US2296194A - Mercury switch - Google Patents

Description

C. W. TRAUTMAN El' AL Sept. 15, 1942.

MERCURY SWITCH Filed July 26. 1940 2 Sheets-Sheet l Mr Il ATTORNEY.

Sept. 15, 1942.

c. w. TRAUTMAN ETAL 2,296,194

` MERCURY swITcH i Filed July ze. 1940 9 2 sheets-sheet 2 il /1 fr? f3 65.

Pf A7p Patented Sept. 15, 1942 MERCURY SWITCH VCharles T'rautman and Herbert E. Bucklen, IIII, Elkhart, Ind., assigner-s to Bucklen-Beai' Laboratories, Inc., Elkhart, Ind., a corporation of Indiana message any ze, 1940, serial No. 347,678

(orcos-152) 'i'` Claims.

This invention relates to mercury switches, and more particularly is directed to the metal envelope 'type of mercury switch incorporating means for assisting in the making of the circuit through the switch by means of a primary electrode contact member formed of a material which is substantially unaffected by the constant arcing usually `found in a switch 4of the metal to mercury contact type.

In the majority of metal envelope mercury switches with Ywhich I am familiar, it has been found desirable to provide "an iron elect-rode which, in turn, is constantly engaged by a retained body of mercury so that upon making or breaking of the circuit, the -arcing will occur between the retained body and a moving body of mercury to shield the metal electrode from the arcs occurring during the switching operations. This has been considered desirable since the mercury arcs impinging on the iron electrode have been found to reduce the life of the switch so that it will withstand only about one-fourth the number of contacts that a switch of the positive mercury to mercury contact type is capable of withstanding. However, there are certain advantages in a direct metal to mercury type of c-ontact insofar as snap action switches are concerned, and also in switches which may be employed as drop-cord switches or level devices in which a narrow angle is desired.

The present invention contemplates providing the electrode with an axially inwardly extending disc portion formed of a material such as tungsten, molybdenum, or tantalum, which will take the initial arcing when c-ontact is made or broken in the switch, and which is not seriously affected by such arcs due to the characteristics of the metal employed.

This simplifies the internal construction of the switch to a considerable extent, since the ceramic may be of simple formation without requiring an undercut or groove for the retained body of mercury, and the electrode construction can be simplified to a considerable extent. The disc of arc resisting material is preferably so arranged with respect to the throat or passageway of the ceramic interposed between the envelope and the electrode as to provide a means for preventing splashing of the mercury during snap action, and provides a control capable of insuring positive, clean breaking of the circuit with no secondary arcing or the like. The arc resisting electrode disc serves as a baffle or damper to prevent surging of the mercury and possible intermittent or secondary contacts thereof with the electrode, which would be the case if the primary disc were not `located the particular position provided.

Another feature of the present invention is the provision of a very simple form of switch structure in which a tungsten or molybdenum shank is projected inwardly `from the elebtrode, and is used as the contact means for the movable bo'd-y of mercury. This shank or pin may `be secured to the main electrode stud in any suitable manner, such as by a press t, threading, or fstakin'g the same into position. Y

Other objects and advantages of the 'present invention will be more apparent from thefollowing detailed description which, taken in cenjunction with the accompanying drawingswill disclose to those skilled in the art the Vparticular construction and operation of a preferred form of the present invention. v

In the drawings:

Figure 1 is a vertical sectional 'view through `a narrow angle snap action type of switch oonstruction embodying the present invention;

Figure 2 is a corresponding sectional view through a switch normally employed as a drpcord switch or level indicating type of switch;

Figure 3 is a sectional view through a modified form of switch provided with an enclosing insulating case; and i Figures 4 to 8, inclusive, are sectional views through still further modified forms of switch structure embodying the `present invention.

Referring now in detail to Figure l, we have provided a switch envelope 5 of generally elongated cup-shape form having the open end portion 6 which is internally bored to'p'rvide the radial shoulder l adjacent the end. The envelope 5 may be formed of any suitable material, such as col-d rolled stock or the like.

Seated against the radial shoulder l `and centered in the counterbored portion 6 ofl theonvelope 5 is a ceramic insert 8 which is provided with the frusto-conical throat portion 9 terminating in a radially extending shoulder Il) against which is seated the electrode disc I2. The di'sc I2 is formed of iron or the like, and is thereby centered in and supported by the ceramic insert 8. The rear face of the electrode disc, as well as the rear or outer end of the insertf', is engaged by a resilient sealing member i3, preferably formed of rubber or the like and having the peripheral flange or skirt I4 overlying a tapered Vshoulder on the outer end of the ceramic to proternal wall of the open end of the switch. The sealing member I3 extends about the shank portion I5 of the electrode, which shank portion extends through the electrode and is provided With a shoulder holding the electrode in engagement with the radial shoulder I0 of the ceramic and provided with the reduced inwardly extending portion I6 which, at its inner end carries a metallic disc Il of a diameter such that it provides a slight annular opening between its periphery and the internal surface of the envelope 5. The extending portion I6 of the electrode shank I5 is provided with a punched over portion I8, which serves to lock the electrode disc I2 against axial movement relative to the shank.

A suitable refractory compression member I9 engages the outer face of the sealing means I3 and holds the same under compression, this stress being exerted through the compression member I9 by means of the spun-over end 29 of the envelope which holds the retaining washer 22 firmly against the rear face of the compression member. This compression member preferably has a reduced cylindrical extension 23 forming an insulating barrier between the spun-over edge of the envelope and the shank of the electrode.

The disc II carried at the inner end of the electrode shank is disposed slightly forwardly of the inner end of the ceramic 8, and is preferably formed of a material which is resistant to mercury arcs, such as tungsten, molybdenum or tantalum. A body of mercury 24 is introduced into the interior of the envelope after the electrode and sealing means has been assembled in position within the envelope through the tubulation 25, which tubulation then serves for evacuating the switch chamber 25 and filling the same with an inert gas under pressure, such as hydrogen. The tubulation is then pinched closed and welded as indicated at 2'I to seal the interior of the switch.

In the operation of the structure thus far described, it will be apparent that when the switch is tilted in a counterclockwise direction the body of mercury 24 runs along the inner surface of the envelope 5 into contact with the disc I1, and

will then be extruded through the annular gap between the periphery of the disc and the envelope and up the throat 9 of the insert into secondary contact with the electrode I2. However, the circuit is made or broken when the body of mercury 24 contacts the disc I'I, and consequently any arcing that may occur will occur between the mercury and the disc I'I. Inasmuch as the disc is formed of an arc resisting metal, this will have no detrimental effect upon the disc. However, the position of the disc and its relation to the interior of the envelope and the ceramic insures that the mercury when moving toward the disc will be trapped thereby on the rear face of the disc, and consequently will not have any splashing or vibrating action which might cause intermittent operation of the switch. As a result, a positive making and breaking of the circuit is provided with no secondary arcing or sputtering, the primary disc I'I serving as a primary contact member, and also as a baffle or dampening means for insuring positive contact and positive breaking of the circuit without any secondary arcing, such as would be the case if the disc were removed and the body of mercury allowed to run up the incline and impinge directly upon the electrode I2. There would be the possibility of it producing either a narrow forwardly extending tongue insufcient to carry the current, resulting in sputtering or frying at the leading edge, which contacts the electrode, and thereby producing secondary contacts, which are extremely undesirable, as well as pitting the face of the electrode.

It will be apparent that this construction provides a narrow angle switch which can be rapidly operated to produce snap action opening and closing of the circuit controlled by the switch,

In the form of the invention shown in Figure 2, the switch envelope is adapted to be mounted in vertical position, and is substantially identical in construction with the exception that the envelope 5 has its tubular body portion foreshortened so that when in vertical position the body of mercury 24', which is of appreciable volume stands at a level closely adjacent the tungsten or similar disc I'I. Here again the disc acts as a baiile preventing splashing of the mercury within the envelope, and also serves as the arc resisting medium between which the initial contact is made from the envelope to the electrode through the body of mercury. Such a switch may be used for closing the circuit when the switch is tilted a predetermined amount from a true vertical position, or for a pendulum type switch in which the circuit is made at opposite ends of its swing with the disc I'I serving as a bale for preventing surging movement of the mercury, which might result in secondary contacts.

Considering now the switch shown in Figure 3, there is provided a switch envelope 3i) having a counterbored portion 32 in which is pressed a ceramic insulating member 33 provided with a central bore. Extending through this bore is a tungsten electrode 34 having the inwardly projecting end 35 adapted to be engaged by the body of mercury 36 within the envelope 30 when the switch is tilted. The electrode 34 is provided with a shouldered portion 31 seating against the rear face of the ceramic bushing 33, and is held in position by means of the resilient compression gasket 38 fitting about the shoulder and against the rear face of the ceramic 33, which is radially expanded into sealing engagement by means of the ceramic compression member 39 which, if desired, may also be formed of hard rubber or the like and which is provided with the extending reduced cylindrical portion 45 radially insulating the projecting shank of the electrode 34 from the spun-over end 24 of the envelope which locks the retaining ring 43 and the sealing means in compressed position. A suitable conductor 44 is secured to the end of the electrode 34 and a second conductor 45 is electrically and mechanically bonded to the envelope 30. A suitable sealing cement or other sealing compound 45 is applied over the end of the envelope about the conductors 44 and 45, embedding them in position to relieve any stresses upon the connections to the electrode and the envelope. Over the external surface of the envelope there is applied an insulating case 41 which may be formed of wood, ber or molded rubber, or the like, and which has a closed end portion 48 provided with the openings 49 through which the conductors 44 and 45 are led out. The opposite end of the case 41 is open and the case is sealed against displacement from the envelope by means of sealing material 50 disposed in the open end thereof, thereby locking the envelope within the case. In this form of the invention the entire electrode 34 is made of a high arc-resisting material, such as tungsten or molybdenum, and

consequently provides a rlow resistance `contact velope. Similar parts are indicated by similar reference numerals throughout these figures. In Figure 4 a metal lenvelope 5l) is provided having the `enlarged end 52 provided with the internal shoulder 53 against which is seated the ceramic 54. 'The ceramic 54 is provided with a cupysl'iaped recess 55 through which projects the 4tungsten `or molybdenum electrode 565-. A suitable body of mercury 51 is provided in the envelope 5l) and when the switch is tilted, iiows into position to make contact between the envelope 50 and the projecting electrode 55. The electrode has its outer end projecting through a -bore in the ceramic 55, and is provided with an annular groove 58, this end of the electrode extending into the recess 59 of the terminal member 59, which may be formed of steel, pure iron, or the like. The terminal member 59 is held in position in the recessed end of the ceramic 54 by means of a resilient compression gaslret 62,

which is pressed against the shouldered head 63 of the terminal member by means of the com- Ipression member 64 formed of rigid insulating material, such as a ceramic, hard rubber, or the like, `the entire assembly being held in compressed engagement by means of the retaining washer .651and the spun-over end E6 of the envelope. The electrode 5S is held in the bore of the head y93 of the terminal member 90 by staking `over a portion of the terminal member at the outer end of the bore, as indicated at 61, into the annular groove 58. This iirmly locks the molybdenum or tungsten electrode in place `and -provides a unitary assembly.

If desired, the interior of the switch chamber may be evacuated through the tubulation 68, which is then pinched and welded closed to provide either a vacuum in the switch chamber, or the switch chamber may be lled with an inert gas under pressure through the tubulation, as described in detail in the copending application of Paul S. Bear, Serial No. 293,690, filed September 7, 1939.

In Figure 5 a similar construction is provided except that the electrode 10 is provided with a threaded end 12 which is threaded into a recess formed in the head portion 13 of the terminal member 14. This also locks the electrode in position since after the electrode has been threaded into position, the end of the terminal member 14 is ring staked about the threads to prevent displacement of the electrode, as indicated at 15. The electrode 1li in this form of the invention may be either molybdenum or tungsten.

In Figure 6 a still further modified form of construction is provided in which the electrode 16, which, in this form must be formed of molybdenum, is welded as indicated at 11 into a recessed portion in the head end 18 in the terminal member 19. The nickel welding material must be on the end of the electrode 16, as shown, the recess in the head 18of the terminal member having a concave bottom to accommodate this welding material. This firmly secures the electrode in position and provides a very compact and easily assembled construction,

In Figure i7 a still further modification of the switch structure is provided in which the electrode `8l) extends into a recess 82 in the terminal member 83, and is held -in place by having a shrink fit in this recess to compress vthe head portion 8`4 of the terminal member 83 about the =ahigh arc-resisting electrode within a metal lenouter end of the electrode 8l). With such a shrink fit, displacement of the electrode is `not possible inwardly, and thus a unitary joining of the electrode and terminal member '83 is provided.

Inthe `forms of the invention shown in Figures r3 to `'7, it is imperative that the radial clearance between the electrode and the internal wall of the envelope be not greater than .122 inch and not less Ithan .062 inch. The purpose of such a clearance is to insure that the body of mercury will readily Aflow into the annular space between the electrode and the envelope, and this clearance must be less than the .meniscus height of the mercury in order to effect positive contact as the .movable body Vof mercury engages `the electrode. .If too small a radial clearance is provided, the

body of mercury will be blocked from flowing into any substantial contact with the annular surface of the electrode, and only point contact will be effected. It is therefore essential that the radial clearance be maintained within the limits specied.

In the form of the invention shown in Figure 8, the envelope 59 is provided with a counterbored portion `providing the radial shoulder against Which the ceramic 85 is engaged. The ceramic 86 is provided with an enlarged outwardly opening recess 81 within which is disposed a cold rolled steel electrode head 88 which is axially recessed in an opposite direction to receive the outer end of a tungsten electrode 39 projecting through the ceramic 85 and extending into the recessed portion of the electrode head 88. The tungsten electrode is provided with an annular groove 90 which is ring staked to the electrode head 881as indicated at 92. This ,provides a very compact electrode structure in which the electrode head 88 terminates substantially in the same radial plane as the outer end of the cemimic-86. The terminal connection to the electrode head 88 is provided by a spring steel disc 93 which has pressure contact with the outer radial face of the electrode head 88 being held thereagainst by the molded rubber gasket 94 compressed tightly thereagainst by means of the retaining washer 95 and the spun-over end 96 of the envelope. The disc has connected thereto the terminal conductor 91 which is soldered or brazed to the disc as indicated at 98, and is provided with the insulating covering 99 protecting the conductor 91 from possible radial flashover to the ring 95 and end 96 of the envelope. With this construction a switch suitable for snap action may be provided and, if desired, the switch may be evacuated and filled with an inert gas by means of tubulation |90, although this is not essential. For snap action, the amount of mercury shown Would be increased since the operating angle of the switch would not be important under such conditions.

It is therefore believed apparent that we have provided a relatively economical switch 'construction which may be either of the unpurnped or the evacuated type, and in which the end assembly is simplified, while yet providing for a high arc-resisting metal contact so that the mercury directly contacts the arc-resisting electrode, which may be of tungsten or molybdenum, and no retained body of mercury is required.

We are aware that a number of changes may be made in certain of the details of the present construction, and we therefore do not intend to be limited except as defined by the scope and spirit of the appended claims.

We claim:

1. A mercury switch comprising a cup-shaped metal shell having a ceramic insert in the open end thereof, a frusto-conical recess in said insert, an electrode closing the small end of said recess and having an externally projecting shank extending axially inwardly through said recess beyond the inner end of said insert, an electrode disc of arc resisting metal carried on the inner end of said shank in radially spaced relation to said shell, said disc being solid and having its periphery spaced from said shell a distance less than the meniscus height of mercury and a body of mercury in said shell adapted to contact said disc to close the circuit through said switch and movable past said disc through said recess into contact with said electrode.

2. A mercury switch comprising a cup-shaped metallic envelope having a radial shoulder adjacent the open end thereof, a refractory insert seated in said end against said shoulder and having an axially extending bore therethrough, an electrode having a radially flanged portion seated in and closing the outer end of said bore and having an axially projecting shank extending outwardly of said envelope and a second shank extending inwardly thereof beyond said shoulder, means forming a resilient seal about the outer radial faces of said electrode flange and insert, an electrode baffle disc on the inner end of said shank radially spaced from the envelope and formed of an arc-resisting metal, and a body of mercury in said switch adapted to bridge between said disc and envelope to close a circuit therebetween and thence movable into contact with said shank and flange, said disc thereby taking any arcing occurring during make or breaking of contact.

3. The switch of claim 2 wherein said disc has its periphery spaced laterally from the interior of said envelope a distance less than the meniscus height of the mercury to insure that initial making and iinal breaking of Contact occurs on said disc.

4. In a mercury switch, a cup-shaped metallic switch envelope having an internal shoulder adjacent the open end thereof, a ceramic seated against said shoulder and having an outwardly facing axial recess, a terminal member having a head end seated in said recess, an electrode shank of arc-resisting metal secured in said head end and extending axially inwardly through said ceramic, said shank terminating at its inner end in a radial disc of arc resisting metal radially spaced from said envelope wall, sealing means for sealing said ceramic and terminal member in the open end of said envelope and a body of mercury in said envelope adapted to make and break the circuit with said terminal member by initial contact with said disc.

5. The switch of claim 4 further characterized in that theradial distance between said envelope and the periphery of said disc lies in the range between 0.062 and 0.122.

6. The switch of claim 4 further characterized in that the axial inner lface of said ceramic has a concave recess therein about said prong to increase the exposed lateral surface of said prong and to form a stop for said mercury body.

7. In a mercury switch, a cup-shaped metallic switch envelope having an internal shoulder adjacent the open end thereof, a ceramic seated against said shoulder and having an outwardly facing axial recess, a terminal member having a head end seated in said recess, an electrode prong secured in said head end and extending axially inwardly through said ceramic sealing means for sealing said ceramic and terminal member in the open end of said envelope, said terminal member terminating short of said open end, and a terminal conductor having resilient contact means at its end held against the terminal member by said sealing means.

CHARLES W. TRAUTMAN. HERBERT E. BUCKLEN, III.

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