US2078776A - Glass-to-metal seal - Google Patents

Description

April 27, 1937. W. A. RUGGLES GLASS-TO"METAL SEAL Filed Sept. l, 1934 lwwentov: William A Fules,

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Patented Apr. 27, 1937 UNITED STATES PATENT OFFICE GLASS-TO-DIETAL SEAL New York Application September 1, 1934, Serial No. 742,411

4 Claims.

The present invention relates to electron discharge apparatus, more particularly to the glassto-metal seals employed in thermionic devices of the metal type.

5 When metal instead of glass is employed for envelope material of the space current or other form of electrical discharge device, one of the problems encountered is that of passing the leading-in conductor through the metal envelope in an insulating manner. Various forms of seals for this purpose have been heretofore proposed.

Some of these seals are constituted by a hollow cylindrical metal member secured to the envelope at a position so as to surround the conductor, with 5 a glass mass between the conductor and said member. In order to provide a strictly hermetic joint between the glass and metal parts, it is customary either to apply pressure radially and inwardly against the metal cylinder to cause it o to contract about the glass or else, to apply a compressional force at the ends of the glass member to cause it to push radially and outwardly against the cylinder. These pressures are often of considerable amount and involve expensive ap- ;5 paratus or fixtures. While seals of this character are satisfactory in providing a tight joint, they are expensive to make and do not lend themselves to quantity production, particularly in the case of small radio tubes where the sealing cost must be kept low.

Accordingly, an object of the present invention is to provide an improved insulating seal for passing leading-in conductors through metal envelopes and which seal does not require the application of pressure other than that exercised by gravity, thus lending the improved seal to quantity production methods. In carrying out this object, I have found that whereas the prior seals employ metal cylinders of uniform diameter surrounding the conductor and require considerable pressure to make the hermetic joint between the metal and glass parts, the coniiguration of the cylinder may be modified in accordance with the present invention to eliminate the necessity for suchfpressure and yet a tight seal may still be obtained. The invention will be better understood when reference is made to the following specication and the accompanying drawing in which Fig. 1 is a cross-sectional view of a tube provided with the improved seals, while Figs. 2,

3, 4, and 5 show the various steps involved in th fabrication of the seal.

I have chosen to illustrate in Fig. 1, the application of my invention to a two-electrode rectier of the all-metal type, although it will be understood that the improved seal is equally applicable to all types of metal tubes, and containing any arrangement of electrodes and number of electrodes from. which leading-in conductors are to be taken through the envelope in an in- 5 sulating manner. In this iigure, numeral l designates a cylindrical envelope of metal which is closed at both ends except for a centrally positioned opening at the upper end (as shown) and several openings at the lower end, for purposes 10 which will be explained hereinafter. The envelope is preferably made in two parts provided with anges at the edges which contact with one another and are soldered or welded at these flanges to constitute a complete cylinder. The upper seclo tion of the cylinder which is provided with a central opening carries a metal tubulation 2 of invar or other suitable and well-known mietal which may be soldered or in any other manner hermetically secured to the envelope. There is a 20 glass tube 3 sealed to the upper end of the metal tubulation by means of a properly directed gas flame. The tube 3 is employed for evacuation purposes and after the tube has been evacuated as will be explained hereinafter, the glass tube is 25 collapsed and sealed off from; the pump in the usual manner.

Within the cylinder i, there is a lamentary electrode 4 which may comprise a horizontally positioned (as shown) helix, which may be coated, if 30 desired, with an electronically. active material. The iilamentary member 4 is supported within the envelope, approximately midway of the length thereof, by means of a pair of rigid rods 5 which may also serve as leading-in conductors. These 35 conductors are taken out through the lower section of the envelope by means of the improved seals which will be described presently.

The lower section of the envelope carries a pair of metal tubulations 6 which take the form 40 generally of a frustum of a cone, and the smaller ends of which are hermetically secured, for example by soldering or welding, to the envelope about each of the openings. The conductors pass through' the openings and through the conical 45 members, and are insulated from the metal parts by means of a mass l of vitreous material such as glass which is hermetically sealed to the conductor and the tubulation 6. The conductor 5 and the metal member 6 are preferably consti- 50 tuted of metals having substantially the same coeiiicient of expansion, while the member 1 may consist oi' ordinary lead glass.

It is apparent that the tube shown in Fig. 1 constitutes a two-electrode device and when heat- 55 ing current is passed through the filament l and an alternating current voltage impressed between the lament and the metal container I, the device will rectify. If desired. an inert gas at suitable and well-known pressures, or a source of vapor may be introduced into the envelope through the tube 3 in order to cause the discharge between the nlament and the envelope to take on the characteristics of either an arc or a glow, depending upon the pressures of the gas or vapor employed.

In the fabrication of the improved seal, it is convenient to form the seal before the two sections of the envelopeare secured together. As shown in Fig. 2, the lower section of the envelope is first placed in an inverted position, i. e. with the openings uppermost, and the metal tubulations l are secured to the envelope section about each of the openings. A conductor 6 is then threaded through an opening in a cylindrical glass member 1, as illustrated i'n Fig. 3 and the conductor and member placed in a cross-fire indicated at B in order to cause the glass to contract and to be fused about the conductor. The combined glass and conductor member is then placed in a vertical position within the tubulation B, as shown more clearly in Fig. 4, with the glass member resting on the interior surface of the tubulation. In order to facilitate this operation, it is found desirable to support the metal envelope section on a heavy base 8 of a. metal or graphite which is provided with countersunk openings III of a sufiicient depth to accommodate the necessary length of conductor 5 without touching when the lower edge of the glass member 'l rests upon the metal tubulation 0 as explained hereinbefore. While each of the tubulations i may be heated by conveniently positioned cross-fires, I prefer to place the entire assemblage, including the base l, in an oven and to heat the members to a temperature sumciently high (e. g. 650 C. to 700 C.) to cause the glass to melt and to iiow outwardly and downwardly, carrying the conductor with it. It has been found that when the proper temperature is provided, the glass will wet the metal and settle of its own weight to such an extent as completely to fill the space between the tubulation and the conductor, forming a hermetically tight seal with the metal members. As stated hereinbefore, no pressure is exerted either against the metal tubulation or the glass during this operation other than that exercised by the combined weight of the glass and of the conductor and yet, a hermetic seal is obtained which is sufilciently tight for high vacuum or gasor vaporfilled tubes which are permanently sealed oil! the pump. The effect of the heating operation is shown in the structure illustrated in Fig. 5. It is obvious that any number of units or assemblages of elements may be heat-treated in the same oven so that the process lends itself to quantity production and produces an inexpensive seal.

After the seal has been made. a helical electrode which in the case of the tube shown in Fig. 1 constitutes the cathode, may be secured to the conductors l, and the metal section thereafter welded or soldered to the other section to constitute a complete envelope.

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

1. In the art of fabricating an all-metal tube containing an electrode and having a leading-in conductor for the electrode passing through the envelope of the tube, the method which consists in threading the conductor through a piece of glass, then heating the glass to cause ittocontract about the conductor, then placing the combined conductor and glass in a vertical position within a hollow metal member which constitutes part of said envelope, finally heating said member to cause the glass to melt and to settle by gravitation only. to form a seal between the conductor. glass and metal members whereby the conductor is insulatingly sealed in said envelope.

2. In the art of fabricating an all-metal tube containing an electrode and having a leading-in conductor for the electrode passing through the envelope of the tube, the method which consists in securing a metal tubulation to the envelope at the position where the conductor is topass through, fusing a cylindrical glass member about the conductor, then placing the combined conductor and glass unit in a vertical position within said metal cylinder, nnally heating said tubulation to cause the glass to melt and to settle by gravitation only, to form a seal between the conductor, glass and tubulation whereby the conductor is insulatingly sealed in said envelope.

3. An electric discharge device including a metal envelope and containing an electrode. a leading-in conductor of substantially uniform diameter for said electrode lpassing through the envelope, and means insulatingly sealing said conductor in the envelope, said means including a conically shaped metal member having its smailer end secured to the envelope and surrounding said conductor, and a glass mass constituting a hermetic seal between the conductor and said member.

4. An electric discharge device including a metal envelope and containing an electrode, a leading-in conductor for said electrode passing through the envelope, 'and means insulatingly sealing said conductor in the envelope, said means including a conically shaped metal member having its smaller end secured to the envelope and surrounding said conductor, and a glass seal between the conductor and said member which is rendered hermetic by pressure exerted solely by the weight of the glass.

WILLIAM A. RUGaLEs.

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