US2561520A - Vacuumtight seal for electrical apparatus and method of forming such seals - Google Patents

Description

y 24, 1951 H. J. LEMMENS ETAL VACUUM TIGHT SEAL FOR ELECTRICAL APPARATUS AND METHOD OF FORMING SUCH SEALS Filed July :5, 1947 FlG.l

H. J. LEMMENS 8 E26. DORGELO AGENT Patented July 24, 1951 VACUUMTIGHT SEAL FOR ELECTRICAL AP- PARATUS AND METHOD OF FORMINQ SUCH SEALS Hendricus Johannes Lemmens and Eduard Gerardus Dorgelo, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application July 3, 1947, Serial No. 758,946 In the Netherlands March 27, 1940 Section 1, Public Law 690, August 8, 1946 Patent expires March 27, 1960 6 Claims. i

This invention relates to vacuumor gas-tight seals of bodies in electric apparatus and more particularly of current-supply conductors in evacuated or gasfllled discharge apparatus, incandescent lamps or in electric apparatus enclosed in a vacuum-tight envelope, one or more conductors being sealed in a body consisting of glass. The invention relates in addition to a method of manufacturing such seals.

For a long time it has been a technical problem to manufacture vacuum-tight leads-through of this kind, more particularly in the case of comparatively high currents. One has endeavoured to overcome difficulties involved therein either by carefully choosing the supply conductors and the surrounding material (glass, quartz or ceramic) of equal or substantially equal coefficients of expansion so that inadmissible tensions with temperature variations of the seal were avoided, or by the use of very thin-walled metal parts whose coeflicient of expansion appreciably differs from that of the sealing material but which are unable, due to the small metal thickness, to cause harmful tensions in the surrounding material.

One example of the first-mentioned case is the known chrome-iron seal and this category is characterised by a comparatively great liberty in the choice of the shape and dimensions of the parts to be sealed but it obliges the man skilled in the art to utilise definite combinations of materials.

One example of the last-mentioned case is the seal having a tapered brass edge sealed in glass of appreciably lower coefllcient of expansion. In this case the diillculty resides in the less desirable properties of very thin metal parts which usually exhibit low mechanical resistance and tend to exhibit phenomena of tiring due to the repeated deformation work with temperature variations and are also to a higher degree exposed to the risk of leak due to oxidation or corrosion.

The two seals above described can be said to be expensive either due to the material used or due to their laborlousness.

The above-stated disadvantages are avoided in a very simple manner by utilising a seal and a method of manufacturing these seals in accordance with the present invention. It is thus possible for metals and insulating materials of greatly different coefllcients of expansion to be sealed together in a gasor vacuum-tight manner in a less expensive and simple manner without the risk of damage to the seal due to crack.

For this purpose a vacuumor gas-tight seal according to the invention consists of a body iii made from glass into which one or more members are sealed and which exhibits a vacuum-tight structure consisting of at least 5% of finely divided holes and having a specific weight which is at least 5% lower than that of the glass present in this body in the homogeneous and practically airor gasfree condition.

It has been found to our surprise that a sealing material of this kind is exceptionally free from harmful tensions and remains free from crack even in those cases wherein a great difference in coefficient of expansion exists between the lead-through conductor and the surrounding glass. Particular forms of construction in this case are not required and since direct connections between the above-mentioned finely-divided holes do not exist vacuum tightness is ensured without the use of covering layers from glass or glaze. One could say that a structure is present which is porous and also vacuum-tight.

It'has been found, for example, that it is possible for iron having a coefficient of expansion of 10-- to be sealed into lead glass having a coefiicient of expansion of 88x10-*, which illustrates the technical possibility which is thus obtained for combining supply conductors of any desired material, for example metal, brass, molybdenum and others, with a wide choice of kinds of glass of different coefilcients of expansion.

Very great freedom from harmful tensions may be obtained by making the seal such that either at least 10% of the volume of the sealing material is constituted by holes or that the specific weight is at least 10% lower than that of the glass present in the body in the homogeneous and practically airor gasfree state.

One particularly advantageous possibility of application for the invention consists in the sealing of current-supply conductors for small and compact vacuum discharge tubes, for example receiving or amplifying tubes for radio purposes, in which the bottom of the tube carrying the supply conductors consists in the manner referred to above of glass with finely divided holes and is sealed to the bulb. The advantages of such a glass body also become manifest in such respect that in practice one is entirely free in the choice of the bulb material. Thus it is possible for a metal bulb, for example an iron bulb to be sealed to a lead glass bottom, but it as well possible to seal a ceramic bulb to a bottom consisting of any desired glass.

In the method according to the present invention use is preferably made of powdered glass which is treated during scaling in such manner that a porous and vacuum-tight body with flnelydivided holes is obtained.

It is known per se to make the bottom part of a discharge tube, for example a receiving tube, from powdered glass. Other components, for example of incandescent lamps, have also been moulded already from powdered glass, such as, for example, the beads by means of which the currentsupply conductors in small incandescent lamps are spaced apart. In all these cases, however, the obtainment of a homogeneous and clear glass body was aimed at, in most cases even by the use of very strong moulding pressure. According to the invention it has been found that this homogenisation is not only superfluous but even harmful since temperature tensions in the glass are thus rendered possible without necessity. In the method according to the invention therefore one proceeds in such manner that sealing is effected without pressure or under but very weak pressure since otherwise the air or gas enclosures are driven out and the porous character of the obtained lead-in gets lost. In this manner it is found with surprise that, if moulding is effected without pressure or under but very weak pressure, a vacuumor gas-tight structure is obtained in which the finely-divided holes are not connected to each other.

In addition to the above described method, in which use is made of powdered glass, it would also be possible to obtain a body of the described structure by utilising in the starting material substances from which a gas, for example carbonic acid, is evolved upon heating so that during the sealing of this material the desired structure is produced due to this formation of gas.

Another domain of application is found, for

example, with incandescent lamps. Thus, with the aid of the present invention it is possible in a simple manner to make a sealing body which also serves as a lamp cap and which for this purpose has externally the appearance of, for example, a screw or bayonet cap.

f It is advisable to utilize the seal and the method according to the invention not only with incandescent lamps or with vacuum discharge-apparatus, such as receiving tubes, amplifying tubes, transmitting tubes, X-ray tubes, cathode-ray tubes, light tubes having gas or vapour filling or current-directing tubes, but also in electric apparatus in which, for example, a condenser or a motor is arranged in a closed atmosphere which mint, however, have electric connection, for example, with the mains. This occurs amongst others with condensers for comparatively high voltages in a gasfllling under pressure, whether or not with the addition of insulation by oil, and with units with motor drive for refrigerating apparatus in which the motor is mounted inside the vessel in which the cooling agent circulates.

With the above-stated applications for discharge tubes, such as receiving and amplifying tubes, various manufacturing methods are possible. In these cases it is possible for a number of current-supply conductors to be sealed in a vacuum-tight manner preferably normal to a discshaped bottom and concentrically with respect to the centre thereof.

In many cases it is advantageous for the complete electrode construction of the tube to be mounted already on the current-supply conductors before the latter are sealed into, the glass mass so that an assembly is obtained which has merely to be provided in the usual manner with a bulb for obtaining the complete discharge tube.

4 It is, however, also possible prior to the forma-. tion of the glass bottom to give the bulb likewise its definite position relatively to the interior and the powdered glass mass and to fuse itsimul taneously with the current-supply conductors in a vacuum-tight manner with the latter. The manufacturing process of the tube is thus combined in one operation and heating and sealing is only once necessary.

The exceptionally great freedom from crack of the sealing material makes it possible, however, to make a step farther and permits of a cap or a plate which serves, for example, for mechanic and/or electric protection or guiding of the tube and for this purpose may have a central guide pin, being fused with the porous glass mass at the same time with the current-supply conductors and/or the bulb. Thus the tube has still to be evacuated "Only and the operation of the separate application of a cap, for example, by means of gypsum or capping paste, is dispensed with. This may frequently lead to even further gain as far as the compactness of the construction of the tube is concerned. If in this case use is made of a metal cap or plate a discharge tube is obtained having a metal perforated bottom through which pass the current-supply conductors, said perforation being fllled up by the glass formed in accordance with the invention.

Instead of using a construction in which the current-supply conductors pass in the above-described manner through a disc or plate of the porous glass material, in some cases use may advantageously be made of a construction in which the glass powder is fused together in the form of a flattened body in which the current-supply conductors are provided in the direction of the largest dimension whilst this body is sealed to the extremity of a tubular part, for example consisting of glass, of the electric apparatus in such manner that one extremity of each of the leadthrough conductors extends into the tube and the other extends to the exterior so that a flat, pinchshaped seal is obtained. This is a construction which in practice is referred to as outer pinch" and is particularly adapted for use with light tubes of elongated structure.

with the use of the method according to the invention the loose glass powder as such may be poured into a mould in which, for example, the supply conductors are already provided in the desired position. In some cases, however, it is advisable for the glass powder to be preliminarily formed into a solid body, preferably with the aid of a binder which decomposes at high temperature, said solid body approximately having its definite shape and, if desired, already comprising the current-supply conductors and being connected thereto in a vacuum-tight manner.

In order that the invention may be clearly understood and readily carried into effect, it will be explained more fully by reference to the constructional examples shown in the accompanying drawing.

' Figs. 1 and 2 show examples of the manner in which a radio receiving-tube according to the invention can be manufactured.

Fig. 3 shows an incandescent lamp comprising a seal according to the invention, and

Fig. 4 shows a seal for a light tube having an incandescent cathode.

Fig. 1 illustrates a mould t containing a quantity of glass powder I and having provided in it a number of supply conductors l and an electrode construction I mounted thereon. A bulb l of glass, metal or ceramic provided with a sealing oif capillary tube is placed on the glass powder 3.

In the glass mass 3 and the mould 6 it is shown in dotted lines how the bottom can be formed in such manner that during the sealing process or in the course of a later operation a glass or metal exhaust tube may be connected to the bottom instead of to the top end of the tube. In the first-mentioned instance the exhaust tube must be preliminarily placed in the mould.

The mould 6 maybe heated in the usual manner either in an oven or inductively by means of a high-frequency coil I. After obtaining the required temperature the glass powder fuses and forms a vacuum-tight junction both with the bulb and with the current-supply conductors.

Fig. 2 illustrates how use may be made of a similar method in which, however, the glass mass ll consists of lass powder held together by a binder which decomposes and volatilises at high temperature,.such as, for example, parafiine, the tablet obtained being provided in a metal bottom piece 8 comprising a central guide pin 9 having a peg-shaped thickening Ill. The mould l2 which may be heated in a manner similar to that of Fig. 1 is indicated only in dotted lines.

Fig. 3 shows an incandescent lamp for high current-intensity whose current-supply conductors l5 for the filament l8 are sealed at M in accordance with the invention, that is to say into tubular protrusions iii of the bottom piece l6 moulded from glass and sealed in the normal manner into the bulb H. In this manner a. disc of glass according to the invention is located at H so that with correct choice of the metal for the current-supply conductor l5 and the sealing glass it is possible to obtain at H a crack-free and good vacuum-tight connection. It has been found, for example, that it is possible for iron tubes of 3 to 4 mms. in diameter and 0.25 to 0.5 mm. wall thickness to be sealed into lead glass, in connection with which it should be considered that the coefiicient of expansion of iron is 120 10 and that of lead glass 88x10- Fig. 4 shows the extremity IQ of a light tube having an incandescent cathode 22 and an anode 23 and in which the current-supply conductors and 2| are sealed into a plane body 24 made in accordance with the invention from glass provided with finely-divided holes, said body in its turn being fused with the extremity IQ of the tube.

According to the invention it is possible to make glass-metal junctions of greatly different kinds free from crack and leak, particular attention having to be paid to the possibility of making in this manner leading-in insulators of electric apparatus such as, for example, the condensers under pressure referred to already hereto-before. The whole insulator in this case may be formed from the glass according to the invention while it is possible also to seal lead-in conductors of comparatively high thickness into an insulator without risk of crack or leak.

The structure of the glass according to the invention is characterised by finely-divided holes which may have, for example, a size of the order of magnitude of 0.1 mm. and are not connected together. This is very well perceptible under the microscope and makes the glass more or less opaque.

What we claim is:

l. A gasand vacuum-tight housing for electrical apparatus, comprising a tubular envelope one end of which is open, an electrically conductive metal member positioned in the open end of the envelope and spaced therefrom, and a nonporous gasand vacuum-tight glass element surrounding the metal member and joined thereto and the envelope for sealing said envelope in a gasand vacuum-tight manner, said glass element comprising a mass of fused glass particles enclosing a myriad of disconnected gas-filled voids constituting about 5 to 10% of the glass volume, the glass element having a specific weight which is about 5 to 10% lower than that of a similar body of homogeneous gas-free glass.

2. A gasand vacuum-tight housing for electrical apparatus, a tubular metal envelope one end of which is open, an electrically conductive metal member positioned in the open end of the envelope and spaced therefrom, and a non-porous gasand vacuum-tight glass element surrounding the metal element and joined thereto and to the walls of the metal envelope for sealing the same in a gasand vacuum-tight manner, said glass element comprising a mass of fused glass articles enclosing a myriad of disconnected gas-filled voids constituting about 10% of the glass volume, the glass element having a specific weight which is about 10% less than that of a similar body of homogeneous gas-free glass.

3. A gasand vacuum-tight housing for electrical apparatus comprising a tubular iron envelope one end of which is open, an electrically conductive metal member positioned in the open end of the envelope and spaced from the walls thereof, and a lead-glass element surrounding the metal member and joined thereto and to the walls of the envelope for sealing the same in a gasand vacuum-tight manner, said lead-glass element comprising a. mass of fused particles of lead-glass enclosing a myriad of disconnected gas-filled voids constituting about 10% of the glass volume, said lead-glass element having a specific weight which is about 10% less than that of a similar body of homogeneous gas-free leadglass.

4. An electric discharge tube comprising an evacuated envelope sealed at one end in a gasand vacuum-tight manner, an electrode system in said envelope, a plurality of spaced electrically conductive metal supply members extending through the sealed end of the envelope and electrically connected to said electrode system, and a glass sealing element surrounding said supply members in the sealed end of the envelope and joined to the supply members and the walls of the envelope in a gasand vacuum-tight manner, said glass element comprising a mass of fused glass particles enclosing a myriad of disconnected gas-filled voids constituting about 5 to 10% of the glass volume, said glass element having a specific weight of about 5 to 10% less than that of a similar body of homogeneous gasfree glass.

5. An electric discharge tube comprising an evacuated metal envelope sealed at one end, an electrode system in said envelope, a plurality of spaced electrically conductive metal supply members extending through the sealed end of the envelope and electrically connected to said electrode system, a glass sealing element surrounding said supply members in the sealed end of the envelope and joined to the supply members and the walls of the envelope in a gasand vacuum-tight manner, said glass element comprising a mass of fused glass particles enclosing a myriad of disconnected gas-filled voids constituting about 10% of the glass volume, said glass element having a specific weight of about 10% less than that of a similar body of homogeneous gas-free glass, and a metal base plate joined to the glass element through which the conductive members pass and are insulated therefrom.

6. A method 0! manufacturing an evacuated tube having an envelope and. a glass element closing said envelope, said glass element having an electrically conductive member sealed therein, comprising the steps of positioning said electrically conductive element in a mass of powdered glass, placing the open end oi said envelope over said electrically conductive member and in said mass of powdered glass contained in a. mold of a desired size and shape. heating the powdered glass to fusion temperature thereby hermetically sealing the glass to the envelope and said electrically conductive member and permanently forming throughout the body of the glass seal a myriad of disconnected gas-filled voids to the extent or at least 5% o! the volume of the fused glass element, evacuating said envelope through a port provided in said tube, and sealing said Port.

HENDRICUS JOHANNES LEIDEENS. EDUARD GERARDUS DORGEIO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Australia May 1, 1942

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