US2794885A - Vacuum switch - Google Patents

Description

J1me 1957 JO EMMETT JENNINGS 2,794,885

V-ACUUM SWITCH Filed Dec. 13, 1954 /NVE N T01? JO EMME 7'7 JEN/V/NGS his ATTOPNE Y United States Patent VACUUM SWITCH Jo Emmett Jennings, San Jose, Calif., assignor to Jennings Radio Manufacturing Corporation, San Jose, Calif., a corporation of California Application December 13, 1954, Serial No. 474,723 7 Claims. (Cl. 200-144) My invention relates to vacuum switches; and particularly to such switches having vapor condensing shields about the inside terminals.

One of the objects of the invention is the provision of an electric switch having its contacts within a vacuumized envelope with vapor-condensing shields so disposed within the enveolpe and about the contact points that no conducting metallic film is deposited on the interior surface of the envelope to short circuit the terminals.

Another object of my invention is the provision of improved and simplified means for dissipating the heat evolved at the contacts during operation of the switch.

Still another object is the provision of means at the contact points for damping or cushioning the shock of impact when the points engage at closing of the switch.

Another object is the provision of a vacuum switch having an internal structure capable of withstanding the high temperatures imposed during induction heating to efiect degassing of the components.

Other objects will be brought out in the following description of the invention. I do not limit myself to the showing made by said description and the drawings, since I may use variant forms of the invention within the scope of the appended claims.

Referring to the drawings:

Fig. 1 is for the most part a sectional view taken in a plane intersecting the long axis of the implement.

Fig. 2 is a detail in axial section showing a modified form of the movable contact point.

In both figures, the switch is shown in open position.

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 belows 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.

The range of movement of the mobile contact rod is very small and extremely rapid. With only /s" of separation between the contact points, the stand-off value exceeds 100,000 volts. A switch such as illustrated in the drawings will safely handle voltages up to 50,000 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 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 efiect a change in directivity characteristics of an antenna. 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 prevention, 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 Fig. l, l 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.

in some uses of my switch, where operation is planned in a normally open circuit, a coiled spring of sufiieient 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 formed of two parts 2 and 3, joined along the line 4 after the assembly in each part of its related components. The shell is closed at its ends with copper caps 6 and 7 connected to the glass by the seals 8. These caps constitute external terminals and also provide lugs 9 and 10 respectively by which the implement may conveniently be mounted in suitable clips or brackets.

The lug 9 of cap 6 is filled with a copper plug 12, brazed in place by high melting point solder spreading from the groove 13. Seated in a deep recess in the plug 12 and brazed therein is a molybdenum post 14 of relatively large diameter. This post rigidly supports all the component parts assembled within the part 2 of the envelope; and its juncture with the plug as Well as the union of the plug with the cap is integral, being secured by means of nickel solder having a melting point above that of the copper seal itself so that maximum conductivity both of electricity and heat is assured, and no weakening or separation occurs during the degassing heating. Although molybdenum has electrical characteristics that make it less desirable for this use than some other available metals, it has qualities of high melting point, mechanical strength, low vapor pressure and relative cost as well as certain physical characteristics, which responding to induction heating during the degassing process, make it desirable for the uses indicated in my implement.

Brazed into a recess in the post with a high melting point nickel solder is a relatively short tungsten rod 16, forming one of the contact points of the switch. Concentrically spaced from and surrounding the rod, and extending well beyond its end is a cylindrical tubular bafflange 19 extending radially from and brazed concentrically on the molybdenum post against the shoulder 21. It willbe clear that heat picked up by the shield during operation of my switch has a free and integral path or line of conduction to the radiating surface of the end cap 6. It is'to be noted that all of this fixed end cap structure of terminal cap, plug, rod and shield are concentrically disposed about the long axis 22 of the structure, and integrally united into one continuous metallic body through which heat picked up by the shield during operation of the switch flows to the, radiating surfaces of the terminal cap.

Atthe opposite end of the glass shell, the copper terminal cap 7 provides a mounting for the mobile contact rod and the bellows by which the envelope is closed and which permits movement of the rod without breaking the extremely high vacuum in the envelope.

The bellows 23 preferably of stainless steel terminates at one end in a-cylindrical sleeve 24, fitting snugly into the cylindrical lug it) of the cap 7. Fitting snugly into the inside of the sleeve is a plug 26, extending well up into the bellows and providing a long journal hearing within which the mobile contact rod 27, also of stainless steel, may slide. Lug 10, sleeve and plug are brazed together so that the three are integrally united.

The bellows is closed at its inner end by the end wall 28, the rod 27 extending to the wall and being brazed to it with high melting point solder. The bellows folds are thus interposed between the rod 27 and the cap 7 and permit limited axial movement of the rod within its bearing plug without injury to the hermetic sealing of the envelope.

The outer end of the rod 27 is provided with threads 29' for connection to an operating means, which may be a solenoid mounted on the same bedplate which holds the bracket clips for the switch.

To the outside of the bellows end wall 28 a molybdenum post 31 is brazed with high melting point solder in axial alignment with rod 2 7 so that the two are essentially one since they are integrally united through the end wall of the bellows. Except for its contact end the molybdenum post 31 is similar to the aligned post 14, but shorter, and extends well into the open end of the shield. Slidably seated in a recess 32 in its end is a short molybdenum plug 33 having a fiat bottom annular groove at its inner end engaged by a retaining stud 34. A spring 36 in the recess below the plug presses it outwardly a bit beyond the end of the post and resists its inward movement with calculated resistance. The outer end of the plug and also the surrounding annular end of the post are faced with tungsten to form movable contact surfaces 37 and 38 respectively engaging the fixed contact 16. The tension of the spring and the proportion of the parts are such that the plug first engages the fixed contact rod when the switch closes, damping or cushioning the impact and materially lessening the cumulative effect of many closing blows.

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.

Integrally united to the molybdenum post 31 are two molybdenum shield plates 41 and 42, which with the tubular shield 17, effectively enclose the contact points and prevent damage to the envelope and copper seal end caps by par cles thrown Ofi at high velocity when the movement of the thimble on the post.

switch is opened and sparking occurs. The shields which are preferably curved as shown form adepository forsome of the particles and also the metallic vapor resulting from operation of the switch, so that no short circuiting film is formed on the inside surface of the envelope. The shields conform to a spherical shape with radius centered at about the intersection of the axis 22 with the end cap lug 9, so that particles thrown from the spark strike in a path tending to prevent return into the spark when they do not adhere to the shield surface.

Shield plate 41 extends from the base of the post 31 where it joins the end of the bellows, and curves around the endof but spaced from the cylindrical shield as shown. Shield plate 42 is brazed against the shoulder 43 on the post just within the open end of the cylindrical shield. It is curved inwardly toward the contact points with its peripheral edge well spaced from the encircling shield.

The shape and arrangement of the parts prevent particles, emanating from a spark between the contact points, striking any portion of the envelope; and impose a tortuous path of movement upon the metallic vapor resulting from the spark.

Like the fixed end structure, the mobile end of terminal cap, bellows, bearing, plug, rod and stiffening cap are concentrically arranged about the long axis 22 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 sole noid (or other operator) pulls the rod 27 outwardly, perhaps Ms", thus separating the contacting points of the two rods and breaking the circuit.

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 efiects 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 conducting layer which eventually shorts across the rods, and of course ruins the switch.

Furthermore, particles from the sparking points traveling at very high velocity bombard the inside of the envelope, and unless intercepted can injure or even pass through the envelope wall at the copper seals, leaving microscopic apertures through which the vacuum is destroyed. I prevent these results by my cylindrical and plate shields which intercept the high velocity particles, and catch and retain any condensed metallic vapor. It will be noted that post 31, rod 27, bellows and end cap 7 form one integrally united metallic conductive path for heat generated in the spark to travel to the cap where it is dissipated into the atmosphere.

In Fig. 2, I have shown a modified form of damping or shock absorbing means to lessen or prevent the bounce which occurs when the contacts close, and which not only tends to shorten the life of the switch, but create extremely high transient currents. In this case, the end 46 of the movable post 31 carries a slidable thimble, comprising a molybdenum tube 47 closed at its free end by a tungsten cap 48, electrically welded to the tube. Interposed in the chamber between the end of the post and the thimble is a quantity of molybdenum granules 49 preferably all about the same size so as to avoid a tendency to pack. A stud 51 set in the thimble to engage a groove on the post end limits to a narrow range any The impact of the closing contact is damped or absorbed by the granules within-the thimble to a material extent so that the cumulative effect of many undamped closings is avoided and the life of the switch prolonged.

I claim:

1. A vacuum switch comprising a vacuumized envelope having metal end caps constituting electrical terminals, a contact rod fixed in one of the terminals and extending 'into the envelope, 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 and its bearing and interposed between the mobile rod and the adjacent terminal, a tubular shield enclosing the contact rods on both sides of their adjacent ends, a bracket flange on one of the contact rods to support the tubular shield and closing its adjacent end, and a curved shield supported on the other contact rod and disposed across and spaced from the open other end of the tubular shield.

2. A vacuum switch comprising a vacuumized envelope having metal end caps constituting electrical terminals, a contact rod fixed in one of the terminals and extending into the envelope, 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 and its bearing and interposed between the mobile rod and the adjacent terminal, a tubular shield enclosing the contact rods on both sides of their adjacent ends, a bracket flange on one of the contact rods to support the tubular shield and closing its adjacent end, a curved shield supported on the other contact rod and disposed across and spaced from the open other end of the tubular shield, and a second curved shield supported on the last named contact rod and disposed within said open other end of the tubular shield and peripherally spaced from the wall of the tubular shield.

3. A vacuum switch comprising a vacuumized envelope having metal end caps constituting electrical terminals, a contact rod fixed in one of the terminals and extending into the envelope, 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 and its bearing and interposed between the mobile rod and the adjacent terminal, a tubular shield enclosing the contact rods on both sides of their adjacent ends and supported on one of the contact rods, and a curved shield disposed across and spaced from an end of the tubular shield and supported on the other contact rod.

4. A vacuum switch in accordance with claim 3 in which the tubular and curved shields are made of sheet molybdenum.

5. A vacuum switch comprising a vacuumized envelope having metal end caps constituting electrical terminals,

a contact rod fixed in one of the terminals and extending into the envelope, 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 and its bearing and interposed between the mobile rod and the adjacent terminal, said mobile contact rod being recessed in its free end to provide an annular contact surface, a plug arranged in the recess for limited movement therein, and means in the recess below the plug for damping its inward movement.

6. A vacuum switch comprising a vacuumized envelope having metal end caps constituting electrical terminals, 2. contact rod fixed in one of the terminals and extending into the envelope, a mobile contact rod extended 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 and its bearing and interposed between the mobile rod and the adjacent terminal, a contact member mounted on the free end of the movable contact rod for limited movement thereon, and means interposed between the contact member and the movable contact rod for damping the blow of the later when it engages the fixed contact rod upon closing of the switch.

7. A vacuum switch comprising a vacuumized envelope having metal end caps constituting electrical terminals, a contact rod fixed in one of the terminals and extending into the envelope, 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 and its bearing and interposed between the mobile rod and the adjacent terminal, a tubular shield enclosing the contact rods on both sides of their adjacent ends and supported on one of the con tact rods, a curved shield disposed across and spaced from an end of the tubular shield and supported on the other Contact rod, a contact member mounted on the free end of the movable contact rod for limited movement thereon, and means interposed between the contact member and the movable contact rod for damping the blow of the later when it engages the fixed contact rod upon closing of the switch.

References Cited in the file of this patent UNITED STATES PATENTS 1,784,302 Milliken et al. Dec. 9, 1930 1,814,851 Prince July 14, 1931 1,875,765 Scherbius Sept. 6, 1932 2,121,180 Vatter June 21, 1938 2,426,387 Caswell Aug. 26, 1947 2,445,588 Skeats July 20, 1948 2,527,475 Bates Oct. 24, 1950

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