US2710713A

US2710713A - Method of sealing evacuated containers

Info

Publication number: US2710713A
Application number: US307773A
Authority: US
Inventors: Saul I Slater
Original assignee: Individual
Current assignee: Individual
Priority date: 1952-09-04
Filing date: 1952-09-04
Publication date: 1955-06-14
Anticipated expiration: 1972-06-14

Description

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June 14, 1955 s. I. SLATER 2,710,713

I METHOD OF SEALING EVACUATED CONTAINERS Filed Sept. 4, 1952 4 Sheets-Sheet 4 United States Patent 0 METHOD OF SEALING EVACUATED CONTAINERS Saul I. Slater, Forest Hills, N. Y.

Application September 4, 1952, Serial No. 307,773

14 Claims. (Cl. 22620.1)

The present invention relates to a method of sealing evacuated containers and particularly to such a method utilizing fusible material, having passageways therethrough, between the opposed walls of a container which is to be evacuated and sealed.

in this method a fusible material is provided with a passageway through which air or other gas is evacuated from the interior of the container and which passageway disappears when the fusible material is heated to seal the adjacent portions of the container together.

One example of a device in which this sealing method is advantageous is a mercury button switch which is a small container having mercury therein, which container is evacuated, filled with hydrogen and then sealed while the hydrogen is under pressure. Such a mercury button and a method of manufacturing it is disclosed in my prior application, Serial No. 237,101, filed July 17, 1951, now abandoned, of which this application is a continuation-in-part.

As explained in the above identified application, two methods of evacuating and filling a mercury button are currently in use, each of these methods involving the use of an exhaust tube.

In one method the exhaust tube is permanently fixed to the mercury button and the tube is sealed off after exhaustion and filling of the button.

In the second method the exhaust tube terminates in a flange which bears against a compressible washer or gasket which in turn bears against the area surrounding a small orifice in one of the end cups of the mercury switch. With the latter method a complex method of spot welding a metal plug or ball positioned through the exhaust tube is utilized.

In the new method of sealing the mercury button a low temperature solder is utilized to seal the metal cupshaped end members to a metalized rim on the ceramic and in addition a gasket is utilized to prevent mercury vapor from penetrating to the soldered areas. As an alternative, the solder ring may be dispensed with and a glass ring substituted therefor, the glass being provided with a passageway therethrough, the passageway permitting the exit of air and the entrance of a filling gas, and the passageway being closed when the glass ring is melted to fuse the glass to the metal cup member and to the glass or ceramic disk.

It is an object of my invention to provide a method of sealing an evacuated container in which fusible material, such as solder or glass, is held between opposing walls of the container, there being a passage or passages about or through fusible material through which the container may be evacuated and in some instances pressure-filled, the space being eliminated when the fusible material is heated to form a seal between the opposed wall portions.

It is another object of my invention to provide a method of assembling a container which eliminates the use of an exhaust tube or an exhaust orifice and which requires a much lower temperature for effecting the sealing operation than it is possible to employ when such tube exhaust means are used.

It is a further object of the invention to effect assembly, insertion of mercury, evacuation, gas filling and final sealing of mercury buttons and the like while utilizing simple machinery and in rapid sequence without interruption, thereby considerably lowering the cost of mercury button switches.

Other objects and features of the invention will be apparent when the following description is considered in connection with the annexed drawings in which,

Figure 1 is a vertical cross-sectional view of a mercury button in accordance with my invention in its assembled position prior to performing the evacuating, filling and sealing operations. The mercury button is shown in position in the apparatus for effecting the operations just above-mentioned;

Figure 2 is a cross-sectional view similar to that of Figure 1, but showing the button completely assembled subsequent to the mercury inserting, evacuating, filling and sealing operations, the button being complete and ready for removal from the apparatus;

Figure 3 is a plan view of the device of Figure 1 with one of the metal cups removed in order to illustrate certain features of the construction;

Figures 4, 5,v and 6 are fragmentary cross-sectional views of the mercury button of Figures 1 and 2 illustrating modifications of the mode of placing sealing gaskets or washers in the metal cups;

Figure 7 is a fragmentary cross-sectional View of the mercury button and apparatus shown in Figures 1 and 2 illustrating particularly an alternative mode of heating solder in order to effect the sealing operation;

Figure 8 is a fragmentary cross-sectional view, showing the use of a notched solder ring to form a seal between a metalized porcelain and a metal wall;

Figure 9 is a horizontal cross-section of the device of Fig. 8, the section being taken on the plane of line 99 of that figure;

Figure 10 is a fragmentary cross-sectional view showing a circumferentially grooved ring to be used in forming a seal between two metal walls, one of which is indicated as being a metalized ceramic;

Figure 11 is a horizontal cross sectional view of the device of Fig. 10, taken on the plane of the line 1111 of that figure;

Figure 12 is a fragmentary vertical cross sectional view illustrating the use of a glass ring which has undulations therein, as a sealing element between two opposed glass walls;

Figure 13 is a fragmentary cross sectional view showing the glass ring of Figure 12, the view being taken on the plane of line 13-13 of Figure 12;

Figure 14 is a fragmentary vertical cross-sectional view showing the use of a circumferentially grooved glass ring between a metal end cup and a glass insulating disk of a mercury button; and

Figure 15 is a horizontal cross-sectional View showing the relationship of such a curcumferentially grooved glass ring to the glass insulating disk.

In describing my invention the use of a solder ring having a gap therein to form a seal between the metalized ceramic disk of a mercury button switch and a metal cupshaped end wall of that switch will first be described.

Referring now to the drawings and particularly to Figure 1, the mercury switch of my invention comprises a ceramic disk 10 which has an aperture 11 extending therethrough, the aperture being eccentric to the axis of the disk. The disk 10 is also provided with an outwardly extending rim 12 and with two

flanged portions

13 and 14 concentric to the disk axis and forming

recesses

15 and 16, one on either side of the disk 10. The switch additionally comprises two

end members

17 and 18 which members are generally cup shaped and are provided with rim portions designated 26 and 21 respectively.

The ceramic disk 10 has metalized areas designated 22 and 23, one on either side of the rim 12 of disk 13, which metalized areas are soldered to the

rim portions

29 and 21 of the

cup members

17 and 18 during the assembly of the button,

Each

cup member

17 and 18 has a groove formed therein adjacent its outer periphery, these grooves being designated 24 and 25. Pressed into the

grooves

24 and 25 respectively are washers or

gaskets

26 and 27 which gaskets are preferably formed of a synthetic rubber such as neoprene or silicone and which, as will later be described, serve to prevent mercury from coming into contact with the solder seal and which likewise serve to prevent contamination resulting from melting of the solder during the sealing process.

As is indicated in Figures 4, and 6 the

flanges

13 and 14 of the ceramic disk may be omitted and the washers or

gaskets

26 and 27 may be modified to form a seal for the prevention of contamination. Thus in Figure 4- the gasket shown at 26' serves the same purpose as does the gasket 26 of Figures 1 and 2. In this form, however, it is unnecessary to form the ceramic disk with the

flanges

13 and 14 and instead the gasket 26 is of sufficient depth to extend to a position closely adjacent to the ceramic disk 10 leaving, however, a space between the gasket and the disk which is less than the space between the disk and the cup rimwhen a solder ring occupies the latter space prior to the final sealing of the device.

Similarly, Figure 5 shows an arrangement in which, by forming the groove 24' in place of the groove 24 of Figures 1 and 2, a relatively shallow gasket or washer 26" may be utilized, while at the same time omitting the flange 13 of the disk 10.

In Figure 6 is shown a method wherein the disk is provided with notches 29 which notches cooperate with a washer 26" to provide a compressed seal when the final soldering has occurred, the gap between the lower face of the gasket 26" and the mating portion of the notch 29 being smaller than the gap between the disk 10 and the rim 20 when the solder ring is in place prior to scaling.

As is clearly shown in the drawing, each cup-

shaped member

17 and 18 is provided with a generally hemispherical depression 31 or 32 which depressions receive trunnions on which the entire button is rotatable when assembled in a switch structure.

Such buttons are normally rotated through cooperation of projecting lugs on a handle with ceitain notches formed in the periphery of the ceramic disk 10 and in the adjacent peripheries of the metal cup members such as 17 and 18. In the past, a single notch only was formed as mentioned above, whereas in the present structure two pairs of notches are formed in each ceramic separator disk. One pair of notches is formed in the side surface of the flange 13 of the disk 10 and indicated in Figure 3 at 33 and 34. The other pair of notches is formed in corresponding positions in the side surface of the flange 14 of disk 10. Reference to Figure 3 will show that notches 33 and 34 are so located with respect to aperture 11 that when the button is mounted in operating position in the switch and the handle caused to cooperate with notch 34, rotation of the switch in a clockwise direction will cause a break of the circuit therethrough, whereas if the button is rotated about an axis through its plane so that the notch 33 occupies the position normally occupied by the notch 34, like rotation of the button in a clockwise direction will cause a making of the circuit. Thus, if two buttons are simultaneously operated by a single handle, the projections of which fit notch 34 of one button and notch 33 of the second button, a three way switch will be formed.

The parts thus far described are assembled in the manner illustrated in Figure 1 being placcd upon a supporting block of Micalex, Transite or the like, designated 23, and positioned by means of the central boss 35 of that block. After placing the lower cup member 13. with gasket 27 in place, upon block 28, mercury desig nated 30 is placed in that cup as shown in Figure l, the amount of mercury being sufficient to properly complete the circuit through the aperture 11 of the ceramic separator disk 18, when the switch is mounted with its axis a horizontal position and the switch positioned so that the aperture 11 is nearly at the bottom. Surrounding the cup 18 is a cylindrical member 36 on the upper edge of which the rim 21 rests. This cylindrical member 36, as will later appear, serves as a heating element to melt certain solder and produce a proper solder joint.

Next, a ring of solder 58 is placed in position on the rim 21 of the cup 18, this ring 58 having a small gap 60 therein as clearly shown in Figure 3. The ceramic separator disk 10 is next positioned as shown in Figure l with the metalized rim portion 23 thereof resting on the solder ring 58 which spaces the outer edge of the flange 14 from the metal cup member 18 as clearly shown in the drawing. The cross-sectional diameter of the solder ring 58 is also sufficiently great so that the space between the rim 21 of cup member 18 and the metalized portion 23 of ceramic disk 10 is greater than the space between the upper surface of gasket or washer 27 and the facing surface of flange 14.

The assembly is completed by placing solder ring 61 and upper cup 17 with its gasket 26 in place in the positions shown which correspond exactly, but in reverse, to the positioning of the ring 58 and lower cup 18.

After the parts have been assembled on the block in the manner illustrated in Figure l and described above, a bell jar 37 is placed over the assembled parts with its lower rim resting on a rubber gasket 33. Bell jar 37 is clamped in position against the gasket 33 by means of an arm 40 pivotally mounted on an upstanding support 41 fixed to table 42 on which the block 23 and gasket 38 rest. A suitable latch member 43 is provided for the arm 49, this latch member being spring pressed by means of spring 44 into position where the edge thereof overlies the edge of arm 40 as is clearly shown in Figures 1 and 2, the latch 43 and spring 44 being supported upon a suitable support 45.

Arm 40 carries a rubber block 46 which bears against the uppermost portion of the bell jar 37 to clamp that bell jar in the position heretofore indicated. Suitably fixed to the interior of the bell jar 37 is a spring 47 which extends downwardly and to the lower end of which a disk of Micalex or Transite 48 is fastened. Disk 48 has an annular shoulder 50 into which fits the upper edge of a metal, carbon, or other cylinder 51 capable of being heated, this cylinder being fastened to disk 48 in any suitable manner as for example by means of pins 52.

Extending through the block 28 and into a communication with the interior of the bell jar 37 is a pipe 53 which pipe may be interconnected by means of a valve 54 with a pipe 55 connected to a vacuum pump, not shown, or to a pipe 56 connected to a source of suitable gas under pressure. The gas utilized should be of high specific heat, such for example as hydrogen or helium.

Surrounding the cylindrical portion of the bell jar 3'7 lying above the block 28, is a high-frequency induction coil 57 which coil is suitably connected to a source of high frequency alternating current.

With the parts thus positioned and with the bell jar in position and clamped down as has been above de scribed, and with spring 47 pressing the parts together, the valve 54 is operated to evacuate the interior of the hell jar. Due to the fact that there is a passageway between

flanges

13 and 14 and the

gaskets

26 and 27 respectively, and through the gaps 60 of the solder rings 53 and the corresponding gap in the solder ring 61 air is evacuated from the interior of the assembled parts of the mercury button.

When evacuation is complete, valve 54 is operated to connect pipe 53 with pipe 56 thereby admitting gas under pressure to the interior of the bell jar. This gas flows through the passageways just above mentioned and fills the interior of the mercury button assembly as well as the interior of the bell jar.

While the pressure is retained a switch is closed and current permitted to flow in the high frequency induction heating coil 57. As a result of this the

cylinders

36 and 51 are heated, the heat being transferred from these cylinders to the

rims

20 and 21 of the

cups

17 and 18. It is to be noted that although the

cups

17 and 18 are metallic, they are relatively cool due to the shielding effect of the

steel cylinders

36 and 51, thereby reducing heating of the mercury in cup 18. It has been found in practice that the solder melts so quickly that escape of mercury vapor is prevented. It is of course possible to heat

cylinders

36 and 51 in any other manner save that a direct flame cannot be utilized.

With the arrangement described, the heat is concentrated on the

rims

20 and 21 of the

cups

17 and 18 and is effective to melt the solder and form a solder joint between the rims of the cups and the metalized

areas

22 and 23 of the rim 12 of ceramic separator disk 10. The melting of the

rings

58 and 61 serves to form a complete solder joint, the gaps such as 60 in the solder rings 58 and 61 disappearing as the joint is made. It

should also be noted that before the solder joints are complete the

gaskets

26 and 27 are compressed against the outer surface of the

flanges

13 and 14 of disk 10, due to pressure of spring 47, thereby assuring that no mercury can pass outwardly into contact with the solder rings 58 and 61, either during the soldering operation or thereafter during the life of the switch. Additionally, no vaporized products of the soldering operation can enter into the interior of the mercury button to contaminate the gas filling thereof.

Figure 2 shows the position of the parts after the solder has softened and spring 47 has caused the washers to be compressed. When the current has been turned off and the solder has hardened the completed device may be removed from bell jar 37, it being understood that valve 54 is at this time in closed position.

Referring now to Figure 7, I have shown therein an alternative method of heating the solder rings 58 and 61 in order to form the solder joint between the metalized

portions

22 and 23 of the ceramic disk and the rims and 21 of the metal cups. In this form the induction heating coil 57 and the cooperating

cylinders

36 and 51 are omitted and the Transite or Micalex disk 48 bears directly against the upper metallic cup 17. In place of the inductive heating I supply two turns of high resistance heating wire which surround the mercury button and are slightly spaced therefrom being placed adjacent to the solder rings 58 and 61 in the manner clearly shown in Figure 7. When the bell jar has been evacuated and filled with gas in the manner described above in connection with Figures 1 and 2, an electrical circuit is completed to the two turns of Wire designated 62 and 63, the circuit extending through the lead 65 and a second lead (not shown).

The turns of

wires

62 and 63 become heated and the heat radiated therefrom both directly to the solder rings 58 and 61 and by radiation to the

rims

20 and 21 and conduction from these rims to the solder rings melts the solder and forms the joint in the same manner as described for the inductive beating.

Whichever method of heating and melting the solder is employed, it will be seen that the general method employed effects a continuous uninterrupted operation during which the mercury button is evacuated, gas filled and sealed, while preventing contamination of the in terior atmosphere of the button arising from the soldering operation and likewise preventing mercury from com- Lil ing into contact with and dissolving the soldered joint during switch operation.

The method described produces mercury buttons much more rapidly, efliciently and economically than any method heretofore in use, such for example, as methods employing exhaust tubes or exhaust tubes in combination with orifices. As will be readily understood, the method provides for the use of any desirable pressure of the filling gas in the mercury button limited only by the mechanical strength of the parts of that button.

In the foregoing description the disk 10 has been described as being of a ceramic material. It is to be understood, however, that glass or other suitable insulating material may be substituted for the ceramic.

Also in the foregoing description, the sealing of a mercury button has been described, the sealing being affected through the use of a particular fusible material, namely solder. However, as has been indicated above, the method of sealing with a fusible material is of general use and furthermore the use of a particular fusible material is not necessary since other materials, for example, glass, may be substituted for the solder.

In connection with the sealing of the mercury button the solder was described as being a ring of circular crosssection having a gap therein through which gas could be removed from, and if desirable, another gas substituted within the container prior to the sealing operation. Not only may the ring he of material other than solder but the particular shape of the ring may be varied.

In Figure 8 there is shown a fragmentary view of a portion of a mercury button or other container indicating the use of a complete ring 70, which ring is notched along its top and bottom surfaces, as indicated at 71 in Figures 8 and 9. The ring may obviously be of any fusible material, for example, solder is adapted to form a completely metallic seal between the

opposed container walls

20 and 22, and glass adapted to form a glass-to-metal seal.

Another method of forming a seal in accordance with my invention is illustrated in Figures 10 and 11. In this form the

container walls

20 and 22 are formed with the depressions indicated at 72 and 73 and the lower depression 73 has granules of the fusible material placed therein as indicated at '74. Here again the fusible material may be either glass, solder or other material which will melt and form a seal with the container walls at a relatively low temperature.

If the walls are of metal, it is preferable to utilize solder although glass may be utilized to form a glass layer between two metal walls.

Figures 12 and 13 show a further modification of the invention in which the fusible material is in the form of a complete ring having undulations therein. This provides a plurality of pasageways through which gas may enter into and exit from the interior of the container and serve the same purpose as do the various forms heretofore described. The undulating ring is indicated in Figures l2 and 13 at 75 cooperating with plane flanges of the

container walls

20 and 22. In this particular instance the container walls are shown as being of glass but it is to be understood that they might also be of metal and that the undulating washer may be of solder or of glass.

In Figures 14 and 15 there is shown a still further modification of the invention wherein the ring of fusible material 76 is provided with circumferential grooves 77 which serve the same purpose as do the other forms of passageways which have been described.

It will be understood that further modifications of the invention may be made. For example, a spiral groove may be substituted for the circumferential grooves 77, or instead of having notches, such as shown in Figures 8 and 9, or undulations such as shown at Figures 12 and 13, small bores may be made in a ring such as 61, to provide passageways to and from the interior of the container.

It will be further understood that the final sealing operation need not occur along a circumferential area, but may occur along a line or at a restricted area and therefore it is only necessary that the fusible material be sutficiently rigid so that pressure may be applied thereto during the evacuating and filling operations and that the fusible material occupy less area than do the opposed Walls and the material when fused serves to seal the opposed walls together and eliminate the passage through which the container was evacuated or evacuated and filled.

While I have described preferred embodiments of my invention, it is to be understood that other various modifications may be made within the scope thereof. I wish, consequently, to be limited not by the foregoing description which was given solely for the purposes of illustration, but rather to be limited only by the claims granted to me.

What is claimed is:

l. The method of evacuating and sealing a container which comprises providing an opening in said container, said opening having substantially parallel opposed walls, placing fusible material between the opposed Walls of said opening and pressing against said opposed walls to hold said fusible material in place, providing passageways in said fusible material leading into said container, placing said container in a confined space, exerting pressure against the opposed walls, evacuating said confined space, thereby evacuating said container through the passageways about said fusible material and heating the area of said container adjacent the said opposed walls of said opening to thereby melt said fusible material permitting the opposed walls to approach each other due to the pressure thereon and fuse the fusible material to said opposed wall openings to seal the container.

-2. The method of evacuating and sealing a container which comprises providing an opening in said container, said opening having substantially parallel opposed walls, placing a rigid body of fusible material between the opposed walls of said opening and pressing against said opposed walls to hold said fusible material in place, providing passageways in said fusible material leading into said container, placing said container in a confined space while exerting pressure against the opposed walls, evacuating said confined space, thereby evacuating said container through the passageways in said fusible material and heating the area of said container adjacent the said opposed walls of said opening to thereby melt said fusible material and fuse it to said opposed wall openings to seal the container.

3. The method of evacuating and sealing a metal container which comprises providing an opening in said container, said opening having substantially parallel opposed walls, placing solder between the opposed walls of said opening and pressing against said opposed walls to hold said solder in place, providing passageways in said solder leading into said container, placing said container in a confined space while exerting pressure against the opposed walls, evacuating said confined space, thereby evacuating said container through the passageways in said solder and heating the area of said container adjacent the said op posed walls of said opening to thereby melt said solder and fuse it to said opposed wall openings.

4, The method of evacuating and sealing a metal container which comprises providing an opening in said container, said opening having substantially parallel opposed walls, placing a rigid body of solder between the opposed walls of said opening and pressing against said opposed walls to hold said solder in place, providing passageways in said solder leading into said container, placing said container in a confined space while exerting pressure against the opposed walls, evacuating said confined space, thereby evacuating said container through the passageways in said solder and heating the area of said container adjacent the said opposed walls of said opening to thereby melt said solder and fuse it to said opposed wall openings.

5. The method of evacuating and sealing a glass container which comprises providing an opening in said container, said opening having substantially parallel opposed walls, placing glass between the opposed walls of said opening and pressing against said opposed walls to hold said glass in place, providing passageways in said glass leading into said container, placing said container in a confined space while exerting pressure against the op posed walls, evacuating said confined space, thereby evacuating said container through the passageways about said glass and heating the area of said container adjacent the said opposed walls of said opening to thereby melt said glass and fuse it to said opposed wall openings.

6. The method of evacuating and sealing a glass container which comprises providing an opening in said container, said opening having substantially parallel opposed walls, placing a rigid body of glass between the opposed walls of said opening and pressing against said opposed walls to hold said glass in place, providing passageways in said glass leading into said container, placing said container in a confined space while exerting pressure against th opposed walls, evacuating said confined space, thereby evacuating said container through the passageways about said glass and heating the area of said container adjacent the said opposed walls of said opening to thereby melt said glass and fuse it to said opposed wall openings.

7. The method of evacuating and sealing a glass container which comprises providing an opening in said container, said opening having substantially parallel opposed walls, at least one of said opposed walls having a depressed area therein, placing granules of a fusible material between the depressed portion of said one wall and the wall portion opposed thereto said granules holding said walls spaced apart, pressing against said opposed wall portions to hold said granules of fusible material in place while providing passages about said granules leading into said container, placing said container in a confined space while exerting pressure against the opposed wall portions, evacuating said confined space, thereby evacuating said container through the passageways separating said granules, and heating the said fusible material to permit said opposed walls to move together and to thereby use said fusible material to the opposed wall portions and seal the container.

8. The method of evacuating, filling and sealing a metal container which comprises providing an opening in said container, said opening having substantially parallel opposing walls, placing said container in a confined space while exerting pressure against the opposed walls of said opening, placing a piece of solder having a length less than that of the opposed opening walls between said opposed walls to resist said pressure, evacuating and filling said confined space thereby evacuating and filling said container through the passageways left at the ends of said piece of solder and indirectly heating at least the area of said container adjacent the said opposed opening walls to thereby melt said solder permitting said opposed walls to approach each other and fusing said solder to the walls to seal said container.

9. The method of producing a mercury switch of the class described, which comprises, assembling a ceramic disk having a metalized annular rim portion with a metallic cup-shaped member, placing a ring of solder between said metalized portion of said rim and an annular portion of said cup-shaped member, said solder ring being incomplete leaving a small gap therein, placing the as sembly in a confined space, evacuating the space to thereby evacuate the interior of the assembly through said solder gap, filling said space with gas under pressure and thereby filling the interior of the assembly with gas under pressure through said gap, and heating the annular portion of said metal cup to thereby form a solder joint between the metalized portion of said disk rim and said metal cup to seal the device.

10. A mehtod as claimed in claim 9, characterized by the compressing of an annular washer between said metal cup and a portion of said ceramic disk as said solder ring melts to form a soldered joist, said compressed washer preventing contact of mercury with the soldered joint and also preventing contamination of said gas filling.

11. A method as claimed in claim 9, characterized in that said assembly is placed in said confined space with a cylinder extending around said cup-shaped member, said cylinder being in contact with the flange of said member, said cylinder being electrically heated and serving to thereby heat said flange and said solder ring.

12. The method of producing a mercury switch of the class described, which comprises assembling a ceramic disk having a rim portion metalized on both sides thereof with two flanged metallic cup-shaped members, one on either side of said disk, placing a ring of solder between each metalized portion or" said rim and the flange of the corresponding cup-shaped member, said solder rings being incomplete leaving a small gap in each ring,

placing the assembly in a confined space with the parts a pressed together, evacuating said space to thereby evacuate the interior of the assembly through said gaps in said solder rings, filling said confined space with gas under pressure thereby filling the interior of the assembly with gas under pressure through said gaps in said solder rings and indirectly heating said metal cups to thereby form a solder joint between the metalized portions of said disk rim and metal cups to thereby seal the device.

13. A method as claimed in claim 12, characterized in that said assembly is placed in said confined space with cylinders are electrically heated by an induction coil located outside said confined space to thereby heat said flanges and solder rings to eficct sealing.

14. The method of producing a mercury switch of the class described, which comprises assembling a ceramic disk having a rim portion metalized on both sides thereof with two flanged metallic cup-shaped members, one on either side of said disk, placing a ring of solder between each metalized portion of said rim and the flange of the corresponding cup-shaped member, said solder rings being incomplete leaving a small gap in each ring, placing the assembly in a confined space with the parts mechanically pressed together, evacuating said space to thereby evacuate the interior of the assembly through said gaps in said solder rings, filling said confined space with gas under pressure thereby filling the interior of the assembly with gas under pressure through said gaps in said solder rings and indirectly heating said metal cups to thereby form a solder joint between the metalized portions of said disk rim and said metal cups to thereby seal the device.

References Cited in the file of this patent UNITED STATES PATENTS 994,010 Langmuir May 30, 1911 2,125,316 Ronci Aug. 2, 1938 2,177,498 Payne Oct. 24, 1939 2,223,031 Edwards Nov. 26, 1940 2,262,176 Geiger et al Nov. 11, 1941 2,326,296 Harrison et al Aug. 10, 1943 2,401,638 Herzog et a1. June 4, 1946 2,426,990 Ellfson Sept. 9, 1947