US2786882A

US2786882A - Lead-in seal for electrical discharge devices

Info

Publication number: US2786882A
Application number: US207687A
Authority: US
Inventors: Krefft Hermann Eduard
Original assignee: Individual
Current assignee: Individual
Priority date: 1951-01-25
Filing date: 1951-01-25
Publication date: 1957-03-26
Anticipated expiration: 1974-03-26
Also published as: GB682376A; DE854686C

Description

March 26, 1957 H. E. KREFFT 2,786,882

LEAD-IN SEAL FOR ELECTRICAL DISCHARGE DEVICES Filed Jan. 25, 1951 2 Sheets-Sheet l 4 8 it 13%: 161:? T f 1' 5 '1' 1" 5 I5 I N VEN TOR. Hf/QMANN [a 0,420 KREFF 7 United States Patent C) LEAD-IN SEAL FOR ELECTRICAL DISCHARGE DEVICES Hermann Eduard Krefit, Buenos Aires, Argentina Application January 25, 1951, Serial No. 207,687

11 Claims. (Cl. 174--50.64)

This invention relates to vapor discharge lamps and more particularly to a gas tight seal for such lamps and to a method of fabricating it. Seals for lead-in conductors in metal vapor high pressure lamps and particularly in so-called super pressure lamps which contain metal Vapors and/or rare gases at operating pressures of over ten atmospheres are known to be subjected to high mechanical and thermal requirements. For this reason they are made with fused quartz or similar glasses of high softening points and characterized by comparatively low coeflicients of thermal expansion. Only highly refractory metals with coefficients of expansion close to that of fused quartz may be used as current lead-ins, and these are generally used in the form of thin foils which can be sealed vacuum tightly into fused quartz.

The manufacture of these lead-in seals is troublesome, since the fused quartz requires high working tempera tures in order to be formed in the desired manner, and since the metals such as molybdenum, tungsten and tantalum which may be considered for use in the manufacture of the lead-in conductors are easily oxidized and consequently must be protected from the blast flame that is used in shaping of the seal. The customary method for manufacturing such seals is to place the current lead inside an evacuated fused quartz tube which is strongly heated and pressed down onto the lead-in by the outside air pressure. Alternatively a protective gas may be passed through the open fused quartz tube containing the leadin, and then the heat-softened fused quartz tube may be pressed down on the lead-in by means of press jaws. The two ends of the lead-in are exposed by cutting off the extending ends of the fused quartz tube so that the lead-in may be further adapted to its intended use.

This hitherto customary method of manufacture is unsatisfactory because much fused quartz is wasted in exposing the ends of the sealed lead-in conductor, and the finished seal is not in a desirable form for use in lamp manufacture. Metal vapor high pressure lemps, and particularly super pressure lamps require current lead-in seals which may be sealed without a resultant so-called dead space as closely as possible to the lamp body, and without in any Way burning the current lead or the electrode fastened thereto and projecting into the bulb. Furthermore, it is desirable to make the mass of the lead-in seal small in order to make its heat capacity small and to improve the operating characteristics of the lamp. Super pressure lamps of small capacity, e. g. 50 watts, require very small lead-in seals, which are diflicult to manufacture. For mass production purposes they should be adapted to be formed economically and to close tolerances. These requirements are not met by the known lead-in seals. In cutting the deformed fused quartz body of the seal from the fused quartz tube, the cut can not be made at a place where the quartz glass is pressed down on the current conductor, thus a small portion of the tube remains attached. Such a tubular ended seal has a large diameter and is therefor unsuitable for later fusion to the lamp body. The similarly remainingtube at the other end of the seal is excessive and represents a waste of material. Furthermore, the mass of the seal is unnecessarily increased. In attempting to fuse such a seal to the generally spherically shaped body of a super pressure lamp it would be difficult to avoid harmful dead space and burning of the conductor and electrode. Such a joint between the seal and the bulb would also be lacking in mechanical strength. Seals made by these customary methods cannot be made to the required tolerances, and economic mass production has not therefore been attempted.

Further deficiencies of the known lead-in seals come from inadequacies in the construction of the lead-in conductor. This customarily consists of an external lead, a molybdenum foil which makes the vacuum seal, and an internal lead which generally is a tungsten or molybdenum wire. It is known that the joining of such a wire with the thin molybdenum foil by means of spot welding presents great difiiculties. The thin foil is easily damaged by welding and in addition to its having small mechanical strength there generally exists a very poor electrical contact between the two parts. Use of the lead-in conductor is very diificult for fabrication purposes due to lack of rigidity of the foil. For this reason it has been suggested to weld a comparatively heavy molybdenum foil or ribbon to the thin foil. This is more easily accomplished than welding a wire to the foil, however, in many instances it is advantageous or even necessary to use a stiff wire, especially as an inner lead upon which the electrode can be fastened. The presently known lead-in conductors which are equipped with such a wire have still other disadvantages. Because of the very small cross section of the foil, that portion of the wire connected thereto must be firmly embedded in the quartz of the seal. However, a clean, bubble-free intimate contact between quartz, spotweld and wire is generally not attained. Consequently, the mechanical strength of the quartz is reduced at this point, and cracks easily develop which lead to the destruction of the lamp.

This invention concerns itself with the removal of these faults, and its object is therefore to provide a new and improved current lead-in seal for metal vapor high pressure and super pressure lamps of quartz or similar glasses which can be economically and mechanically produced in large quantities to tolerance and which possess a form especially suited to the construction of such lamps. These lead-in seals are equipped with a new and improved current lead-in conductor which can be simply constructed, possess improved mechanical properties and can be imbedded neatly in the quartz of the seal without producing injurious strains. A further object is the provision of a current lead-in seal which is equipped with an evacuating tubulation. The invention also concerns the process by which the new seal is produced.

In accordance with this invention the current lead-in seal for electrical high pressure discharge lamps cornprises a current lead-in conductor vacuum tightly embedded in a glass body which consists of a main body portion and a tubular glass plug, said main body portion being formed by pressing a wide glass tube, and said plug being fitted into the wide tube but being itself undeformed. The plug provides a means for fusing the lead-in seal to the bulb of the lamp and serves to protect the inner lead wire which is centrally located within the tubular plug but not sealed therein. The remaining portions of the lead, composed of the sealing foil and the ribbon shaped external lead joined thereto are completely embedded in the rnain body portion of the seal, the external end of which is pressed out very thin for the purpose of exposing the external lead. According to a further characteristic, the component parts of the current lead are made from thin sheet metals and foils by stamping and pressing whereby they obtain an especially well adapted shape for the assembly of the current lead. In particular the internal end of the lead is formed by pressing a thin plate into the shape of a tube which is particularly well adapted for attachment to the wire which supports the electrode, and makes possible the formation of a pump channel which passes through the pressed and formed glass body of the seal to a tubulation which is fused thereto.

The invention may best be understood from the following description of one embodiment thereof taken in connection with the accompanying drawing in which:

Fig. l is a longitudinal sectional view of a seal constructed in accordance with the invention,

Fig. 2 is a sectional top view taken on the line 2-2 of Fig. 1,

Fig. 3 is a longitudinal sectional view of the lead-in conductor, greatly magnified, for the seal,

Fig. 4 is a top view of the lead-in conductor shown in Fig. 3,

Figs. 5, 6 and 7 are sectional views on the lines 5-5, 6-6 and 77 respectively on Fig. 4,

Fig. 8 illustrates diagrammatically how the seal of the invention may be formed,

Fig. 9 illustrates another step in the forming of the seal,

Fig. 10 is a sectional view of a lamp provided with lead-in'seals according to the invention,

Fig. 11 is a sectional view of a portion of the seal greatly magnified, illustrating a seal provided with an evacuation tube.

Like numerals designate corresponding parts throughout the several views in the drawing.

Referring to Figs. 1 and 2, the seal comprises a mai body portion 1 of quartz, or the like, with a tubular plug 2 located at one end thereof and a flat projection 3 of slight thickness formed at its other end.

A current lead-in seal made in this manner possesses a particularly well suited structure for the construction of quartz lamps, especially metal vapor superpressure lamps. The plug 2 which serves to join the seal to the lamp body has a comparatively small diameter and can be made to close tolerances. Hence, the place where it is joined to the lamp body is small and possesses great mechanical strength. The sealing process can proceed rapidly without danger of devitrification of the quartz glass and oxidation of the electrode structure. The thin quartz layer of the projection 3 protects the outer lead 4 from burning up during the sealing process. The projection may then be removed as by bending the embedded portion of the lead, so that the outer current lead becomes exposed for connection to the electrical circuit for the lamp. In this manner one obtains a current lead-in seal whose external end is made to tolerances, is clean, and free of excessive quartz glass material, while its inner end presents a form especially well suited for lamp manufacture.

The value and efiiciency of a current lead-in seal depends 'to a large extent on the quality of its current lead-in conductor. The current carrying capacity of the conductor is fundamentally limited by the dimensions of the exceedingly thin sealing foil, yet numerous other factors that concern the composition assembly and construction of the conductor are of importance in its manufacture. For example, that portion of the lead-in seding foil necessary to attain and maintain a vacuum tight seal should be kept to a minimum in order that its resistance and the heat generated in the seal be negligible. It is also of great importance to exercise extreme care in making electrical and mechanical contact between the thin foil and the outer and inner leads in order to avoid contact resistance which would reduce the capacity of the seal and would produce undesirable heating. It is known that just as the quartz of the seal is subjected to great strain by the foil, the lead-in conductor is subjected to mechanical strains that can be withstood it the conductor is properly formed. During the sealing-in operation when the heated quartz glass is pressed by means of jaws against the current lead-in conductor the conductor is subjected to high mechanical requirements. Hence, it must have sufficient stability to resist deformation which can lead to breaking of the lead-in. The current lead of this invention has been made with these observations in view. The details of construction of the lead-in conductor are best shown in Figs. 3 to 7, inclusive. The outer lead 4 is formed from a plate approximately 0.1 mm. thick and is provided with side folds 8 and a lip 9 cut from the center of the plate leaving the hole 10. The folds 3 grip the edges of the sealing foil 5 onto which they are tightly pressed. The thin foil 5 has a small hole 11 through which the lip 9 projects and is then folded over to press down on foil 5. In this way the

portions

4 and 5 are attached to one another in an exactly defined relative position. Since such a method of connection is not electrically sufficient, they are permanently connected by spot welding as shown at 12. This welding is easily accomplished since the delicate thin foil 5 ests between two heavier plates at the-spot welding points. The inner lead 6 is similarly made from a plate about 0.1 mm. thick. It is attached to the other end of the sealing foil in the same manner as the outer lead 4, that is, foil 5 contains a small cutout 17 to accommodate lip 16. Folds 15 are bent over the foil 5 along its edges and the two portions are permanently joined by means of spotwelds 12. All three portions of the lead are suitably cut and formed in a press. Hence they have the same dimensions thus simplifying assembly of the lead. They may be made in the most varied forms possible with this mode of forming as desired for the production of the lead-in seal. It is of especial advantage to provide that portion of the inner lead which is not attached to the sealing foil as already described with a cylindrical shape, as shown in Figs. 3 and 4 and in cross section in Fig. 7. The plate of molybdenum, or the like, from which the inner lead is cut and formed serves as a tubular extension'iS which in the completed seal as shown in Figs. 1 and 2 is enclosed with a very slight clearance by plug 2. Since extension 18 projects into the lamp body it is especially well suited for the support of'the electrode. This is suitably accomplished by inserting and welding into tube 18 a fitted support rod. If it seems necessary to make the electrical contact between the support rod and the inner lead deep within the seal where the lead is tightly embedded in the quartz, the inserted end of the support rod maybe provided with solder metal which will melt when plug 2 is fused to the lamp body. The sealing toil may be rendered more rigid by providing it with ribs 14, as shown in Fig. 6,'by the stamping and forming process already described. Fig. 6 shows the edges 13 of the sealing foil to be pointed in a wedge shape. This shape is very essential for the production of a vacuum tight seal with a quartz glass. Shaping of the foil edges is accomplished by means of a properly designed cutting and pressing matrix which bends the edges out of the plane of the foil thereby giving it added rigidity. This method of forming makes it possible to'give the foil edges equal and optimum angles and hence leads to the production of exceptionally serviceable current lead-in seals.

A current lead-in conductor having the above stated characteristics provides a current lead-in seal which is comparatively free of harmful strains. The pressed quartz glass contacts only current lead parts (made pref ably from molybdenum sheets) whose shape, cross s tion and dimensions can be suitably made by the pro dure described. The formerly customary welded joint of wire and foil which seldom results in a clean job, and the direct contact between quartz glass and stiff wire are avoided by means of'this invention. Also the comparatively thick plates of the outer and inner leads may face is roughed by sanding or etching. :also suitably used for the other portions of the lead, though the invention is not limited thereto.

be embedded in quartz Without the appearance of large strains, for it is known that ribbons of molybdenum up to 0.1 millimeter thick can be sealed-in vacuum tightly if edges and cross section are properly dimensioned. It is also very important that the inner lead does not directly touch the tubular plug 2 which surrounds it, since no strains can be tolerated at this location which is to be fused to the lamp body, for experience has shown this to be the weakest point in the completed lamp. The

holes

11 and 17 in the sealing foil aid in strengthening the seal. At these places the pressed quartz from the opposite sides of the seal can come into direct contact. These direct unions may be compared with rivets which hold the quartz together at both ends of the current lead. It was found that consequently the length of the seal foil could be appreciably shortened, thereby reducing its resistance and increasing its current carrying capacity. It is also very advantageous that in this way the length and volume of the seal are reduced. This is welcomed from the standpoint of lamp construction. Experience shows that

lips

9 and 16 are advantageaous. It is known that the current carrying capacity of a given foil can be increased by welding to it thicker plates that can cover an appreciable portion of the foil. They may not, however, form a closed path. Obviously a comparatively short length of thin foil suffices to make a vacuum tight seal which meets thermal and mechanical requirements. Hence, the current lead of the invention is preferably equipped with

lips

9 and 16 which form part of the outer and inner leads and reach far into the interior of the sealing foil.

As is commonly known, a thin molybdenum plate,

:approximately 0.02 millimeter thick, is used as the seal- It can, however, be chosen thicker if its sur- Molybdenum is ing foil.

The method for producing the new current lead-in :seal in accordance with this invention is exceedingly :simple and economical and may be mechanized. It is suitable for mass production of quartz lead-in seals which are required in great quantities for the manufacture of high and super high pressure lamps.

In the manufacture of such seals a jacket containing the lead-in to be sealed is commonly used. This present invention concerns itself with the form and construction of this jacket from the point of view of making the sealing operation simple, as well as with the object of making a suitably constructed current lead-in seal economically by mechanized methods.

According to the invention the jacket for the seal is made of two quartz glass tubes of different diameters. The larger of these has an inside diameter large enough to accommodate the comparatively wide sealing foil, while the inside diameter of the smaller tube is only slightly larger that the diameter of the inner lead. Fig. 8 shows an example of the assembly and construction of the lead-in seal prior to the pressing operation. The

quartz glass tubes

21 and 22 are secured in

clamps

23 and 24, respectively, of a sealing machine which may be stationary or rotatable.

Tubes

21 and 22 are used in suitable lengths of, for example, about 100 cm. The ends 25 and 26 of these tubes are fused together by means of the gas-oxygen torches 27 and 28. During this operation the current lead is outside of the heated zone but is introduced through tube 21 after fusion of the two tubes. The lead is then positioned as shown in Fig. 8 so that the tubular shaped inner lead 18 is pushed as far as possible into tube 22. A protective gas such as nitrogen, argon or helium is then passed through tube 22 to remove the air surrounding the lead-in. At the same time the quartz tube containing the current lead is heated. This is done by means of ribbon or fishtail burners 29 whose form and dimensions are dependent on the area of the quartz tube to be softened. As may be seen in Fig. 8, only the wide portion of the jacket is subjected to the torches since the pressing operation is to be confined thereto. As soon as the jacket is suificiently soft the glowing flexible quartz glass is tightly pressed by means of pressing jaws, not shown in the diagram, onto the current lead thereby forming the main body of the seal. This phase of the production process is schematically shown in Fig. 9. Since the pressing jaws are made in the form of a mold which conforms to the shape of the lead-in seal, the thin walled extension 3 containing the free end of the external lead 4 is formed adjacent to the thick walled quartz glass body 1. Only a small portion of tube 22, which becomes heated up to the vaguely defined limit of the softened zone, is pressed onto the inner lead so that the greater portion of tube 18 extends freely into jacketing tube 22.

As shown in Fig. 9, the jacketing tube 21 is severed from the thinly pressed extension 3 of the seal during the pressing operation. In order to simplify this operation, chuck 23 and the tube 21 which is held by the chuck are pulled away just prior to pressing so that tube 21 is stretched thin before it is pressed out and cut off. The seal is easily cut off from the jacket tube 22 since the tubular shaped inner lead 18 is not embedded therein, hence an abrasive cutting wheel 31 may be used. Finally, the closed end 30 of jacket tube 21 is cut oif with a cutting wheel 32 and both

jacket tubes

21 and 22 are again in their original form ready for the manufacture of the next seal.

This method of manufacture which forms a part of this invention possesses exceptional advantages. With the use of a rotating sealing machine it permits fully automatic and economical production in large volume of current lead-in seals through quartz. It is also economical because only very small quantities of comparatively expensive quartz glass :are wasted, i. e. merely the ends 30 which must be cut ofi and the left overs from the jacketing tubes. The seals are in a form suitable for immediate use in the assembly of quartz lamps. The use of a jacket composed of two different tubes for the lead-in seal is advantageous in that its shape is suited to that of the lead-in which is desirable for the pressing operation. It must be noted that the deformation of materials occurring during this process takes place under high temperatures and comparatively high viscosity of the quartz which subjects the lead-in to severe requirements.

In pressing the quartz onto the current lead the tubular thin walled inner lead 18 may become undesirably deformed, preventing later deep insertion of the electrode support rod. This disadvantage is avoided in accordance with this invention by inserting a mandrel into the tubular inner lead prior to the sealing operation and removing it afterwards. Use of this aid makes it possible to utilize a tube 18 of the inner lead so short that it will be embedded in its entirety in the main body. of the seal. In this case the mandrel consists of a carefully cylindrically polished tungsten rod which can easily be removed after completion of the seal even if it is partially embedded itself. A seal made in this manner, therefore, contains a hollow space which is encircled by the cylindrical plug leading into its interior. In order to attach an electrode support rod securely to the lead, a suitable solder is applied to the end of the rod and the rod is then placed into the interior of the tube 18 where later, during the fusing operation between seal and lamp body, it melts and the desired soldered joint between current leads is produced.

An example of the use of the new lead-in seal in the manufacture of :a super pressure lamp is shown in Fig. 10. It shows a seal made in accordance with this invention equipped with an electrode 33 and electrode support rod 34. The suppoit rod 34 is permanently secured inside the tube 18 of the inner lead and good electrical contact is made by means of a solder 35 introduced into -4 laid bare with a wire 39 welded'thereto.

. informing channel 44.

tube-18 by the rod 34. The lamp body 36 isessentially spherical and heavy walled, and possesses two

short necks

37 and 38 which serve for sealing on the lead-in seals. As is shown in the Fig. 10, plug 2, is seated in the neck 38. Because'tube 18, electrode 33 and support rod 34 are easily oxidized, sealing of the neck to the plug must be done with the exclusion of oxygen, hence, a protective gas atmosphere must be provided. For this reason a good seat and fit of plug 2 inneck 38 is very important tothe production of a lamp having satisfactory life and brightness. Hence, it is expedient to grind plug 2 to the exact inside diameter of neck 38 which itself can be made to very close tolerances. During the sealing of the lead-in seal to the'larnp body the solder on the end of the support rod is sufficiently heated tomake the necessarily good contact between current lead and electrode support rod. .Fig. 10 also shows the external lead In accordance'with the procedure herein disclosed the outer lead 4 has a thin layer of quartz covering which is not tightly fused to the lead and caneasily be removed by bending the lead.

The tubular shape of the inner lead 6 and the use during production of the seal as already described of a mandrel therein to prevent collapse of the thin walled tube 18 during pressing, provide a pumping channel in the seal for use in evacuating the lamp and filling it with rare gas and the required metal. Fig. 11 shows an example of such a seal Whose lamp end is greatly magnified. It consists of the main body portion 1 and the plug 2 as well as the sealed-in lead, of which only the-sealing foil 5 and inner lead 6 which passes over into the tube 18 are shown. The fold 15 serves to attach the sealing foil to the inner lead. This seal is equipped with an evacuating tube 40 which is fused to the main body 1 inthe vicinity of the toil end of tube 18. For this purpose the main body possesses a depression 41 which extends to thevicinity of the inner lead. The depression 41 has a recessedrim 42 which accommodates the reduced end 43 of the evacuating tube 40. Thus the tube 49 may be easily sealed and fused into the depression 41. In the interior of the main body 1 is located a channel 44 which is a direct extension of the space 45 formed by tube 18 and leads through the quartz to the depression 41 and opens up into evacuating tube 40. An electrode support rod 34 of tungsten is secured in tube 18 by means of the soldered joint 35 whereby a permanent and electrically conducting contact is made. Tube 18 is provided with openings 46 for providing communication between the interior of the lamp and the evacuating tube through the clearance space 7, space 45, and channel 44.

The production of this seal follows in a manner similar to that already described and illustrated in Figs. 8 and 9. However, in order to form the pumping channel 44 the mandrel, above referred to is provided with an axial opening. As already described, this mandrel protects the thin walled tube 13 from being collapsed by the press jaws. The axial opening of the mandrel provides a channel between jacket tube 22 and the interior of the seal, which channel leads to the quartz embedded end of the tube 18. In order to produce channel 44 the pressure of the inert gas being fed into jacket tube 22 is immediately and rapidly increased upon completion of the pressing operation to cause a blowout from tube 18 through the main body of the seal to the outside. This procedure should be done with care so that the channel forms in the desired manner. For this purpose, during the pressing operation there is produced a depression 41 which leads close to the orifice of tube 18 so that only a small amount of material must be overcome by the pressure of the inert gas During this operation a small needle flame is directed at the bottom of depression 41 in order sufficiently to soften the wall which is to be blown through. The depression 41 is formed by means of a pin contained in the press mold which forms a seal. The depression is suitably equipped with an enlargement 42 which serves to receive the reduced end 43 of the evacuating tube and simplifies its fusion to the main body immediately after production of the channel 44. The seal is then completed as already described. Jacket tube 22 is cut from plug 2 and the mandrel is removed from tube 13 so that an electrode support rod may be introduced as shown in Fig. ll. During the pressing and forming operation the danger exists that the pin which forms depression 41 may use the current lead to be displaced from its desired axial position. This difiiculty is overcome by locating a second pin in the press jaw opposite to the first one in order to counteract displacement of the lead by making a second depression 47.

in lamps with two lead-in seals as shown in Fig. 10 it is permissible as is generally customary to use one seal with evacuating tube and one seal without since in general one pumping channel is sufficient for pumping and filling the lamp. In order to prevent closing off of the pumping channel in assembling the lamp, plug 2 is first superficially sealed to the neck of the lamp body, and only after completion of the pumping procedure and sealing oil of evacuating tube 49 is a permanent fusion made whereby at the same time channel 4 and

depressions

41 and 47 are filled in and all contingent cavities are eliminated.

This invention is not to be limited to the illustrative examples described and shown in the drawings. Though the new current lead-in seal is especially suitable for use in the production of electrical high and super high pressure discharge lamps, there are other highly evacuated chambers made of quartz glass or glasses similar to quartz for which the seals of this invention may be used in the same form or with certain modifications adopting in principle the modes of action here presented. In some cases it may be suitable to make both leads extending out of the seal to be ribbon shaped or tubular shaped. Modifications of the jacket or of the current leads in such cases, as well as contingent changes in the methods of production will be apparent to those skilled in the art.

What I claim is:

1. A lead-in seal for an electric discharge device which provides for the reception of the electrode support rod of a. gaseous discharge electrode, comprising an electric lead-in conductor, said conductor being of substantially fiat shape and formed of an inner lead, an outer lead, and a thin foil strip interconnecting the ends of said leads, the seal also including a main body portion of vitreous material, a tubular plug of vitreous material fused to one end thereof, said foil being vacuum tightly sealed in said main body portion, said inner lead having a slotted tubular portion extending into and located centrally of said tubular plug spaced from the inner walls thereof, said support rod being fitted into and fastened to the tubular portion of the inner lead.

2. The lead-in seal of claim 1 wherein the inter-connection between the thin foil strip and said leads is formed by fold-over portions on each of said leads extending longitudinally thereof which are in engagement with and fastened to the foil strip, and said leads are further interconnected to said foil by tongue-like portions extending from said leads and passing through openings in said foil, the ends of said portions projecting through the openings in the foil eing bent over and fastened to said foil.

3. A lead-in seal according to claim 1 wherein said foil includes at least one longitudinally extending rib, the longitudinal edges of said foil being at least in part bent over and extended above the plane of the foil, the trailing edges of said bent over portion being wedge shaped.

4. The lead-in seal of claim 1, wherein said main body portion has an evacuating channel therein communicating with the space between said inner lead and the inner wall of said tubular plug.

5. The lead-in seal according to claim l wherein said main body portion is flattened around said outer lead to a thin vitreous coating which can be removed by bending said outer lead.

6. A gaseous discharge device comprising an envelope of vitreous material having at least two openings therein, a pair of electrodes one adjacent each of said openings, an electrode support rod connected to each electrode and extending into an opening, a lead-in seal mounted in each of said openings providing for the reception of the electrode support rod and comprising an electric lead-in conductor, said conductor being of substantially flat shape and formed of an inner lead, an outer lead, and a thin foil strip interconnecting the ends of said leads, the seal also including a main body portion of vitreous material, a tubular plug of vitreous material fused to one end thereof, said foil being vacuum tightly sealed in said main body portion, said inner lead having a slotted tubular portion extending into and located centrally of said tubular plug spaced from the inner walls thereof, said support rod being fitted into and fastened to the tubular portion of the inner lead and said plug being fused to said envelope into an opening thereof.

7. The gaseous discharge device of claim 6 wherein the interconnection between the thin foil strip and said leads is formed by fold-over portions on each of said leads extending longitudinally thereof which are in engagement with and fastened to the foil strip, and said leads are further interconnected to said foil by tongue-like portions extending from said leads and passing through openings in said foil, the ends of said portions projecting through the openings in the foil being bent over and fastened to said foil.

8. A gaseous discharge device according to claim 6 wherein said foil includes at least one longitudinally extending rib, the longitudinal edges of said foil being at least in part bent over and extended above the plane of the foil, the trailing edges of said bent over portion being wedge shaped.

9. The discharge device of claim 6, wherein said main body portion is flattened around said outer lead into a thin vitreous coating which can be removed by bending said outer lead.

10. A gaseous discharge device comprising an envelope of vitreous material having at least two openings therein, a pair of electrodes, one adjacent each of said openings, an electrode support rod connected to each electrode and extending into an opening, a lead-in seal mounted in each of said openings providing an electric lead-in conductor formed of an inner lead, an outer lead, and a thin foil interconnecting the ends of said leads, said interconnection being formed by fold-over portions on each of said leads and tongue-like portions extending from said leads and passing through openings in said foil, at least one fold-over on each of said inner and outer leads being in engagement with and fastened to the thin foil, said tongue-like portions being bent over and fastened to said foil, said foil including at least one longitudinally extending rib, the longitudinal edges of said foil being at least in part bent over and extended above the plane of the foil, the trailing edges of said bent-over portion being wedge shaped, a main body portion of vitreous material, a tubular plug fused to one end thereof, said foil being vacuum-tightly sealed in said main body portion, said inner lead being in part located axially of said tubular plug, having a slotted tubular shape and being spaced from the inner walls of the plug, a support rod fitted in and fastened to the tubular portion of the inner seal, said plug being fused at its other end to said envelope into the opening, the main body portion being flattened around the outer lead into a thin vitreous coating which can be removed by bending said outer lead.

11. A lead-in seal for gaseous discharge devices comprising an electric lead-in conductor formed of an inner lead, an outer lead, and a thin foil interconnecting the ends of said leads, said interconnection being formed by fold-over portions on said leads and tongue-like portions extending from said leads and passing through openings in said foil, at least one fold-over on each of said inner and outer leads being in engagement with and fastened to the thin foil, said tongue-like portions being bent over and fastened to said foil, said foil including at least one longitudinally extending rib, the longitudinal edges of said foil being at least in part bent over and extended above the plane of the foil, the trailing edges of said bent-over portion being wedge shaped, a main body portion of vitreous material, a tubular plug fused to one end thereof, said foil being vacuum-tightly sealed in said main body portion, said inner lead being in part located axially of said tubular plug, having a slotted tubular shape and being spaced from the inner walls of the plug, a rod adapted to support an electrode fitted in and fastened to the tubular portion of the inner lead, the main body portion being flattened around the outer lead into a thin vitreous coating which can be removed by bending said outer lead.

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