US1456110A - Seal for electric devices - Google Patents

Description

Patented May 22, 1923.

,UNITED STATES PATENT- OFFICE.

. GEORGE MACKAY, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIO COMPANY, A CORPORATION OF NEW YORK.

SEAL roa ELECTRIC DEVICES.

Application filed J'an'uary 21, 1921. Serial No. 438,899.

To all whom it may con/cm:

Be it known that I, Gnonen M. J. Mao- KAY, a citizen of the United States, residing for Electric Devices, of which the following is a specification.

and shell. My

The present invention comprises a new seal for electric devices which is particularly useful for making a gas-tight seal in containers consisting of electrically conductive material.

' It is often highly desirable and sometimes necessary to enclose electrical apparatus within a sealed metal container. For example, refrigerating apparatus utilizing irritating or poisonous gases are enclosed advantageously in a sealed metal receptacle. In other cases, highl evacuated devices, such, for example, as ra tubes and electron discharge devices of a l sorts, also electric are devices in some cases are provided with metal enclosures, particularly when of high current capacity. In all such cases, it is necessary to pass an insulated electrical conductor into the metal enclosure, and it has always been a serious problem to provide electrical insulation which will withstand variations of temperature and mechanical shocks without permitting the leakage of gas in orout of the sealed container.

As a result of my invention -I have provided an electrical conductor. capable of bein sealed into a metal container and comrislng a conductive core surrounded by a layer of vitreous material which is in turn surrounded by and maintained under compression by a metallic shell, the -vitreous nvention includes both a new article and thb method of making the article.

In the accompanying drawing, Fig. 1 is a longitudinal section of an insulated conductor embodyin myiinvention; and Fig. 2 is a end view 0 a multiple conductor embodying an invention.

. Fig. 1 s ows the finished article consisting of a shell or sleeve 1, an axially located ,core 2 and an intervening layer of vitreous material 3. The shell has been screwthreaded at 4 for convenience of attachment.

In the preparation of a composite conductor embodying my invention, the conductor core 2 is threaded thru a tube 3 of glass 1 and these two elements of the conductor are in turn surrounded by a metallic shell or sleeve 1. The original members when assembled may have the diameter'of the screwthreaded part 4, as shown in the drawing, the reduced diameter of the adjoining section being produced by the subsequent swaging. The surface of the core, and the inner face of the shell are adapted, as later described, to be wetted by the vitreous material when lastic so as to produce a gastight seal. For example, when using ordinary lead glass as the insulating and sealing layer 3, I employ preferably a core 2 consisting of a nickel iron alloy having a somewhat lower expansion coefficient than lead glass, and provided with a superficial layer of copper. The wine as a whole has approximately the same coeiiicient of expansionas lead glass. Copper coated tungsten or molybdenum may be similarly used. The shell may consist of steel coated with copper upon the inner surface which is in contact with the glass layer, or it may consist of copper, and various other materials. In the case be chosen somewhat higher than the expansion coefiicient of the glass. In generaLthe expansion coeflicient of the core should be equal to or somewhat lower than that of the vitreous layer, while the expansion coefficient of the shell preferably should be somewhat higher than that of the vitreous layer. It is possible, althou h not preferable, to

produce my new artic e when the expansion coefficient of the core, shell and intervening glass layer are all equal.

Before assembly the surface of the core and the inner surface of the shell are treated with a borax solution in accordance with the process described in Van Keuren Patent 1,268,647 of June 4,1918. Thereupon, the core, insulator and shell are assembled and heated to a temperature at which the insulator is plastic. but not fluid. In the case of lead glass about 800 C. is a suitabletemperature for working. The insulated conductor when assembled and heated to a workable condition is swaged or otherwise treated to reduce its diameter. A suitable swaging mechanism is described in U. S. Patent 1,082,933 of December 30, 1913. As by this treatment the diameter of the shell and insulator is reduced, the initial diameterof the article prior to swaging should be reater than the desired diameter of the completed articles. The reduction in diameter due to swaging is shown in the drawing by contrast with the screw-threaded part 4. The diameter of the core remains substantially unchanged by the swaging treatment. A firm adherence of the insulator 3 with the core and. the shell are produced while the glassy mass remains unbroken. This treatment may be repeated with intervenin reheating until the article has been recuced to a desired diameter. The mass of vitreous material is maintained under pressure by the shell when the thermal expansion coefiicient of theshell is somewhat greater than the expansion coefiicient of the glass.

In the same way an article containing a plurality of insulated conductors may be produced, as illustrated in Fig. 2. The article here illustrated may be made by proceeding in essentially the same manner as above described. A cylinder 5 (shown at end) consisting, for example, of ordinary carbon steel is bored out at a desired number of places to produce openings running lengthwise through the cylinder. The walls of these openings preferably are plated with cop er and borated. A thick walled tube 6 0 glass, or the like containing a conductor 7 closed and prepared as above described are inserted and the whole article thus assembled is heated and swaged while the glass is plastic to cause the glass layers 6 to be firmly packed in the massive state in the space intervening between the core and shell. The cylinder 5 finally may be machined in any desired manner and inserted in a metal enclosure, or used in any other desired manner. Preferably the completed articles are cooled slowly to anneal the same.

As result of my invention an insulated seal for an electrical conductor is produced which remains gas impervious even when subjected to changes of temperature and mechanical vibration, or shocks.

What I claim as new and desire to secure by Letters Patent of the United States, is 1. A as-tightseal comprisin -a core of conductive material, a layer 0 glass surrounding said core, and a metallic shell surrounding said glass layer, the glass layer making a gas-tight'joint with said core and shell.

2. An article of manufacture comprising the combination of a conductor, a surrounding shell and an intermediate layer of vitreous material adhering to said core and shell, and being homogeneous and gas-impervious.

3. An article of manufacture comprising an enclosing shell, a core of conductive material therein spaced away from said shell and a layer of vitreous material adhering to said core and shell and filling the intervening space in a gas-impervious condition, the thermal coefiicient of expansion of said shell being at least as great as that of said vitreous material, and the thermal coetlicient of said core being no greater than the expansion coefiicient of said material.

4. A seal for electric devices comprising in combination a cylindrical shell of metal,

,a core of conductive material spaced away from said shell and a unitary mass of vitreous material completely filling the space be tween said core and shell in a gas-impervious state.

5. The method of making a gas-impervious insulating seal between a conductor and an enclosing metal shell which consists in interposing between said conductor and said shell a mass of vitreous material, heating said assembled article to the softening telnperature of said vitreous material, and me chanically reducing the diameter of said shell while thus heated, thereby causing said vitreous material to completely fill the space between said core and shell, and to adhere to the contiguous surfaces of said core and shell.

6. A seal for electric devices comprising the combination of a core of nickel-iron alloy having a lower coeflicient of expansion than lead glass and provided with a coating of copper, a layer of lead glass surrounding said core and a shell of steel having the inner surface thereof coated with a flux, compressively surrounding said glass layer, the contiguous surfaces of members adhering to each other in a gas-tight condition.

In witness whereof, I have hereunto set my hand this 17th day of January, 1921.

GEORGE M. J. MACKAY.

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