US3320352A - Quartz-to-metal seal - Google Patents

Description

May 16, 1967 D. D. KERSHAW QUARTZ-TO#META L SEAL 3 Sheets-Sheet 1 Filed Sept. 29, 1964 w :mm Ts n Ow w T J1 Q M I /u e H b D. D. KERSHAW QUARTZ-TO-METAL SEAL May 16, 1967 5 Sheets-Sheet 2 Filed Sept. 29, 1964 Tnvewtor: DeLmaT D. K rshaw by &

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His A t tor'nea United States Patent 3,320,352 QUARTZ-TO-METAL SEAL Delmar l). Kershaw, Cleveland, Ohio, assignor to General Electric Company, a corporation of New York Filed Sept. 29, 1964, Ser. No. 400,267 6 Claims. (Cl. 17450.63)

This invention relates to quartz-to-metal seals for electric discharge devices such as high pressure vapor or gas discharge lamps operating at high currents.

The molybdenum foil pinch seals used in mercury vapor lamps are not practical for currents much in excess of amperes. High intensity compact source lamps operate at currents ranging from 50 to several hundred amperes. Such lamps may comprise a thick-walled spherical quartz envelope having seals in the form of protruding stems supporting the electrodes, and containing a filling of xenon or a metal vapor. With such lamps, two types of seals have achieved commercial status at the present time. The first type is the graded seal wherein the stresses due to the different rates of expansion of quartz and tungsten are reduced to a safe level by interposing a series of glasses with intermediate coeflicients of expansion between the quartz envelope and the tungsten conductor. The disadvantage of this type of seal is that it requires a skilled worker to make it and its reliability is not always satisfactory. The second type of seal utilizes multiple molybdenum foils connected in parallel and generally disposed between a pair of concentric quartz tubes sealed together. Since the foils are extremely thin, careful handling by skilled workers is again necessary; also the resulting seals become very bulky in high current designs.

A third form of high current seal is described in Patent 2,504,522-Greiner, Quartz-to-metal Seal, and follows the Housekeeper principle of separating the sealing portion from the current conductor. The seal is in the form of a stem comprising a heavy current conductor or rod extending through a cup or thimble having a feathered sealing edge embedded in the wall of the stem tube. Among the reasons why the Greiner seal did not find commercial acceptance were the excessive cost of machining the molybdenum thimble, the weakness of the thimble so produced, and the difficulty of uniting the thimble to the tungsten rod in a permanently satisfactory fashion. In my copending application, Ser. No. 400,268, filed of even date herewith, entitled Thimble Seal, assigned to the same assignee as the present invention, I have described and claimed a molybdenum thimble or cup construction and a method of manufacturing same and of uniting it to the tungsten rod conductor which is practical and low in cost.

An object of the present invention is to improve the effectiveness and reliability of the thimble type seal by choice of proportions and by utilizing to advantage the stresses inherently present in the seal to counter other stresses resulting from the high internal operating pressure of the lamp. A further object is to provide a convenient and practical method of manufacturing the seal.

Briefly stated, one aspect of my invention results from the advantageous utilization of the fact that the metal to quartz interface is in compression on the inside of the thimble whereas it is in tension on the outside. Consequently a design that seals off the pressurized gas within the lamp at the inside interface of the thimble achieves a very substantial advantage in seal reliability over one sealing off at the outside interface. In practice, the advantage is realized by facing the open end of the thimble towards the lamp envelope or source of gas pressure, such being the reverse of the arrangement adopted by the Greiner patent. Other advantages result from the selection of cup dimensions and proportions of isolating .foils.

For further objects and advantages and for a better understanding of the invention, attention is now directed to the following description and accompanying drawings of a preferred embodiment and its manufacture. Features of the invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawings:

FIG. 1 is a side view of a compact source xenon lamp having stems with quartz-to-metal seals embodying the invention.

FIG. 2 is a side view, partly sectioned, of the cup and rod conductor assembly.

FIG. 3 is a side sectional view of a vitreous tube assembly which will form part of the stem.

FIG. 4 is a side sectional view of the vitreous tube assembly assembled with the cup-rod assembly for fusion together.

FIG. 5 is a View similar to FIG. 4 with the stem elements fused together.

FIG. 6 is a side sectional view of the fused stem elements with the inner end cut away.

FIG. 7 is a side sectional view of the completed stem with capillary joined to the inner end.

FIG. 8 is a cross sectional view through the stem along section line 88 in FIG. 7.

FIG. 9 is a side sectional view of the stem shown rotated 45 on the stem axis relative to the view of FIG. 7 and joined to a lamp envelope fragment.

Referring to the drawings and more particularly to FIG. 1, the illustrated lamp 1 is a compact source high pressure gas discharge lamp. It comprises a generally spherical clear quartz envelope 2 having aligned stems 3, 4 protruding from diametrically opposite sides and provided with quartz-to-metal seals. The stems 3, 4 are identical in structure and have inlead conductors including tungsten rods 5, 6 extending through quartz stem tubes and carrying electrodes at their inner ends, a cathode 7 and a more massive anode 8. Rods 5, 6 have flexible pigtail leads 9, 11 attached to their outer ends through connectors 10; the flexible leads are used to connect the lamp to power supply terminals. Protective metal tubes 12, 13 are provided over the stems 3, 4 and serve as bases in mounting and mechanically supporting the lamp.

Lamps of this kind are described as compact source or short are lamps because the arc discharge takes place between the tips of the electrodes 7, 8 closely spaced within the quartz envelope 2. The lamp contains a filling of an ionizable gas, preferably xenon at a pressure of several atmospheres. During operation, a gas pressure of the order of 300 pounds per square inch or 20 atmospheres may be produced in the lamp. The arc is characterized by extremely high brightness over a small area and, in the case of xenon, a well balanced spectral distribution in the visible region and a total spectrum approximating that of solar radiation. A typical lamp of the kind illustrated having an envelope diameter of approximately 3 /2" will have a power consumption of 5,000 watts with an operating current of amperes at 34.5 volts and the initial output will be 275,000 lumens.

On account of the large currents which must be carried, the tungsten rods 5', 6 must be of such large diameter that quartz cannot be fused directly thereto in a joint which will remain hermetic under the conditions of operation. To provide such a joint, cups or thimbles 14 of refractory metal, such as molybdenum or tungsten, are used to effect the seals in conjunction with the tungsten rods 5, 6. The rods extend through the cups and are hermetically joined thereto where they pass through the closed end. The thimbles have a feathered sealing edge 15 and the quartz of the stems 3', 4 is fused to both the inner and outer surfaces of the cup about the dge as will be described more fully below. In accordance with the invention, the open ends 15- of the thimbles face in the direction of the envelope volume and this orientation achieves a stronger and more temperatureresistant seal. The quartz parts of the stem surrounding the cups and the rods provide mechanical support for the rods in order to maintain the relatively heavy electrodes 7, 8 in place within the envelope 2.

The importance of facing the open end of the thimble towards the envelope may be understood by considering the stresses developed in a vitreous material (glass or quartz) which is sealed to the inside and outside of a thin-wall metal cylinder such as a molybdenum or tungsten thimble. In the quartz immediately adjacent the metal cylinder, three components of stress must be considered, these components being in the radial (P the tangential (P and the axial (P dimensions. The metal has a much higher coefficient of expansion than the glass or quartz and the seals are formed at the softening temperature of the quartz which is much higher than any temperature subsequently encountered in the use of the seal. Therefore as the seal cools towards room temperature the glass or quartz will be placed in compression in the axial and tangential direction, and this will be so at both the outer and inner surfaces of the metal thimble. The radial stresses however will differ as between inside and outside, being in tension on the outside and in compression on the inside. The situation may be summarized in the following table wherein the minus sign indicates compression and the plus sign indicates tension.

STRESS IN VI'IREOUS MATERIAL SEALED TO A METAL CYLINDER Axial Tangential Radial Outer Surface Inner Surface The significance of the radial tensile stress at the outer surface simply means that the metal is tending to pull or break away from the glass. A homely comparison might be made to a 'belt sewn in the one case to the inside, and in the other case to the outside of a garment. Where the belt is sewn to the inside, the stitching is placed in tension and tends to give way as the belt is tightened around the body of the wearer, but this is not so where the belt is on the outside.

It will be noted that the stresses in the glass or quartz on the inside of the thimble are all of the same sign, namely compressive. This is a desirable condition because glass is much stronger in compression than under tension, the ratio being about to 1. A high degree of seal reliability may therefore be expected at the inside sealing surface and, in accordance with the invention, this characteristic is utilized to advantage by facing the open end of the thimble towards the envelope volume in which gas must be maintained at a high pressure. At the outer surface of the thimble, the radial tension does cause a tendency for the quartz to break or shale off. However, the envelope volume is sealed off at the inside surface of the thimble and a crack at the outer surface does not cause a leak and so is not important.

The seal construction in accordance with my invention will be most readily understood by following the process of manufacture with reference to FIGS. 2 to 7.

In FIG. 2 a suitable molybdenum thimble-tungsten rod assembly is illustrated. The considerations affecting the designs of the thimble are threefold:

(1) The thimble should have sufficient thickness at the closed end to braze or weld to the rod conductor passing through it.

(2) The thimble walls should be strong enough to withstand the high operating pressure of the lamp.

(3) The thimble wall thickness should be as small as possible in order to obtain a seal with maximum reliability.

The most important consideration in the design is meeting the requirement for sufiicient strength with a sealing edge thin enough to seal satisfactorily. I have found that a relatively long or deep thimble is much preferable to a short, squat cup or thimble in meeting these requirements. In general, :a thimble having a ratio of length to diameter not less than 1.75 to 1 is desirable: in the illustrated example, the length is 1.00" and the diameter is .47", such corresponding to a ratio of length to diameter of 2.1 to 1. A long length of thimble permits a relatively thick closed or domed end 16 with a gradual taper to the thin sealing edge 15. In addition, the relatively thick walls at the domed end will withstand atmospheric pressure without distortion during the initial part of the sealing operation to be described below. By way of example, the illustrated thimble is .020" thick at the domed end and radiused at the corners; the walls taper rapidly in thickness from .010 to .005" close to the corners, and thereafter taper gradually to .0003" at the feathered edge.

The molybdenum thimble is hermetically joined to the tungsten rod by a fusion process using molybdenum metal to form the fillet 17. This is much preferable to conventional brazing wherein a different metal such as platinum is used at the junction. For further details on the thimble and the fusion thereof to the tungsten rod, reference may be made to my aforementioned copending application Thimble Seal.

In fabricating a stem, a vitreous assembly is first prepared as illustrated in FIG. 3. It comprises an outer section of stem tubing 18 which is necked down at 19 to smaller diameter tubing 20. A short length of intermediate diameter tubing 21 is provided with a flare 22 at the end facing neck 19, which flare is sealed peripherally into the outer stern tubing 18. An inner tube 23 of yet smaller diameter is sealed at 24 to the end of the intermediate tubing opposite from the flare, and retroverts through the intermediate tubing to the vicinity of the neck 19 where its end is closed at 25. During the forming of the seal, it is difficult to get sufficient heat to the internal glass parts of the seal. Therefore it is helpful to make the inner tube 23 and the intermediate tube 21 of quartz-like glass such as Vycor which has a softening point approximately lower than quartz or pure silica. The outer tube 18 is desirably made of quartz.

Prior to inserting the thimble-rod assembly into the stern assembly, it is provided with three molybdenum isolation foils. These foils may be about .001 thick and their principal function is to prevent the quartz from bonding to the metal except in those areas where a hermetic seal is to be achieved. If a bond were allowed to occur at a place where the cross-section of the metal is too great, the bond would rupture upon cooling and the quartz might crack. At the same time, the foils serve as cushions between the unsealed metal and quartz parts and thereby eliminates excessive play. The outer foil 27 is preformed into a cylinder and placed around the thimble star-ting at the closed end and extending in the direction of the open end. The edge 28 of the foil in the direction of the open end is preferably acid-etched beforehand down to .0003" in order to reduce the stress concentration at this point in the seal. It is convenient in manufacture to hold the foil in place with a few turns of fine molybdenum wire 29, for instance .002" Mo wire. The inner isolation foil 30 is preformed into a cylinder with a serrated end turned in at 31. An isolation foil 32 is also provided around the portion of rod 5 within the thimble. The inner end of foil 32 is likewise serrated and is turned out at right angle and overlapped by the serrated end of foil 30. lFoils 30 and 32 prevent the Vycor glass inner and intermediate tubes of the stem assembly from sticking or bonding to the closed end of the thimble and for a distance along its interior Wall, and also from sticking to the tungsten rod where it passes through the thimble.

After the isolation foils have been placed in position, it is desirable to fire the entire metal assembly in wet hydrogen. A suitable way of doing this is by the use of a radio frequency heater capable of holding the parts at about 1100" C. for 5 minutes. It is desirable to tire in hydrogen only such number of thimble-rod assemblies as can readily be used within an hour.

The thimble-rod assembly is inserted into the stem preassembly which is placed in a conventional glass lathe including jacobs chucks 33, 34 (shown in phantom), along with drive means for rotating the head and tail stock chucks synchronously. A rotary vacuum swivel is provided at each end to allow either vacuum or suitable gas pressure to be applied to either end. The work is done with the vitreous assembly revolving in the glass lathe and heat is applied to the work by means of a pair of oxyhydrogen burners which direct flames against the work from opposite sides and which can readily be moved along the work. After the thimble-rod assembly is inserted into the stern pre-assembly, it is desirable to lock it in position before starting to rotate the work; this is done by means of a short piece of glas rod 35 which may be tacked in place, as indicated in FIG. 4, by applying heat momentarily to the outer stem tubing 18. The stem tube preassembly is then mounted in the right-hand chuck of the glass lathe and a piece of flared tubing 36 is mounted in the left chuck. By applying heat as required and moving the chucks together, tubing 36 is joined at 37 to the left end of the stem pre-assembly as illustrated in FIG. 4. The left side of the stem assembly is connected through tube 36 to a vacuum system. The right side of the assembly may be connected through tube 20 alternately to a vacuum system or to a nitrogen pressure system by means of a suitable valving arrangement. The left side of the stem assembly is exhausted and then filled with nitrogen, the process being repeated four times withthe glass moderately iheated between cycles. This degassing process is necessary toobtain a seal that does not have excessive metal oxide at the interface. Seals made with a poor vacuum or excessive water show a greater tendency to shale and are less reliable. After the stem assembly is degassed, the left side is sealed off (by heat collapsing exhaust tube 36) when the vacuum gauge indicates a pressure of approximately 1 micron. The right side is left connected to the nitrogen pressure system set at approximately 2 pounds per square inch gauge pressure.

The basic problem in sealing quartz or quartz like glass to both inner and outer surfaces of the thin-walled molybdenum thimble is that of obtaining a good internal seal without distorting the metal. Since heat is applied from the outside, the tendency is for the outer vitreous portions to become hotter .and collapse onto the thimble before the inner vitreous portions are heated enough to deform and give support to the thimble walls. This problem is overcome in accordance with the invention by the use of a thimble which is long relative to its diameter, by a sealing system which applies vacuum on one side of the glass parts and gas pressure (nitrogen) on the opposite side, and finally by control of the initial heating of the stern assembly. The molybdenum thimble wall thickness decreases from about .0 at the closed end to about .0003" at the feathered open end. I find that it is desirable to confine the initial heating of the thimble and vitreous assembly to an area extending approximately 10 millimeters along the thimble from its closed end. In this area, the minimum wall thickness is .003" and assure-s sulficient rigidity to prevent deformation despite the fact that atmospheric pressure is pressing the quartz of outer tube 18 against the thimble walls. After about 3 minutes of heating, the intermediate and inner tubes 21, 23 of quartz-like (Vycor) glass are raised to softening temperature. The combination of vacuum on one side and nitrogen pressure on the other side causes the glass to conform and seal to the inner metal surfaces as illustrated at 2'1, 23' in FIG. 5. The nitrogen pressure inside the thimble then becomes effective in supporting the thimble walls. The sealing process is continued by displacing the burners slowly to the right, that is towards the open end of thimble, resulting in an inner sealing that supports the thin open end of the thimble at the same time as the outer quartz tubing 18 under atmospheric pressure collapses into engagement with it, as shown at 18'. By the use of nitrogen pressure on the open side of the thimble and a slow rate of heating, the tendency for the quality of the seal to be adversely affected by dimensional variations in the glass tubing is substantially overcome. However if the glass tubing is matched to the internal dimensions of the thimble, the seal can be made in a much shorter time.

To complete the manufacture, outer quartz tube 18 and inner quartz glass tube 23 are cut off at line AA beyond the place where the flare of intermediate tube 21 was originally joined to outer tube 18, as illustrated in FIG. 6. Then a piece of heavy capillary or thick-walled tubing of a length appropriate to the lamp size and electrodes is sealed to the end of tube 18 to complete the seal assembly. As an economy measure, I prefer to save the piece 18a that was cut off from outer tube 18 and use it as a sleeve around a quartz capillary tube 38 of smaller diameter so that the two parts together make up the desired size. This also facilitates using the vacuum-nitrogen system to prevent oxidation of the metal parts during sealing. In sealing, it is preferable to seal only sleeve portion 18a to the outer tube 18 to leave a gap between the end 23a of the inner tube portion and the end 39 of capillary tube 38. By so doing, the possibility of stress in the vitreous parts by reason of the fact that inner and outer vitreous portions may have been sealed together at different temperatures is avoided.

The capillary tube is not sealed to the tungsten rod and, during subsequent lamp manufacture, it is necessary to exhaust and gas fill the cavity within the interior of the cup. In order that this may be done rapidly, I prefer to use a capillary tube 38 having a passage 40 of square cross-section through it, as shown in FIG. 8. During seal manufacture, after sleeve 18a has been joined to outer tube 18, vacuum is applied and the outer sleeve is caused to collapse onto capillary tube 38 by running the flame along it. Also the capillary tube is vacuumformed, that is collapsed at least partially, onto the tungsten rod 5 for a short distance near the end in order to provide a rigid support for the tungsten rod when the heavy electrode is attached thereto. An isolation foil 41 is wrapped around the tungsten rod to prevent sticking of the quartz to the rod in the area that is vacuumcollapsed.

In the finished stem, the portion of sleeve 18a projecting to the right beyond capillary tube 38, and also the portion of outer tube 18 projecting to the left beyond the closed end of the thimble are cut off and discarded. The stem then has the appearance shown in FIG. 7 and is ready for attachment of an electrode to the end of the tungsten rod, after which it may be sealed to a quartz envelope in manufacturing a lamp. To complete a quartz envelope, the inner end of the stem may be inserted into a necked opening in the envelope and the neck wall is then heat-collapsed onto the stern as shown at 43 in FIG. 9. Alternatively, the inner end of the stem may be flanged and the flange then fused to the envelope wall. The lamp is completed by steps well known in the art, including evacuation and introduction of the gas filling, whereupon the envelope is tipped off at 42.

In FIG. 9, the arrowheads indicate the extent of penetration of pressurized gas from lamp envelope 2 into the stem. Starting at curved arrows 45, gas penetrates along rod 5, by isolation foil 41 and along square crosssection passage 40, into the hollow cavity within the thimble, as indicated by curved arrows 46. Then proceeding from curved arrows 47, gas penetrates under inner quartz tube 23, along the closed end of the thimble, and along intermediate tubing 21' up to the end of isolation foil 30. At this point the quartz is hermetically sealed to the inside surface of the thimble and this is the limit of gas penetration. The quartz at the inner interface is in compression in all three directions, namely in the axial, tangetial and radial directions so that a strong reliable seal is achieved.

A hermetic seal also exists between the quartz and the outer surface of thimble 14 beyond the end of outer isolation foil 27. This serves to back up the seal at the inner surface and to strengthen the assembly. As previously explained, the quartz at the outer interface is in radial tension and therefore is more subject to cracking and shaling. However, because the present seal structure effectively seals off the gas pressure at the inner interface, shaling at the outer interface does not result in a leak and therefore is not fatal to the lamp. In fact I-have operated many lamps with the quartz shaled at the outer interface of the thimble seal with no deleterious effects.

While a certain specific embodiment of the invention has been illustrated and described in detail, the same is to be considered as an example of the invention whose scope is to be determined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A sealed vitreous electric device having a high pressure resistant stem sealed thereto comprising a vitreous outer stem tube, a rod conductor extending through said tube, an elongated metal thimble encircling said rod, said rod extending through said thimble and being hermetically joined thereto at its closed end, said thimble having its open end facing in the direction of the inner end of said stem which is sealed to said electrical device, the open end of said thimble having a feathered edge sealed to said outer stem tube, and a capillary vitreous portion within said outer stem tube at its inner end having an aperture therethrough through which said rod extends.

2. A sealed vitreous electric device having a high pressure resistant stem sealed thereto comprising a quartz outer stem tube, a tungsten rod extending through said tube, an elongated molybdenum thimble encircling said rod, said rod extending through said thimble and being hermetically joined thereto at its closed end, said thimble having its open end facing in the direction of the inner end of said stem which is sealed to said electric device, the open end of said thimble having a feathered edge sealed to the wall of said outer stem tube, and a capillary quartz portion within said outer stem tube about its inner end having an aperture therethrough through which said rod extends.

3. A sealed vitreous electric device having a high pressure resistant stem sealed thereto comprising a vitreous outer stem tube, a rod conductor extending axially through said tube, an elongated metal thimble encircling said rod, said rod extending through said thimble and being hermetically joined thereto at its closed end, said thimble having its open end facing in the direction of the inner end of said stem which is sealed to said electric device, the open end of said thimble having a feathered edge, the inner surface of said feathered edge being sealed to a vitreous portion extending from said outer stem tube into said thimble and the outer surface thereof being sealed to said outer stem tube, and a capillary vitreous portion within said outer stem tube at its inner end having an axial aperture therethrough through which said rod extends.

4. A sealed vitreous electric device having a high pressure resistant stem sealed thereto comprising a quartz outer stem tube, a tungsten rod extending axially through said tube, an elongated molybdenum thimble encircling said rod, said rod extending through said thimble and being hermetically joined thereto at its closed end, said thimble having its open end facing in the direction of the inner end of said stem which is sealed to said electric device, the open end of said thimble having a feathered edge, the inner surface of said feathered edge being sealed to a quartz-like vitreous portion extending from said outer stern tube into said thimble and the outer surface thereof being sealed to said outer stem tube, said quartz-like portion having a lower softening temperature than said outer stem tube, and a capillary quartz portion within said outer stem tube at its inner end having an axial aperture through which said rod extends.

5. A sealed vitreous electric device having a high pressure resistant stem sealed thereto comprising a vitreous outer stem tube, a rod conductor extending axially through said tube, said rod having an outer end for connection to a current source and an inner end projecting into said sealed device, a metal thimble having its closed end at the outer end of said stem and its open end facing in the direction of the inner end of said stem, said thimble encircling said rod conductor, and said rod conductor extending through said thimble and being hermetically joined thereto at its closed end, said thimble having a ratio of length to diameter in excess of 1.75 to 1 and having a feathered sealing edge at its open end, a portion of said outer stem tube passing around said thimble and being bonded to the outside of the feathered edge thereof, a vitreous portion extending from said stem tube into said thimble and being bonded to the inside of the feathered edge thereof, metal foil covering the portions of said thimble remote from said open end, and a capillary vitreous tube portion extending through and fused to said outer stem tube at its inner end and having an axial aperture through which said rod extends, said capillary portion providing mechanical support to the inner end of said rod.

6. A sealed vitreous electric device having a high pressure resistant stern sealed thereto comprising a quartz outer stem tube, a tungsten rod extending axially through said tube, said rod having an outer end for connection to a current source and an inner end supporting an electrode within said sealed device, a molybdenum thimble having its closed end at the outer end of said stem and its open end facing in the direction of the inner end of said stem, said thimble encircling said rod conductor, said rod conductor extending through said thimble and being hermetically joined thereto at its closed end, said thimble having a ratio of length to diameter in excess of 1.75 to 1 and having a feathered sealing edge at its open end, a portion of said outer stem tube passing around said thimble and being bonded to the outside of the feathered edge thereof, a vitreous portion extending from said stem tube into said thimble and being bonded to the inside of the feathered edge thereof, metal foil covering the portions of said thimble remote from said open end and having a wall thickness too great for hermetic bonding to quartz, and a capillary quartz tube portion extending through and fused to said outer stem tube at its inner end and having an axial aperture through which said rod extends, said capillary portion providing mechanical support to the inner end of said rod.

References Cited by the Examiner UNITED STATES PATENTS 1,564,690 12/1925 Kruh et al 287189.365 2,103,081 12/1937 Kreift 313-318 X 2,504,522 4/1950 Greiner 1745().63

LEWIS H. MYERS, Primary Examiner.

H. W. COLLINS, Assistant Examiner.

Claims (1)

1. A SEALED VITREOUS ELECTEC DEVICE HAVING A HIGH PRESSURE RESISTANT STEM SEALED THERETO COMPRISING A VITREOUS OUTER STEM TUBE, A ROD CONDUCTOR EXTENDING THROUGH SAID TUBE, AN ELONGATED METAL THIMBLE ENCIRCLING SAID ROD, SAID ROD EXTENDING THROUGH SAID THIMBLE AND BEING HERMETICALLY JOINED THERETO AT ITS CLOSED END, SAID THIMBLE HAVING ITS OPEN END FACING IN THE DIRECTION OF THE INNER END OF SAID STEM WHICH IS SEALED TO SAID ELECTRICAL DEVICE, THE OPEN END OF SAID THIMBLE HAVING A FEATHERED EDGE SEALED TO SAID OUTER STEM TUBE, AND A CAPILLARY VITREOUS PORTION WITHIN SAID OUTER STEM TUBE AT ITS INNER END HAVING AN APERTURE THERETHROUGH THROUGH WHICH SAID ROD EXTENDS.

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