US2142522A - Plunger switch - Google Patents

Description

N. M KINNEY PLUNGER SWITCH Jan. 3, 1939.

Filed Dec. 14, 1937 w c R M m R NU E E0 T w@ r 0 NH VI Patented Jan. 3, 1939 UNITED STATES PATENT OFFICE PLUNGER SWITCH Application December 14, 1937, Serial No. 179,839

2 Claims.

My invention relates to an electric circuitbreaker, and particularly relates to liquid contacts for completing an electric circuit.

Heretofore, mercury tube switches have been employed to open or close electrical circuits. Although it has been found that the mercury will take part of the arc when the circuit is broken, nevertheless the electrode from which the mercury recedes when the circuit is broken takes part of the arc and eventually becomes pitted and deteriorated. Various structures have been proposed from time to time in which the contact wear and erosion are greatly reduced.

Provisions have been made to surround one of the fixed electrodes in the switch with mercury, but the problem has always arisen as to the manner of sealing a cup or other suitable container for the mercury about one of the electrodes and which cup will withstand the change in temperatures to which the unit is subjected. As different elements expand and contract at diflerent rates, one element may have a coefiicient of expansion different from the other element so that a breaking of the fragile insulator element occurs. This difiiculty has resulted in practically no successful commercial mercury switches being used wherein electrical contacts of mercury as one conductor engages another portion of mercury as the second conductor. r

With the above difilculties to be overcome, it is an object of my invention to utilize a liquid conductor for making and breaking an electric circuit within a sealed container.

Another object of my invention is to construct a mercury electric switch of material so that electrolysis will not form a permanent electrical circuit.

Another object of my invention is to provide a circuit making and breaking unit in which a new electrical contact surface is provided at each make and break of the circuit and in which the contacts are maintained in a clean condition by reason of the quick movement of the plunger which displaces a portion of the contact forming liquid so that an electrical contact is formed.

Another object of my invention is to provide two electrodes within a single housing which electrodes emerge from the same area or base-this structure enables both electrodes to be simultaneously sealed and eliminates one operation over the devices of the prior art, and it also simplifies the replacement of the mercury switch in an outside circuit connecting unit.

Another object of my invention is to construct a mercury switch wherein the metallic plunger or mercury displacer will not oxidation.

A still further object of my invention is to provide a seal which will join and expand in unison with two elements each of which has a different coefiicient of expansion from the other element.

A still further object of my invention is to eliminate or reduce the hum where the mercury switch of the plunger type is employed in conjunction with alternating current.

Other objects of my invention are to provide an improved device of the character described that is easily and economically produced, which is sturdy in construction and which is highly efilcient in operation.

With the above and related objects in view, my invention consists in the details of construction and combination of parts, as will be more fully understood from the following description, when read in conjunction with the accompanying drawing, in which:

Fig. 1 is a fragmentary side elevational view of an electric mercury switch embodying my invention together with an electromagnet shown in operative position and a board on which electrical terminals connect the circuit to the switch.

Fig. 2 is an enlarged perspective view of the ceramic, or insulating liner adapted to surround the interior surface of the metallic plunger.

Fig. 3 is a perspective view of the magnetizable metal plunger.

Fig. 4 is a plan view of the mercury switch terminal connector and the mercury switch attached to the connector.

Fig. 5 is an enlarged sectional view showing a plurality of sealing beads, each bead having a different coefiicient of expansion.

Fig. 6 shows the magnetic field core which supports the electromagnetic coil E and a cylindrical magnetic ring which interfits with the field core. The magnetic ring assists in lifting the plunger.

Referring now to the drawing, I disclose a hermetically sealed tubular container or envelope, generally designated as A, made of heat resistant glass. The base in of the tube has two spaced electrodes or terminals l2 and It pass therethrough so that each electrode extends into the chamber of said glass tube. The electrodes l2, H are preferably composed of tungsten and are surrounded by seals of heat resistant beads l6 and I8, respectively, at the junction of the tubular container and the electrodes. These beads eventually are fused to the envelope so that an integral unit is formed.

The electrode I4 is oilset so that it lies within be discolored as by the vertical center of the tube, and it may be partially encircled or encompassed by a spaced ceramic cylinder or tube, generally designated as B. The lower end of the ceramic cylinder B may be annealed to and attached to the upper part of a circular heat resistant bead 24, as shall here-' inafter be further explained.

Since the ceramic cylinder and the heat resistant glass have different coeificients of expansion, difiiculty has been experienced in uniting the adjacent ends of such materials because of breakage. I seal two elements of different coefiicients of expansion together by a series of beads or cylinders 20, 22, and 24, each of a different coeflicient of expansion in order to allow for the different degrees of expansion. As an example, the bead or cylinder 20, which has one end joined to the top of the heat resistant bead I 8--the latter encircles the part of electrode l4 passing through the envelope Ahas a coeificient of expansion almost equal to that of the heat resistant bead. The bead or cylinder 24, having its upper edge joined to the lower end of the ceramic cylinder 13, has a coeflicient of expansion almost equal to that of the mercury retaining cylinder B. The intermediate bead or cylinder 22, encircling a part of the electrode l4, has its ends joined to the adjacent ends of the beads 20 and 24 and has a coefiicient of expansion intermediate the coeificient of expansion of the beads 20 and 24. If the above graded sealings are not sufilcient, additional graduations of beads or cylinders having still different coefficients of expansion may be employed.

Mercury, generally designated as H, fills the lower end of the envelope A and a part of this mercury fills the hollow ceramic cylinder B which surrounds the electrode. The ceramic tube B projects above the electrode l4 which is within the tube, and the mercury therein is in electrical contact with the electrode.

A hollow cylindrical magnetic plunger or liquid displacer, generally designated as P, having an inner quartz or heat resistant glass cylindrical liner 28 is buoyed or floats upon the mercury H within the lower end of the envelope. The metal plunger or armature P is adapted to move vertically upwardly and downwardly under control of an electro-magnet, generally designated as E, so that as the'electro-magnet E is energized, the plunger or armature P is pulled downwardly into the mercury causing the mercury to rise upwardly over the top of the cylinder L so that the circuit is completed. Upon the electro-magnet being deenergized or the flux field being reduced, the plunger will be buoyed upon the surface of the mercury, and the level of the mercury will fall because the mercury now displaces the plunger which formerly displaced some of the mercury. Hence, a portion of the mercury will remain within the ceramic tube in engagement with the center electrode l4, and the mercury surrounding the outside of the tube will recede to a level below that of the top of the cylinder. Hence, the circuit will be opened.

It should be particularly noted that the makeand-break of the electrical circuit is completed solely by a mercury to mercury contact and not against either one or the other of the electrodes l2 or l4. In this way there is no danger of the electrodes being pitted or corroded, and the ceramic tube is such that it will not take a coating of mercury; other materials, such as glass, may have a coating of metal electro deposited thereon. The use of a ceramic mercury retainer eliminates any permanent circuit being established within the tube.

The magnetic plunger P is made of a single stamping of magnetizable metal and has a plurality of small extensions or projections 30 on its outer curved bounding surface 32; these projections engage the envelope A, and because they present a small contact surface they reduce friction between the wall of the envelope and the plunger. The plunger has an inwardly extending ridge or a series of inwardly extending indentations 34 adjacent its upper edge; the ridge or indentation limits movement of the ceramic liner 28 in an upwardly direction as Fig. 1 is viewed. The plunger P has a plurality of inwardly extending integrally formed tabs 36, 38 which engage a portion of the lower end of the ceramic liner 28 to prevent the liner from moving in a downwardly direction with respect to the plunger P, as Fig. 1 is viewed. Since the plunger is of a single stamping, itis formed into a cylindrical shape with its vertically extending edges 40, 4| spaced apart to form an air gap 42. Since about 98% of the mercury switches under discussion are used in alternating current circuits, the A. C. hum is eliminated or greatly reduced because of the air gap. The reason for, the reduction or elimination of the hum is that the plunger is unsymmctrically formed with respect to the elecalso aids in the ready sliding of the magnetic plunger when and as it engages the inner wall of the tube. By using an enamel, the cost of the plunger is materially reduced and serves as an easy and ready way of insulating the shell.

Annealing process Heretofore, the metallic plunger has been decolorized or oxidized during the annealing process. To prevent the oxidation or discoloring of the magnetic alloy of the plunger P in order to eliminate the expensive bright dipping of the plunger to a saleable condition, the glass unit blank of the envelope is evacuated after the electrodes and magnetic plunger are placed within the glass envelope, the mercury alone being omitted. The lower end of the tube where the electrodes join the tube is then annealed. After the annealing process the tube is opened, mercury is poured therein, then the tube is exhausted so that a vacuum is formed, and the tube is sealed without any decolorization of the plunger.

The switch mounting block In order to facilitate the replacement of the mercury switch, I provide a convenient base and terminal connection illustrated in Fig. 1. The electro-magnet E is formed as a toroid, and through its hollow center the switch envelope A is placed so that the plunger P is buoyed on the mercury, and upon the energizing of the electromagnet E the plunger P-is pulled into the mercury to establish an electrical contact.

The electrodes l2 and I4 slip into electrical engagement with terminals, generally designated as T and T The terminal T of electrical conducting metal has a bifurcated end defined by a slot 44 between the parallel legs 46, 41. An enlarged circular-like opening 4. between the legs 46, 41 receives one oi the electrodes, and a binding nut ll passing through an opening 52 in leg 41 and screw-threaded into leg 46 holds the electrode securely in position. A holding nut 54 passing through a threaded opening 56 at one end of the terminal holds the terminal to the tube and electro-magnet mounting blocks, generally designated as D. This feature eliminates pig-tail leads and also butt-welding of borated copper in order to solder the said pig-tail leads to the electrodes.

As the terminals T and T are identically constructed, a description of one terminal will sumce as a description of both terminals.

The electro-magnet E is held between a magnetic yoke or field structure, generally designated as F. The magnetic yoke or field structure F comprises two parallel by a back piece ll. The parallel arms 60 have aligned central openings 64 and 65 therein so that the tube A may pass therethrough, and each of the legs ll, 62 are slotted as at 66, 68, respectively.

A magnetirable ring, generally designated as G, has a slotted cylindrical surface Ill concentric about the inner portion or the toroidal electromagnetic coil E and is located so that it is between the spaced legs 02. The magnetizable ring G has a flange I2 so that it does not slip through the electro-magnetic coil. The slotted magnetic ring assists in lilting the plunger upspaced arms 60, 82 joined wardly in a rapid manner. Hence, the time of arcing is diminished.

Although my invention has been described in considerable detail, such description is intended as illustrative rather than limiting, since the invention may be variously embodied, and the scope of the invention is to be determined as claimed.

I claim as my invention:-

1. A process of treating an electromagnetic actuated mercury switch wherein the magnetic plunger is not discolored comprising the steps of forming an envelope, inserting the magnetic plunger therein, inserting the electrodes within one end of the tube, compressing said electrodes into the envelope in a single operation, creating a vacuum within said envelope, annealing the tube, inserting mercury within said envelope, exhausing the air therefrom, and sealing the envelope.

2. A process of forming an electromagnetic actuated mercury switch which comprises the steps of forming an envelope, stamping a magnetic plunger, forming the plunger so that a small air gap exists between its ends, inserting the magnetic plunger within said envelope, inserting and compressing the electrodes within said tube, creating a vacuum within said envelope, annealing the tube, inserting mercury within said envelope, exhausting the air from said envelope, and sealing the envelope.

NORMAN MCKINNEY.

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