US3214558A

US3214558A - Contact arrangement exhibiting reduced material migration

Info

Publication number: US3214558A
Application number: US218419A
Authority: US
Inventors: Huber Christian
Original assignee: Siemens AG
Current assignee: Siemens and Halske AG; Siemens AG
Priority date: 1961-08-25
Filing date: 1962-08-21
Publication date: 1965-10-26
Anticipated expiration: 1982-10-26
Also published as: BE621720A; GB1000478A; CH416863A; SE317144B; FI40293B; NL282431A; DE1178533B

Description

Oct. 26, 1965 c. HUBER 3,214,558

CONTACT ARRANGEMENT EXHIBITING REDUCED MATERIAL MIGRATION Filed Aug. 21, 1962 United States Patent 4 claims. or. 200-166) The invention disclosed herein is concerned with a contact arrangement comprising a layer of contact material provided upon a carrier. The object of the invention is to improve electrical contacts of the kind used, for example, in the communication arts.

Such contacts suffer from the phenomenon of migration of material, resulting, generally after a multitude of switching operations, in the formation of crater-like pits upon the side of a contact from which the material migrates while forming on the other side elevations facing the respective pits. These structures have usually rough surface textures and contacts deformed in this manner therefore tend to interlock or freeze after operative closure thereof, thus making the desired selective contact actuation impossible. Moreover, such deformation is considered by itself very undesirable because it changes the contact spacing which generally must conform to a given amount, thereby introducing the danger of arcing. The contact deformation referred to usually also entails an increase of the contact resistance in the closed position of the respective contact points.

Material migration in electric contacts is described in the periodical The Bell System Technical Journal, 1955, pages 1081-1102 and 1191-1223. On page 1082, thereof, it is stated that the erosion of contact surfaces, which is responsible for the material migration, depends on various parameters, among others on the material and the surrounding atmosphere. On pages 1083 and 1084, appears a discussion of the direction of transfer, and on page 1097, it is stated that the individual contact materials differ in cathode evaporation, palladium, iron and nickel having a strong cathode evaporation which predominates over the anode, while for silver, gold and copper the opposite holds true. In the article, starting with page 1191, reference is made to the material migration of so-called reed relays, and thus sealed tube contacts. From the table on page 1214 it may be learned that, depending on the kind of gas employed in the glass tube, altogether different discharge relations result, including both glow discharges and are discharges, which is discussed in the text, it being pointed out on page 1218, paragraph 3, that a special phenomenon is the variable flow of the charge.

Attempts have been made to overcome these difficulties by providing the contact points of electrical contacts with particular contact materials which have only a slight material migration tendency, so as to reduce material migration as much as possible. However, a complete elimination of the material migration cannot be obtained by the use of such expcdients.

The invention described herein shows a way for eliminating the detrimental effects of material migration, whereby material migration as such is, however, purposely tolerated.

The contact arrangement according to the invention provides upon a carrier a layer of contact material, the direction of material migration if which is opposed to the direction of material migration of the carrier material, the layer of such contact material being so thin that no crater or elevation formation can result from material migration within the contact material.

32%,5153 Patented Get, 26, 1065 The invention is based upon recognition of the fact that various metallic substances which are to be considered respectively for contact carriers and contact materials, exhibit oppositely directed material migration. While the material migration is purposely admitted, the directions thereof, in the substances used, are mutually attuned so that the contact material can migrate away from one contact side until the carrier is finally exposed, coming thereafter upon the carrier to a standstill, owing to the oppositely directed material migration thereof. In order to avoid, as a consequence of the material migration, the formation respectively of craters and elevations, which would lead to the previously mentioned detriments, the layer of con-tact material is made so thin that the giving off and building up of the contact material is incident to the material migration effected practically plate-like. It was found in practical use of the invention that layers of contact material with a thickness of about 20 microns satisfy the above noted requirement.

In order to protect electrical contacts against the infiuences of the ambient atmosphere or against contamination, they may be disposed in a hermetically sealed space which is filled with a protective gas or a noble gas. Such expedient makes it possible to also influence the direction of material migration of the materials employed since such direction, as it was found, also depends upon the kind of gas used and upon the pressure thereof. The composition and the pressure of the gas used are appropriately selected so as to obtain the desired direction of migration of the contact material.

The principle underlying the invention may also be utilized in the event that the use of a given carrier material is respectively specified or required, which does not have the desired direction of migration of the material, under consideration of the contact material to be employed, by providing upon the carrier a layer which has the desired material migration direction.

Examples of the invention will now be described with reference to the accompanying drawing.

FIG. 1 shows a contact arrangement plated with appropriate contact material;

FIG. 2 represents a contact arrangement which had been changed by material migration;

FIG. 3 illustrates a contact arrangement comprising a carrier provided with a layer having a definite direction of material migration; and

FIG. 4 illustrates how contacts of the type involved, may be assembled in a socalled protective tube.

The electrical contact shown in FIG. 1 comprises two contact tongues or

springs

1 and 2 the oppositely disposed ends of which are provided with contact material indicated respectively by numerals 3 and 4. This contact material exhibits a material migration direction which is opposed to that of the material of which the carrier springs 1 and 2 are made. The material of which the

springs

1 and 2 are made (carrier material) is assumed to be an iron-nickel alloy, such as is used, for example, in connection with sealed-in, socalled protective tube or protective gas contacts, requiring for the operative actuation thereof a magnetic flux which causes the springs to be drawn together. The contact material may in such a case consist of a platinum-tungsten alloy containing approximately 5 percent tungsten and percent platinum. It is likewise possible to use an alloy of palladium and silver in approximately equal amounts of these two materials. Contact materials of these kinds are known and frequently used.

Upon employing the contact arrangement shown in FIG. 1, for the switching of a direct voltage, there will occur a material migration which causes contact material to migrate from one to the other side of the contact, depending upon the direction of the current flowing over the contact in closed position thereof. Since the contact material is provided on the

springs

1 and 2 in the form of plates which are so thin that no crater or elevation formation can practically occur incident to the material migration, such migration proceeds in practice so that material is on one side over a relatively large contact area carried off and in table or plate-like manner built up on the opposite side. This process can last only so long as contact material is available at the side from which it is carried otf. Once this material is exhausted by migration thereof, the carrier material will be practically exposed, and such latter material cannot be carried off owing to its oppositely oriented direction of material migration.

This results in a terminal state such as is illustrated in FIG. 2 in which the

contact springs

1 and 2 are shown farther apart so as to make the entire contact area of the spring 2 visible. The contact material has migrated from the spring 2, for the area of contact making, to the contact layer 3 of the spring 1, forming on the layer 3 the plateor table-like accretion 6 shown by shading. The contact spring 2 has lost the corresponding amount of contact material, only a small strip 5 of the original contact layer 4 (FIG. 1) being left thereon. The contact making areas are in this state formed by the part 6 on the spring 1 and the area 7 of the spring 2. Accordingly, the contact material of the part 6 and the oppositely disposed area 7 of the carrier material of the spring 2, constitute the contact making materials. A stable condition is thus reached for the further contact operation, so far as the material migration is concerned.

No crater formation or formation of elevated portions could occur during the entire material migration process from the initial condition shown in FIG. 1 to the condition shown in FIG. 2, and the contact making operation therefore remained unaffected. This also aplies to the further contact operations taking place after the condition is reached which is shown in FIG. l2, since the material migration is terminated in such latter condition.

In the event that the exposed area 7 of the spring 2 should tend, owing to the nature of the carrier material, to accept any foreign matter, for example, due to corrosion, the contact arrangement can be disposed, for example, in a hermetically sealed space containing a protective gas or else, a carrier material can be used which is resistant to detrimental influences, for example, a noble metal or an alloy containing a noble metal.

FIG. 4 illustrates how contacts embodying the invention can be disposed in a hermetically sealed tube T which may contain a protective gas, the tube construction illustrated being similar, for example, to that illustrated in Patent No. 2,506,414.

In case there should be for some reason only a carrier material available, the material migration direction of which is unsuitable for the purpose in view, such material can nevertheless be used by providing thereon a layer of a material which has the desired material migration direction. The resulting contact structure will thus comprise a carrier which is plated with the appropriate material, the latter carrying the contact material provided thereon. Such a structure is illustrated in FIG. 3.

Referring to FIG. 3, the contact springs 8 and 9 are at their inner oppositely positioned ends provided with layers of materal indicated respectively at 10 and 11, such layers having a direction of material migration which is oriented oppositely to that of the contact material provided thereon as indicated respectively at 12 and 13, the thickness of the latter being such that no craters or elevations can form within the contact material incident to the material incident to the material migration, which might affect the contact making operations. Upon material migration such as described in connection with FIG. 2, there will be reached a condition in FIG. 3, in which contact material has completely migrated from one spring to the respectively cooperating contact of the other spring, resulting in an exposed zone over the

layers

10 and 11. The terminal condition obtained in such case will be in principle the same as shown in FIG. 2 except that the contact spring itself is not exposed at the area of material migration but that an area of the

layer

10 or 11 will be exposed, thereby bringing to an end the further material migration. It may be mentioned in conclusion, that the

layers

10 and 11 may consist of a material which fulfills not only the requirements relating to the desired orientation of the direction of the material migration, but also serving as a protection against contact contamination and corrosion, respectively.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

I claim:

1. An electrical contact arrangement having contact means between which occurs migration of material incident to the operative actuation thereof, such material migration leading ordinarily respectively to the formation of craters and elevations which detrimentally afiect the contact-making operation, a construction whereby such detriments are avoided, comprising a carrier, a layer of contact material disposed upon such carrier, the contact material of said layer having a direction of migration which is oriented oppositely to that of the carrier material, the thickness of said layer being less than that required for material migration in the formation of craters or elevations which might affect the contact making operation.

2. A contact arrangement according to claim 1, wherein the required direction of migration of the material of the carrier is obtained by the provision thereon of a layer of material having such direction of material migration.

3. A contact arrangement according to claim 1, which is to be disposed in a hermetically sealed space filled with a given gas, the composition of said gas and the pressure thereof being so selected as to result in the desired direction of migration of the contact material.

4. A contact arrangement according to claim 1, which is to be disposed in a hermetically sealed space filled with a given gas, the composition of said gas and the pressure thereof being so selected as to result in the desired direction of migration of the contact material, the required direction of migration of the carrier material being obtained by the provision thereon of a layer of a material having such direction of material migration.

References Cited by the Examiner UNITED STATES PATENTS 2,379,641 7/45 Keitel 200l66 2,506,414 5/50 Ellwood 200l66 2,653,199 9/53 Brown et al 200l66 2,793,273 5/57 Underwood et al. 200l66 BERNARD A. GILHEANY, Primary Examiner.

Claims

1. AN ELECTRICAL CONTACT ARRANGEMENT HAVING CONTACT MEANS BETWEEN WHICH OCCURS MIGRATION OF MATERIAL INCIDENT TO THE OPERATIVE ACTUATION THEREOF, SUCH MATERIAL MIGRATION LEADING ORIDINARILY RESPECTIVELY TO THE FORMATION OF CRATERS AND ELEVATIONS WHICH DETRIMENTALLY AFFECT THE CONTACT-MAKING OPERATION, A CONSTRUCTION WHEREBY SUCH DETRIMENTS ARE AVOIDED, COMPRISING A CARRIER, A LAYER OF CONTACT MATERIAL DISPOSED UPON SUCH CARRIER, THE CONTACT MATERIAL OF SAID LAYER HAVING A DIRECTION OF MIGRATION WHICH IS ORIENTED OPPOSITELY TO THAT OF THE CARRIER MATERIAL, THE THICKNESS OF SAID LAYER BEING LESS THAN THAT REQUIRED FOR MATERIAL MIGRATION IN THE FORMATION OF CRATERS OR ELEVATIONS WHICH MIGHT AFFECT THE CONTACT MAKING OPERATION.