US2284899A - Method of making mercury switches - Google Patents

Description

Ju ne 2, 1942.

u. c. HEDIN 2,284,899 'METHOD oF MAKING MERURY SWITCHES Filed March 21, 1940 ATTORNEY.

Patented June 2, 1942 MET HOD OF MAKING MERCURY SWITCHES Uno C. Hedin, Elkhart, Ind., assigno' to Buckle- Bear Laboratories, Inc., Elkhart, Ind., a corporation of Indiana V Application March 21, 1940, Serial No. 32.5,154

o Claims. (Ci. 29-155.5'

This invention relates to a method of making' mercury switches, and more particularly is' con- -cemed with the method of assembling and treating the partsof a. metal envelope switch, such as the type shown in the patent to Paul S. Bear, No. 2,132,921, issued October 11, 1938.

In themanufacture of switches of this type in which hydrogen is employed as the atmosphere within the switch envelope in which the mercury opertes, I have found that the iron shell or envelope forming the switch body contains impurities and occluded gases. These gases, as well as water vapor which may be present in connection with the oxides in the iron, render the mercury impure after the switch has been operated for any appreciable period of time, resulting in the changing of its Operating angle, and in some cases being such as to render the switch inaccurate in operation, or even entirely inoperative.

The present invention is directd particularly to a switch of the type in which a drawn metal shell of cup shape is provided with an open end 'in which is inserted a ceramic or refractory insert having a bore therethrough, this bore forming a communicating passageway between mercury carried within the metal shell and a body of mercury retained in contact'with an electrode carried by the insert. It is to b-e understood, of

course, that the switch maybe *of the direct metal to mercury contact type in which the mercury in the shell is movable through the bore i in the insert into and out of contact with a metal `electrode or the like.

`I have found that the ceramic inserts which are prepared by molding and firing do not come out as perfectly cylindrical bodies, but' may be of slightly eliptical shape. The metal shell, on the other hand, when drawn properly, 'has its open end in the form of a true cylinder adapted to receive the ceramic. consequently, the ceramic does not fit the interior of the shell in a positive manner. This is undesirable since mercury may run between the outer surface of the ceramic and the inner surface of the end of the shell, and in such case, may contact the rubber scaling means producing a deleterious effect' on the rubber.

Another disadvantage found in connection with such switches is that the iron shell is susceptible to the hydrogen gas, and if not properly treated, provides an absorptive body which tends to absorb the hydrogen within the envelope, reducing the internal pressure of the hydrogen and thus reducing its eflect upon the mercury and impurities within the envelope.

Another disadvantage, which has been noted in connection with the forming of such switches. is that the bond formed beneath the tubulation by' which the switch is evacuated and filled with gas. and the interior surfaceof the 'switch is sometimes not perfectly gas tight due to impurities in the iron which prevent a positive weld of the tubulation flange within the end of the envelope.

It is there'fore a primary object of the present invention toprovide a metal envelope mercury switch of this type in which the shell and tubulation parts, as well as the electrodes and ceramics, are first heated to a relatively high temperature in a hydrogen annealing iurnace whereby the metal parts are expanded and the oxides and occluded gases are driven off and replaced by the hydrogen. This renders the metal surfaces bright and clean, and the high temperature causes the metal to expand, opening up its pores and forming a water vapor from the oxides in the iron and the hydrogen case present' The impurities are completely burned up and the pores of the metal are filled with pure hydrogen gas. It is well known to those skilled in the art thata perfectly pure iron will not rust, but that impurities in the iron form small elements in the metal, creating electrolysis effects which corrode the 'metal. The hydrogen annealing process cleans the iron in such a high degree that even the outside of the envelope is practically rust-proof after annealing, and iron lends itself readily to soldering when the Copper leads are applied without first being tin plated.

Another feature of the hydrogen annealing process resides in the complete elimination of the acid cleaning to which such parts are normally subjected before being put into the annealing furnace, providing, of course, that the parts are v first washed in carbon tetrachloride.

still another feature of the hydrogen annealing process is that the tubulation tubes and the iron envelopes are perfectly cleaned before being welded together. and consequently a perfect welding joint is formed assuring a perfect leakproof connection between the tubulation and the closed end of the envelope. In this connection. since the annealing process makes the metal Softer, the tubulation tubes can be pinched more readily after evacuation and hydrogen filling of the envelope, and thus form 'an excellent gas-. proof seal. i

Another very important advantage obtained of round, the metal tube shrinksthereabout and takes the shape of the ceramic, forming a very satisfactory sea] preventing the mercury from running down between the ceramic and the iron body. At the same time the metal parts are subjected to a hydrogen atmosphere, contraction of the metal closes up the pores, trapping hydrogen gas therein in place of the impure occluded a gases. the parts are placed in the hydrogen annealing iurnace, they are not again touched by hand until after the ceramics have been inserted in the ends thereof and the desired shrinkage has been obtained to produce the tight fit of .the end of the envelope about the periphery of the ceramic.

Other objects and advantages of the present invention will appear more fully from the following detailed description which, taken in conjunction with. the accompanying drawing, will disclose to those skilled in the art the particular enlarged end of the envelope;

Figure 4 is-a corresponding sectional view of the end of the ceramic;

Figure 5 fllustrates the manner in which the shell shrinks about the periphery of the ceramic;

'and

Figura 6 is a transversesectional view through an assembled switch structure embodying the present process. I

Considering the drawing in detail, a hydrogen annealing furnace is indicated generaly at 5 and has disposed therein the conventional tray 6 upin place are then returned to the furnace. It is apparent that by completely burning up all the impurities, the metal parts have been cleaned to such a high degree that a perfect welding joint is provided and a positive leak-proof seal is eflected between the tubulation and the envelope end. g

Considering Figure 3, it will be noted that the enlarged end !5 of 'the she'll which is joined to being cooled in a chamber in which they are still It is to be understood that once on which are mounted the shells 1, tubulations 8,

electrodes 9, and ceramics n. These parts are subjected in the fu'nace to an intense heat in the presence of a hydrogen atmosphere being annealed at a temperature of approximately 2000 F. The iron shells are preferably formed of a material identified as SAE-l315, and when subjected to the annealing temperature of 2000 F. in a hydrogen atmosphere, the pores of the metal are expanded, forcing out the occluded gases and the impurities, such as the oxides, and these gases are completely bumed up and the pores filled with pure hydrogen gas.

After the iron shells 1 and tubulations &have

thus been annealed, and while still hot. they are' taken from the furnace and 'the tubulations are inserted through the small end of the envelope 'I with the flange portion l2 of the tubulations engaging the internal rounded surface of the ends [3 of the envelopes. These are then welded in position, as indicated at ll, substantially in the manner described in the copending application of Paul S. Bear, Serial No. 293.690, filed September 7, 1939. The shells with the tubulation welded the main body portion of the shell by the shoulder IS is a true cylinder that the ceramics n, due to the fact that theyare never perfectly round when moded or fired, since they are heated in a kiln at approximately 2600 F. when made, may be out of round, as indicated by the dotted lines IS in Figure 4. As a consequence, after the annealing has been completed and the pores of the iron shell filled with hydrogen, the ceramics are placed in the ends !5 thereof while still hot and the parts are then allowed to cool in a hydrogen atmosphere which causes the shell ends |5 to shrink down from their original contour, indicated by the dotted lines I'I, to the contour of the ceramic, forming a substantially perfect mechanical engagement about the periphery of the ceramic such that no gaps or voids are provided therebetween which might allow mercury to leak therepast. Since the ceramics have relatively little or no coefllcient of expansion when heated, while the iron has an appreciable expansion upon heating, it is apparent that upon shrinking, the iron will decrease in size to shrink about the contour of the ceramic.

At the same time, this cooling produces a closing of the pores of the metal envelope, trapping hydrogen therein in place of impurities and thus providing a clean rust-proof iron shell. It is to be understood that the ceramic is placed in the end of the envelope immediately upon removal from the furnace 5. This is preferably accomplished mechanically so that the ceramics are never touched by hand after having once been placed in the annealing furnace. After cooling in the hydrogen atmosphere to shrink the end |5 of the envelope about the ceramic, the electrode 9 is placed in the recess |8 of the ceramic and is engaged by the'resilient sealing gasket IS and the compression member' 20, which may be formed of Bakeliteor a ceramic. suitable axial pressure is placed upon the assembly and a retaining ring 22 engages the'compression member 20 to hold the 'same under compression while the end 2| of the envelope is spun over to lock the 'parts in sealed position. The particular manneof effecting this end seal is disclosed in the copending application of Paul S. Beat, Serial No. 211,420, filed June 2, 1938.

The shank 23 of the electrode projects outwardly through a cylindrical extension on the compression member, and at its outer end, is threaded to receive the nut 24 by means of which a suitable conductor can be connected to the electrode. i

It will be noted that the ceramic o is provided with a radial shoulder portion 25 at the inner end of the cup-shaped electrode head 26, which forms an annular groove for retaining a body of mercury 2'I in contact with the electrode. A second body of mercury 28 is introduced into the envelope through the tubulation 8, and upon tilting of the envelope, it will be apparent that a circuit is made and broken between the envelope 'l and the electrode 9 at the sharp cutting edge 29 between the retained body of mercu-y 21 and the moving body of mercury 28. `I! desired, a suitaas-1,899

. expand the envelope and open its poresfor reof the .switch is then subjected to a vacuum' throughthe tubulation 8, and all gases which may have been trapped therein during the end assembly are withdrawn. After evacuation, the tubulation 8 is connected to a source of hydrogen gas under pressure and this gas is introduced intothe interior oi! the envelope under a pressure ranging irom 3 to 4 atmospheres. while still being subjected to the gas under pressure, the tubulation O is flattened, as indicated at III, to seal otr the interier of the envelope, and this flattened portion 30 is then welded to form a perfect gas tight seal. The pinching of the tubulation to form the portion 30' is facllitated bev cause, the metal has been `aottened during the annealing process. After welding, a portion 30 is cut as indicated by the line 32, thus completing the formation oi the switci':-=Preierably, the switch is immediately flashed after this operation to fix its operating characteristics. i

It will therefore be apparent that the hydrogen annealing performs two important unctions in the process of assembling such a switch. In the first place, it removes all impurities in the iron parts oi the switch, iacilitating welding oi the tubulation and also trapping hydrogen gas within the pores of the metal. Secondly, the expansion of the metal during the annealing process drives out the occluded gases, and also provides tor shrinkage at the enlarged end oi! the envelope over the ceramic to seal cit any possibility of mercury passing between the ceramic and the shell and coming into contact with the resilient seal !9. This shrinkage allows the end of the envelope to fit around the contour of the ceramic and produce a tight fit therebetween. V

I am aware that various changes may be made in certain details 'of the process as herein described, and I therefore do not intend to be limited except as deflned by the scopeand spirit ot the appended claims."

I claim:

1. In the process of manuiacturing a metal envelope mercury switch having a ceramic insert in one end thereof and a tubulation in the opprise placing the envelope, insert and tubulation individually into a fumace, heating said parts in a hydrogen atmosphere to expel occluded gases therefrom and simultancously expand said metal parts to open the pores thereot to hydrogen, inserting said ceramic into the end of said envelope while hot, and cooling said parts in a hydrogen atmosphere to shrink said envelope about said insert and simultaneously close said envelopepores to trap hydrogen therein.

2. In the process of manuiacturing a metal envelope mercury switch of'the typehaving a refractory disposed in the open end thereof, the novel steps which comprise placing the unassembled envelope and refractory in a furnace, heating these parts to a temperature of approximately 2000 F. in a hydrogen atmosphere to moval of oxides and occluded gases therefrom,

inserting th reractory into the open end of' said envelope while said portsj are heated, and cooling said parts in a hydrogen atmosphere to shrink'said envelope about the refractory and simultaneously trap hydrogen in the pores of the envelope. 4 L

3. The process of claim 2 wheren said lastnamed step comprises water cooling of said parts to produce rapid contraction ot said envelope.

4. In'the process of manufacturing a metal envelope mercury switch having a refractory in- `sert adapted to be disposed in the open end thereoi', the novel steps which comprise heating a said envelope to a temperature sumcient to expand the same and open its pores, inserting said rei'ractory into the open end thereof while expanded. and rapidly cooling said envelope in a,

' lindrical' end, the novel steps which comprise heating said envelope in a hydrogen atmosphere to expand said end and drive OI any "gaseous impurities and replace them with hydrogen, inserting a generally cylindrical refractory. into said end while heated, and then rapidly cooling said end to shrink said end closely around the Vposite end thereof, the novel steps which comexternal contour ot said refractory.

6. In the process of manufacturing a metal envelope mercury switch having an enlarged open end and-a closed end provided with a' bore, the novel steps` which comprise heating said 'envelope in a hydrogen atmosphere to drive out occluded gases and burn ofl impurities therein. simultaneously heating a flanged tubulation adapted to project outwardly through said bore, welding the flange of said tubulation to the internal defining edge of said bore while said pieces are hot, reheating said welded assembly in a -hydrogen atmosphere, and then rapidly cooling said assembly in a hydrogen .atmosphere to trap hydrogen in the pores of said envelope.

7. The process of claim 6 further characterized by the steps of heating a reiractory in said hydrogen atmosphere while reheating said welded assembly, and inserting said refractory into the open end of the envelope while hot whereby upon said rapid cooling said open end shrinks about the reiractory to closely embrace the external contour thereo. p

8. A method of manufacturing a cup-shaped 'metal envelope type mercury switch which comprises heating said envelope in a hydrogen atmosphere to drive off occluded gases and fill the pores of said envelope with hydrogen simultaneously heating a metallic tubulation, 'welding said tubulation to said envelope adjacent the closed end th'ereof, reheating the welded assembly in a envelope mercury switch having a metallic filling tubulation connectedtherewith, the steps which comprise placing said envelope and said tubulation indivldually in a iumace and subjecting them to a i'eiativeiy high heat in 'a hydrogen atmos'phere to drive of! occluded cases 'and impurities presentin the metal parte and to open the pores thereof, removing the parts from said furnace', welding said tu'buation to said enveiope, reheating the ase'mbly in said hy drogen turnace, and quickly cooling said assembly in the presenceof hyd'ogen to' trap hydrogen in the pores ot the metal.

10. In the process of manufacturing a metal envelope mercury switch having an open end, a refractory insert adapted to be disposed in the open end of said envelope and an evacuating and filling tubulation connected to and communicating with the interier of said envelope, the

steps which 'comprise heating said assembled envelope and tubulation' in a -hydrogen atmosphere to a temperature sumcient to drive out occluded gases andburn ofl impurities therein, simuitaneously heating said refractory, inserting said refractory in the open end of said envelope while hot, rapidly cooling said assembly to shrink the end of said envelope tightly about said reractory, additionaly scaling the open end of said envelope. evacuating the contents of. said envelope and then filling it with hydrogen through said tubulation, and scaling oi! said tubulation before discontinuing the flow of hydrogen into said envelope. c

UNO C. HEDIN.

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