US3644693A

US3644693A - Nonsticking relay contacts

Info

Publication number: US3644693A
Application number: US880128A
Authority: US
Inventors: Sheldon S Bitko
Original assignee: Fifth Dimension Inc
Current assignee: PNC Bank NA
Priority date: 1969-11-26
Filing date: 1969-11-26
Publication date: 1972-02-22
Anticipated expiration: 1989-02-22
Also published as: GB1326760A; DE2058271A1; JPS4840934B1; FR2068655B1; FR2068655A1; NL7017265A; CA929997A

Abstract

A mercury relay having nonsticking mercury wettable surfaces, one of the surfaces carrying a button of mercury wettable material surrounded by a rim of nonmercury wettable material, preferably tantalum, which extends beyond the button and forms a physical barrier against physical impact between the mercury wettable surfaces.

Description

United States Patent Bitko [54] NONSTICKING RELAY CONTACTS [72] Inventor: Sheldon S. Bitko, Cherry Hill, NJ.

[73] Assignee: Fiith Dimension, Inc., Princeton, NJ.

[22] Filed: Nov. 26, 1969 [2]] App]. No.: 880,128

[52] US. Cl. ..200/166 C, 200/152 K [5i] int. Cl..... H0lh 1/08 [58] FieldofSeal'ch ..200/166 C, 152 K [56] References Cited UNITED STATES PATENTS 3,155,804 11/1964 Gewirtz ..200/166 C 115] 3,644,693 1451 Feb. 22, 1972 Courtney-Pratt ..200/166 C Janninck ..200/166 C UX Primary Examinerl-l. 0. Jones Altorneyl-iurvitz & Rose [57] ABSTRACT v A mercury relay having nonsticking mercury wettabie surfaces, one of the surfaces carrying a button of mercury wettabie material surrounded by a rim of nonmercury wettable material, preferably tantalum, which extends beyond the button and forms a physical barrier against physical impact between the mercury wettabie surfaces.

8 Clai 4 i i 'iisqsss PATENTEDFEH22 m2 3.644.693

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ATTORNEYS NONSTICKING RELAY CONTACTS BACKGROUND OF THE INVENTION Whenever two mercury wet metallic elements are brought into metal-to-metal contact, separated only by a very thin layer of mercury, atoms of the solid metal diffuse through the mercury, and sticking occurs. Diffusion is accelerated at elevated temperatures at an exponential rate. It is an object of the present invention to provide a relay which completes its circuit through mercury via wettable surfaces while maintaining a spacing between the wet surfaces which is greater than that which permits appreciable diffusion of metal from one surface to the other, by interposing a nonwettable metallic spacer or interposer between the wettable surfaces.

SUMMARY OF THE INVENTION a relay contact operating in mercury which has a mercury wettable surface which is prevented from contacting an opposing contact during operation of the relay by interposing a mercury nonwettable barrier which surrounds the wettable surface,

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in side elevation of two contacts according to the invention, at a first stage of their fabrication;

FIG. 2 is a view in side elevation of the contacts of FIG. 1, after a second step has been completed;

FIG. 3 is a view in side elevation of contacts according to the invention, in completed state; and

FIG. 4 is a view in side elevation of the contacts of FIG. 3, but including a globule of mercury.

DESCRIPTION OF THE PREFERRED EMBODIMENT Assume that the present invention is applied to a mercury contact reed switch, a typical example of which is the switch disclosed in the US Pat. to Barlow No. 3,431,377, issued Mar. 4, 1969. One of the contacts 10, in FIG. I, is assumed mercury wettable, and the other contact arm 11, includes an Hg wettable element 12, which may be arcuate in form as viewed from contact 10, although the precise shape of element 12 does not go to the essence of the invention. The contact arm 11 and the element 12 are coated with a nonwettable metal or oxide coating 13.

In FIG. 2, a flat has been ground or otherwise removed from element 12, sufficiently to expose a flat surface 14 of element 12.

In FIG. 3, a depression 15 is formed in flat surface 14, which falls deeper than the remaining ground edge 16 of the mercury nonwettable coating 13. The depression 15 may be formed by etching, for example with hot mercury, which attacks the wettable area 14, but not the nonwettable area 16.

Surface tension will leave a globule of mercury 17 on the surface of the wettable metal, now identified as 120, but none will adhere to the nonwettable metal or oxide at 16 (FIG. 4), thus forming a circular globule of mercury which is constrained within fixed boundaries.

Now, when contact and contact arm 11 impact, one against the other, as occurs in normal operation of a relay, physical metal-to-metal contact will occur at a mercury nonwettable surface, but an electrical circuit will exist, primarily through the mercury via two opposed but separated mercury wettable surfaces. The mercury-wet metallic surfaces do not approach each other sufficiently, in contacts arranged according to the invention, to enable substantial diffusion of metal through the mercury, as would occur on physical metal-tometal contact between two wettable surfaces, where diffusion can occur either by direct contact, or through a layer of mercury which is only a few atoms thick. Experience shows that maintaining physical spacing between mercury wettable contacts at a value of about 0.001 inch or slightly less, is adequate to prevent sticky contacts, and further that operation is then bounce free.

Contact materials must be selected so that they are easily Hg wettable, are of proper magnetic character, and are relatively insoluble in Hg and in each other. Suitable contact materials include Copper, Nickel, Platinum and various alloys of these.

While the present invention relates directly to reed switches, the principles of the invention are applicable to any mercury switch, and particularly to a shuttle switch such as is illustrated in US. Pat. to Donath 3,144,533, issued Aug. 11, 1964.

It is also clear that both contacts may be identical, if desired, which can increase the spacing between mercury wettable surfaces existing on physical impact of the switch contacts.

It has been determined that tantalum and niobium are superior interposer materials in that they do not become wettable by impact against mercury wettable metal and do not alloy with the latter, to an extent far surpassing any other materials tested.

I claim:

1. Mercury relay contacts, comprising a first contact having at least a first mercury wettable surface,

a second contact, said second contact including a mercury wettable second electrical contact surface,

a mercury nonwettable barrier element surrounding said electrical contact surface and having a location and shape which prevents physical contact of said first and second surfaces when said first and second contacts impact but which assures sufficient proximity of said areas to assure completion of an electrical circuit therebetween in the present of a globule of liquid mercury on said electrical contact surface.

2. The combination according to claim I, wherein said electrical barrier element surrounds said second electrical contact surface.

3. A mercury contact, comprising a supporting element,

a button of mercury wettable material extending from said supporting element, said button of mercury wettable material having a face and having a peripheral surface,

a layer of mercury nonwettable material secured about said peripheral surface and extending beyond said face to form a physical barrier against physical impact against said face.

4. A mercury switch element, including a contact carrying element,

said element being mercury nonwettable and said contact being of Hg wettable material, and

a barrier of mercury nonwettable material surrounding said wettable material and extending beyond the surface thereof for about 0.001 inch, whereby a globule of Hg may attach to said wettable material and be bounded by said barrier of mercury nonwettable material.

5. A nonsticking contact for a mercury switch, comprising a support,

a mass of mercury wettable material secured to said support and having a surface displaced from said support to a first extent, and

a barrier of mercury nonwettable material extending from said surface to a still greater extent, said still greater extent being about 0.001 inch.

6. A nonsticking contact for a mercury switch, comprising a mercury wettable surface, and

a nonmercury wettable barrier layer bounding said surface and extending beyond said surface about 0.001 inch.

7. A nonsticking contact for a mercury switch, comprising a mercury wettable circuit completing surface, and

an adjacent nonmercury wettable barrier extending beyond said surface about 0.001 inch.

8. The combination according to claim 7, wherein said mercury wettable surface is cup-shaped.

' I i l l 1

Claims

1. Mercury relay contacts, comprising a first contact having at least a first mercury wettable surface, a second contact, said second contact including a mercury wettable second electrical contact surface, a mercury nonwettable barrier element surrounding said electrical contact surface and having a location and shape which prevents physical contact of said first and second surfaces when said first and second contacts impact but which assures sufficient proximity of said areas to assure completion of an electrical circuit therebetween in the present of a globule of liquid mercury on said electrical contact surface.

2. The combination according to claim 1, wherein said electrical barrier element surrounds said second electrical contact surface.

3. A mercury contact, comprising a supporting element, a button of mercury wettable material extending from said supporting element, said button of mercury wettable material having a face and having a peripheral surface, a layer of mercury nonwettable material secured about said peripheral surface and extending beyond said face to form a physical barrier against physical impact against said face.

4. A mercury switch element, including a contact carrying element, said element being mercury nonwettable and said contact being of Hg wettable material, and a barrier of mercury nonwettable material surrounding said wettable material and extending beyond the surface thereof for about 0.001 inch, whereby a globule of Hg may attach to said wettable material and be bounded by said barrier of mercury nonwettable material.

5. A nonsticking contact for a mercury switch, comprising a support, a mass of mercury wettable material secured to said support and having a surface displaced from said support to a first extent, and a barrier of mercury nonwettable material extending from said surface to a still greater extent, said still greater extent being about 0.001 inch.

6. A nonsticking contact for a mercury switch, comprising a mercury wettable surface, and a nonmercury wettable barrier layer bounding said surface and extending beyond said surface about 0.001 inch.

7. A nonsticking contact for a mercury switch, comprising a mercury wettable circuit completing surface, and an adjacent nonmercury wettable barrier extending beyond said surface about 0.001 inch.