US3814640A - Process for preparing composite silvercadmium oxide alloy contact with silver-cadmium surface - Google Patents

Abstract

A COMPOSITE ELECTRIC CONTACT COMPRISING A SILVERCADMIUM OXIDE ALLOY AS THE CONTACT MATERIAL OR ELEMENT AND HAVING A SILVER-CADMIUM LAYER INTEGRALLY FORMED ON THE FACE OPPOSITE TO THE CONTACT FACE IS PREPARED BY APPLYING AN ANTI-OXIDANT LAYER TO THE CONTACT-FORMING FACE, OXIDIZING THE CONTACT MATERIAL WITH AN OXIDIZING ATMOSPHERE, THEN REDUCING THE OXIDIZED FACE TO FORM AN INTEGRAL SILVER-CADMIUM LAYER ON THE FACE OPPOSITE SAID CONTACTFORMING FACE AND THEN REMOVING THE ANTI-OXIDANT LAYER.

Description

June 4, 1974 AKIRA SHIBATA 3,314,640

' PROCESS FOR PREPARAING COMPOSITE SILVER-CADIIUM OXIDE.

ALLOY CONTACT WITH SILVER-CADMIUM SURFACE Original Filed Feb. 8, 1971 Wmmwwww wwwummmmw muw'mm "United States Patent Ofice 3,814,640 Patented June 4, 1974 3,814,640 PROCESS FOR PREPARING COMPOSITE SILVER- CADMIUM OXIDE ALLOY CONTACT WITH SILVER-CADMIUM SURFACE Akira Shibata, Tokyo, Japan, assignor to Chugai Electric Industrial Co., Ltd., Tokyo, Japan Original application Feb. 8, 1971, Ser. No. 113,541, now Patent No. 3,688,067. Divided and this application Apr. 10, 1972, Ser. No. 242,859

Int. Cl. C23f 7/02; H01]: N02

US. Cl. 148-63 2 Claims ABSTRACT OF THE DISCLOSURE A composite electric contact comprising a silvercadmium oxide alloy as the contact material or element and having a silver-cadmium layer integrally formed on the face opposite to the contact face is prepared by applying an anti-oxidant layer to the contact-forming face, oxidizing the contact material with an oxidizing atmosphere, then reducing the oxidized face to form an integral silver-cadmium layer on the face opposite said contactforming face and then removing the anti-oxidant layer.

This is a division of application Ser. No. 113,541, filed Feb. 8, 1971, now Pat. No. 3,688,067.

This invention relates to a novel electric contact and a process of producing the same, and more particularly, to a novel electric contact employing a silver-cadmium oxide alloy as a contact material and having a silvercadmium layer integrally formed on the opposite face with respect to the contact face thereof, and a process of producing said electric contact by one-face internal oxidation and reduction.

The conventional processes of producing contact materials of silver-cadmium oxide alloy are generally classified into two methods; one is a sintering method by powder metallurgy and the other is a method of internal oxidation of an alloy. The internal oxidation method is, as well known, a method of obtaining a contact material of a silver-cadmium oxide alloy by subjecting a silver-cadmium alloy (cadmium content: 520% by weight) to an oxygen atmosphere at a high temperature to cause oxidation of cadmium and other metals contained in the alloy so that the oxidation proceeds from the circumferential area of the contact material. However a silver-cadmium oxide alloy is diflicult to braze to brass or Phosphor bronze etc. used as a backing metal or a spring material. There are two methods used to solve this problem. One is a method of applying a silver layer onto the brazing face of a contact material, wherein the silver layer is generally pressure-bonded to a silver-cadmium alloy. According to this method, oxidation progresses towards the inside from the circumference, and due to the way the oxidation of a silvercadmium type alloy progresses, a thin oxide layer is present in the central portion around the midst of its sectional area. Such contact material may often show some serious defects such as increase of wear and decrease of weldability, when practically used, as wear of the contact develops from the contact face into the area of said thin oxide layer.

Another method to solve the problem in brazing is what is generally called a one-face oxidation method, wherein one face of a contact, namely the brazing face, is left unoxidized. In order to leave some portion unoxidized, the fact that oxidation proceeds from the circumference towards the inside of the material is taken advantage of; that is, two pieces of the contact material mated with each other before oxidation may be welded at their mated faces, followed by oxidation for a given period of time so as to leave one face of the contact material unoxidized. It is, however, almost impossible practically at the present stage to weld miniature contacts one by one, so usually two sheets of a contact material of a silver-cadmium alloy are mated and welded prior to oxidation, and they are separated in sheets again at the welded faces after oxidazation. Then each sheet is cut to a given size. In this method, however, as the mated faces of the two sheets, which serve as brazing faces in finished contacts, should be left unoxidized, the period of oxidation is restricted and a desired thickness of oxidation can hardly be obtained.

For overcoming the defects of such conventional contacts, there is described in US. Patent Application No. 815,677, now Pat. No. 3,596,030, a composite electric contact element of silver-cadmium oxide alloy and a process of producing the same which comprises providing an element formed of an alloy of silver-cadmium,

one face of which is a contact-forming face; bonding a layer of silver to the face opposite to said contact-form ing face of said element; applying a barrier layer to said contact-forming face to inhibit oxygen diffusion therethrough and into said contact-forming face; subjecting said element with said layers thereon to an oxygen atmosphere at an elevated oxygen diffusion temperature whereby to oxidize the cadmium in said alloy to cadmium oxide as particles distributed from said silver layer to said barrier layer; and then removing said barrier layer from said contact-forming face; whereby a composite electric contact element is produced having a contact face on one side and a silver layer on the opposite face, and in which the cadmium oxide particles increase from a minimum at the contact face to a maximum towards the face with the silver layer.

The composite electric contact obtained according to the above-described U.S. Patent Application No. 815,- 677 has the advantage of providing a constantly equal contact resistance over the entire period of its life, since a layer containing a rather coarse distribution of cadmium oxide forms the initial contact face and a large pressure is applied to the contact face from a base material, and when the contact material is gradually worn away and the pressure applied from the base material to the contact face is gradually reduced, a layer comprising more thickly distributed cadmium oxide begins to appear on the surface forming the contact face. The composite electric contact produced by this method, however, has a disadvantage, namely, that it employs an expensive silver material on the brazing face. It also has an additional defect of insutficient strength, because said silver layer is formed by means of pressure-bending silver to the contact material. It is, therefore, the primary object of the present invention to provide a novel electric contact of a silvercadmium oxide alloy and a process of producing the same which maintains the advantages of the above-described composite electric contact, that is, forming a cadmium oxide layer which is coarsest on the contact face of the contact material and becomes gradually thicker towards the brazing face opposite to said contact face, but is superior in its strength and economic properties to the abovedescribed composite electric contact which uses a silver layer on the brazing face.

The gist of the present invention lies in a novel electric contact of silver-cadmium alloy and a process of producing the same comprising a contact material formed of a silver-cadmium oxide alloy, one face of which is a contact-forming face; applying an anti-oxidant layer to said contact-forming face to inhibit oxygen diffusion therethrough and into said contact-forming face; subjecting said contact material with said layer to an oxygen atmosphere at an elevated oxygen diffusion temperature thereby tact material of a silver-cadmium oxide alloy. The brazing face is the opposite face with'respect to theco'ntact face.

of said electric contact. Such electric contact is remarkedly superior in strength and economic properties to the above-described composite electric contact having a brazing face formed by pressure-bonding of silver.

Various further objects, features and advantages of the present invention will be apparent from the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 is a sectional view of a contact material with an anti-oxidant layer applied thereto according to one embodiment of the present invention;

FIG. 2 is a sectional view of the same showing a state of internal oxidation of a contact after being treated;

FIG. 3 is an enalrged sectional view of the contact material as shown in FIG. 2 cut into the shape of a contact and showing the state of internal oxidation thereof;

FIG. 4 is a sectional view of a contact material according to another embodiment of the present invention; and

FIG. 5 is a sectional view of a contact material according to still another embodiment of the present invention.

In FIGS. 1 to 3, 1 is a piece of a contact material formed of a silver-cadmium alloy. 4 is an anti-oxidant layer of a metal such as nickel, chromium, aluminum, copper, iron, or alloys thereof which can serve as an anti-oxidation layer in an oxidation atmosphere at a high temperature. The anti-oxidant layer 4 is applied in a thickness of lop-100,0. to one face of the contact material 1. Said anti-oxidant layer 4 which is used only for preventing oxidation, is not required to be thicker, but if it is too thin, it cannot serve as anti-oxidant. The antioxidant layer may be applied by any method such as pressure-bonding, plating and vaporizing. 'The contact material to which an anti-oxidant layer is applied as shown in FIG. 1 is heated to be oxidized in an oxidation atmosphere such as oxygen or air at a temperature of 600800 C. The heating time varies depending on the temperature and the kind of the oxidation atmosphere used. As the degree of oxidation progresses almost in proportion to the square of time, the oxidizing time can be adequately selected depending on the thickness of the contact material to be oxidized. After oxidation is attained, the material is taken out of the furnace, and is heated at 500-800" C. in a reducing atmosphere such as hydrogen, carbon monoxide or ammonia for reducing the previously oxidized surface thereby to form an exterior layer of the original silver-cadmium alloy which serves as a brazing face of the contact product. The heating time for the reduction treatment is selected as to obtain the exterior layer of a silver-cadmium alloy thick enough for brazing, usually aboutJ/ of the thickness of the finished contact for instance, when the thickness of the contact is 2 mm., a heating time of 2-10 hours is preferable. After the reduction treatment iscomplete the layer 4 comprising oxide of a metal of nickel, chromium,

aluminium, copper or iron or alloys thereof is removed with pincers, or by a severing orpickling treatment, there by obtaining a contact of the'desired shape. FIGS. 2 and 3 show the state of internal oxidation of the contact after reduction treatment-and after the shaped being intoan individual contact. 2 is an oxidized layer and'3 is a silvercadmium layer formed by the reduction. As seen in the figures, said contact has excellent contact properties, as

the oxidized layer of cadmium is the coarsest on the cono d o of. c dm um. an

; sslge tq,

. plate to obtain a contact of the present invention. The thus obtained contact was mounted on an electromagnetic tact fage ie. the face that layer, and becomes gradually thicker towards the opposite brazing face, that is, the silver-cadmium layer 3, and moreover, it is superior in strength due to its integrally formed brazing face. Referring to FIG. 4, another embodiment of this invention is illustrated. Two pieces of,

contactmaterial of silver-cadmium alloy 1 and 1a are mated together and welded at their mated faces Sinto a singleplate, then subjected to oxidation and reduction treatment as described in FIGS. 1' to 3; After said treatments are completed, said metal composite plate is sepsaid two pieces are adapted to serve as an anti-oxidant for each other.

A still another embodiment'is illustrated referring to FIG. 5. A piece of a contactrr'haterial 1b of a silver-cadmium alloy twice as thick as the desired size of a contact is treated similarly as explained in FIGS. 1 to 3, and then cut in half, each of which is thencut to a desired shape of the contact. v

The contacts prepared by the above-idescribed methods have excellent characteristics,compared with those produced by the conventional methods. In the conventional contact prepared by pressure-bonding of silver and oxi-. dizing from the circumference, the particles of the oxide become larger and their distribution becomes more coarse towards the central area from the'circumferential area. Considering the phenomenon from the standpoint of hardness, such a contact is .hard around'the circumferential area and soft around the central area; In case of oneface, oxidation the contact is hard near the contact face and becomes softer towards the brazing face. According to the present invention on the contrary, the contact is soft near the contact face and becomes harder towards the brazing face; consequently, it shows a stable contact resistance from the beginning. Comparing these three kinds of contacts from a viewpoint of wear, an extraordinary wear occurs around the central area of the contact prepared by pressure-bonding of silver and oxidizing fromthe circumference. The ;;contact;formed by one-face oxidation, shows a tendency that the thinner the'contact becomes by wearing, the more rapid the wear occurs. The wear resistance of the present invention, however, tends to increase as the thickness of the contact "decreases by wearing.

In addition, a brazing face is formed as a silver-cadmium layer by reduction integrally with the contact material of a silver-cadmium oxide according to the present invention, the strength of the contact is greatly improved, compared with a contact prepared by applying silver by pressure-bonding for forming a brazing face.

The present invention is further concretely illustrated.

by the following examples.

EXAMPLE 1 surface obtained by said reduction-treatment was 0.3 mm; 1

Adisc of 8 mm. in diameter was punched out from said shearing tester.-These values were" also determined on 'a conventional silver-cadmium oxide 'contac'tof 8 mm. in

diameter and 1.5 mm. in thickness prepared byapplying wa jac t e ant x nt.

silver and oxidizing from the circumference under the same conditions as in this invention (hereinafter referred to as Control Sample A) and a contact of the same dimensions prepared by the method of Us. Patent Application No. 815,677 (hereinafter referred to as Control Sample B) and the results were compared. The lives of the contacts were also compared. The results are shown in Table 1.

The same plate of alloy as used in Example 1 was rolled into a plate of a thickness 1.5 mm., and plated over with chrominum of 0.01 mm. in thickness, then the plate was oxidized at 800 C. under 1 atm. in an oxygen atmosphere for 96 hours; then it was taken out of the furnace, and reduced at 400 C. under 1 atm. in a CO atmosphere for 5 hours. The thickness of the silvercadmium layer on the surface obtained by the said reduction treatment was 0.3 mm. A disc of 8 mm. in diameter was punched out from said plate to obtain a contact of the present invention. The obtained contact and Control Samples A and B were tested as described in Example 1 and the results are shown in Table 2.

Two plates of a thickness of 1.5 mm., were prepared by rolling the same plate of alloy as used in Example 1. The thus obtained two plates were mated with each other and welded at the mated faces. The resultant plate was oxidized at 800 C. under 1 atm. in an oxygen atmosphere for 96 hours, taken out of the furnace, and reduced at 300 C. under 2 atm. in a hydrogen atmosphere for 4 hours. The thickness of the silver-cadmium layer on the surface obtained by said reduction treatment was 0.2 mm. The welded faces were cut and separated to obtain two plates, and from each plate a disc of 8 mm. in diameter was punched out to obtain a contact of the present invention. The obtained contact and Control Samples A and B were tested similarly as in Example 1 and the results are shown in Table 3.

6 EXAMPLE 4 The same plate of alloy as used in Example 1 was rolled into a plate with a thickness of 3 mm., double the size of those used in the previous examples. The obtained plate was oxidized at 800 C. under 1 atm. in an oxygen atmosphere for 96 hours, taken out of the furnace, and reduced at 750 C. under 1 atm. in a CO atmosphere for 2 hours. The thickness of the silver-cadmium layer on the surface obtained by the said reduction treatment was 0.2 mm. The plate was cut in half to obtain two plates, and from each plate a disc of 8 mm. in diameter was pushed out to obtain a contact of the present invention. The obtained contact and Control Samples A and B were tested similarly as in Example 1 and the results are shown in Table 4.

What is claimed is: 1. A process for preparing an electric contact, comprising:

providing a contact material formed of a silver-cadmium alloy wherein one face of said contact material is a contact-forming face; applying to said contact-forming face an anti-oxidant layer of a metal selected from the group consisting of nickel, chromium, aluminum, copper, iron and alloys thereof, to inhibit oxygen diffusion therethrough into said contact material having said anti-oxidant layer thereon in an atmosphere containing oxygen at a temperature of 600 to 800 C. to eflect internal oxida tion of the cadmium to form cadmium oxide throughout said contact material, with the cadmium oxide being coarsest adjacent the contact-forming face and being progressively thicker towards its opposite face; then heating the thus-oxidized contact material having said anti-oxidant layer thereon in a reducing atmosphere of hydrogen, carbon monoxide or ammonia at a temperature of 500 to 800 C. to reduce the cadmium oxide to cadmium in a zone extending from the exposed surface of said contact material partway through said contact material to obtain an integral silver-cadmium alloy exterior surface layer of selected depth on the exposed surface of said contact material; then removing said anti-oxidant layer from the contact material and obtaining an electric contact from said contact material.

2. A process according to claim 1, in which the thickness of said anti-oxidant layer is from 10 to 100 References Cited UNITED STATES PATENTS 3,596,030 7/ 1971 Shibata 200-166 C 3,607,244 9/1971 Kabayama 200-166 C X 3,688,067 8/ 1972 Shibata 200166 C RALPH S. KENDALL, Primary Examiner US. Cl. X.R.

. UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION June 4, 1974 Patent No 3 1 Dated Inventor(s) Akira Shibata It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as'shown below:

Col. 6, line 35; change "contact material" to --contact forming face; heating said contact material.

Signed and sealed this 17th day of September 1974,

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM po-mso (10-69) USCOMWDC 6o376 p69 U.S. QOVERNMENT PRINTING OFFICE: @959 O3S6-3344

Images