of the metal part in the form of a firmly adhering coat of high wear-resistance.
In a preferred embodiment of the novel method the metal part prior to the application of the sulfides or other dry lubricating agents is provided with a metallic plating. By the choice of an appropriate metal and by suitable metal-depositing methods a network of fine fissures or cracks is produced on the surface of the metal plating, the sulfide being anchored in such fissures or cracks.
According to another embodiment of our invention, the surface of the metal part prior to the application of the sulfide is subjected to a mechanical or chemical treatment rendering the surface rough or porous. Such treatment may also involve the action of electrical current on the surface.
A particularly effective adhesion of the sulfides to the surface of the metal is attained by the simultaneous deposition of metal sulfides and of a suitable plating metal on the surface of the metal part. As a plating metal chromium is preferably employed. For simultaneously depositing a plating metal and metal sulfide, we prefer to use an electrolytic process. In this process an electrolytic bath is employed comprising a solution of a salt or another chemical compound of the plating metal, such solution containing the metal sulfide in finely divided suspended condition, the bath being agitated during the electrolytic deposition of the plating metal on the metal part being treated. The deposition of the metal sulfide coincidentally to the deposition of the plating metal is enhanced by electrophoresis provided that a suitable electrical voltage is employed.
A number of embodiments of the novel method will be described hereinafter.
The machine parts are chromium-plated by a wellknown electrolytic process at a temperature of from 40 to 80 C., the process selected being one which results in a very high hardness of the chromium layer. When the latter has reached a thickness of 0.02 mm., zinc sulfide is admixed to the electrolytic bath containing chromic acid, from 10 to 50 grams zinc sulfide being added per litre, and the process is continued for a suitable length of time while the electrolytic bath is agitated continually. The current density amounts to about 600 amperes/dm? at a voltage of at least 10 volts. As a result, the zinc sulfide will be embedded in the surface of the chromium plating. In lieu of zinc sulfide, cadmium sulfide may be employed. In lieu of chromium, nickel or iron may be employed to provide the metal part with an intermediary layer on which slbsequently chromium and a suitable sulfide are deposited in mixed condition. a a
For the purpose of producing cracksiin the chromium plating an ordinary electrolytical chromium process is used, but this process is modified by alternately periodically reversing the polarity of the electrodes.
A suitable mechanical method of providing the metal element with a porous surface comprises lapping such surface by a jet of a suitable material produced by a suitable medium under pressure.
A chemical process for providing the element with a porous surface comprises treating the element for a period of 10 seconds at a temperature of 20 C. with a chromic acid solution containing to 200 grams chromic acid per litre water. In lieu of chromic acid, hydrochloric acid may be used.
Alternatively, the surface of the metal element may be made porous by chromium-plating the element with a porous layer of chromium. To this end, the ordinary electrolytic chromium-plating process may be modified by using a very high current density.
For the purpose of promoting the deposition of the metal sulfide by electrophoresis, the voltage employed in the electrolytic deposition may be three times the customary voltage.
While the invention has been described in connection with several different embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention .pertains, and as fall within the scope of the invention or the limits of the appended claims.
What we claimis:
' 1. Method of increasing the wear resistance of a metal element which comprises the steps of applying a layer consisting essentially of metal and of metal sulfide on the surface of the element, said layer being applied by simultaneously electroplating said metal and electrophoretically depositing said sulfide from a bath consisting essentially of a salt of said metal in solution and of said sulfide in suspension.
2. Method as claimed in claim 1, further comprising the step of making the surface of said metal element porous prior to the application of said layer con- 7 sisting essentially of metal and of metal sulfide.
3. A method for producing a wearand impact-resistant surface on a metal element comprising the steps of applying a layer consisting essentially of a metal selected from the group consisting of chromium, nickel and iron and of a metal sulfide selected from the group consisting of zinc sulfide and cadmium sulfide, said layer being ap plied by simultaneously electrolytically applying said metal and electrophoretically applying said sulfide to said metal element from a bath including a compound of said metal in solution and including said metal sulfide in suspension.
4. In a method of increasing the wear-resistance of a metal element, the steps of initially electroplating said metal element with a metal layer, and thereafter applying a layer consisting essentially of metal and of metal sulfide onto the initially applied layer, said last-mentioned layer being applied by simultaneously electroplating said metal andelectrophoretically depositing said sulfide from a bath consisting essentially of a salt of said metal in solution and of said metal sulfide in suspension.
5. Method as claimed in claim 4 in which said bath is agitated during the electrolytic deposition of said layer.
6. Method of increasing the wear-resistance of a metal element which comprises applying a wear-resistant, impact-resistant layer consisting essentially of metal and metal sulfide on the surface of said element, said metal and said metal sulfide being simultaneously applied on said element as a cathode by passing electric current through a bath consisting essentially of a metal salt in solution which metal -is'capable of being electrodeposited, and of a metal sulfide in suspension which sulfide is capableot being electrophoreticallydeposited, whereby electrodeposition and electrophoresis occur simultaneously.
References Cited in the file of this patent UNITED STATES PATENTS 1,702,927 Bezzenberger Feb. 19, 1929 2,269,720 Johnson Jan. 13, 1942 2,283,581 Scalzitti May 19, 1942 2,314,604 Van der Horst Mar. 23, 1943 2,420,886 Laif oon May 20, 1947 2,622,993 McCullough Dec. 23, 1953 2,760,925 Bryant Aug. 28, 1956 2,861,935 Fahnoe et a1. Nov. 25, 1958 FOREIGN PATENTS 677,240 Great Britain Aug. 13, 1952 OTHER REFERENCES Modern Inorganic Chemistry, J. W. Mellor, Longrnans, Green & 00., New York, N.Y., 1925, page 492. Inorganic Chemistry, F. Ephraim, 5th edition, edited 20 by P.C.L, Thorne and E. R. Roberts, Interscience Publishers Inc., New York, N.Y., 1948, page 542.