US3198662A

US3198662A - Process of applying a silver layer on an aluminum electrical contact

Info

Publication number: US3198662A
Application number: US217966A
Authority: US
Inventors: Philip M H Seibert
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-08-20
Filing date: 1962-08-20
Publication date: 1965-08-03
Anticipated expiration: 1982-08-03

Description

Aug. 3, 1965 P. M. H. SEIBERT PROCESS OF APPLYING A SILVER LAYER ON A ALUMINUM ELECTRICAL CONTACT Filed Aug. 20, 1962 nqled Par'f'icles oF Silver and flluminum Philip m.

INVENTOR. H. SQ i b e r'l' Qb-h ornaus United States Patent This invention relates to aluminum electrical contacts and more particularly to a process of applying a silver layer on an aluminum electrical contact.

A specific use of an aluminum electrical contact embodying the present process is in electric sub-station installations where switches must be operated automatically or by remote control. Aluminum contacts are normally subject to oxidization which usually retards the flow of current and heretofore, it has been normal to employ a silver inlay or a silver plating on one or both of the contacting parts. The silver inlay has been of around 0.010 inch in thickness and in the event a silver plating is employed the thickness thereof has been not over 0.002 inch. Such inlays or platings wear thin in a relatively short period of time upon continued operation of an electrical switch or the like on which the contacting parts are positioned.

The present invention comprises a process for applying a silver layer on one or both aluminum contacting parts by fusing the silver to the aluminum through heating both the metals and thereby forming an intermediate layer of intermingled silver and aluminum particles of a thickness between about .002 inch and .010 inch which is effective to Withstand any of the conditions ordinarily exerted on the contacting parts. By providing a fused layer, the contacting areas are more abrasive resistant and a relatively large number of contacts can be made without failure or undue wear of the fused layer on the contacting parts.

7 It is an object of this invention to provide a process of fusing a layer of silver on an aluminum electrical contact comprising heating the aluminum electrical contact to a temperature of between 400 F. and 900 B, thereafter spraying molten silver onto the aluminum contact at a sufficient velocity so that the molten silver particles impinge against the surface of the heated aluminum contact area and penetrate the alurninum to form an intermediate fused layer of mixed aluminum and silver particles between .002 inch and .010 inch in thickness. A zinc coating of .0000015 inch is normally provided on the aluminum contacting parts as a protective coating against oxidization and any such zinc coating is vaporized or burned off the surface of the aluminum contacts when the molten silver is sprayed thereon.

As an example illustrating a specific use of my process, show a switch in the accompanying drawing, forming a of this application, in which:

' 1 is an elevational view of a movable blade pobetween a pair of spaced contact leaves with the "1g shown in open position and the electrical eas of the blade and the leaves having a fused of intermingled aluminum and silver particles of nckness between .002 and .010 inch;

FIG. 2 is an elevational view of the apparatus shown in FIG. 1 but showing the blade in closed position and contacting the spaced pair of leaves whereby electrical contact is made between the leaves through the blade; and,

FIG. 3 is an enlarged sectional view taken through an electrical contact area of a leaf and showing the several layers there-at.

Referring to the drawing, a switch is shown generally diagrammatically and comprises a blade indicated generally by the numeral and spaced contacting spring leaves indicated generally by the numerals 11 and 12.

3,198,662 Patented Aug. 3, 1965 Blade 10 and leaves 11 and 12 are formed of aluminum with blade 10 positioned between leaves 11 and 12 and adapted for movement between open position shown in FIG. 1 and closed position shown in FIG. 2. Electrical contact areas 13 are formed on the ends of blade 10 and contact areas 14 are formed on leaves 11 and 12.

It is highly desirable to remove any aluminum oxides from the contacting areas to be fused with silver before the present process is applied as the fusing of silver is retarded by the presence of aluminum oxides. Aluminum oxide has a melting point of around 3600 F. against a melting point of 1220 F. for aluminum and around 1760 F. for silver. To remove aluminum oxides from the electrical contacting parts before the present process is applied, it is desirable to employ a zinc immersion treatment comprising cleaning the parts with a mild alkaline cleaner, dipping the parts in acid for one to three seconds, rinsing the parts in water, and then dipping the parts in a zinc oxide bath from one-half to one minute at 60 to F. with a water rinse thereafter, all as well known in the art under the term zincating process. Through the immersion treatment, a zinc coating of around .0000015 inch in thickness is provided on the aluminum parts and protects the aluminum from surface oxidization for a relatively short period of time.

It is understood that my process may be employed on other types of aluminum electrical contacts than the specific apparatus shown in the drawings and that such -apparatus is shown only for the purpose of illustration. The term part as employed herein is interpreted as including all electrical contacting parts such as switches, circuit breakers, electrical connectors, and the like. In the process of fusing silver to the aluminum contacts, the

aluminum contact areas

13 and 14 are heated to a temperature of around 650 F. preferably. Temperatures between 400 F. and 900 F. will work satisfactorily. Before the aluminum contact areas lose their temperature they are sprayed with molten silver entrained in a stream of gaseous material. For spraying the silver a silver Wire is fed through a metalizing gun which atomizes the wire into a stream of molten silver particles. The particles are uniformly heated and the rate of spray is well controlled by the metalizing gun. is melted by a combination of gases at a uniform rate of speed. The gases comprise oxygen combined with one of the following: acetylene, propane, butane, or hydrogen. Also, natural or manufactured gas may be combined with the oxygen. The gases arebalanced along with compressed air that is also used to atomize the molten silver and a neutral flame neither oxidizing nor can bonizing is formed in which the silver wire is atomized. The molten particles of silver are entrained in a stream of oxygen free air formed from the compressed air and the oxygen mixture which stream is at a temperature in excess of 4000 F. The blast of hot air and the finely divided superheated silver particles vaporize the zinc coating on the aluminum contact parts and the molten particles of the atomized silver impinge against the aluminum contact parts and penetrate it to a depth of between .002 inch to .010 inch. The metalizing gun is held about 4 inches from the surface of the aluminum contact parts to which the silver is to be fused and the silver particles move at a maximum velocity of around 225 feet per second.

Referring to FIG. 3 an intermediate layer 16 is formed beneath the surface of the aluminum contact part and is composed of mixed particles of silver and aluminum being of a thickness of between .002 inch and .010 inch corresponding to the penetration of the silver particles.

An outer layer 17 of silver is formed of a thickness above .020 inch and is built up on intermediate layer 16 above the surface of the

aluminum contact parts

10, 11 and 12. A thickness of around .030 inch for outer The silver wire V layer 17 has been found to be preferable although thicknesses over .015 inch will work effectively. Thus, particles of silver and aluminum are fused in intermediate layer 16 so as to secure in permanent fashion outer silver layer 17. The precentage of silver in the intermediate layer is variable but it increases from its innermost penetration of the aluminum outwardly to the surface of the connector. After the aluminum contact parts having been sprayed with silver, they are cooled rapidly in water or a mist which keeps the oxidizing of the surface of the silver at a minimum during cooling.

From the foregoing it will be understood that I have provided a process for applying a silver layer on aluminum electrical contact parts by heating the parts and then spraying silver onto the surface at the contact areas thereof. By removing aluminum oxides and zincating the contact parts, then heating the contact areas and spraying molten silver particles at a sufficient velocity, the silver particles penetrate the surface of the aluminum and form an intermediate layer of intermingled silver and aluminum particles between .002 inch and .010 inch in thickness thereby fusing the silver and the aluminum. The silver layer may be provided in a minimum of time and any outer zinc coating on the contact areas is vaporized or burned off by the hot air and other gases in which the molten silver particles are entrained when the silver is sprayed onto the aluminum parts. The term aluminum is employed herein to describe the contact parts is interpreted as including aluminum alloyed with other metals.

While I have shown my invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed (a) zincating the surface of the aluminum part to remove any aluminum oxides from the surface thereof and to form a protective zinc coating thereon,

(b) heating the aluminum contact part to a temperature between 400 F.'and 900 F., and

(c) spraying molten silver entrained in a blast of gas under pressure onto the heated aluminum part whereby the gas vaporizes the zinc coating to remove it from the surface of the aluminum part, said silver being sprayed at a sufiicient velocity to form a layer of intermingled silver and aluminum particles between .002 inch and .010 inch in thickness on which an outer layer of silver may be formed.

2. The process of fusing a silver layer on an aluminum electrical contact part comprising (a) zincating the surface of the aluminum part to remove any aluminum oxides from the surface thereof and to form a protective zinc coating thereon,

(b) heating the aluminum part to a temperature between 400" F. and 900 F., and

(c) spraying molten silver entrained in a stream of gas under pressure onto the heated aluminum part whereby the gas vaporizes the zinc coating, said silver being sprayed at a velocity on the order of 225 feet per second whereby they penetrate the surface of the aluminum to form an intermediate fused layer of mixed silver and aluminum particles of from .002 inch to .010 inch in thickness and an outer layer of silver of at least .015 inch in thickness on the intermediate layer.

References Cited by the Examiner UNITED STATES PATENTS RICHARD D. NEVIUS, Primary Examiner.

Claims

1. THE PROCESS OF FUSING A SILVER LAYER ON AN ALUMINUM ELECTRICAL CONTACT PART COMPRISING (A) ZINCATING THE SURFACE OF THE ALUMINUM PART TO REMOVE ANY ALUMINUM OXIDES FROM THE SURFACE THEREOF AND TO FORM A PROTECTIVE ZINC COATING THEREON, (B) HEATING THE ALUMINUM CONTACT PART TO A TEMPERATURE BETWEEN 400*F. AND 900*F., AND (C) SPRAYING MOLTEN SILVER ENTRAINED IN A BLAST OF GAS UNDER PRESSURE ONTO THE HEATED ALUMINUM PART WHEREBY THE GAS VAPORIZES THE ZINC COATING TO REMOVE IT FROM THE SURFACE OF THE ALUMINUM PART, SAID SILVER BEING SPRAYED AT A SUFFICIENT VELOCITY TO FORM A LAYER OF INTERMINGLED SILVER AND ALUMINUM PARTICLES BETWEEN .002 INCH AND .010 INCH IN THICKNESS ON WHICH AN OUTER LAYER OF SILVER MAY BE FORMED.