Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS2210699 A
Publication typeGrant
Publication dateAug 6, 1940
Filing dateOct 21, 1936
Priority dateOct 21, 1936
Publication numberUS 2210699 A, US 2210699A, US-A-2210699, US2210699 A, US2210699A
InventorsWalter E Bahis
Original AssigneeWestinghouse Electric & Mfg Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Vacuum-tight insulated lead-in structure
US 2210699 A
Abstract  available in
Images(4)
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

8- 9 w. E. BAHLS 2.210.699

YACUUM TIGHT INSULATED LEAD-IN STRUCTURE I Filed Oct. 21, 1956 4 Sheets-Sheet 1 50/1/17 Jam INVENTOR WaizerE .Ba/7/5.

ATTORN Aug. 6, 1940. w. E. BAHLS 2.210,699

VACUUM TIGHT INSULATED LEAD-IN STRUCTURE Filed Oct. 21, 1936 4 Sheets-Sheet 2 lvllllllillltlllvl I Aug. 6, 1940. w. E. BAHLS VACUUM TIGHT INSULATED LEAD-IN STRUCTURE Filed 001:. 21, 1936 4 Sheets-Sheet 3 Jarfiarundzln .lflfl'e r! IIII IIII' dam INVENTOR Wa/Zer 550/719.

ATTORN Y I Cararzm WITNESSES:

Patented Aug. 6, 1940 UNITED STATES VACUUM- TIGHT INSULATED LEAD-IN STRUCTURE Walter E. Bahls, Forest Hills, Pa., assignor to Westinghouse Electric 8: Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 21, 1936, Serial No. 106,798

6 Claims.

My invention relates to a vacuum-tight insulated lead-in construction and especially such construction applied to electron discharge devices. I

An object of my invention is to provide a very strong vacuum-tight lead-in construction that will withstand a great difference of pressure on its opposite sides.-

Another object of my invention is to provide a lead-in construction for vacuum devices which will permit the utilization of much higher temperatures during the exhausting and degasifying of the parts.

Other objects and advantages of my invention will become apparent from the following de-- scription and drawings, in which: I

Figure 1 is a view through a hot cathode device incorporating my invention with the walls in cross section and the lead-in and interior parts in elevation.

Fig. 21s a sectional view of a modification of Fig. 1.

Fig. 3 is a sectional view of a still further modiflcation of Fig. l. 1

Fig. 4 is a view through a mercury pool type of device incorporating my invention with the walls in cross section and the lead-in and interior parts in elevation.

Figs. 5, 6, 7 and 8 are modifications of the leadin construction of Fig. 4.

Fig. 9 is a view principally in cross section of another mercury pool type of device incorporating further modifications of my invention.

Fig. 10 is a view principally in cross section of a lamp incorporating my invention.

Fig. 11 is a view mainly in cross section of a still further modification of the lead-in construction as applied to the mercury pool type of device of Fig. 4.

Figs. 12, 13 and 14 are still further modifications of the seal of Figs. 4 and 11; and,

Figs. 15 and 16 are curves illustrating the expansion of preferred materials utilized in the preceding seal construction.

In the prior art devices employing seals between lead-ins and metal containers, glass has been heretofore utilized. In such constructions, principally that of vacuum electron discharge tubes, it is necessary that the device be heat treated at a very high temperature in order to degasify the interior elements. An extensive portion of a glass wall cannot be utilized with such heat treatment because the glass will become molten and collapse. On the other hand, if not much glass is used, there is apt to be a very short (Cl. 250 -2'l.5)

distance between the lead-in and the metal wall of the container that will provide a leakage path with the accumulation of dirt and moisture.

It is an object of my invention to utilize a ceramic material for the body of insulating material and to utilize a coating of glass 'to seal the ceramic material to the metal casing. I also contemplate using special forms by which the device will withstand pressure from within or without.

Figure 1 illustrates a particular type of discharge device utilizing my invention. This device has a container wall In of metal and preferably of an alloy of 24% to 30% nickel, 5% to 25% cobalt, less than 1% manganese and the remainder iron and known under the registered mark Kovar. The container wall is in the form of a tube with one end It closed and the open end having a flange l2 extending preferably outward. .On this flange II is placed an annular ring l3 of ceramic material, preferably porcelain, and having a certain desired number of openings l4 therethrough. These openings l4 have a tapered contour l5 preferably decreasing in diameter towards the inner portion of the device. The lead-in connection I6 is preferably formed with a similar contour H. The top portion is preferably closed with a plate l8 of metal preferably similar to that of the container wall l0 and this plate has the desired tubulation l9 through which the device is exhausted. This tubulation I9 can, of course, be at any other convenient portion of the device and it is understood that this tubulation, whileit is not illustrated in the other figures, can be applied thereto. In assembling the device, the openings are coated with a glaze or sealing material, preferably of glass and such glass is preferably of the horn silicate type of glass. This glass has a major percentage of silicon dioxide and also preferably has such silicon dioxide in an amount from to This glass also preferably has less than 10% PhD, less than 6% A1203 and 10% to 25% B203. The particular type of glass that I prefer to use has the following analysis:

Per cent S102 67.3 B203 24.6 A1203 1.73 NaaO 4.6 K20 .94 A5203 .14

The surfaces 2| and 22 of the porcelain ad-. joining the metal portions 62 and I8 are also coated with this glass material. The lead-in wires with their tapered contour are pushed into the tapered openings l4 and the interior structure assembled on their inner ends. Such interior structure may, for example, be the cathode 23, which may be of the'directly heated type, and the grid structure 24. The device is then exposed to a high temperature at which the glass melts and seals the metal to the porcelain. The device is then evacuated. To facilitate the exhaust the device is heated to a high temperature and preferably to as high a temperature as the structure will withstand because the higher the temperature, the easier the gas will be evolved from the parts. Because of the arrangement of parts the device can be heated to the order of 700 C. or even above which temperature is above the melting point of the glass. Althoughthe glass is softened, yet it will remain in place due to its thin film and very high viscosity. It will be noted that due to the tapered contour of the lead-in l6 and the opening l4 in the porcelain that a very firm seal is made therethrough and that the vacuum within the container will draw the lead-in tapered pin into a tighter seal in the opening. In other words, a greater pressure on the exterior of the device will only more firmly seal the tapered pin in the tapered opening in the porcelain material.

Also to facilitate exhaust by the cleaning up of oxides on the parts, I prefer to utilize an atmosphere of hydrogen about the device during part of the exhaust. At the high temperatures permitted by my arrangement the hydrogen will diffuse through the walls and reduce the oxides.

The glass, although utilized to seal the metal and porcelain, may also be used as a glaze to cover the exposed parts of the porcelain. Porcelain has a generally rough surface that would tend to retain dirt and moisture that would make a leakage path across its surface. Such dirt and moisture is not so apt to remain on a. smooth glass surface. For this purpose any standard glazes may be utilized.

The parts disclosed in Fig. 1, as well as in the other figures, can be made self aligning and thus the need for a skilled glass blower will be eliminated.

Fig. 2 shows a somewhat similar construction utilizing somewhat the same container I I! with its flange l2. In place of the annular ring of Fig. 1, a plate or disc 30 of ceramic material which may be coated with a glass 3| is utilized. The lead-ins 32 preferably have the same tapered contour 33 but these are preferably sealed in tapered vertical openings 34 in the plate 30. The assembly of Fig. 2 is similar to that of Fig. 1.

In Fig. 3, the construction is still further modified in which a tapered disc or plate of porcelain 40 is utilized and is sealed in the tapered opening 4| of a metal plate 42 by means of a coating of glass 43 preferably similar to that previously described. The lead-ins 44 may have a very small head or tapered portion 45 to be matched by a similar slightly tapered contour of the exterior portion of the openings 45. The construction of Fig. 3 is especially adaptable where the metal portion 42 sealed to the porcelain or ceramic material is rather expensive and it is desired to utilize some other cheaper metal, such as steel or iron, for the major portion ID of the metal casing. Any suitable material can be used for portion I!) provided it is sufliciently non-porous and can be welded or otherwise made sufiiciently vacuum tight to the portion 42.

Fig. 10 has a further modification f the invention applied to a lamp in which a glass container I0 is sealed to a porcelain disc 50 at H. The filament structure 52 has lead-ins 53 welded or copper sweated into pins 54. These pins 54 are of the preferred glass sealing metal of iron, nickel and cobalt described above. These pins have a tapered contour 55 that is sealed in tapered openings 56 in the disc 50, as described in connection with Fig. 1. I

It will be noted that in Figs. 1, 2 and 3, the exterior casing ID has been illustrated as that of an anode, although it is apparent that the tube structure might be modified to utilize it as one of the other electrodes. In the other figures i1- lustrating the complete device, I have shown the exterior casing as making a. connection to the cathode, which is disclosed as a mercury pool. In Fig. 4, for example, the metal container 60 has the mercury pool 59 forming the cathode therein. To this container Ellis welded a metal plate 6| preferably of the nickel cobalt iron alloy previously described, and having an outwardly extending tubular flange 62. If desired the flange part 62 only may be of this nickel cobalt iron alloy. This tubular flange 62 is sealed to an annular ring 63 of porcelain. This annular ring has preferably a slot 58 into which the edge of the flange 62 extends and which slot is filled with glass, preferably of the boro silicate type previously described for making a vacuum-tight seal between the metal 62 and the annular ring 63. A cup shaped cap 64 has preferably a downward extending flange 65 fitting into an upper annular slot 66 of the porcelain ring and sealed thereto by means of the aforementioned glaze. A leadin 61 of any desired metal is welded to the inner side of the cup and at its inner end preferably supports an electrode such as the anode 68. An exterior conductor 69 can then be welded to the exterior surface of the cup to make contact therethrough to the interior electrode structure.

This type of device may have any one or a combination of auxiliary electrodes. One such type would be a make-alive l0 constructed of a high resistance material such as carborundum or boron carbide in contact with the mercury and supported by a conductor II. This conductor ll could have an exterior connection 12 connected to conductor II by a cap 13 sealed in a ceramic ring 14 similar to the supporting and connecting structure of the anode 68.

Fig. illustrates a modification of the seal of Fig. 4. In Fig. 5, the flange 16 has preferably an outwardly tapered portion 11. The porcelain section 18 has a similar contour 19. The upper portion of the porcelain section also has a downwardly tapered opening 80 terminating in the fiat portion 8| adjacent the central opening 82. The metal closing portion for this porcelain section has a corresponding taper 83 similar to tapered opening 80 and also a fiat area 84 to rest upon the flat area 8| and to close the central opening 82. The anode conductor 85 is welded to the under side of this metal closure and an exterior conductor 86 is welded to the upper side of the metal closure 84. The metal portions are sealed to the porcelain by means of the glass glaze 81 previously described. It will be noted how the tapered portion of the porcelain at 19 and the tapered portion, 11 of the metal casing will provide a very tight seal if a vacuum is maintained within the device and the exterior pressure will cause the porcelain to set more firmly on the tapered flange l1.

Fig. 6 illustrates a modification of the upper portion of the device in Fig. 5. in which the metal portion 88 is tapered down and outwardly instead of upwardly as in Fig. 5. The flat portions 8| of Fig. 5 may be eliminated, as shown inFig. 6.

Fig. 7 illustrates a very firm seal in which the ceramic portion 90 has an inwardly tapered portion 9I extending to a small diameter portion 82. Surrounding this ceramic portion is a tubular metal portion, 93 extending inwardly at 94 to meet the tapered portion 9| at 95 and then extending in a contour at 95 similar to that of the porcelain until it forms an extending tubular portion 91 for the large diameter of the porcelain. A cap shaped metal closure member 98 seals the central opening of the porcelain containing the conductor 98. An exterior lead I is welded to the cap 98. In this construction, the cap 98 and the tubular member 93 may be of the nickel cobalt iron alloy previously described which will seal to the glass coating IIII of porcelain and other metal material may be used for the main portion of the metal container I02.

In case it is not desired to have the sealed lead-in construction extending from the exterior portion of the casing but to be placed mainly within the confines of the casing, a structure such as that illustrated in Fig. 8 may be utilized. In this case, a tube I is welded to the interior side of the casing I06 adjacent the opening I01 for the lead-in I08 therethrough. The inner end I08 of this tube is tapered and the porcelain section IIO has a similar tapered portion III that fits snugly adjoining the tapered portion I09. A sealing glass material II2 such as the hero silicate glass previously described seals the porcelain to the metal. The exterior lead-in I08 is welded to a cap II3 which may be similar to the caps previously described, such as that of Fig. 5, and this cap in turn has the anode conductor II4 welded to its inner surfaces.

The lead-in structures which have been previously described may be easily modified or combined to give a double or concentric type of lead. An example of such a lead for a pool type tube in which the starting electrode comes through the anode is disclosed in Fig. 9. The metal casing I containing the mercury pool I2I is illustrated in cross section. Preferably on the upper portion of this container is a metal tube I22 having a flange I23 sealed to and supporting a porcelain ring I24 similar to the porcelain rings of Figs. 5 and 6. A metal cap I25 preferably similar to the cap 88 of Fig. 6 is sealed to the porcelain ring I24. Instead of this cap closing the large opening I25 in the porcelain ring I24, it has an opening I21 centrally located therein and formed by a downwardly tapered flange I28. A smaller porcelain tube I29 is sealed to this flange I28 at its similar tapered portion I30.- A cap I3I closes the central opening in this porcelain tube I29. This cap may be of any of the types previously described and as illustrated it is similar to that of Fig. '1. An exterior lead-in I32 is welded to the cap I 3| and aconductor I33 is welded to the interior portion of the cap I3I and extends downwardly and has a make-alive I35 supported in position thereon to make contact with the mercury I2I. Surrounding this make-alive lead-in construction is preferably an insulating quartz sleeve I34.

Welded to the interior side of the cap I25 is a tubular conductor I36 supporting on its inner end an anode I31 which, of necessity, has a hollow opening therethrough for the passage of the make-alive conductor and insulating sleeve. If

in Fig. 9 is illustrative of a preferred combine tion of the shapes of elements previous disclosed and that other specific shapes may be substituted in this combination.

Sometimes it is found desirable in the construction of metal tubes, for example, to assemble all the parts and then copper sweat all the vacuum Joints. In a case of this sort, it is necessary to still have the leads come in through insulation. This type of assembly, however, presents a difficulty because of the decomposition of the glass glaze under the conditions for making the copper sweat joints. I have devised a structure in which the Joints can be copper sweated and the parts cemented together with a high temperature cement or mechanically clamped. The structure is thus held rigidly in place while it is heated up to the temperature necessary to melt the copper or whatever metal may be necessary for the sweating process. After the sweating has been done, the glass may be put on to make the vacuum-tight joints.

In Fig. 11 is disclosed such a device incorporating my invention as applied to a mercury pool type of device having a metal container I50. It is desired to have an insulated lead-in for the anode I5I through an opening I52 in the metal casing. A porcelain tube I53 surrounds the anode lead I54 and has an extension I55 extending through the opening I52 of the metal casing. Another porcelain tube I58 surrounds the interior portion of the anode lead I54 and has a depression I51 into which the extension I55 of the outer porcelain piece fits. A metal portion I58 on the inner portion of the anode lead and a similar metal portion I59 on the exterior portion of the anode lead I 54 tightly clamp the two porcelain sections I53 and I55 together about the opening I52 in the top cover I 50 of the tube. This arrangement is assembled preferably by first spot welding the metal portion I59 in place on the anode lead I54, placing the other parts thereon and spot welding the metal part I58 while the parts are held tightly in position. A tubular section I60 surrounds the exterior portion of the porcelain tube I53. A similar construction may be utilized to support the make-alive I81. The metal joints of the casing will then be sweated together at such joints as I62, I53 and I54. After this is done, the pocket formed by the extensions I and I66 of the interior metal portion I59 and the exterior portion I60 extending above the surface of the porcelain tube I53 is then filled with a glass material I61 to provide a vacuum-tight seal across the upper surface of the porcelain. In case it is desired to increase the creepage distance between these two metal portions an insulator I68,

which may have any desired shape such as the form of a ring having a reverse bend, is sealed into the glass I61.

Fig. 12 disclosesanother modification in which the porcelain section I1I is placed on lead-in I12 and enclosed in tubular shell I13. The porcelain section I10 is then placed on the lead-in and cemented in position to shell I13. The lead I12 preferably has raised or ring portions I14 upon which the two porcelain portions I10 and HI clamp. The shell I13 preferably has the tapered flange I15 to maintain the lower porcelain section in position. The shell I13 is preferably of the (Lil nickel cobalt iron alloy previous described and is copper sweated at I16 to the container wall I11. Thereafter, the upper portion I18 of the nickelcobalt-iron shell is filled with a sealing glass material I18 to provide a vacuum-tight seal between the anode lead-in I12 and the shell portion I13 that forms an extension of the metal casing.

Fig. 13 illustrates a type of device in which the lead-in combines all the features of mechanical clamping as well as the sealing of the metal, glass and porcelain. The metal container I has a tubular extension I8I welded or copper sweated thereto. The anode lead I82 is provided with a ring I83 thereon. The tubular section I8I has a constricted portion I84 that preferably has a tapered portion I85 similar in contour with the bottom I86 of a porcelain ring I81. This insulator is placed around the lead-in I82 and the lead-in dropped in place after the porcelain is coated with a glass sealing material. The lead-in construction is then heated and sealed together and the top porcelain ring I88 is put in place. While the structure is being heated, a tool is placed on top of the tube I8I and spins or swages the upper portion I88 down over the top of the porcelain. It is then permitted to cool and the glaze hardens or sets. The top portion need not be glazed.

In Fig. 14 is disclosed another type of insulator in which the tube I80 is sealed by means of glass I8I to the lower tubular tapered portion I92 of an elongated insulator I 93. The upper tapered portion I 94 of the insulator is closed with a cap I85 which has an exterior lead I86 and an interior lead I81 welded thereto. The insulator I93 preferably has extensions I88 to provide a greater creepage distance between the metal portions I80 and I85.

I have previously described a preferred sealing metal as being a nickel-cobalt-iron alloy and also the glass as being a boro-silicate type because these substances have a similar coeflicient of expansion, substantially in the region of 4.6 to 7.0x 10- cm. per degrees centigrade. I also desire to utilize the ceramic material such as porcelain of a substantially similar coeflicient of expansion. One such type of porcelain is composed of 30% feldspar, 25% flint and 45% clay. A typical chemical analysis of a particular type of this In Fig. 15 I have shown curves disclosing the unit expansion over a temperature range for these three materials.

The metals, porcelains and glasses do not necessarily have to have the same coefiicient of expansion throughout the temperature range, but

do have to have substantially the same coeificient of expansion in the annealing range of the glass as illustrated in Figs. 15 and 16. After the sealing has taken place, for example, in the temperature range 800 to 1100 C., the assembly is cooled to the annealing range of the glass and any stresses developed due to the difference of expansion as the different parts cool are then relieved because the glass, although set, is still plastic enough to relieve stresses. The time required for this annealing will depend upon the exact type of glass, the temperature at which it is held and how closely the various materials match in the higher temperature range. This time will, in general, be from a few minutes to four hours. The seal may then be rapidly cooled, and only care taken that improper cooling does not crack the porcelain.

The annealing range covers from the strain point to the annealing point. The strain point is defined as that temperature at which practically all stresses or better) are relieved in a period of four hours. The anneal point is defined as that temperature at which practically all stresses are relieved in fifteen minutes.

The porcelains and glasses are of brittle type materials which are stronger in compression than tension. It is accordingly desirable that the metal should have a slightly higher unit expansion in the annealing range so that, after the seals have been annealed and are cooled, the

metal contracts slightly more than the porcelain and tends to clamp on the porcelain putting it slightly in compression.

Other types of porcelain with the desired coefllcient of expansion may, of course, be substituted for this particular Derry plastic. Fig. 16 discloses a curve for such a. body which I have designated as'a special Derry body" in which pyrophyllite was substituted for the flint in the regular Derry plastic body, together with curves for the preferred metal and glass in Fig. 15.

Although I have shown and described the invention applied to discharge tubes, many other applications of my invention are possible. Such applications include bushing or lead-in for condensers, especially where such bushings must be oil or air-tight, electrical lead-in for hermetically-sealed refrigerators, lead-in bushings for sealed oil-filled transformers, lead-in for motors having a special cooling atmosphere as hydrogen, etc. This list is to be taken as illustrative and not as a limiting list.

My Patent No. 2,147,417 has claims covering the seal of Fig. 5 herein, and my Patent No. 2,144,558 has claims covering Fig. 9 herein.

Also, although I have described various modifications of my invention, various changes may be made in the shape, arrangement, selection and application of the various elements and combinations disclosed. I accordingly desire only such limitations to be placed on the following claims as is necessitated by the prior art.

I claim as my invention:

l. A terminal for a metallic enclosure comprising a porcelain member at least partially surrounded by a wall portion, said Wall portion forming a part of said enclosure and having a surface adjacent said porcelain member comprising an alloy of 28% to 34% nickel, 5% to 25% cobalt, less than 1% manganese and the remainder substantially iron, the space between said porcelain and said surface being filled with a glass fused to said porcelain and to said alloy. 1

2. A terminal for a metallic enclosurecomprising a porcelain member at least partially surrounded by a wall portion, said wall portion forming a part of said enclosure and having a surfaceadjacent said porcelain member comprising an alloy of 28% to 34% nickel, 5% to 25% cobalt,

less than 1% manganese and the remainder sub-} stantially iron, the space between said porcelain and said surface being filled with a bore-silicate glass fused to said porcelain and to said alloy.

3. A terminal for a metallic enclosure comprising a member or ceramic material at least partially surrounded by a wall portion, said wall portion forming a part of said enclosure and having a surface adjacent said member of ceramic material comprising an alloy of 28% to 34% nickel, 5% to 25% cobalt, less than 1% manganese and the remainder substantially iron, the space between said ceramic material and said surface being filled with a glass fused to said ceramic material and to said alloy.

4. A terminal for a metallic enclosure comprising a porcelain member at least partially surrounded by a wall portion, said wall portion forming a part of said enclosure and having a surface adjacent said porcelain member comprising an alloy of 28% to 34% nickel, 5% to 25% cobalt, less than 1% manganese and the remainder substantially iron. the space between said porcelain and said surface being filled with a glass fused to said porcelain and to said alloy, said porcelain member having a hole therethrough, a conductor extending through said hole and having at least its surface adjacent said porcelain member composed oi the aforesaid allay, and a layer of glass between the last-mentioned surface and said porcelain member forming fused joints therewith.

5. A terminal for a metallic enclosure comprising a porcelain member having a hole therethrough, a conductor having a surface comprising an alloy of 28% to 34% nickel, 5% to 25% cobalt, less than 1% manganese and the remainder substantially iron adjacent said porcelain member, and a layer of glass forming a fused junction to both said surface and said porcelain member.

6. A terminal for a metallic enclosure comprising a porcelain member having a hole therethrough, a conductor having a surface comprising an alloy of 28% to 34% nickel, 5% to 25% cobalt, less than 1% manganese and the remainder substantially iron adjacent said porcelain member, and a layer of boro-silicate glass form 20 ing a fused junction to both said surface and said porcelain member.

WALTER E. BAHLS.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2422546 *Jan 23, 1945Jun 17, 1947Asea AbLeading-through insulator
US2431277 *Apr 11, 1945Nov 18, 1947Hartford Nat Bank & Trust CompMetal-glass joint
US2438489 *Feb 16, 1944Mar 30, 1948Andrew CorpCable terminal
US2459988 *Jun 12, 1945Jan 25, 1949Amalgamated Wireless AustralasRadio-frequency oscillator power supply circuits
US2591205 *May 15, 1948Apr 1, 1952Sylvester & CompanyHermetically sealed insulator bushing assembly
US2654070 *Apr 7, 1948Sep 29, 1953Weston Electrical Instr CorpSealed instrument
US2806166 *Aug 30, 1952Sep 10, 1957Rca CorpElectron discharge device
US2944102 *Dec 21, 1956Jul 5, 1960Bell Telephone Labor IncHigh pressure hermetically sealed terminal
US2951133 *Jan 11, 1954Aug 30, 1960Cutler Hammer IncHermetically sealed electromagnetic contactors and the like
US3009012 *Sep 12, 1958Nov 14, 1961Gen ElectricHeader construction
US8082663 *Nov 11, 2008Dec 27, 2011Sandia CorporationMethod for hermetic electrical connections
DE1033864B *May 26, 1954Jul 10, 1958Siemens AgElektrische Durchfuehrung mit einem Isolierkoerper aus Glas