US2935587A - Mercury switch with overload protection - Google Patents

Description

y 3, 1960 R. B. KHNKAEDE 2,935,587

I MERCURY SWITCH WITH OVERLOAD PROTECTION Filed Oct. 7, 1958 2 Sheets-Sheet 1 flll/efl/zor Ross 5. Km azaze R. a. KINKAIDE MERCURY SWITCH WITH OVERLOAD PROTECTION Filed Oct. 7, 1958 May 3, 1960 2 Sheets-Sheet 2 .772 0 are 22617 25. fi fafaaa e/ United States Patc MERCURY SWITCH WITH OVERLOAD PROTECTION Ross B. Kinkaitle, Elkhart, Ind., assignor to The Adlake Company, a corporation of Illinois Application October 7, 1958, Serial No. 765,803 Claims. (Cl. 200-112) of this type are employed in street lighting circuits in which mercury vapor lamps are used, the switch carries a rather high overload for a number of seconds when the lights are first turned on.

Switches of this type generally comprise an upright electrode mounted centrally of a hermetically sealed en velope which serves as the other electrode, with a sleeve like magnetic plunger received about the electrode and within the envelope for displacing the mercury fill as required to establish an electrical connection between the two electrodes. T he plunger may be actuated by energizing'an appropriately positioned relay coil of any suitable design.

It is well known that the mercury forming electrical contact between the switch electrodes tends to whirl or motorize under the action of electromagnetic forces acting on it under overload conditions. If this motorizing action in switches of the typementioned above becomes severe enough, the mercury under the action of centrifugal force builds up in the space between the plunger and the envelope, thereby dropping the level of the mercury adjacent the central electrode sufficiently to break the circuit. The motorizing or whirling action ceases when the circuit breaks, which permits the mercury adjacent the central electrode to re-establish contact that is maintained until the motorizing action again lowers the level of the mercury. The result is a rapid making and breaking of the circuit with consequent arcing that produces tremendous heat and destroys the switch.

A principal object of my invention is to provide a mercury switch in which circuit interruptions of the type described above are prevented.

A further principal object of the invention is to provide a mercury switch that will safely carry excessive overloads for brief periods of time without damage to the switch.

A further object of the invention is to generally improve upon the design of switches of this type.

Yet another object of the invention is to provide a simple and yet efiective method of eliminating the adverse elfects caused by the motorizing or whirling of mercury under overload conditions.

Stillanother object of the invention is to provide a mercury switch that is economical of manufacture, eificient in operation, and readily adapted for use under all conditionsunder which conventional mercury switches of the type described in said patent are used.

Otherobjects, uses, and advantages will be. obvious "ice or become apparent upon a consideration of the following detailed description and the accompanying drawings.

' In the drawings:

Figure l is a vertical cross-sectional view through a mercury switch relay of the type shown in said patent, illustrating my invention applied thereto;

Figure 2 is an exploded perspective view of the elements forming the plunger of the device shown in Figure 1;

Figure 3 is an end view of the plunger shown in Figure 1, the spring elements shown in Figure 1 being omitted;

Figure 4 is a side elevational view of the outer or magnetic element of the plunger of the device of Figure 1;

Figure 5 is a cross-sectional view along line 5-5 of Figure 4;

Figure 6 is a view similar to that of Figure 1 but illustrating the plunger in its maximum mercury displacing position in which current flows through the switch;

Figure 7 is an enlarged fragmental vertical crosssectional view of the upper portion of the switch shown in Figure 6, better illustrating my improvement and its result;

Figure 8 is a diagrammatic cross-sectional view along line 8-8 of Figure 7;

Figure 9 is a side elevational view of a ceramic insert forming a part of the illustrated magnetic plunger;

Figure 10 is an end view of the element shown in Figure 9; and

Reference numeral 10 of Figures 1 and 6 generally indicates a mercury switch of the type to which my invention may be applied, though it is to be understood that the specific switch shown is provided for illustrative purposes only. Switch 10 includes the basic components of the switch shown in said Patent No. 2,417,764 and generallycomprises a tubular envelope or shell 12, a base or cap 14, a top or cap 15, a central electrode 16, a magnetic plunger 18, and a mercury fill 20. The switch 10 is associated with an appropriate relay coil 22, and when coil 22 is energized, the magnetic plunger moves downwardly into the body of mercury to displace same and raise the level of the mercury adjacent the central electrode sufficiently so that it will cover the bared end 24 of electrode 16 and thereby establish electrical contact between the electrode 16 and the envelope 12, the envelope 12 serving as the second electrode of the switch.

Referring to Figure 7, under excessive overload conditions, the above mentioned whirling or motorizing action of the mercury tends to drop the mercury level at the center of the switch at least the distance between broken lines 26 and 28. This is because centrifugal force tends to build the mercury up around the side of the switch and in the space 21 between the plunger and the envelope. When the mercury level at the center of the switch drops to approximately the level of line 28, the electrical circuit breaks intermittently, with consequent arcing that produces tremendous heat which quickly destroys the switch.

In accordance with my invention, I provide the plunger 18 with a plurality of mercury return ports 30 that are aligned with the bared electrode end 24 when the plunger is in its maximum mercury displacement position. Under overload conditions, when the mercury builds up in the space 21 between the plunger and the envelope, it is returned to the space within the plunger through ports 30. This has the efiect of maintaining the mercury level at the center of the switch regardless of the overload conditions imposed upon the switch I the material 35,

Specific description The envelope 12 may be in the form of a cylindrical shell having its ends beveled as indicated at 36. Pref? erably, it is made from a non-magnetic material such as 18-8 stainless steel. The base or cap 14, preferably made of a material known as Kovar, manufactured by the Stupakoif Ceramic and Manufacturing Company of Latrobe, Pennsylvania, is received in the lower end of cylinder 36 and carries centrally disposed electrode 16. The electrode 16 is formed from molybdenum and carries a glass insulating sleeve 33 formed from a material such as #7052 glass made by Corning Glass Works of Corning, New York, which is telescoped over and fused to the electrode. Electrode 16 is sealed in place by a glass to metal seal, attachment being made by means of a glass sleeve 35 of suitable material such as #704 or #733A glass, also made by the Corning Glass Works of Corning, New York. sleeve 35 to both sleeve 38 and base or cap 14.

The material from which the base or cap 14 is made, and the material forming sleeve 38 should have coeificients of expansion that are similar to the coefiicient of expansion of the electrode.

Lead wires 2 and i3 are secured to the electrode 24 and the base 14, respectively, so that the switch envelope itself forms one side of the electrical circuit and the exposed end 24 of the electrode 16 forms the other side Seal is accomplished by joining of the circuit. A ceramic cup 43 is fused to the top of,

sleeve 38 by sealing sleeve 48a formed from cane glass of appropriate specifications such as #7052 cane glass rod made by Corning Glass Works; the cup 48 contains a body of mercury 47 which is in constant contact with the exposed electrode end 24. Preferably a ceramic ring 49 is received about the electrode 16 above the termination of glass sleeve 38 for the purpose of preventing chips of glass from breaking loose from sleeve 38.

The magnetically controlled displacer or plunger 18 in accordance with my invention generally comprises (see Figure 2) a cylinder 56 formed with spaced ridges 52 that are provided with a plurality (six in the illustrated embodiment) of level surfaces 54. The upper end of the cylinder 50 is formed with a plurality (six in the illustrated embodiment) of perforations 58 that in part define ports 36 of the plunger. The cylinder 50 is also formed with a perforation 66 for a purpose hereinafter made clear. I

The protuberances 55 remaining after surfaces 54 are formed serve as guiding spacers that maintain the proper positioning of the plunger within the envelope. As indicated in Figure 4, each perforation is conveniently located by drilling same half in. a fiat surface 54 and half in the adjacent rounded surface of the cylinder 50, at the point where these two surfaces merge (surfaces 54 being tangent to the rounded surfaces of the cylinder 5% at that point).

The cylinder 5i? carries a non-magnetic steel spring 62 at its upper end and a similar spring 64 on its lower end, the respective cylinder ends being somewhat reduced to receive the respective springs. Springs 62 and 64 may be made of the same material as the switch envelope 12 and the use of this material prevents the cylinder 50 from adhering to the top and bottom closures of the envelope when it is made of cold rolled steel or other magnetic material. Springs 62 and 64 are proportioned at their inwardly directed ends to frictionally engage the reduced ends of cylinder 59; at their outwardly directed ends, the last turns of the springs should be proportioned to freely receive and release the reduced ends of cylinder" 56?, and to project sufiiciently far from the cylinder ends to provide the necessary cushioning effect on actuation of plunger 18 that renders the switch silent in operation.

Mounted inside cylinder 50 is a ceramic insert 66 that is received in a counter-bore 68 formed in the ele meat 50. Ceramic insert 66 (see Figures 9, l0, and 11) is formed with a plurality (six in the illustrated embodi ment) of holes 70 that are spaced to line up with perforations 58 of the cylinder 5%. However, the axes of the individual holes 70 incline downwardly approximately 20 degrees as indicated in Figure 11. The insert 66 is also formed with a hole 74 that is positioned to be aligned with perforation 69 of cylinder 50. When the ceramic insert is positioned inside cylinder 50, the perforations 58 and the holes 76 form the ports 30 of Figure 7 and the inwardly turned end 78 of spring 62 is received in and extends through aligned holes 60 and 74 to secure the insert 66 to the cylinder 50.

It is important that the cylinder 50 and insert 66 be securely held together to insure that their perforations remain in alignment. This may be achieved by forming end 78 of spring 62 so that it binds the cylinder and insert to each other. I have found that, instead of disposing end 78 along a line coinciding with a plane extending through the axis of the spring, the end 78 should be disposed at an angle of approximately 30 degrees to such plane, thus bending it to an angle of approximately 60 degrees on itself, and also the end should be angled downwardly from the last turn of the spring approximately 20 degrees. With the spring end 78 so disposed, it tends to bind the cylinder Sit and insert 66 after being positioned on the plunger with end 78 inserted in holes 60 and 74.

The upper end of the envelope 12 is closed by appropriate cap 15 that receives a pin 82 through its center. Preferably, the switch 10 is hermetically sealed, and this is done by introducing a gas fill through the central opening of the cap 15 and then the pin 82 is welded to this cap.

In operation, when the coil 22 is energized, the plunger 18 moves from the position of Figure l to the position of Figure 6 thereby covering the exposed end 24 of electrode 16 with mercury. Current then passes through the switch between the leads 42 and 43. Under overload conditions, when the mercury fill tends to build up in the space 21 between the plunger and the envelope and drop at the center of the switch, as soon as the mercury level outwardly of the plunger reaches ports 30, mercury is returned to the space within the plunger in sufficient quantity to maintain the level of the mercury approximately as shown in Figure 7 regardless of the current load imposed upon the switch. By forming the holes 70 so that they are inclined downwardly, every bit of mercury that enters ports 30 is sure to drop therethrough into the space within the plunger.

Thus, the head applied to the mercury fill by centrifugal force under overload conditions may be relied upon to J return the mercury through the ports 30 and thus back into the center of the switch.

My invention insures that a sufiicient quantity of H181- cury will be maintained about the exposed end 24 of the electrode 16 so that intermittent making and breaking of the switch is avoided. As a result, switch 10 is able to carry excessive overloads for unusually long periods of time without damage to the switch. For instance, I have found that switches of the type illustrated that are nor mally rated at 30 amps. have been able to carry 200 amps. overload for brief periods. As a practical matter, the load limitations of switches in which my invention is embodied are now dictated by the leads and other circuiting rather than the switch components. I

I have found that the ports should not be less than .076 inch in diameter when they are rounded as ports 30 are. This provides a total cross-sectional area for mercury flow of .0270 square inch, with the cross-sectional area of each port 30 being .0045 square inch. However, ports 30 need not be rounded nor six in number, so long as the minimum cross-sectional area for mercury flow of each Port is at lea q al to .0045 square inch, and the total was.

cross-sectional area for mercury flow provided by the ports employed is not less than .0270 square inch. Thus, alternately, ports 30 may taice the form of four equally spaced quadrilaterally shaped slots proportioned to provide a total mercury return cross-sectional area of .0270' inch. However, at least two ports, substantially equally spaced from each other, are required; where more ports are employed, they should be substantially equally spaced from each other.

The ports 30 or their equivalents when proportioned in accordance with the above minimum figures provide the substantially unimpeded flow of mercury therethroug'n which is essential to the proper functioning of my invention.

In making the switch 10, a process similar to that described in said patent may be employed. However, I prefer that the cap 14 be welded into place before the electrode 16 is sealed in this element. The cylinder 50 of the plunger is preferably formed from a free machining, cold rolled steel, such as the product sold under the trademark LaLed and marketed by La Salle Steel Company of Chicago, Illinois. The ceramic insert 66 is preferably formed from No. 3135 Cordierite material or its equivalent. This material is made by the said Stupakofi Ceramic and Manufacturing Company. The ceramic cup is formed from Almanox 4462 made by Frenchtown Porcelain Company of Frenchtown, New Jersey. Ceramic ring 49 is made from RA-747 ceramic material, made by the Norton Company of Worcester, Mass.

In a specific embodiment of the invention, the envelope 12 is 2 /2 inches long; it has an external diameter of .876 inch and an internal diameter of .780 inch. The bottom cap 14 is made from .030 inch Kovar metal and is .337 inch in axial length; it is also .812 inch in maximum outside diameter. The top cap 15 is made from .0299 deep drawing steel and is .250 inch in axial length; it is .812 inch in maximum external diameter.

The magnetic cylinder 50 is .699 inch in external diam eter and .570 inch in internal diameter, and is 1.526 inches long; the cylinder measures .764 inch between opposed protuberances 55. Plunger perforations 58 and 60 are .076 inch in diameter. The ceramic insert 66 is 1 inches long and measures .569 inch in external diameter and .430 inch in internal diameter; holes 70 of the insert are .1015 inch in diameter and are at an inclination of 20 degrees with respect to a transverse plane perpendicular to the central axis of the switch. Hole 74 of insert 66 measures .0635 inch in diameter.

The electrode 16 is .125 inch in maximum diameter and .080 in minimum diameter; it is 2M inches long. Glass sleeve 38 is 1 inches long and ceramic tip 49 is Ms inch long and measures inch in external diameter and inch in internal diameter. The ceramic cup 48 is inch long and has an external diameter of Mt inch and an internal diameter of inch; the upper end of the cup 48 is spaced inch from the top of electrode 16.

The spring 62 is made from .040 diameter stainless steel wire while the spring 64 is made from .045 inch diameter stainless steel wire. It is important that the spring 62 and holes 60 and 74 of the plunger 18 and ceramic sleeve 66, respectively, should be proportioned, and the inwardly turned end 78 of spring 62 so angled,

0 that the ceramic insert and plunger 18 are securely locked together to prevent any rotation motion with respect to each other, as any rotation motion of the insert 66 with respect to plunger 16 would throw holes 58 and 70 out of alignment and thereby impede the mercury flow on overload conditions.

This application is a continuation-in-part of my application, Serial No. 655,104, filed April 25, 1957, the disclosure of which is hereby incorporated herein by this reference.

The foregoing description and the drawings are given merely to explain and illustrate my invention and the manner in which it may be performed, and the invention is not to be limited thereto except insofar as the appended claims are so limited, since those skilled in the art who have my disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention.

I claim:

1. In a mercury switch of the mercury displacement type, the combination of a cylindrical switch envelope, a mercury fill in the envelope adapted to be connected to one side of an electrical circuit, an axially positioned electrode in the envelope adapted at times to make contact with the mercury fill andhence complete a circuit through the switch, a magnetically responsive plunger telescoped over the electrode for controlling the level of mercury within the plunger and hence the condition of the circuit through the switch, said plunger having opposed ports in its upper region located so that when the plunger is in its circuit making position the ports are above the mercury level within the plunger at which the circuit is made and broken, said ports being of such size and combined area as to cause free flow of mercury from the outside of the plunger to the inside thereof to maintain the closed condition of the switch whenever the mercury level on the outside of the plunger rises a specified distance above the inside mercury level due to excess current flow through the switch.

2. The combination set forth in claim 1 wherein the combined area of said ports is at least .027 square inch and wherein the area of each of said ports is at least .0045 square-inch.

3. The combination set forth in claim 1 wherein said ports are at least two in number.

4. The combination set forth in claim 1 wherein said plunger comprises a cylindrical member formed from a magnetic material, a ceramic sleeve concentrically received within said cylindrical member, said cylindrical member and said sleeve being for-med with aligned openings forming said ports, and means for securing said cylindrical member and said sleeve together against relative movement therebetween.

5. The combination set forth in claim 4 wherein said openings of said sleeve are directed downwardly.

References Cited in the file of this patent UNITED STATES PATENTS

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