US1918794A - Mercury switch - Google Patents

Description

July 18,1933. RSBEAR 1,919,794

MERCURY SWITCH Filed Feb. 13, 1930 a above the mercur Patented July 18, 1933 UNITED STATES PATENT OFFICE PAUL S. BEAR, OF ELKH'ART, INDIANA, ASSIGNOR, BY MESNE ASSIGNMENTS, TO MINNEAPOLIS-HONEYWELL REGULATOR COMPANY, OF MINNEAPOLIS, MINNESOTA,

A CORPORATION OF DELAWARE MERCURY swrrcn Application filed February 18, 1930. Serial No. 428,019.

This invention relates to mercury switches.

Heretofore it has been proposed to so construct mercury switches as to adapt them to be machine sealed thereby facilitating the production of the switches on a large scale.

In the so-called machine sealed type of switch the outer glass envelope has one end softened by heat and then pressed or pinched into sealing engagement with the lead-in wires, both of which are extended in through the end of the envelope at which the seal is to be formed. The lead-in wires may constitute the electrodes of the switch but usually separate electrodes arewelded thereto. With prior switches of this type the arcing usually occurred in close proximity to the seal-ins and welds and consequently such switches were adapted for handling only small currents as the severe arcing of large currents would result in the break down of the seals or welds. To avoid this it has been proposed to extend the electrodes to the end of the envelope opposite that of which the seal-ins and welds are located but this is not entirely satisfactory and has the disadvantage of disposing electrodes for practically their entire extent in the gas atmosphere The presence of metal in the gas atmosp ere above the mercury is undesirable as the mercury vapor is con- ,stantly condensing on the electrode wires.v

Another type of switch that has been pro posed and which is adapted to stand up in operation and handle rather large currents, is what is known in the industry as a sleeve type switch, such a switch comprising an outer envelope. of soft glass and an inner sleeve or trap of hard glass or other are resistant material supported on the outer envelope by a cement impregnated ring of asbestos or supported on one of the electrodes. The disadvantage of this type of switch is that it is not adapted to machine production. In fact,the production of such switches approaches a laboratory process because it is diflicult to getjust the proper relation between the wall thickness of the inner sleeve, the wall thickness of the outer envelope or case and the clearance allowed for the cement.

If this operation is not properly done a loose rents and which sleeve 0r cracked case results. A further disadvantage occurs during the annealing of such switches for the reason that when the glass is being worked or annealed any mass capable of receiving or giving off heat, as for instance the inner sleeve connected by the cement impregnated partition or by cement to the outer case or envelope, will tend to retard the heating or cooling of that portion of the outer envelope engaged by the cement or partition with the result that a rather large percentage of the-envelopes are cracked during the manufacture of the switch. One of the principal objects of the present nvention is to provide a mercury switch which is adapted for machine production, which has the capacity to handle heavy curavoids the disadvantages of the prior types of switches utilizing inner protective elements of are resistant material. In carrying out the present invention a mercury switch is provided which has an outer envelope of soft glass or other suitable material and an inner protective element of are resistant material, one end of which is closed and the other end of which is opened. The open end of the inner protective element is loosely engaged with and supported upon the outer envelope. Through one end of the outer envelope lead-in wires are sealed by the pinch or machine seal. Electrodes are welded tothe lead-in wires and one of the electrodes extends through and is cemented to an aperture in the closed end of the protective element whereby the protective element is supported upon one of the electrodes as well as loosely supported on the case or outer envelope. The other electrode extends into the space between the inner wall of the outer envelope. A body of mercury is provided in the outer envedope and has a portion entrapped in the inner protective element and a portion in the space between the inner protective element and the outer envelope. A suitable arc suppressing atmosphere or gas is provided in the outer envelope after it has been exhausted of air and, of course, the switch is sealed by forming the usual sealing tip on the tubulation, provided for facilitating the evacuation of normally a the air and the filling of the switch with the inert arc suppressing gas.

In the operation of the switch the two portions of mercury unite and divide on the inner surface of the protective element adjacent its open end. One of the electrodes is always submerged and the other electrode has only a small portion exposed and such exposed portion is located sufliciently remote from the arcing zone to avoid any disadvantages, that is to say, there are no extensive areas of the electrodes on which the mercury vapor is continuously condensing.

A mercury switch constructed in this manner lends itself to quantity production or mavchine production in accordance with a novel method which avoids the necessity of accurate fitting of the component parts of the switch and the consequent loss when all parts are not exactly proportioned and which also avoids loss or breakage during annealing. In carrying out this method one of the electrodes is first assembled with the inner protective element after being welded to its leadin wire and after the lead-in wire has a glass bead placed thereon. This assembly and another lead-in wire with glass bead thereon and electrode welded thereto are then mounted in a chuck and the chuck is placed in the ordinary machine used for machine sealing. The outer envelope which is in the form of an open ended tube then has one "end positioned over the lead-in wires, the protective element and electrodes being received within the adj acent portion of the outer envelope. The end of the outer envelope overlying or surround! ing the lead-in wires is then heated and pinched or pressed down about the glass beads of the lead-in wires, in accordance with the usual practice. Following this a tubulation is formed on the outer envelope, the other end thereof is rounded and sealed, air is exhausted from the envelope through the tubulation, and mercury and an arc suppressing atmosphere are introduced into the switch through the tubulation. The usual sealing tip is then formed of material of the tubulation and the structure of the switch is complete. 7

Other objects and advantages reside in certain novel features of the construction, arrangement and combination of parts which will be hereinafter more fully described and particularly pointed out in the appended claims, reference being had to the accompanying drawing forming a part of this specification, and in which:

Figure 1 is a view in elevation showing the glass tube of which the outer envelope of the switch is formed;

Figure 2 is a view in end elevation showingzthe' inner protective element;

igure 3 1s a view in side elevation showing the inner rotective element and the two electrodes an lead-in wires assembled in a chuck Figure 4 illustrates the switch assembly after the machine sealing operation;

Figure 5 is a view in side elevation showing the switch structure following the formation of the tubulation;

Figure 6 shows the switch structure as it appears after the open end of the switch is rounded and closed; and

Figure 7 is a view inlongitudinal vertical section showing a completed switch embodying the present invention.

Referring to the drawing, and more particularly to Figure 7 the numeral 1 designates an outer envelope, which may be of soft glass or other suitable material and which hasbne end flattened and sealed about leadin wires 2 and 3, the inner end of which are welded as at 4 and 5 to electrodes 6 and 7. An inner protective element in the form of a cup or thimble 8 is provided and may be constituted of any suitable arc resistant ma terial such as ceramic, hard glass, quartz, porcelain, or the like. The protective element 8 has one end closed as at 9 and its other end open as indicated at 10. The open end is provided with integral legs 11 which extend angularly from the lower portions of the protective element as shown in Figure 2 and with an upper lug 12, the legs 11 and lug 12 being designed so as to loosely fit in the outer envelope. Clearance of five to fifteen thousandths of an inch is usually sufiicient for the purposes of the present invention. As will be understood from the drawing, the legs 11 and the lug 12 loosely support the open end of the thimble 8 on the outer envelope but for the major portion of its extent the thimble is maintained in spaced relation to and out of contact with the outer envelope. The closed end 9 of the protective element 8 is provided with an aperture 13 through which the electrode 6 passes, the electrode 6 having its inner end of angular form and extending down to the lower portion of the protective element. A coating of cement designated at 14 is ap lied to the electrode 6 and to its weld 4, or the dual purpose of securing the electrode 6 to the protective element 8 and providing an insulating covering or coating over a portion thereof, thereby preventing short circuiting of the electrodes.

A body of mercury 15 is provided in the outer envelope and when the envelope is appropriately tipped or tilted this body of mercury divides into two portions, one of which is entrapped in the thimble 8 and the other of which is contained in the space within the outer envelope on the outside of the thimble. The portions of mercury unite and divide on the inner surface of the protective element 8 and preferably the parts are so proportioned and the quantity of mercury provided is such that the portions of the mercury unite and divide at approximately the point designated at w in Figure 7. Thus the arcing-zone is located at a point within the outer envelope remote from the seal-ins and welds and the protective element 8 is interposed between the arc and these seal-ins and welds -as well as between the arc and the outer envelope. Only a portion of the electrode 6 is located adjacent the arcing zone and even such portion is spaced some distance therefrom so that there are no extensive areas of electrode wire on which mercury vapor is continuously condensing. 1

In manufacturing the switch shown in Figure 7, the lead-in wires 2 and 3 are first welded to the electrodes 5 and 6 and then glass beads 16 are applied to the lead-in wires, the beads 16 being wetted to and surrounding portions of the lead-in wires. The electrode 6 is then extended through the opening 13 in the thimble 8 and cemented thereto. The next step in the operation consists in clamping the lead-in wires 2 and 3 in a chuck designated at 0, the protective element 8 being at this time supported by the electrode 6 welded to the lead-in wire 3. Following this, the glass tube T from which the outer envelope 1 is to be constructed is slipped-over the electrode and protective element amembly while the same is mounted in the chuck and then the pinch seal P is formed in the usual manner. The switch is then completed in accordance with standard practice, that is, tubulation T is formed, the end of the tube then remaining open is rounded andclosed, mercury is introduced into the switch, air evacuated therefrom and an arc suppressing gas introduced thereinto and the sealing tip S is formed. There is thus provided a mercury switch which lends itself to a speedy and economical mode of manufacture, that is, to the machine sealing of the lead-in wires to the outer envelope thereof. At the same time a mercury switch is provided which can handle heavy currents due to the protection of the outer envelope and due to the protection of the welds and seal-ins and also to the avoidance of any extensive exposed areas of electrodes on which the mercury vapor incident to arcing is continuously condensing.

It is to be understood that the term electrode as used in the claims is employed in a v generic sense and intended to comprehend all of the various types of conductors with which the mercury coacts to form a conductive path in completing the circuit. Usually these conductors comprise lead-in wire and separate electrodes welded thereto and in the claims the term electrode is intended to comprehend such a construction as well as a single piece conductor sealed through the outer envelope, except, of course, where the same claims recite not only electrodes but also lead-in wires.

The invention claimed is:

1. A mercury switch comprising an outer envelope, electrodes extending thereinto, a

pinch seal between said envelope and both of said electrodes, an inner cup of are resistant material having its closed end adjacent to said pinch seal and supported upon one of said electrodes, the electrode upon which the cup is supported extending thereinto, the other electrode extending into the space between the cup and the envelope, and a body of mercury uniting and dividing on a surface of the cup.

2. A mercury switch comprising an outer envelope, electrodes extending thereinto, a pinchseal'between said envelope and both of said electrodes, an inner cup of are resistant material having its closed end adj acent to said pinch seal and supported upon one of said electrodes, the electrode upon which the cup is supported extending thereinto, the other electrode extending into the space between the cup and the envelope, means at the open end of the cup loosely engaging the outer envelope for supporting the open end of the cup therein, and a body of mercury uniting and dividing on a surface of the cup.

3. A mercury switch comprising an outer envelope, electrodes at one end thereof, a pinch seal between said end of said envelope and said electrodes, a trap of are resistant material having a closed end adjacent said pinch seal and having an open end remote therefrom and provided with means loosely engaged with said outer envelope to support the open end of the trap thereon, said closed end of said trap having an aperture through which one of said electrodes is extended, cement between the wall of the aperture and the electrode extended therethrough, said cement being extended along said last mentioned electrode to provide an insulating covering for the portion of the electrode between the trap and the outer envelope, said other electrode extending into the space between the trap and the outer envelope, and a body of mercury having a portion confined in the trap and a portlon in the outer envelope outside of the trap, said portions of the mercury uniting and separating within and on a surface of the trap when the switch is operated.

4. A mercury switch comprising an outer soft glass envelope, an inner cup of are resistant material, having a closed end and an open end, electrodes extending into the outer envelope, a pinch seal between one end of the envelope and the electrodes, one of the electrodes extending into and supporting the closed end of the cup, legs at the other end of the cup for loosely supporting the same on the outer envelope, the other electrode extending into the space between the outside of the cup and the outer envelope, and a body of mercury uniting and dividing on the surface of the cup.

5. A mercury switch comprising an hermetically sealed outer envelope, a thimble of are resistant material having an open end loosely supported on the outer envelope, and having a closed end adjacent one end of the outer envelope, electrodes sealed through the outer envelope adjacent the closed end of the thimble, said thimble having an aperture in its closed end through which one of the electrodes passes, means for securing the thimble to the electrode extending through the aperture thereof, the other electrode extending into the space between the outer envelope and the thimble and a body of mercury in the outer envelope and having portions uniting and dividing on a surface of the thimble.

6. A mercury switch comprising an hermetically sealed outer envelope, a mercury trap of arc resistant material positioned with the outer envelope and having an open end loosely engaged with and supported on the outer envelope and also having a closed end formed with an aperture, an electrode supported on the outer envelope and extending through the aperture of the trap and into the interiorthereof, yieldable means for securing the electrode to the trap, a second electrode sealed through the outer envelope and extended into the space between the outer envelope and the trap, and a body of mercury having a portion confined in the trap and a portion in the outer envelope outside of the trap, said portions of the mercury uniting and separating within and on a su face of the trap when the switch is tipped.

PAUL S. BEAR.

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