US2794101A - Vacuum switch - Google Patents

Description

y 28, 1957 JO EMMETT JENNINGS 2,794,101

VACUUM SWITCH Filed Aug. 29, 1955 8 W H mm d $4 NT 5 Q 5 &

his ATTORNEY United States Patent VACUUM swrrcn Jo Emmett Jennings, San Jose, Calif., as ignor to Jennings Radio Manufacturing Corporation, San Jose, Caiifl, a corporation of California Application August 29, 1955, Serial No. 539,996

My invention relates to vacuum switches, and particularly to vacuum switches in which are included shields or baffles around the contact points.

One of the objects of the invention is the provision of a switch having contact points surrounded by a vapor condensing shield or baffle so that a build-up of conducting metallic film on the interior of the chamber is prevented.

Another object is the provision in a switch of the character described, of means for the rapid dissemination of heat evolved at the contact points.

Another object is the provision of a switch of the character described which lends itself to quick manufacture of parts and their rapid assembly, without sacrifice of a high standard of accuracy and durability in service.

Another object is concerned with rigidity of construction and prevention of vibration.

The invention possesses other objects, some of which with the foregoing will be brought out in the following description of the invention. I do not limit myself to the showing made by the said description and the drawings, since I may adopt variant forms of the invention within the scope of the appended claims.

Referring to the drawings:

The figure is a sectional view taken in the long central axis of the implement.

My vacuum switch comprises a vacuumized envelope in which metallic contact rods, one fixed and the other movable, are arranged in axial alignment. The interposition of a flexible metallic bellows between the mobile rod and the envelope wall permits operative movement of the mobile rod by means external to the envelope.

Since normal atmospheric pressure tends to expand the bellows into the envelope, the atmospheric pressure may be utilized to hold the contact points together in normally closed position, and to speedily close the gap between them upon release of separating pressure applied externally when the circuit through the switch is to be broken. in some uses, the contact points may be held in normally open position by interposition of a spring tensioned to overbalance atmospheric pressure.

The range of movement of the mobile contact rod is very small and extremely rapid. With only As" of separation between the contact points, the stand-01f value exceeds 100,000 volts. A switch such as illustrated in the drawings will safely handle voltages up to 50,006 and is capable of conducting continuously current volumes up to 50 amperes.

Although arcing between the contact points is at a minimum in the vacuumized envelope, some vaporization of the metal contact points occurs. If this vapor is allowed to condense and gradually build up on the inside surface of the envelope, it forms a conducting path between the inside terminals, thus shorting the contact points and seriously limiting the useful life of the unit. My invention provides a surface on which substantially all but a negligible amount of the vaporized metal, condenses without providing a conducting path around the contact rods, so that the useful life of the device is extended indefinitely.

One of the many applications of my switch is that of an overload relay in high voltage direct or alternating current uses. Thus it may operate as a protective instrument in high voltage rectifiers where an external overload or an internal flash back of a tube may occur; and because of its extremely rapid action in opening the circuit, it prevents other damage. Also in low voltage alternating current lines, my relay provides protection against overloads and short circuits.

Another use of my relay is in the broadcasting field where energy is to be shifted from one antenna to another, or to effect a change in directivity characteristics of an antena. Since my relay is capable of withstanding much higher voltages than those at which they are operated, they may be used in hot condition; that is, while the station is in full operation. So far as I am aware this has never before been possible.

My switch finds a useful application in electrical circuits known as interlocks in which it is operated to interrupt the controlled circuit by linkage to the actuating element.

Perhaps the most important application of my switch, at least in the field of accident preventing, is its use where explosion due to flame or spark is a hazard. The vacuum tight envelope, enclosing the contact points, insures complete immunity.

In the drawing, I have shown a relay designed for use in a normally closed circuit where the pressure of the atmosphere tends to hold the contact rods together, and reestablishes contact after it has been broken. By proper designing of the end cap structure in which the contact rods are mounted, stresses may be distributed, so that when the contacts are closed, a balance of pressures on the end caps results, with a planned proportion of the atmospheric thrust upon the end cap structures carried by the engaged contact rods.

In some uses of my switch, where operation is planned in a normally open circuit, a coiled spring of sufiicient strength to overbalance the atmospheric pressure may be interposed between the exterior end of the mobile contact rod and the end cap structure. The thrust of the operator is then inwardly to close the contacts.

In detail my vacuum switch comprises a glass shell 2, closed at the ends with copper caps 3 and 4, joined to the glass by the well known Housekeeper seal 6. The caps constitute the external terminals of the switch and also provide lugs or bosses 7 and 8 respectively by which the implement may conveniently be mounted in suitable clips or brackets, usually in a horizontal position. Instead of brackets, a flange 9 may be brazed to the lug at each end for more rigid and secure mounting on suitable panels.

The structurally complete implement is exhausted through the usual tubulation 10, so that there is a very high degree of vacuumization within the envelope formed by the glass central portion and the two metal end caps.

The cylindrical lug '7 which has a diameter about two thirds the diameter of the glass portion of the envelope is closed by an annular filler 11, having an outwardly extending flange 12 integrally united as by brazing to the inside face of the lug, and an inwardly extending concentric flange 13 brazed to the inwardly opening thirnble 14, which provides a rigid and secure socket in which to braze the outer end of the fixed contact rod 16. The rod is thus mounted so that flow of current between lug and rod is direct and unobstructed; and heat generated by the spark is radiated into the atmosphere from the exposed surfaces of lug, flange, filler and thimble. With heavy current and many operations, the generation of heat'poses a hard problem, audits rapid conduction to radiating surfaces is essential. In the construction shown I have been able, even with heavy loading, to keep the temperature rise well within workable limits. Much of this efiiciency both in conducting heavy currents and in dissipation of heat into the atmosphere is due to the integral union of the parts of the end mounting structure and to provision .of large radiating areas in spite of severe structural and functional limitations. The contact rod 16 is preferably of tungsten and forms the fixed or stationary contact point of the switch.

Spaced from and surrounding the rod and extending well beyond its end is a cylindrical glass tube 17 integrally connected through the narrow neck 18 with the mount ing flange 19, which in turn is integrally united to the glass .of the envelope adjacent'the seal union 6 with the copper end. The neck 18 closely surrounds the rod, leaving but a narrow annular space as shown therebetween. This space is 'baflied by the thin nickel shield plate 21, encircling the rod close to the neck and fixed in place by the flanged collar 22, all being brazed together. All of this fixed end structure, terminal cap or lug, annular filler, thimble and contact rod are concentrically disposed about the long axis 23 of the structure; and are integrally united into one continuous metallie and conductive body.

At the opposite end of the glass shell 2, the copper terminal cap 4 provides a mounting for the mobile contact rod 24 and the bellows 26 by which the envelope is closed, and which permits movement of the rod without breaking the extremely high vacuum in the envelope.

The bellows 26 preferably of copper, or bronze of a 95-5 composition, terminates at one end in a cylindrical sleeve 27, fitting'snugly into the cylindrical base flange .8 of'the cap 4. Fitting snugly into the inside of the sleeve is a hollow plug 28, extending as a smaller diameter sleeve well up into the bellows and providing a long journal bearing 29 within which the mobile contact rod 24 may slide. Base flange, sleeve and plug are brazed together so that the three are integrally united for the better conduction of current and heat.

The bellows is closed at its inner end by the end wall 30, reenforced on the inside with an annulus 31 of copper, the rod 24 extending through the annulus to the wall and being brazed to it with high temperature silver solder fusing at about 1000" C. The bellows folds are thus interposed between the rod 24 and the cap 4; and so permit limited axial movement of the rod within its bearing plug without injury to the hermetic sealing of i the envelope.

The outer end of the rod 24 is provided with threads 32 for connection to an operating means, which may be a solenoid mounted on the same panel or-bedplate which holds the mounting means for the switch.

Because of the relative costs of steel and tungsten and for other reasons, the rod 24 may be made of stainless steel or bronze up to its union with the end wall of the bellows. To the outside of the bellows a tungsten rod 33 is brazed with high melting point silver solder in axial alignment with rod 24 so that the two are essentially one since they are integrally united through the bronze end wall of the bellows. The tungsten end of the rod extends into the open end of the tube 17, and into contact with the end of the fixed contact rod.

In order to connect the rod 24 more closely to the folds of the bellows and avoid a loss of motion because of flexibility in the end wall 30, a generally conical coupling block or structure 34 of copper is interposed between the bellows and the rod, the block being recessed on both large and small ends to provide socket seats in which the bellows end and adjacent end of' the rod respectively are brazed, so that a continuous and integral metallic path is formed between the free end of the rod 33 and the external electrode or terminal, 8.

4 Besides rigidly connecting the rod 33 to the bellows and rod 24 to prevent vibration, the conical block facilitates the fast transmission. of heat from the tungsten rod through the bellows and rod 24 to the radiating surfaces of the mobile end structure. So too is provided a large surface area for current flow.

Tungsten is preferred for the engaging ends of the contact rods because it has the highest melting point and the lowest vapor pressure of the refractory metals available, in addition to low electrical resistance and a low temperature gradient.

Like the fixed end structure, the mobile end of terminal cap, bellows, bearing tube, rod and stiifening block are concentrically arranged about the long axis 23 and integrally united into one continuous metallic body. The sizes and relation of parts are such that when the envelope is fully evacuated, the two contact rods are pressed together with the full force of atmospheric pressure. Under operating conditions, and when energized, the solenoid (or other operator) pulls the rod 24 outwardly, perhaps A3, thus separating the contacting points of the two rods and breaking the circuit.

Since the atmospheric pressure against the inside of the bellows is substantially constant, the contact points are again engaged when the solenoid is deenergized, to reestablish the circuit through the contact rods. By making the seals or end cap structures the same diameter, atmospheric pressure inwardly against the seals may be equalized, so that in the open position of the switch unnecessary stresses in the end cap structures are avoided; and in the normally closed position, the inward pressures on the cap structures largely balance each other because of the intervening engaged contact rods.

The interruption of the circuit in the vacuumized envelope is attended with a minimum of arcing between the separating tungsten points of contact. This minimum is strongly influenced by the speed of separation; and use of a properly designed solenoid effects an almost instantaneous break and resultingly, there is a very minimum of sparking. However, it is impossible to wholly prevent all arcing and to the extent it occurs, tungsten is vaporized. Without a bafile or barrier means of some kind, the vaporized metal condenses on the inside surface of the glass shell, and builds up thereon a conduct ing layer which eventually shorts across the rods, and of course ruins the switch.

I prevent this result, although I cannot Wholly prevent the cause, by surrounding the arcing points with the glass baflle tube 17. The tube extends a substantial distance on each side of the break point where arcing occurs; and the vaporized tungsten is caught by and deposited on the inside surface of the tube. The small quantity of vaporized metal passing through the annular space in the neck is caught on the shield plate 21. A metallic shield cup 36 having its bottom spaced from and extending across the open end of the shield tube 17, is brazed to the conical block 34, the cylindrical side of the cup extending well past the free end of the tube 17 and spaced therefrom. The shield cup is effective as a bafiie for vaporized tungsten thrown toward the movable end of the implement, and together with the shield tube 17 and the shield plate 21 provide an effective though incomplete closure surrounding the contact points for preventing harmful deposits of vaporized metal on the interior of the envelope, while still leaving visible from outside, the spark between the points.

Component parts of my switch are assembled and brazed in opposite ends of the two halves of the envelope, which are then joined at the central bead 40, and the envelope baked out and exhausted.

I claim:

1. A vacuum switch com rising a vacuumized envelope having a central cylindrical glass wall, and metal end walls constituting external terminals on the long axis of the envelope, a, contact: rod fixed in one of the terminals and extending concentrically into the glass wall portion of the envelope, a cylindrical glass shield tube integrally united with the glass wall and extending concentrically past the end of the fixed contact rod, a mobile contact rod extending into the envelope and slidably journaled in the other terminal and aligned with and adjacent to the fixed rod, a bellows surrounding the mobile rod adjacent its bearing and interposed between the mobile rod and the adjacent end wall and integrally united to both, and a shield cup fixed on the mobile contact rod concentric with and surrounding the adjacent end of the shield tube.

2. A vacuum switch in accordance with claim 1 in which the glass shield tube has a constricted neck adjacent its union with the glass wall, and a shield disk fixed on the fixed contact rod and extending across the neck opening and spaced from the shield tube.

3. A vacuum switch in accordance with claim 1 in which the mobile contact rod comprises an outer journaled part integrally united to the end of the bellows on the inside thereof and an aligned inner part integrally united to the end of the bellows on the outside thereof.

4. A vacuum switch in accordance with claim 3 in which a coupling block is interposed between the end of the bellows and the inner part of the mobile contact rod and is integrally united to both, and the shield cup is mounted on the coupling block.

5. In a vacuum switch, a vacuumized envelope having a central cylindrical glass wall and a metal end wall constituting an external terminal on the long axis of the envelope, an inwardly opening thimble disposed axially within the end wall, an annular filler piece having an inner flange integrally united to the thimble and an outer flange integrally united to the end wall, a fixed contact rod seated in the thimble and integrally united therewith and extending concentrically into the glass wall portion of the envelope, and a cylindrical glass shield tube integrally united with the glass wall and surrounding and extending concentrically past the end of the fixed contact rod.

6. In a vacuum switch, a vacuumized envelope having a central cylindrical glass wall and a metal end wall constituting an external terminal on the long axis of the envelope, an inwardly opening thimble disposed axially within the end wall, an annular filler piece having an inner flange integrally united to the thimble and an outer flange integrally united to the end wall, a fixed contact rod seated in the thimble and integrally united therewith and extending concentrically into the glass wall portion of the envelope, a cylindrical glass shield tube integrally united with the glass wall and surrounding and extending con- 6 centrically past the end of the fixed contact rod and having a constricted neck adjacent its union with the glass wall, and a shield disk fixed on the contact rod and extending across the neck opening and spaced axially therefrom.

7. A vacuum switch comprising a vacuumized envelope having a central cylindrical glass wall and metal end walls constituting external terminals on the long axis of the envelope, an inwardly opening thimble disposed axially within one of the end walls, an annular filler piece having an inner flange integrally united to the thimble and an outer flange integrally united to the adjacent end wall, a fixed contact rod seated in the thimble and integrally united therewith and extending concentrically into the glass wall portion of the envelope, a mobile contact rod extending into the envelope and slidably journaled in the other end cap and aligned with and adjacent to the fixed rod, and a bellows surrounding the mobile rod adjacent its bearing and interposed between the mobile rod and the adjacent end cap and integrally united to both.

8. A vacuum switch comprising a vacuumized envelope having a central cylindrical glass wall and metal end walls constituting external terminals on the long axis of the envelope, an inwardly opening thimble disposed axially within one of the end walls, an annular filler piece having an inner flange integrally united to the thimble and an outer flange integrally united to the adjacent end wall, a fixed contact rod seated in the thimble and integrally united therewith and extending concentrically into the glass wall portion of the envelope, a cylindrical glass shield tube integrally united with the glass wall and extending concentrically past the end of the fixed contact rod and having a constricted neck adjacent its union with the glass wall, a shield disk fixed on the fixed contact rod and extending across the neck opening, a bellows having a closed end extending into the envelope and an open end integrally united to the other end wall, a mobile contact rod comprising an outer part slidably journaled in said other end wall and integrally united to the end of the bellows on the inside thereof, and an aligned inner part aligned with the fixed rod and integrally united to the end of the bellows on the outside thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,784,302 Millikan et a1 Dec. 9, 1930 1,875,765 Scherbius Sept. 6, 1932 2,121,180 Vatter June 21, 1938

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