US1971924A - Mercury contact device - Google Patents

Description

Aug. 28, 1934. w. R. WALKER MERCURY CONTACT DEVICE Filed Feb. 20, 1950 HIS ATTORNEY Patented Aug. 28, 1934 UNITED STATES PATENT OFFICE NIERCURY CONTACT DEVICE Application February 20, 1930, Serial No. 429,355 10 Claims. ((31. 200-152) The present invention relates to devices having sealed vitreous envelopes such as electric switches of the fluid flow type, and particularly to mercury switches, and I the method of production thereof.

A particular object of the invention is to provide a device such as a fluid flow switch which may be evacuated and sealed off through an inlead. Another object of the invention is to provide a fluid flow switch containing an arc suppressing atmosphere which is under considerably greater than atmospheric pressure. Another object of the invention is to provide a method for hermetically sealing such devices. Another object of the invention is to provide a fluid flow switch which will be sensitive to slight movements thereof. Another object of the invention is to provide inleads having a large area of contact with the mercury or other fluid. Still another object of the invention is to provide inleads which may be readily sealed into a soft glass envelope. Another object of the invention is to provide a switch in which the envelope is protected by the conducting fluid from the arc of rupture. A further object of the invention is to provide a method for manufacturing such a switch. Still other objects and advantages of the invention will appear from the following detailed specification or from an inspection of the accompanying drawing.

The invention consists in a fluid flow switch or other similar device having the several new and novel features hereinafter set forth and claimed.

Mercury switches and the like having vitreous envelopes within which is a vacuum or a conditioned atmosphere have heretofore been evacuated and the desired atmosphere admitted thereto through a vitreous tubulation which was thereafter sealed off as close as practicable to the envelope. The tip thus left has always been undesirable because it greatly increased the breakage hazard. Furthermore the pressure of the atmosphere within such devices has had to be limited heretofore to substantially atmospheric pressure since during seal-off the softened glass will not withstand greater internal pressure. I have discovered that by making the inleads with suitable openings therethrough these envelopes may be evacuated through said inleads, eliminating the usual vitreous seal-off tip entirely. With such a construction the pressure which may be used within the envelope is limited only by the mechanical strength of the envelope. This makes it possible to produce a switch employing relative- 1y high gas pressure in which the arc of rupture will be suppressed in an extremely short interval.

When the pressure 'm'thin the envelope is appreciably in excess of atmospheric pressure I employ a novel method of my invention to hermetically seal the opening through the electrodes. According to this new method a thin-walled tubular section of the electrode is flattened by mechanical pressure, by hand or machine, and the tube then closed by the application of welding heat thereto, provision being made to prevent the rupture of the tube between the weld and the envelope. In some cases the softening of the metal under the welding heat is utilized to facilitate the flattening of the tube. These operations are conveniently carried on while the tubular part of the electrode is still connected to the system on which it was evacuated and through which the gas under pressure was admitted, although the mechanical closure of the tube may be relied upon to maintain the seal for a short time if it is desiredto remove the device from the system before welding or otherwise hermetically sealing the tube. While this method has special advantages when used to seal switches having an internal pressure in excess of atmospheric, it is likewise employed when sealing switches having less internal gas pressure, since its convenience and effectiveness make it superior to other methods by which these openings could be hermetically sealed.

While any of the inlead materials heretofore used, such as platinum, tungsten, dumet, and the like may be used, I have found that in the manufacture of mercury switches the use of chrome iron is especially desirable. All of the metals heretofore used for this purpose amalgamate to some extent with the mercury, especially under the influence of the electric arc, so that under operating conditions the electrodes thereof soon become coated with a layer of amalgam to which the mercury adheres. While for many purposes this is desirable, it proves highly undesirable in those cases where operation of the switch upon slight movement thereof is required. I have discovered that an electrode of chrome iron alloy may be used in such switches with great success due to the fact that this material does not amalgamate with the mercury during operation of the switch, with the result that the electrode always presents a surface to which the mercury does not cohere and adheres but slightly.

The use of this material for the electrodes also simplifies the problems encountered in sealing the electrodes into soft glass envelopes. Neither dumet nor platinum, the materials which have been heretofore commonly used in seals to soft Platinum is too expensive to use in switches in the case of large current capacities.

I have discovered that chrome iron. alloy, in addition to being suitable for the contacting electrode, can be sealed directly into a soft glass envelope, thus solving the problem in a simple manner. Since the chrome iron alloy has a slightly greater coefficient of expansion than lead glass it is preferably sealed thereto in such a fashion that any strains on the glass will be compressive, as by sealing the glass to the inside wall of a cup-= shaped electrode. An electrode of this shape is furthermore decidedly advantageous in a mercury switch, since it permits a large contact area with the mercury, with a correspondingly low internal resistance characteristic and a correspondingly high current capacity for a switch so constructed. I have also found that by a novel arrangement of the electrodes within the envelope the mercury or other fluid may be made to shield the vitreous envelope from the arc of rupture, greatly increasing the life of the switch.

For the purpose of illustrating my invention I have shown one embodiment, together with several variations thereof; in the accompanying drawing, in which Fig. 1 is a longitudinal section of a mercury switch of the metal to mercury type, shown in the open circuit position,

Fig. 2 is a similar view of the switch of Fig. 1, shown in a closed circuit position,

Fig. 3 is a sectional view of one of the electrodes of the switch shown in Figs. 1 and 2,

Figs. 4-6 are sectional views of modifications of the electrode of Fig. 3, showing various methods of attaching current carrying leads thereto,

Fig; 7 is a longitudinal section of a switch similar to that of Fig. 1, but having an opening through one of the electrodes which is closed by a tubular tapped lead which is hermetically sealed near the end thereof,

Fig. 8 isa longitudinal section of a modification of the switch of Fig. 7 in which both electrodes have tubular leads integral therewith, each of said leads having the opening therein hermetically sealed in a suitable manner, a larger quantity of mercury likewise being shown in this switch, and

Fig. 9 is a sectional view of a fragment of the switch of Fig. '7 showing an alternative method of sealing the opening in the electrode, and the manner of sealing a chrome iron inlead into a glass having a materially lower coefiicient of expansion.

In the drawing, with particular reference to Figs. 1-3, a vitreous envelope 1, of fused silica, pyrex, nonex or the softer glasses, but preferably of soft glass, such as lead or lime glass, has sealed thereinto the electrodes 2 of chrome iron alloy or the like. One such alloy which I have found to be suitable for these electrodes is a chrome iron alloy sold by the Crucible Steel Co. of

America under the trade name of Stainless Iron 23/30 Chrome Annealed, although other similar alloys having a coefi'icient of expansion not materially greater than that of soft glass and having the property of not amalgamating with mercury may be used. These electrodes are each cup-shaped, with the closed end thereof extend ing downwardly into the envelope 1, the glass walls of which are fused to the inner wall of each cup near them thereof, the inner wall of each of these electrodes being preferably beveled in order to facilitate the sealing of the glass thereto. An upwardly extending projection 4 is left in the bottom of each of the cups 2 in order to facilitate the welding of the leads 5 thereto. The external ends of the leads 5 are preferably coated with solder or the like in order to prepare them for the attachment of suitable flexible leads. A body of mercury '7 is enclosed within said envelope 1, which is preferably provided-with a hydrogen atmosphere and sealed off at 8. In order to gain sensitivity one electrode 2 is placed near the end of the envelope 1 but at a considerable distance from the bottom thereof, so that the circuit between the mercury and said electrode will be broken while said mercury is still directly below said electrode, while the other electrode 2 is made to extend nearer the botom of the envelope so as to ensure contact with the mercury 7 at the time that the circuit is made or broken between said mercury and said first mentioned electrode 2.

In Fig. 4. there is shown a similar electrode 12 with modified lead-attaching means in the form of a tapped socket 13 in said electrode into which av suitable current lead may be inserted. In a variation of the electrode of Fig. 4, the electrode 22 of Fig. 5 has a central threaded stud 23 which is integral with said electrode, to which an external lead may be attached in an obvious manner. Another means of attaching the leads to electrodes of this type is illustrated in Fig. 6, where the electrode 32 is shown fused to a fragment of .a vitreous envelope 1, with a flexible lead 33 extending downwardly into proximity to said electrode, a mass of solder or other easily fusible metal 34 filling the cup-shaped opening formed by said electrode and said envelope 1, whereby said lead 33 is connected to said electrode 32. As will be obvious any of these or other variations may be substituted for the electrodes 2 in the switch of Figs. 1 and 2v without affecting the operation thereof.

In Fig. '7 there is shown a mercury switch ,having the same operating characteristics as the switch of Figs. 1 and 2, but differing therefrom in several important details of construction. The envelope 11 is similar to the envelope 1 of Figs. 1 and 2, for instance, save that the seal-off tip 8 is here omitted. An electrode 12', which differs from the electrode 12 of Fig. 4 in that the tapped opening 13' extends entirely through the bottom of said electrode 12', is substituted for one of the electrodes 2.

A threaded tubular lead 15 of any suitablematerial, such as nickel, which will not contaminate the mercury and which is easily welded is screwed into the opening 13, said lead 15 being thereafter preferably soldered or welded to the electrode 12' to ensure a hermetical seal therebetween. The tubular lead 15 provides a convenient opening through which the envelope 11 may be connected to a system for evacuation and for the admission of mercury and a suitable arc suppressing atmosphere at any pressure, several atmospheres if desired, said lead 15 being thereafter flattened and the sides thereof welded together at 16 to hermetically seal the opening therethrough. When pressures appreciably in excess of atmospheric pressure are employed Within the envelope 11 I preferably employ means such as a mechanical gas tight pinch of the tubular lead 15 between the point where the weld 16 is to be made and the interior of the envelope 11 to prevent rupture of the softened metal wall of said lead 15 during the welding process. As an alternative, jaws conforming to the shape of the tubular lead 15 may be made to grip said lead adjacent to the weld 16 during the welding thereof, so that rupture of the lead is prevented. In

either case the weld 16 is conveniently made by applying the .jaws of an electric welding machine under heavy pressure to opposite sides of said tube 15. In some cases where the walls are of considerable rigidity, the walls may not collapse until the welding heat is applied thereto, but in any case the weld results in a perfect hermetical seal of the opening through the lead 16. In switches having atmospheric pressure or less within the envelope 11 the precautions against rupture of the tubular lead 15 may, of course, be omitted.

An electrode 12 is likewise substituted for the other electrode 2, a solid threaded lead 5' being used to make the connection therewith. The external ends of the leads 15 and 5 are preferably solder dipped to facilitate the connection of a suitable flexible lead thereto; or a flexible lead may be inserted in the open end of the lead 15, being held in place therein either by soldering, welding or by mechanically crimping said lead 15 down onto said flexible lead.

The switch of Fig. 8 is a modification of the switch of Fig. '7, two electrodes 22' having tubular leads 23' integral therewith being utilized in this switch, so that a suitable gas may, if desired, be admitted through one of the leads 23' and drawn 7 oif through the other lead 23', making possible a circulation of the gas in the envelope 1 which is extremely effective in flushing said envelope of deleterious gases. After conditioning the atmos phere therein and admitting the mercury thereto said envelope is sealed oil by flattening and welding the leads 23' at 24, according to the method described in connection with the switch of Fig. 7, or in any other suitable manner. Flexible leads may be attached to said leads 23 in any of the ways mentioned in connection with the previous figures. A larger quantity of mercury 7 is also introduced in this switch, preferably sufiicient to almost touch the electrode 22 which is adjacent to the end of the envelope 11 when said envelope is in the position shown in Fig. 8 in order to provide greater sensitivity.

Under certain circumstances the use of a tubular lead, such as is shown in Figs. 7 and 8, may be unnecessary. For example, a switch such as shown in Fig. '7, but with the lead 15 omitted, may be inserted within a suitable chamber which is then evacuated, and later filled with an arc suppressing gas such as hydrogen at a pressure somewhat in excess of atmospheric. By inserting a lead 5' in the opening 13', as shown in Fig. 9, immediately after removal from this chamber the switch will be closed oil without appreciable contamination of the gaseous contents through diffusion of air thereinto. The joint between the lead 5' and the electrode 12 may be later soldered or welded to protect against possible leakage therethrough.

In some cases, as where exceptionally large currents are to be interrupted, it may be desired to construct the switch envelope 1 or 11 from a glass having the property of withstanding high temperatures and rapid fluctuations in temperature, such as a boro-silicate glass or fused silica, while retaining the advantages oifered by the chrome iron electrodes. While these glasses have a materially lower coeflicient oi expansion than chrome iron, the latter may be sealed into envelopes thereof by the use of a graded seal between the envelope and the chrome iron inlead, using glasses of intermediate coefficients of expansion therebetween. In Fig. 9 I have shown the details of such a seal, which may be employed in the switches of any of the previous figures, the various steps of the seal being indicated at 10.

In the use and operation of the switch of Figs. 1 and 2, as the electrode end of the envelope is depressed from the .position shown in Fig. 1 the mercury 7 flows toward that end ofsaid envelope, increasing in depth therein until it makes contact with the right hand electrode 2. Further depression of that end of the envelope 1 causes a further rise in the mercury level until the other electrode 2 is also in contact with said mercury 7, as shown in Fig. 2. As the switch is moved back toward the position shown in Fig. 1 the mercury level falls until contact is broken at the left hand electrode 2, thus rupturing the circuit through said switch, the bottom of. the envelope 1 being shielded from the arc of rupture by the pool of mercury '7, which is still di rectly below said electrode. Since the mercury adheres but-little to the chrome iron inlead 2 the circuit will be ruptured at substantially the same angular position of the envelope 1 as was required to close the circuit through said switch. This is a highly desirable result of the present invention which was unattainable with switches of the prior art in which electrodes which amalgamated readily with the mercury were employed, since the great adhesion of the mercury for electrodes of the latter type resulted in the necessity of a relatively large angular movement of such switches between the point of making and the point of rupturing a circuit therethrough. The large contact area between each of the electrodes 2 and the mercury 7 is also of great value, since it decreases the internal resistance, and therefore the heating, of said switch, with the result that the current carrying capacity is greatly increased.

The switch of Fig. 7 has the same operating characteristics as that of Figs. 1 and 2, and hence the mode of operation need not be described. The elimination of the need for an exposed sealofi tip in a switch of this construction, with the resulting decrease in the breakage hazard, is an important feature thereof, as is the fact that greater pressures of arc suppressing gas may be employed therein. The greater heat conductivity of the compressed gas also materially increases the current which may be safely controlled by such a switch. I

The switch of Fig. 8 is an extremely sensitive switch, useful in cases where operation thereof with very small angular movement is desired. Due to the large quantity of mercury 7' used in the envelope 11 of thisswitch very slight changes in the angular position of said envelope 11 are suflicient to make or break the contact between the mercury 7 and the left hand electrode 12-, since the movement of mercury to or from said electrodes is accomplished by a readjustment of level within the mercury pool rather than by the rapid longitudinal movement of a globule thereof along the envelope as has heretofore been the case, thus reducing the retarding efiect due to adhesion and friction between the mercury and the glass. The mercury '7 is, of course, a very effective shield for the bottom of the envelope 11, whereby the destructive effect of the arc thereon is eliminated.

The electrode assembly of Fig. 9, as well as the graded seal shown therein, may be used in any of the switches illustrated in the other figures without changing the mode of operation thereof.

The advantages afforded by switches of my new construction are manifold. The current carrying capacity of these switches is greatly in excess of that of switches of the same size which are constructed according to the prior art, while the cost of manufacture is greatly reduced. Furthermore these switches may be made to interrupt relatively large currents in an extremely short time interval which cannot be equalled by fluid flow switches of the prior art. The sensitivity of my new switches to slight angular movement thereof also far surpasses that attainable with mercury switches of like size of the priorart, due both to the inlead material and to the novel arrangement of the mercury therein.

While I have described my invention by reference to certain switches herein illustrated it, is

to be understood that it is not limited thereto, but that it may be applied to various other devices of similar nature, and that various changes, omissions, and substitutions, within the scope of the appended claims, may be made therein without departing from the spirit of my invention.

l. The method of producing a sealed vitreous envelope which comprises fusing to said envelope a metallic tubulation, adjusting the gaseous content of said envelope through said tubulation to a pressure in excess of atmospheric pressure, and thereafter hermetically sealing said tubulation by the application of welding heat thereto.

2. The method of producing a device having a closed vitreous envelope with electrical inleads fused thereto which comprises forming one of said inleads with an opening therethrough, hermetically sealing said inleads into said envelope, adjusting the gaseous content of said envelope through said opening to a pressure in excess of atmospheric pressure and thereafter hermetically sealing said opening by the application of pressure and welding heat thereto.

3. The method of producing a mercury switch which comprises fusing an inlead having an opening therethrough into a vitreous envelope, sealing another inlead-into said envelope, evacuating said envelope through said opening, admitting mercury and a desired gaseous atmosphere at a pressure in excess of atmospheric pressure to said envelope through said opening and thereafter hermetically sealing said opening by deformation and fusion of said metal member.

4. The method of producing a mercury switch which comprises forming an inlead with an opening therethrough, said opening terminating in a metal tube, fusing said inlead into a vitreous envelope, sealing another inlead into said envelope, evacuating said envelope through the opening in said inlead, admitting mercury and a desired gaseous atmosphere at a pressure in excess of atmospheric pressure to said envelope through said opening and thereafter applying welding heat to the tubular portion of said inlead to hermetically seal. the opening therethrough.

5. In a mercury switch, a glass envelope and a hollow electrode of chrome iron alloy in cup form, the rim of said cup being sealed to said envelope, while the bottom thereof extends downwardly within said envelope and serves as a contact making electrode of large area.

6. In a mercury switch of the tilting type, an elongated envelope, mercury therein, and electrodes sealed into said envelope, at least one of said electrodes being above said mercury in an open circuit position of said switch to which mercury will not adhere and consisting of a chrome iron alloy, said mercury extending substantially the entire length of said envelopein both the open and closed circuit positions whereby the tilting of said envelope to produce sufiicient change in the level of said mercury to make and break contact with said electrode thereabove does not produce appreciable longitudinal displacement of the mercury in said envelope.

7. A mercury switch of the tilting type comprising a sealed envelope of soft glass, mercury in said envelope, cup-shaped electrodes of chrome iron alloy sealed into said envelope, one. of said electrodes extending downwardly toward said 100 mercury and presenting a substantially plane surface thereto, and another electrode incontact with said mercury in a closed circuit position and in an open circuit position of said switch, said firstmentioned electrode terminating at an appreciable distance from the bottom of said envelope whereby upon tilting of said envelope the contact between the mercury and said electrode is interrupted before said mercury flows from beneath said electrode.

8. A mercury switch of the tilting type comprising a sealed envelope of soft glass, mercury in said envelope, cup-shaped electrodes of chrome iron alloy sealed into said envelope, one of said electrodes extending downwardly toward said 115 mercury and presenting a substantially plane surface thereto, another electrode in contact with said mercury in a closed circuit position and in an open circuit position of said switch, said first mentioned electrode terminating at an appreciable distance from the bottom of said envelope whereby upon tilting of said envelope the con tact between the mercury and said electrode is interrupted before said mercury flows from beneath said electrode, and an arc suppressing atmosphere at a pressure in excess of one atmosphere in said envelope.

9. A mercury switch comprising a vitreous envelope, said envelope having an all metal tubulation fused thereto which is hermetically sealed by a weld, a gaseous atmosphere within said envelope at a pressure in excess of atmospheric pressure, mercury within said envelope, and

WARREN R. WALKER.

CERTIFICATE OF CORRECTION.

Ma No. 1, 911,924. August 28, 1934.

WARREN R. WALKER.

It is hereby certified that error appears in the printed specification of the above numbered patentrequiring correction as follows: Page 4, lines 86-87, claim 6, strike out the words "to which mercury will not adhere" and insert the same afterv"alloy" in line 88, ofsaid claim; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 9th day of October, A, D. 1934.

Les] ie Frazer (Seal) Acting Commissioner of Patents,

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