US3231704A

US3231704A - Hermetically sealed switch with tubular dielectric portions united to a relatively larger metallic intermediate vapor condensing portion

Info

Publication number: US3231704A
Application number: US271696A
Authority: US
Inventors: Lester O Jacobs
Original assignee: Jennings Radio Manufacturing Corp
Current assignee: Jennings Radio Manufacturing Corp
Priority date: 1963-04-09
Filing date: 1963-04-09
Publication date: 1966-01-25
Anticipated expiration: 1983-01-25
Also published as: CH436421A; GB1118620A; BE672696A

Description

1965 L. o. JACOBS 3, 3 ,704 HERMETICALLY SEALED SWITCH WITH TUBULAR DIELECTRIC PORTIONS UNITED TO A RELATIVELY LARGER METALLIC INTERMEDIATE VAPOR CONDENSING PORTION Filed April 9, 1963 INVENTOR. 4 LESTER O. JACOBS United States Patent Y 3,231,704 HERMETICALLY SEALED SWITCH WITH TUBU- LAR DIELECTRIC PORTIONS UNITED TO A RELATIVELY LARGER METALLIC INTERME- DIATE VAPOR CONDENSING PORTION Lester 0. Jacobs, San Jose, Calif., assignor to Jennings Radio Manufacturing Corporation, San Jose, Calif., a corporation of Delaware Filed Apr. 9, 1963, Ser. No. 271,696 5 Claims. (Cl. 200144) This invention relates to switches and more particularly to high power switches of the hermetically sealed and vacuum types for interrupting electrical currents of large magnitude.

One of the limiting factors in conventional power switches is the construction of the envelope, which may be designed to withstand an internal pressure, as where the envelope is gas filled, or which may be designed to withstand atmospheric pressure, as where the envelope is evacuated. In either case, it has been found that Where the envelope is fabricated in part from glass and in part from metal that the union of the glass to metal. portions of the envelope constitute weak points in the construction, and prevent outgassing of the envelope parts at elevated temperatures. Accordingly, it is one .of the objects of the invention to provide a hermetically sealed switch incorporating an envelope fabricated from materials which may be flexibly united and outgassed at a considerably higher temperature than when glass is used.

In the fabrication of glass and metal switch envelopes it has been common practice to use the well known Houskeeper seal in which a thinly feathered metallic flange is embedded in the glass, the theory being that if the metal is thin and sufliciently ductile it be dominated by the glass. Because this construction is inherently weak, attempts have been made to substitute a metallic member having a coefficient of thermal expansion and contraction more closely approximating that of glass, as for instance Kovar, and casting glass about an unfeathered flange. While this construction is an improvement over the conventional Houskeeper seal, it still imposes problems such as reduced electrical conductivity of the metal portions and destructive thermal shock to the glass if removed from the casting mold before it has cooled sufficiently, thus increasing .the elapsed time required to fabricate a switch. Accordingly, another object of the invention is the provision .of an envelope construction in which glass is eliminated and in whichceramis and metal are associated in a manner to provide a strong yet flexible hermetic union between the partswhich will accommodate differences in the thermal expansion and contraction characteristics of the dissimilar material.

Another problem .that has defied solution has been containment to prescribe-d areas within the envelope of metal particles and vaporized contact metal sputtered from the switch contacts upon the striking of an are.

In switches utilizing a thin flexible bellow high velocity metallic particles often puncture the bellow, thus destroying the envelope. The same problem exists with Houskeeper seals in which the thinly feathered metal-lie flange may be punctured by fast moving metallic particles blown from the contacts. To meet this problem shield structures of various designs have been utilized to shield both the bellow and the Houskeeper seals. These shield structures are diflicult to fabricate, are not complete'ly effective and increase the cost of each unit, therefore making it less available for applications where cost is an important factor. Accordingly, still further object of the invention is the provision of aswitch envelope fabricated from ceramic and metal, and which incorporates an intermediate heavy metallic toroidal shell portion easily fabricated, and preferably arranged, with re 3,231,794 Patented Jan. 25, 1966 spect to the switch contacts, so as to intercept and condense a large portion of the metal particles and vapor emanating from the switch contacts.

Manufacturers of high power switches have also been plagued by the tendency of vaporized contact metal to condense on the inner surface of dielectric members Whose function it is to electrically insulate spaced metallic members. Shields of this type are often mounted directly on current carrying elements of the switch, and are therefore maintained at a temperature sufliciently high as to be detrimental to their normal function of condensing vaporized contact metal. It is therefore still another object of the present invention to provide shielding for the ceramic components of the switch envelope such that heat in the shield structure is conducted out of the envelope to thus increase the effectiveness of the shields.

Shields of this character have in the past been secured as by brazing to associated structure, which procedure complicates assembly and fabrication of the switch and increases the cost thereof. It is therefore a still further object of the invention to provide a hermetically sealed power switch incorporating shield structures therewithin secured in their position by associated structure without the need of brazing, thus facilitating fabrication of the switch.

Another problem that has become apparent from the use of shields in the immediate area surrounding the contacts of a power switch has been confinement of ionized vapor surrounding the switch contacts and thus preventing rapid extinguishing of an arc. It is therefore another object of the present invention to provide an envelope in which the condensing surfaces for vaporized material are spaced relatively far away from the contacts which they surround.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be apparent from the following description and the drawing. It is to be understood however that the invention is not limited by the said description and the drawing but may be embodied in various forms within the scope of the appended claims.

Broadly considered, the power switch of the invention comprises an hermetically sealed envelope including a pair of elongated axially aligned and spaced tubular dielectric members, preferably of ceramic, held apart and hermetically united to an intermediate heavy metallic toroidal envelope section by flexible ceramic-to-metal unions. Each opposite end of the composite structure so formed is closed by a metallic end cap structure hermetically united to the associated end of the tubular ceramic member by flexible ceramic-to-metal unions. Mounted on each end cap structure and extending into the envelope coax'ially with respect to the tubular ceramic members is a conductive metallic stem having a contact member fixed of its inner free end lying within the confines of the intermediate toroidal envelope member. To provide for axial displacement of one of the two opposing contacts, one of the stems is slidably arranged with respect to its associated end cap structure and the slidable union is appropriately sealed as by a flexible metallic bellow hermetically interposed between the stem and end cap structure. Thus, opening of the switch contacts under load, which usually causes arcing between the contacts, will result in :the evaporation of contact metal, but such vaporized metal will be condensed on the inner surface of the intermediate toriodal section of the envelope. Because there is the possibility that some of the vaporized contact metal will deposit itself on the inner surfaces of the tubular ceramic members unless prevented, appropriate shields are provided interposed between the contacts and the associated tubular ceramic members. As illustrated in the drawing, each shield is trapped between the associated ceramic member and a peripheral edge" portion of the' intermediate toroidal envelope section without the need for brazing.

Referring to the drawings:

The figure is a vertical sectional view partly in elevation showing the details of construction of the switch. The figure is drawn approximately actual size.

In more specific terms, the power switch of the invention comprises an hermetically sealed envelope including elongated tubular

dielectric portions

2 and 3, preferably fabricated from ceramic, axially aligned and spaced apart by an intermediate metallic toroidal envelope section 4, having a pair of peripheral edge portions 6 and 7, the peripheral edge portion 6 being hermetically united to the associated end of the tubular ceramic 2 by a thin flexible annular metallic sealing structure 8. As illustrated, the sealing structure includes a radially inwardly extending flange 9 brazed to the metalized end of the tubular ceramic, and a cylindrical flange 12 brazed to the peripheral edge portions 6-7 of the intermediate toroidal envelope section. The hermetic union between flange 9 and the associated tubular ceramic 2 or 3 is strengthened by a dielectric back-up member or ring 13 brazed to the associated flange 9 but free to slide on the supporting peripheral edge portion of the intermediate envelope section, or on an intermediate structure interposed between the back-up ring and each portion 6 or 7. Thus, diflerences in thermal expansion and contraction between the parts is accommodated by the slidability of the ceramic back-up ring 13 on the adjacent metallic structure, while the sandwiched flange 9 is dominated by the ceramics between which it is brazed.

The ends of the tubular

ceramic envelope portions

2 and 3 remote from the intermediate metallic envelope section 4 are closed by

end cap structures

14 and 16, respectively. The end cap structure 14 comprises an annular flat metallic plate section 17, and an integral tubular central section 18. The outer peripheral edge portion of the annular plate portion 17 is hermetically united to the associated end of ceramic 2 by a flexible metallic sealing structure 8 similar to that previously described and functioning in the same manner. This union also utilizes a back-up ring 13 brazed on the one hand to the sealing structure 8 and slidably abutting plate member 17 to accommodate differences in thermal expansion and contrac tion between the dissimilar parts.

Supported within the central tubular portion 18 of end cap 14 is a conductive metallic stem 19 extending coaxially into the envelope and provided on its inner free end with an integral contact button 21 having a contact surface 22 lying in a median plane between peripheral edge portions 6 and 7 of the intermediate metallic envelope section 4.

The end cap structure 16 is somewhat diflerent from the end cap structure 14 in that a separate flexible sealing structure 8 is not used to unite this end cap to the associated end of ceramic 3. Instead, the end cap 16 is provided with an integral flexible metallic radially outwardly extending flange 23 hermetically brazed between the metalized end of ceramic 3 and ceramic back-up ring 24. The flange 23 merges immediately Within the inner periphery of the ceramic 3 with a thin cylindrical flange exten sion 26 concentrically arranged with respect to

dielectric members

23 and 24. The change of direction of the flange at this point is important in that it takes out'of the plane of the union between flange 23 and the associated ceramics the mass of material making up the remainder of the end cap structure so that differences in thermal expansion and contraction of this larger mass is accommodated'by flexure of the lever arm formed by cylindrical flange 26 while the flange 23 is dominated by the ceramics. The end cap structure 16 is completed by

annular plate portions

27 and 28 joined by cylindrical flange 29, and a tubular centrally disposed flange 31.

Br-azed within the cylindrical flange 31 is the outer open-end 32 of a flexible metallic bellow 33, the inner end 34 of which is hermetically brazed to an intermediate section of a cylindrical conductive stem 36, slidably supported on the end cap structure 16 within the central flange 31', and which extends into the bellow as shown. A relatively larger diameter stem extension 38 integral with the stem 36 is provided with a contact button 39 having contact surface 41 adapted to make and break contact with contact surface 22 of the opposing contact button. To actuate the movable contact assembly formed by stem 36, stem extension 38, and contact button 39, the end of the stem 36 is provided with a tapped hole 42 for engagement by any suitable actuating means such as a solenoid.

To shield the inner surface of the tubular

cerami envelope portions

2 and 3, respectively,

shield structures

42 and 43 are provided, each having cylindrical portions disposed concentrically with respect to the associated tubular ceramic and lying between the ceramic and the contact buttons 21 and 39. Each of the shield structures is provided with a radially outwardly extending flange 44 caught between the associated back-up-ring 13 and the adjacent peripheral portion 6 or 7 as shown. The flange 44 is provided with a jogged portion forming a shoulder to guide nesting of the shield structure on the peripheral edge portion of metallic toriodal envelope section 4. This construction facilitates fabrication of the switch because it permits automated stacking and selfalignment of the parts, thus facilitating machine assembly and brazing of the assembly in a single operation.

To further insure that vaporized metal is not deposited on the inner surface of the tubular dielectric envelope portion 3, or that high velocity metallic particles do not puncture the flexible bellow 33, an auxiliary shield 47 is provided having a flat plate portion 48 caught between the inner end of bellow 34 and stem extension 38, and a cyclindrical portion 49 concentrically interposed in radially spaced relation between the cylindrical shield 43 and the adjacent tubular ceramic envelope portion 3. Thus, before vapor or metallic particles can reach the dielectric envelope portion they must pass through the labyrinth formed by the

shields

43 and 47. Experience has shown that very little metal is deposited on the inner surfaces of the ceramics in the envelope illustrated.

I claim:

1. A switch comprising an hermetically sealed envelope including a pair of axially aligned tubular dielectric envelope portions having adjacent ends spaced apart and hermetically united to an intermediate annular metallic shell portion of the envelope relatively larger in diameter than said aligned tubular dielectric envelope portions, end cap structures closing opposite ends of the tubular dielectric envelope portions, axially aligned fixed and movable conductive contact stems mounted on opposite end caps, conductive contact surfaces on the inner ends of the contact stems within the intermediate annular metallic shell portion of the envelope, and a flexible bellow hermetically interposed between one of the end caps and the movable contact stem to accommodate axial displacement of the movable contact stem with respect to the envelope to make or break a circuit through the switch; said relatively larger metallic shell portion forming condensing surfaces spaced relatively far away from the contacts, said surfaces condensing vaporized material emanating from said contact surfaces.

2. The switch according to claim 1, in which the intermediate metallic annular shell portion comprises a pair of axially spaced inner peripheral edge portions connected by an intergal semi-cylindrical section concave in a direction facing the contacts.

3. A switch comprising an hermetically sealed envelope including a pair of axially aligned tubular dielectric portions having adjacent ends spaced apart and an intermediate annular metallic shell portion interposed between the spaced apart ends of the tubular dielectric portions, a seal assembly flexibly uniting hermetically one end of each tubular dielectric portion with the intermediate annular metallic shell portion, said seal assembly including a dielectric back-up ring supported by the intermediate annular metallic shell portion, end cap structures closing opposite ends of the tubular dielectric portions, axially aligned fixed and movable conductive contact stems mounted on opposite end caps, conductive contact surfaces on the inner ends of the contact stems within the intermediate annular shell portion of the envelope, a flexible bellow hermetically interposed between one of the end caps and the movable contact stem to accommodate axial displacement of the movable contact stem with respect to the envelope to make or break a circuit through the switch, and a shield structure within the envelope interposed between each tubular dielectric envelope portion and the contacts to intercept vaporized material therefrom and including a mounting flange slidably caught between the back-up ring of each seal assembly and the associated peripheral edge portion of the intermediate annular metallic shell portion so as to conduct heat from the shield to the intermediate annular metallic shell portion.

4. The switch according to claim 3, in which each shield structure includes a tubular shell coaxially arranged in radially spaced relation with respect to the associated tubular dielectric portion of the envelope.

5. The switch according to claim 4, in which an auxiliary shield is mounted on the movable contact stem to shield the bellows from destructive metallic particles emanating from the contacts, said auxiliary shield including a cylindrical flange portion concentrically arranged in radially spaced relation between the adjacent tubular dielectric portion and the coaxially arranged tubular shell of the associated shield structure.

References Cited by the Examiner UNITED STATES PATENTS 2,965,734 12/ 1960 Timmerman 200144 2,979,588 4/1961 Jennings 200144 3,038,980 6/1962 Lee 200144 FOREIGN PATENTS 769,935 3/ 1937 Great Britain. 135,939 2/1962 Russia.

KATHLEEN H. CLAFFY, Primary Examiner. ROBERT K. SCHAEFER, Examiner.

Claims

1. A SWICH COMPRISING AN HERMETICALLY SEALED ENVELOPE INCLUDING A PAIR OF AXIALLY ALIGNED TUBULAR DIELECTRIC ENVELOPE PORTIONS HAVING ADJACENT ENDS SPACED APART AND HERMETICALLY UNITED TO AN INTERMEDIATE ANNULAR METALLIC SHELL PORTION OF THE ENVELOPE RELATIVELY LARGER IN DIAMETER THAN SAID ALINGED TUBULAR DIELECTRIC ENVELOPE PORTIONS, END CAP STRUCTURES CLOSING OPPOSITE ENDS OF THE TUBULAR DIELECTRIC ENVELOPE PORTIONS, AXIALLY ALIGNED FIXED AND MOVABLE CONDUCTIVE CONTACT STEMS MOUNTED ON OPPOSITE END CAPS, CONDUCTIVE CONTACT SURFACES ON THE INNER ENDS OF THE CONTACT STEMS WITH THE INTERMEDIATE ANNULAR METALLIC SHELL PORTION OF THE ENVELOPE, AND A FLEXIBLE BELLOW HERMETICALLY INTERPOSED BETWEEN ONE OF THE END CAPS AND THE MOVABLE CONTACT BETWEEN TO ACCOMODATE AXIAL DISPLACEMENT OF THE MOVABLE CONTACT STEM WITH RESPECT TO THE ENVELOPE TO MAKE OR BREAK A CIRCUIT THROUGH THE