US3229354A

US3229354A - Method of assembling a mercury button switch

Info

Publication number: US3229354A
Application number: US104939A
Authority: US
Inventors: Leonard W Cook; Edward R Coutant; Arville W Gilmore
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1961-04-24
Filing date: 1961-04-24
Publication date: 1966-01-18
Anticipated expiration: 1983-01-18

Description

Jan. 18, 1966 w. cooK ETAL 3,229,354

METHOD OF ASSEMBLING A MERCURY BUTTON SWITCH Filed April 24, 1961 [aye/Mans: Zea/yard 14/ (00/6, [dward F dad Jam,

4/147/9 M GM/no/e.

United States Patent Ofifice 3,229,354 Patented Jan. 18, 1966 3,229,354 METHOD OF ASSEMBLING A MERCURY BUTTON SWITCH Leonard W. Cook, Varwick, 13.1., Edward R. Coutant,

Stratford, Conn, and Arville W. Gilmore, Warwick,

12.1., assignors to General Electric Company, a corporation of New York Filed Apr. 24, 1961, Ser. No. 104,939 8 Claims. (Cl. 29155.5)

The present invention relates to a mercury button switch in which the ceramic member of the button is bonded to the header, and which eliminates organic materials from the internal construction.

Cook and Passarelli Patent No. 2,916,589, which is assigned to the same assignee as the present application, disclosed a mercury button switch in which a cylindrical shell was capped by a retainer ring which maintained an axially positioned terminal pin in position by means of an annular glass seal. A ceramic barrier and sealing gasket combined with the glass seal to insulate the terminal pin from the retaining ring so that an electrical circuit from the terminal pin had to pass through mercury positioned in the ceramic barrier to the metal shell. In the conventional mercury button switches manufactured prior to the Cook and Passarelli invention, a pair of symmetrical metal shells were sealed against a ceramic barrier by means of a glass seal forming a rim. Because of the differences in coefficients of expansion of the ceramic, metal, and glass, this construction has always offered difiiculties from a manufucturing point of view.

In the switch of the Cook and Passarelli patent, it was necessary that the retaining ring he insulatingly sealed from the terminal pin and this was accomplished by means of a resilient silicone washer. Not only was the silicone material costly, but it introduced a slight quantity of organic material to the interior of the mercury button. While a silicone can withstand relatively high temperatures, its presence in an arc path on the higher cold lamp loads such as a 15-an1pere alternating current cold lamp load will result in its decomposition. In a mercury button this decomposition can produce end products which are highly deleterious. Accordingly, one of the objects of the present invention is to produce a mercury button switch which does not contain any organic material in the interior thereof.

Another object of the invention is to produce a mercury button switch in which the ceramic barrier of the button is sealed to the header to insulate the terminals electrically by a bond impervious to liquid mercury and mercury vapor, and mechanically strong enough to withstand normal handling and thermal shock.

Other objects of the invention will be apparent from the following specification and the drawing wherein:

FIG. 1 is a perspective view of a mercury button switch made in accordance with this invention;

FIG. 2 is a sectional view of the switch illustrated in FIG. 1;

PEG. 3 is an exploded view of the switch illustrated in FIG. 1;

FIG. 4 illustrates in section the apparatus used in direct-bonding the interior assembly of the mercury button switch illustrated in FIG. 1; and

FIGS. 5, 6, and 7 are broken perspective views of the ceramic barrier of the switch illustrated in FIG. 1 showthe present invention is directed to a mercury button vention operates.

Briefly stated, in accordance with one of its aspects, the present invention is directed to a mercury button switch comprising a metal shell with a closed terminal end and open end and an axis of rotation through the ends. Welded to the shell as a closure assembly to hermetically seal the shell is a retaining ring which is part of the closure assembly including a central terminal pin sealed in position by means of an insulating element such as glass and having a ceramic barrier directly bonded to this insulating element around their engaging surfaces. The interior of the button contains a measured quantity of mercury movable within the ceramic barrier to make and break electrical contact between the shell and central terminal pin in accordance with the spatial orientation of the button.

Glass-to-metal bonds and seals are well known and in general are accomplished either by matching the coeflicients of expansion of the metal and glass or by intentionally mismatching the coefficients as by providing a metal ring of greater coeflicient of expansion than glass which is compressed within the metal ring. Glass-toceramic seals also require a matching of the expansion coefficients and thus the use of a single glass element as a bond for both a metal and a ceramic becomes difficult to accomplish. The present production mercury button (see US. Patents 2,101,092; 2,153,000; 2,177,498; and 2,175,306) has a giass-metal-ceramic seal in which the linear coefficients of thermal expansion are matched while the header of this invention has a compression type seal in the header itself and a matching type for the ceramic-to-header bond.

Referring to the drawing, the button switch 10 consists of a cylindrical shell 11 with a closed end 12 and an open end having an outwardly extending flange 14 with a lip 15. The remaining solid elements of the switch comprise a terminal metal pin 20 centrally positioned with respect to a retaining ring 22 by means of a glass seal 21 which is preferably formed from a preform. Directly bonded to the glass seal 21 is a cylindrical ceramic barrier or liner 25 which has an aperture through which mercury can flow, as will be explained later. When direct-bonded, the pin 20, glass seal 21, retaining ring 22, and barrier 25 form an assembly which is sealed, as by welding of the ring 22 to the flange 14, to the shell 11 with the barrier 25 on the interior thereof.

The present invention is directed particularly to the means of bonding and sealing the assembly comprising the terminal pin 20, glass member 21, retaining ring 22, and barrier 25 and this invention will be described with reference to this assembly before the remaining elements of the switch are identified and its operation described.

We have found that if a glass preform is used in making the glass seal 21 and the sealing temperature is carefully controlled, not only will the seal be gas-tight but the bond will be strong enough to withstand rough usage in the field. The preform may be molded into the form illustrated in FIG. 3 to minimize the quantity of glass needed and the glass flow required. In a preferred form it is composed of fine glass particles mixed with a binder and pressure molded to shape. As shown in FIG. 3, the preform preferably has an annular groove 21a in which an annular protuberance 25a of the barrier 25 seats during the sealing operation.

The glass preform 21 may be made of relatively soft glass, i.e., glass having a relatively low content of silica and magnesia and a relatively high content of sodium oxide and boron oxide. Easily reduced oxides, such as lead oxide, should be omitted from the composition as arcing might be more deleterious to glass compositions containing such oxides. Glass compositions suitable for making preforms usable in the present invention are disclosed in Stanworth Patent No. 2,719,932, which is assigned to the same assignee as the present invention. It is understood, however, that glass composition is not particularly critical in the present invention. The socalled soft glasses melt at a lower temperature and are therefore easier to work with but glasses having high softening points may also be used. Where the glass preforms used in this invention are of the powdered type, they are quite porous and therefore contain quantities of gas. As the preform is heated, these gases expand and begin to escape. However, when the glass reaches its softening point, a glaze is formed and thereafter the gases cannot escape. As a result, the preform expands as the temperature is raised above its softening point and this expansion is much greater than would be the case if the gases were not present. Upon expansion, such a glass will readily bond to an oxidized metal surface or to a ceramic surface since the ceramic itself is an oxide even though there is a considerable gap between mating surfaces. On cooling, the glass contracts at a differential rate down to its softening point as the gases contract but does not draw back from an oxide surface which has been wetted by the glass while it was in a molten state. If the initial wetting of the sealing surfaces by the glass was made under compression, the effect of shrinkage upon cooling is minimized and the mechanical stresses from the shrinking retaining ring 22 aid in developing the ultimate hermetic seal by holding the glass in compression. Thus, we have found that the glass preform 21 can readily seal and bond the terminal pin 20, retainer ring 22, and barrier 25 into an assembly in accordance with the method outlined in greater detail hereinafter.

Referring particularly to FIG. 4, in sealing and bonding the pin 20, ring 22, and barrier 25 of this invention by means of the glass preform 21, it is desirable that the parts be positioned by means of a carbon block or fixture 4 and 6. Preferably, the metal ring 22 and terminal pin 20 are acid-etched for several minutes (concentrated bydrochloric acid is satisfactory for the metal parts when they are composed of cold-rolled steel) and carefully rinsed. This etching roughens the surface of the metal parts to increase the bonding area. The etched surface is then oxidized as by heating in air or other oxidizing atmosphere or by contact with an oxidizing agent to promote adherence. The terminal pin 20, glass preform 21, retaining ring 22, and ceramic barrier 25 are then assembled in the carbon block fixture 4 and 6 as illustrated in FIG. 4. The fixture and parts are then heated, as in an electric furnace, preferably in a non-oxidizing atmosphere such as that provided by dissociated ammonia.

The fixture and parts are preferably first pre-heated for several minutes at a temperature of about 750 F. The temperature is then raised to a point 200 F.450 F. above the softening point of the particular glass preform used and maintained at this temperature until the glass preform has softened and wet the bonding surfaces of the pin 20, ring 22, and barrier 25. The conventional soft glass preform temperatures would normally be 1600 F. to 2000 F. for periods of time ranging from as low as two minutes to as high as thirty minutes depending on the particular glass composition used. For a conventional soft glass preform a temperature of 1950 F. for five minutes is suflicient to accomplish this bonding. During the bonding operation, it is preferable that the parts be maintained in pressure contact with each other. After the bonding is complete, the assembly is cooled slowly to minimize local stresses.

While the single-step bonding and sealing of the parts as described above is the preferred form of this invention, it may also be practiced by a two-step process in which the terminal pin 20 and retaining ring 22 are first bonded and sealed in accordance with the method described above, and the barrier 25 is then bonded and sealed by a reheat step.

Where the glass preform is solid rather than powdered it is preferable that the preform be subjected to a degree of compression during the molten stage in order to insure intimate contact between the glass and the metal and ceramic elements. This pressure must be controlled in order to avoid squeezing the glass through any open spaces.

The principal element of the switch is the ceramic barrier or liner 25 which, as best seen in FIG. 2, has a transverse central partition 26 which serves to divide the interior of the switch 10 into pools of

mercury

29 and 30. As best shown in FIGS. 5, 6, and 7 the partition 26 has a circular opening or port 27 and a reservoir or cavity 28 in one side thereof. The through opening 27 is designed to permit the mercury on both sides of the partition to flow together at the center of the opening and complete an electrical circuit between the metal shell 11 and the head 23 of the terminal pin 20. It is important that the switch be capable of operation within a rotational angle of 20 or less. Accordingly, the through opening 27 is located as far as possible from the geometric center axis of the metal shell. The reservoir or cavity 28 is positioned with its lower edge on a line drawn through the center axis of the shell and the center axis of the through opening 27. Referring to FIGS. 6 and 7, as the switch is rotated in a counter-clockwise direction, the through opening 27 will begin to sink below the top level of the mercury pools 29 and 36. This begins to remove the obstruction between the two pools and they enter the through opening 27 with rounded

frontal surfaces

31 and 32, as illustrated in FIG. 6. As these two bodies of liquid mercury come into contact, a high inrush current will immediately vaporize the frontal surfaces of the mercury bodies. Final circuit closure might occur only after two or more such vaporizations or explosions. The purpose of the reservoir 28 is to dump the last traces of mercury into the mercury stream at the opportune moment when the two pools begin to merge at the center of the through opening 27. This action increases the kinetic energy of the moving mercury bodies and minimizes the local explosive effects of the contacting surfaces of mercury. When the switch is turned to open circuit position, the reservoir 28 again serves to increase the kinetic energy of the moving mercury bodies as they begin to separate. The metal shell 11 has an indexing notch 37 which is utilized for positioning and rotating the switch. A complementary notch 38 on the surface of the ceramic barrier 25 insures the proper orientation of the barrier 25 within the metal shell 11. Prior to the final sealing of the pin 20, ring 22, and barrier 25 assembly and mercury within the shell 11, a non-oxidizing atmosphere is provided within the switch. Preferably this atmosphere is predominantly argon with hydrogen added for alternating current operation. For direct current operation, the atmosphere is preferably predominantly hydrogen and both alternating and direct current operation may be at a pressure above atmospheric, e.g., 40 pounds per square inch.

In operation, a switch handle (not shown) is seated on the outer cylindrical side of the shell 11 in the indexing notch 37 to impart rotary motion within a restricted arc to the mercury button switch. Rotation of the switch produces the opening and closing of the electric circuit from the terminal pin 20 to the shell 11 by means of the mercury pools 29 and 30, as previously described with reference to FIGS. 5, 6, and 7. While the invention has been described with reference to a particular embodiment thereof, it is obvious that there may be many variations which fall within the true spirit of the invention. Therefore, the invention should be limited in scope only as may be necessitated by the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. The method of making a mercury button switch which comprises: forming powdered glass containing a binder into a disk with a central aperture; mounting said disk on a metal terminal pin, positioning said pin and disk in a metal retaining ring horizontally on a support surface provided with a complementary receptacle for the outer extension of said terminal pin, and positioning a ported ceramic barrier to engage the outer perimeter of said glass disk and the inner perimeter of said retaining ring and thereby forming a mercury pool; heating the disk, pin, ring, and barrier to a temperature of 200 F. to 500 F. above the softening point of the glass disk to direct-bond the parts into an integral assembly, positioning a quantity of mercury in said pool; and hermetically sealing said assembly in a metal housing by means of said retaining ring whereby electrical contact between said pin and housing through said mercury is controlled by the spatial orientation of said housing about its axis horizontally.

2. The method of claim 1 wherein the heating step is carried out in a non-oxidizing atmosphere.

3. The method of claim 2 wherein the atmosphere is dissociated ammonia.

4. The method of claim 1 wherein the glass disk has an annular groove near the perimeter of the interior side thereof and the ceramic has an annular protuberance which seats in said groove.

5. The method of making a mercury button switch which comprises: forming powdered glass particles containing a binder into a disk with a central aperture; mounting said disk on a metal terminal pin and mounting said pin and disk in a metal retaining ring horizontally on a support surface provided with a complementary receptacle for the outer extension of said terminal pin; heating said disk, pin, and ring to a temperature above the softening point of the glass to expand the gas in said glass to form an intimate bond between said pin and ring and said glass, and cooling said pin, ring and glass; positioning a ported ceramic barrier in engagement with the outer perimeter of said glass and the inner perimeter of said ring and thereby forming a mercury pool; heating said glass, pin, ring, and barrier to a temperature above the softening point of said glass to direct-bond said glass, pin, ring, and barrier into an assembly and cooling said assembly; positioning a quantity of mercury in said pool; and hermetically sealing said assembly in a metal housing by attachment of said retaining ring to said housing whereby electrical contact between said pin and housing through said mercury is controlled by the spatial orientation of said housing about its axis horizontally.

6. The method of claim 5 carried out in an atmosphere of dissociated ammonia.

7. The method of making a mercury button switch which comprises: forming powdered glass containing a binder into a disk with a central aperture; roughening and lightly oxidizing the surfaces of a metal terminal pin and retaining ring; mounting said glass disk on said pin and positioning said pin and disk within said retaining ring horizontally on a support surface provided with a complementary receptacle for the outer extension of said terminal pin; positioning a ported ceramic barrier in engagement with the abutting surfaces of said disk and ring and thereby forming a mercury pool; heating said pin, ring, disk, and barrier above the softening point of said disk to enable the gases in said disk to expand the disk to bond and hermetically seal said pin, disk, ring, and barrier into an assembly; positioning a quantity of mercury in said pool; and sealing said assembly by means of said retaining ring in a cylindrical metal shell Whereby electrical contact between said pin and said shell is selectively established through said mercury in accordance with the spatial orientation of said shell about its axis horizontally.

8. The method of claim 7 wherein the atmosphere is dissociated ammonia.

References Cited by the Examiner UNITED STATES PATENTS 1,935,513 11/1933 Massey 29--155.55 2,279,168 2/ 1940 Kalischer et al -59 XR 2,458,552 1/1949 Blattner 29--155.55 2,504,303 4/ 1950 Clark et al. 6559 2,561,520 7/1951 Lemmens et al. 65--59 2,570,095 10/1951 Bucklen et al. 200-152 2,597,978 5/1952 Doran 65-59 XR 2,770,923 11/1956 Dalton et a1 65-59 XR 2,916,589 12/1959 Cook et al. 200-152 WHITMORE A. WILTZ, Primary Examiner.

ROBERT K. SCHAEFER, ARTHUR M. HORTON,

JOHN F. CAMPBELL, Examiners.

Claims

1. THE METHOD OF MAKING A MERCURY BUTTOM SWITCH WHICH COMPRISES: FORMING POWERED GLASS CONTAINING A BINDER INTO A DISK WITH A CENTRAL APERTURE; MOUNTING SAID DISK ON A METAL TERMINAL PIN, POSITIONING SAID PIN AND DISK IN A METAL RETAINING RING HORIZONTALLY ON A SUPPORT SURFACE PROVIDED WITH A COMPLEMENTARY RECEPTACLE FOR THE OUTER EXTENSION OF SAID TERMINAL PIN, AND POSITIONING A PORTED CERAMIC BARRIER TO ENGAGE THE OUTER PERIMETER OF SAID GLASS DISK AND THE INNER PERIMETER OF SAID RETAINING RING AND THEREBY FORMING A MERCURY POOL; HEATING THE DISK, PIN, RING, AND BARRIER TO A TEMPERATURE OF 200*F. TO 500*F. ABOVE THE SOFTENING POINT OF THE GLASS DISK TO DIRECTED-BOND THE PARTS INTO AN INTEGRAL ASSEMBLY, POSITIONING A QUANTITY OF MERCURY IN SAID POOL; AND HERMETICALLY SEALING SAID ASSEMBLY IN A METAL HOUSING BY MEANS OF SAID RETAINING RING WHEREBY ELECTRICAL CONTACT BETWEEN SAID PIN AND HOUSING THROUGH SAID MERCURY IS CONTROLLED BY THE SPATIAL ORIENTATION OF SAID HOUSING ABOUT ITS AXIS HORIZONTALLY.