US2297924A - Mercury switch - Google Patents

Description

Oct 6. 1942- C; w. rRAuTMAN :TAL

MERCURY SWITCH Filed May 8, 1940V s sheets-sheet 2 l?? Q/Lww 0d 6, ,19.4% c. w. TRAUTMAN .E-rm. 2,297,924

MERCURY SWITCH Filed May 8, 1940 5 Sheets-Sheet 3 Patented 0ct. 6, 1942 MERCURY SWITCH Charles W.' Trautman,

E. Schirmer, Buchan Bncklen-Bear Laborat a corporation of Indiana Elkhart, Ind., and Walter an, Mich., assignors to cries, Inc., Elkhart, Ind.,

Application May 8, 1940, Serial No. 333,922V

9 Claims.

This invention relates to mercury switches, and more particularly is directed to a metal envelope switch of the type in which two metal envelopes are arranged in telescoping relation and suitably insulated and sealed to define a switch chamber having an insulating barrier betweenA the interiors of the two envelopes over which bodies of mercury contained in each of the envelopes are adapted to make and break circuit through'the switch.

One of the primary objects of the present invention is'to provide a switch construction of the typein which one metal envelope has a portion thereof radially larger than the other envelope intorwhich the open end of the second envelope isv adapted to project, with suitable means for clamping the two envelopes in telescoping relation and' sealing and insulating them from each other in position to define a sealed switch chamber composed of the two envelopes and an insulating barrier therebetween.

Still another object of the present invention isv to provide a construction in which two ceramic or refractory molded inserts are provided between which is clamped the flanged end of one of the metal envelopes. Preferably, suitable resilient sealing means are provided which are adapted to be compressed into sealing engagement between the two-envelopes during assembly to prevent leakage of gas or the like into or out of the envelope.

Still another feature of the present invention is the provision ofv a structure in which separate gaskets are provided for sealing one of the envelopes with respect to the refractory inserts' and for sealing the refractory inserts with respect to the other envelope. By the use of such sealing means, a cushioned action is provided in the assembly of the switch preventing any damage-to the ceramics and at the same time insuring positive sealing of all possible leakage paths between the component parts of the switch.

Still another feature of the present invention is the provision of an insulator or insert of* this type which has glazed surfaces to eliminate the passage ci' gas therethrough, thereby reducing the amount of sealing required so that the only seals necessary are those between the inserts and the respective envelopes, no seal being required between the two inserts themselves.

A still further feature of the present invention is the elimination from the sealing means of the function of centering or supporting the inner envelope in position, whereby this function is accomplished entirely by the inserts, thus relievingV the sealing meansfof any of the stresses incident to such a function.

A stilly further object secured by the present inventionfis the provision of a structure in which one body of mercury is retained in contact with onefof the envelopes and merely moves relative to the face of such envelope, while the other body of mercury is movable across the insulating barrier into and out of contact with the first body of mercury. Preferably, the two bodies of mercury are'of substantially equivalent volume and the design is such that both have relative movement with respect to the point of making and breaking of circuit through the switch so that the rate of such making and breaking 'is the sum of the rates of movement of the two bodies.

Another important feature of the present invention is the provision of a switch structure in which; in place of a resilient seal such as rubber or4 the like for insuring sealing of all leakage paths from the interior of the switch chamber to atmosphere, a plastic or similar insulating material is poured in liquid form into a sealing recess, and when cooled, sets in position as a semi-elastic non-current carrying sealing means. The plastic is of such a type that it expands slightly-upon setting, thereby insuring a positive seal in the structure, or, if desired, the plastic in liquid form.may be maintained under pressure so that when it sets, it will retain this pressure against the` surfaces to be sealed.

The plastic may be introduced through tubulation` into the sealing recess, or may be merely poured into a, form which defines the sealing recess after the switch parts have been assembled.

Another-advantage secured by the present invention is that the two mercury bodies are in contact with exposed metal envelopes, whereby radiation and dissipation of heat is provided, producing cool operation and therefore increasing the current carrying capacity.

Other objects and advantages of the present invention will be more apparent from the following detailedk description, which, taken in conjunction with the accompanying drawings, will disclose to those skilled in the art the particular construction and operation of a preferred form of the present invention.

In the drawings:

Figure 1 is a sectional view through one form of switch embodying the present invention ;v

Figure 2 is a corresponding View showing a slightly modified electrode construction;

Figure 3 is a view showing a telescoping arrangement for the inserts which separate the two electrodes and. which insures positive pressure contact upon each of the separated sealing means;

Figure 4 is a construction embodying the same principle as that shown in Figure 3 but employing a modified type of envelope structure;

Figure is a view corresponding to Figure 4 with a further modification of one of the electrodes;

Figure 6 is a View corresponding to Figure 4 showing a different arrangement of the sealing means;

Figure 7 illustrates a switch structure employing a liquid setting cement or plastic as a sealing means;

Figure 8 illustrates a switch similar to Figure 7 with a modif-led type of sealing recess; and

Figure 9 is a sectional view of a two-envelope switch construction of simplified design.

Referring now in detail to the drawings, in Figure 1 I have illustrated a main switch envelope 5 which is of generally cup-shaped form having a slightly frusto-conical switch joining the main body portion to the enlarged cylindrical end portion 1. Disposed within the envelope 5 is a ceramic insulator or insert 8 which may be of any desired refractory having arc resisting characteristics, which is seated against the internal shoul-.

der 6 and has an axially extending bore 9 extending for an appreciable distance toward the closed end of the envelope 5. At its outer end the insert 3 is provided with the annular recess ID in which is centered the flanged end l2 of a second envelope or electrode I3, also of cup-shaped form which telescopes into the open end of the envelope 5 and is centered in the recess I0 of the insert 8, Extending about the cylindrical portion of the envelope I3 is a second insulating compression member or insulator I4 which, in the present form of the invention, is provided with a reduced cylindrically extending portion I5 serving as an insulating barrier between the spunover end I6 of the envelope 5 and the lateral surface of the envelope I3. A suitable annular metallic retaining ring I1 may be provided between the spun-over iiange I6 and the shouldered portion of the ceramic I5 to prevent possible cracking or chipping of the corners of the ceramic.

Intermediate the inserts 8 and M and closely embracing the annular surface of the envelope I3 is a resilient sealing gasket I8 which is preferably formed of rubber or the like, and which has a short tapered peripheral ange I9 adapted to radially overlap the insert 8. In the assembly of the structure thus far disclosed, the insert 8 is rst positioned within the envelope 5, and the anged end I2 of the envelope I3 is then centered within this insert. The gasket I8 is then forced over the envelope I3 against the outer face of the ange I2 and about the tapered end of the insert 8. The compression member is then placed in position and suitable axial pressure applied thereto to axially compress the sealing gasket I8, expanding the same into positive sealing engagement between the electrode envelope 5 and the envelope I3, The end I6 of the envelope 5 is then spun over to lock the compression member in position and maintain the gasket I8 under pressure. The end face 2@ of the envelope 5 is provided with a short tubulation 22, and in the desired form of the invention this tubulation is employed to first introduce mercury comprising the mercury bodies 23 and 24 into the envelope or switch chamber, and is then used to evacuate the chamber for drawing from all cracks or crevices therein any occluded gases or the like. The tubulation is then connected to a source of hydrogen under pressure which is forced into the envelope under a pressure substantially above atmospheric, after which the tubulation is pinched and welded as indicated at to seal the interior of the switch.

In the operation of the switch shown in Figure 1, tilting of the switch in a counter-clockwise direction results in the body of mercury 23 which lays in the annular groove 26 formed about the projecting portion of the bore 9 rising up over the internal face of the end 2D of envelope 5 to protect this face from the body of mercury 24, which is moving through the bore 9. As a result, when Contact is made, it is effected between the bodies of mercury 23 and 23 approximately at the inner end of the bore at the point indicated at 2l, which is at a point remote from the envelope 5 so as to prevent any possibility of arcing or transfer of heat thereto. Similarly, when the switch is tilted in the opposite direction, both bodies of mercury 23 and 2d tend to run at the same time, the body of mercury 23 tending to run back into the annular recess 25, while the body of mercury 211i tends to run outwardly through the bore 9. As a result, the circuit is broken over the edge 2l, thereby insuring that any arcs produced in the switch will be produced adjacent this point. In order to insure this, the bore 9 is very slightly tapered with its small end disposed tovvard the electrode face so as to insure that the breaking point will occur at the edge 21.

Considering now the switch structure shown in Figure 2, similar reference numerals have been applied to similar parts. In this form of the invention, the envelope 5 is of uniform diameter and is of a slightly greater axial length than the envelope 5 of Figure l. The insert 8 disclosed therein is of the same general form as the insulator 3 with the exception that it is not provided. with the beveled shoulder for engaging the bevel 3, as described in connection with Figure 1, but instead has abutting engagement with the sleeve secured within the envelope 5 as by welding or the like. The sleeve 3i) forms the outer defining surface of the annular recess 26 in which is retained the body of mercury 23. However, in this form of the invention, to insure that there will be no metal to mercury contact within the switch, the base portion of the cupshaped sleeve 3Q is apertured, as indicated at 32, to receive the projecting portion 33 of an insulating disc 33, which may be formed of a ceramic or similar material which is thereby located between the base 23 of the envelope 5 and the sleeve in such manner that there will be no metal in direct alinement with the bore 9 through the insert 8', which bore is tapered in a manner corresponding to that described in connection with Figure 1. In this form of the invention, the tubulation is disposed at the closed end of the envelope I3, as indicated at 35, instead of being located in the envelope 5'. This is due to the fact that the insulator 35.1 precludes the arrangement shown in Figure l. The switch is assembled, filled with mercury, evacuated and lled with hydrogen in the same manner as described in connection with Figure 1, and the same tilting action operates the switch in the same manner as described in Figure l. Due to the fact that the volume of mercury 23 is in contact over an appreciable area of the sleeve 33, it is apparent that the internal resistance of the switch is thereby materially reduced and, as a result, such a switch is capable of handling relatively large currents. By use of the insulating center 33 in the sleeve 30, it is obvious that it will be impossible to produce a metal to mercury Contact in a switch of this design, which therefore eliminates any possibility of pitting or corroding the metal due to arcing between the metal and the mercury.

In the embodiment shown in Figure 3, a cupshaped metal envelope 43 is provided having the enlarged open end 42 in which is. disposed the insulator 43 seated against the frusto-conical shoulder 44 formed in the envelope. The insulator 43 is provided with a tapered axial bore 45 opening at its larger end into the1 closed end of the envelope 45 and having the annular space 46 extending thereabout within the small cylindrical portion of the envelope. At its opposite end the bore 45 opens into an annular recess 41 which is closed at the outer end by means of the electrode dis-c 48 having the projecting shank 49. The cylindrical flange portion of the insulator 43 defining the recesg 41 an external diameter less than the internal diameter of the enlarged portion 42 of the envelope, thereby providing an annular recess which is adapted to receive the ring-like resilient sealing gasket 59. A suitable compression member 52 preferably formed of a refractory insulator or the like is inserted into the open end of the envelope, and is provided with a counter-bored portion receiving the electrode disc 46. The denning flange portion 53 of the compression member 52 has telescoping engagement about the ange 54 of the insulator 43, and upon axial inward movement, provides for axial compression of the gasket 5i) to provide iirm sealing engagement between the' gasket and the insulator. Disposed in the base of the recess formed by the flange 53 of the compression member 52 is a disc-like resilient gasket 55 which is adapted to be compressedY by abutment of the electrode disc 48 against the radial face of the flange 54. Upon axial compression of the assembly thus far described, it will be apparent that both of the gaskets 5i) and 55 are compressed into sealing engagement as the two flanges 53 and 54 move in telescoping relationship. A suitable metallic retaining ring 55 is provided upon which pressure is applied to move the member 52 axially inwardly, and while the envelope is retained in this position, the end 5'? of the envelope is spun over to lock the parts in sealed engagement.

A suitable body of mercury 58 is adapted to be retained in the bottom of the annular recess im 41 in contact with the face of the electrode 48, and a second body of mercury 59 is disposed in the main body portion of the envelope 4i?, and upon tilting of the switch, is movable through the bore 45 into engagement with the body of mercury 58 which, at the same time moves across the central portion of the face of the electrode disc 48. By reason of such a constructionA a posh tive mercury to mercury contact is provided.

The undercut 45 and bore 45 cooperate to control the angle of operation of the switch, and can be designed to provide any desired angle. By providing the undercut 45, the mercury 'builds up in this space upon tilting, and thus the angle of tilting is increased.

Inasmuch as certain types of refractory inserts are porous in character and will allow slow dissipation of gas therethrough we preferably provide for glazing certain faces of the insulator 43 and the compression member 52 to render the f same impervious to the passage of gas therethrough. These surfaces are indicated at 50 and may be glazed in any suitable manner to facilitate both the sliding enga-gement and also to insure that there will be no leakage path between the flange 54 and 53 where they lie in overlapping relation. Thus a positive seal is provided by this structure.

Considering now the form of the invention shown in Figure 4, a rst envelope or electrode B2 is provided having the enlarged portion 63 within which is disposed the insulator 64, this insulator seating against the frusto-conical shoulder 65. The insulator 64 is provided with a frusto-conical axial throat or passageway 56 extending therethrough and opening at the small end of the bore into the annular recess 61 formed about the projecting lip defining the small end of the insert, with the small end of the bore being spaced an appreciable distance away from the end face 68 of the envelope 62. A suitable body of mercury 69 is retained in the recess and is of suiiicient volume to rise radially to the small end of the bore, thereby overlying a portion of the face 68 of the envelope.

Also seated in the enlarged end 53 of the envelope is a ceramic compression member 1S which has a main body portion 12 bored to receive the second metallic envelope or electrode 13 and provided with a radially offset cylindrical flange portion 14 which is adapted to have telescoping engagement over the iianged end 15 of the envelope 13 and over the shoulder 16 formed on the outer end of the insulator 64 against which the flange 15 abuts. Two separate gaskets preferably formed of resilient insulating material, such as rubber or the like, are provided for sealing the interior of the envelope against leakage. One such gasket, indicated at 11, is disposed radially about the shoulder 1S of the insulator 64 and is adapted to be compressed by the inner radial face of the ange 14 of the compression member 12. The other gasket 18 of similar composition is compressed by the radial portion of the compression member 18 disposed radially within and axially offset from the face of the flange 14. This compresses the gasket 18 up against the outer face of the ilange 15 of the envelope, thereby providing a positive and effective seal between the envelope and the compression member. Similarly, the gasket 11 provides an effective seal between the envelope 62 and the insulator, and by suitably glazing the adjacent surfaces of the insulator 64 and compression member 1l) a positive leak-proof switch construction is provided. The envelope 13 is adapted to carry a movable body of mercury 1B which, upon tilting of the switch, moves upwardly along the frusto-conical throat 61 and into contact with the body of mercury 69 which, at this time, has moved out of the recess 61 to a point where it over-lies that portion of the end face 68 of the envelope 52 which is in alinement with the bore 55. Thus, a positive mercury'to mercury contact is provided.

The tilting of the switch in the opposite direction results in both bodies of mercury moving away from the acute angle at the small end of the throat 66 resulting in a rapid breaking of the circuit over this angle at a rate substantially equal to the sum of the rates of movement of the two bodies of mercury.

In the form of the invention shown in Figure' 5, similar parts have been designated by similar reference numerals.

The insulator 8G* in this form of the invention is provided with the short tapered axial bore B2 opening into the annular recess or switch chamber 83 disposed between the end face 98 of the envelope 62 and the inner radial face of the insulator 80. The insulator is provided with a cylindrical peripheral flange portion 84 extending into the cylindrical portion 63 of the envelope 62 and adapted to receive therein the forwardly extending flange portion 85 of a compression member B6, which compression member is bored out to receive the second metallic envelope or electrode 8l. The envelope 8l is provided with a flanged open end having the radial flange 88 bearing against the face of the insulator 80 within the flange 84. The compression member IBS is recessed, as indicated at 89, adjacent the flange 8B, and a suitable gasket 9|) is interposed therein and is adapted to seal the external surface of the envelope 81 with respect to the compression member 86. Similarly, a gasket 92 of resilient material is interposed between the end of the flange 84 and about the projecting portion 35 of the compression member 86, and is adapted to be compressed therebetween for sealing the compression member 86 with respect to the envelope 62. These two gaskets are compressed by axial inward pressure upon the member 89, this member being held in compressed position by spinning over the end 93 of the envelope 62. Preferably, the facing surfaces of the insulator 99 and compression member 8S are glazed, as described in connection with Figures 3 and 4, to prevent any possibility of gas under pressure, which. may be introduced in the switch envelope from leaking out through the pores of the ceramics. It will be obvious with this construction that the volume of the body of mercury 94 retained in the envelope 62 is substantially equal to the volume of mercury 95`carried in the envelope 81. Both of these bodies are of sufficient size so that a substantial area of contact is provided between each of the bodies and their associated metal envelopes whereby upon making of current between the two mercury bodies, relatively low internal resistance is introduced into the switch.

The telescoping action of the compression member 86 into the insulator 86 serves not only to center the insulator in position but also provides for uniform unit pressure against both of the independent sealing means, thereby insuring positive sealing engagement at all points within the switch.

The for-m shown in Figure 6 is similar to that shown in Figure 4 except that a different type of compression member and sealing means is provided. The envelope 13 in this form of the invention has its flanged end t abutted against the insulator 64 about the opening of the frustoconical throat 66. Disposed about the envelope 13' and recessed to receive the flange l5 is la compression member 9S having a radially enlarged abutting face portion 91 which engages against the planar radial face of the insulator about the flange l5 to hold the insulator in seating engagement against the shoulder on envelope 62. The compression member 96 is provided with a semi-cylindrical recess adapted to receive the resilent gasket 98, whereby when the envelope i3 is pushed through the bore of the compression member, the gasket 93 provides a positive seal about the lateral surface of the envelope.. Disposed about the reduced portion of the compression member 96 is a sealing gasket 99 which is compredsed through the retaining ring lill) and the spun-over edge 93 of the envelope into sealing engagement between the external surface of the compression member and the internal surface of the portion 63 of the envelope. As a result, the envelopes are both positively sealed through the gasket means 98 andl 99, and preferably the two abutting faces of the insulator and the compression member are glazed to prevent leakage of gas therebetween. The switch is adapted to operate in the same manner as described in connection with Figure 4.

Referring now to the modification of the invention shown in Figure '7, this -comprises a switch envelope 5' corresponding to that shown in Figure 2, which envelope has seated adjacent its closed end the sleeve 39 yprovided with the aperture 32 receiving the projecting portion of the insulator disc 34. The insulator corresponds to the insulator 8 in that it is -centered within the envelope and held against axial movement by abutment against the forward end of the sleeve 30. The insulator is provided with the bore |06 opening into the second envelope |91 having the flange |98 centered in a facing recess in the insulator |95. Disposed adjacent the end of the envelope 5' is a refractory insert |99 which forms an insulating rbarrier between the envelope |91 and the spun-over edge HIJ of the envelope 5. Disposed against the inner face of the compression member |09 is a gasket member H2 which may be of Bakelite, or any other similar material having some degree of elasticity. This leaves an annular gap or chamber I |3 between the forward radial face of the insulator |95 and the inner face of the gasket H2. A suitable tubulation H-'l is adapted to extend through the envelope at this point to communicate with the chamber H3. Through this tubulation a liquid plastic of the self-setting type is forced under heat and pressure so that as it cools and dries, it sets within the chamber H3, as indicated at H5, to provide a semi-elastic non-current carrying sealing means. The liquid is introduced under pressure so that when cooled and set it expands slightly rather than contracts. To key the insulator |95 in position, a portion of the peripheral edge thereof is chamfered, as indicated at l I6, to allow keying engagement therewith of the plastic sealing material. This material which is used as a seal in the chamber H3 may be of the type commercially known as Durez, or may be any other liquid plastic material having insulating and sealing characteristics .which does not contract when set. After the liquid has been introduced, the tubulation may be closed in any suitable manner and the switch is then ready for operation, it being understood that previous to this time or during the introduction of the liquid, the main body portion or switch chamber has been lled with the mercury bodies H1 and H8 through tubulation H9, and the interior of the switch envelope can then be evacuated, lled with hydrogen under pressure and sealed. The switch operates in the same manner as described in connection with Figure 2, and no further discussion is believed necessary insofar as its operation is concerned.

In the form of the invention shown in Figure 8, the same ty-pe of switch is employed but the xtures are indicated for holding the switch parts in position during the filling operation. In this form of invention, the envelope |29 has therein the sleeve 30 provided with the insulating disc 34 against which the insulator |22 is disposed to form the annular recess in which is retained the body of mercury |23. This entire end of the switch envelope |20 is carried in a suitable fixture |24 having a flanged recess |25 for receiving the envelope |20. A second envelope |26 has its flanged end |21 centered in the insulator |22, and the forward edge of the envelope is then flanged over as indicated at |28 to receive a iixture |29 embracing the same and formed with an axially extending recess |30 disposed annularly about the fbody of the envelope |26. A suitable tubulation |32 is formed in the end of the envelope |26 for introducing the mercury bodies |23 and |33, and for then evacuating the switch chamber and iilling the same with hydrogen under'pressure. A suitable fixture |34, which may be hydraulically operated, presses against the outer end of envelope |26 to hold it in rm engagement in the recessed portion of the insulator |22. This is done prior to the evacuation yand hydrogen lling of the switch envelope. As the parts are held in position by the xtures |24, |29 and |34, the liquid plastic is forced into the space |35 and the recess |30 in the fixture |29 either through tubulation |36 in the lateral wall of the envelope |20, or as indicated in dotted lines through a tubulation |31 formed in the fixture |29. The plastic when pouredV into position takes the form of a compression insulator 'and sets in this position to provide a positive seal between the flanged end of the envelope |29, the insulator |22 and the envelope |20. After this seal has set in this position and hardened, the tubulation may be closed off if in the form of the tubulation |36 or the fixture |29 may be removed and the switch then evacuated and filled With hydrogen under pressure in the usual manner. This provides a simplified form of construction without requiring the use of resilient gaskets formed of rubber or the like, and without the necessity of providing for axial compression means for expanding the gaskets in sealing engagement.

The structure shown in Figure 9 employs a cup-shaped envelope |49 having the frusto-conical lip |42. Within the envelope is seated a reversely disposed sleeve member |43 having the radially inwardly extending flange |44 forming a centering means for the refractory bushing |45. Seated in the end |46 of the envelope |43 Within the sleeve is a disc |41 which may be formed of tungsten, molybdenum, or a similar highly conductive aro-resisting metal, and the body of mercury 48 therefore lies in Contact with the sleeve |43, flange |44, and with the face of the disc |41, The bushing has a frusto-conical forward peripheral surface about which is disposed a gasket |49, which also serves to radially over-lap the cylindrical portion of the sleeve adjacent the flange |44. The gasket |49 may be formed of a suitable insulating material such as paper ber or a molded insulation, such as substantially pure rubber or a molded phenol compound. Lying in seating engagement about the surface of the gasket |49 is the frusto-conical flange end |50 of a second cup-shaped envelope |52 forming the other electrode of the switch, Suitable axial pressure is imposed between the envelopes 40 and |52 to provide for seating the flange |50 rmly in seating engagement over the gasket |49. A suitable gasket |53 is then laid over the flanged end of the envelope |52, and when so positioned, the end |42 of the envelope |40 is spun thereover to lock the parts in firm sealing engagement. It will be noticed that the inner end of gasket |53 lies over the flange |50,

as indicated at |54, to provide insulation between the envelopes |52 and |40, and similarly, the outer end |55 of the gasket |53 overlaps the envelope I 52 to insulate it from the flange end |42 of the envelope |40. As a result, a very simple form of two-envelope switch structure is provided which is capable of carrying currents, although, of course, not of the capacity such as is possible in switches in previous embodiments of the invention described.

It is therefore believed apparent that the present invention provides a novel type of mercury switch structure employing two telescoping cup-shaped envelopes which are suitably sealed and locked together in such manner as to render the interior thereof closed against the escape of gas under pressure or the like, with certain forms of the invention embodying the feature of telescoping the ceramic inserts in such manner that relatively simple and economical forms of sealing gaskets may be employed.

In addition, by the use of a double envelope switch structure of this type, it is possible to provide a mercury switch construction in which no resilient rubber gaskets need be employed, but the seal is effected by self-setting plastic cement which is poured into place in liquid form and when cooled and dried, sets to form a perfect seal. This material preferably is of the type which does not contract upon setting, and, being introduced under pressure, lls all crevices and provides an absolutely positive seal for the structure.

We are aware that various changes may be made in certain of the details of the present construction, and We therefore do not intend t0 be limited except as deiined by the scope and spirit of the appended claims.

We claim:

1. A mercury switch comprising a cup-shaped metallic envelope having a radial shoulder intermediate its ends and an enlarged open end, an insulator axially seated against said shoulder in said enlarged end and having a reduced outwardly directed extension, annular sealing means about said extension, an electrode disc in axial abutment with the radial face of said extension and having a reduced portion projecting outwardly of said envelope, an insulating compression member about said reduced portion and having an annular radial face portion axially overlying said disc and axially engaging said sealing means, said compression member having an axially offset radial face portion, resilient sealing means between said offset face portion and the outer face of said electrode disc about said reduced portion, and means at the end of said envelope holding said compression member in position to axially compress both said sealing means.

2. A mercury switch comprising a cup-shaped metal envelope having a ceramic in the closed end thereof, a cup-shaped sleeve telescoped into said envelope with the base apertured to receive said ceramic, an insulator axially abutting the annular edge of said sleeve having a tubular bore terminating short of the ceramic to provide a radial gap therebetween, a recess in the outer face of said insulator about the bore opening, a cup-shaped electrode having a flanged end centered in said recess and opening into said bore, sealing means engaging over the outer radial faces of said insulator and flange, and means for retaining said sealing means in sealing engagement between said envelope and electrode.

3. The switch of claim 2 wherein said lastnamed means includes an insulating compression member and a spun-over edge on said envelope.

4. In combination, in a mercury switch, a cupshaped metal envelope having a sleeve therein forming a radial abutment, an insulator having an axial bore therethrough axially seated against said abutment, said insulator having an annular recess in its outer face about the bore, a second cup-shaped envelope having a radially outwardly iianged open end axially centered in said recess on the outer face of said insulator and telescoping within said open end of said first envelope, an oppositely extending flange on the end of said first envelope, and insulating and sealing means secured between said flanges.

5. A mercury switch comprising a cup-shaped metal envelope having a radial shoulder intermediate its ends, an insulator seated against said shoulder having a tapered axial bore, a second cup-shaped envelope having a radially outwardly anged end abutting said insulator about the outer end of said bore, a ceramic compression member about said second envelope having a peripheral cylindrical extension telescoping over said iiange end and having an outer radial shoulder portion engaged by the spun-over edge of said rst envelope, sealing means compressed between said insulator and said extension of said compression member axially inwardly of said flange and of said second envelope, and separate sealing means between said compression member and the outer radial face of the flanged end of said second envelope.

6. A mercury switch comprising a rst cupshaped metal envelope having an enlarged open end, a ceramic insulator seated in said end and having an axial bore, a cup-shaped tubular electrode having a radially flanged open end abutting said insulator about said bore, a ceramic compression member about said electrode having a recess receiving the flanged end thereof and having radial abutment with said insulator about said flanged end, resilient sealing means carried by said compression member engaging the external annular surface of said electrode, and resilient sealing means compressed between the end of said envelope and the outer face of said compression member.

7. The switch of claim 6 wherein the abutting faces of said insulator and compression member are glazed to seal olf interporous communication therebetween.

8. A mercury switch comprising a first cupshaped metal envelope having an enlarged open end, a ceramic insulator sealed in said end and having an axial bore, a tubular cup-shaped electrode envelope having a flanged end abutting said insulator about said bore, a ceramic compression member carried on said electrode and iitting into said open end, telescoping anges on said insulator and compression member, independent resilient sealing means compressed between said insulator and compression member and between said compression member and said flanged end upon axial inward telescoping movement of said compression member, and means at the end of said envelope for maintaining said member in seal compressing position.

9. In combination, in a mercury switch, a cupshaped metal envelope having a sleeve therein forming a radial abutment, an insulator axially seated against said abutment, a second cupshaped envelope having its open end in abutment against the outer face of said insulator, oppositely extending means on the ends of said envelopes, insulating and sealing means secured between said iiange means, and a disc of arcresisting metal centered in said sleeve at the closed end of said rst envelope.

CHARLES W. TRAUTMAN. WALTER E. SCHIRMER.

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