US2132783A - Electron discharge device - Google Patents

Description

Oct. 11, 1938. P. c. GOLDMARK ELECTRON DISCHARGE DEVICE Filed April 24. 1936 p INVENTOR 2 M ATT RNEYS Patented Oct. 11, 1938 UNITED STATES ELECTRON DISCHARGE DEVICE Peter C. Goldman-k, Brooklyn, N. Y., assignor to Markla Corporation, New York, N. Y., a corporation of New York Application April 24, 1936, Serial No. 76,112

4 Claims.

This invention relates to electron discharge devices and particularly to electron discharge devices which have a composite envelope partly of vitreous material and partly of metal.

The invention has for its object the provision of a device of the character described with an improved construction and arrangement of parts whereby the same may be readily and economically manufactured.

More specifically, an object of the invention is to provide an electron discharge device with an evacuated envelope composed of vitreous portions and of metallic portions which are joined together with a sealing substance that eifects 16 a hermetical seal and has such a low vapor pressure that the vacuum within is not liable to deteriorate substantially over relatively long periods.

Still another object is to provide an electron 20 discharge device having a composite envelope and an electrode arrangement adapted to discharge electrons in a beam against a wall with an improved window for observing the discharge effect without distortion.

Still another object is to provide an improved construction for a cathode ray tube which may be made in relatively large sizes at relatively small expense and'has an evacuated envelope constructed partly of metal and partly of vitre- 30 ous,members. I

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises'the fea tures of construction, combination of elements,

35 and arrangement of parts, which will be exemplifled in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims. y

For a fuller understanding of the nature and 40 objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:

Fig. 1 is a longitudinal sectional view through 45 a cathode ray tube having a composite envelope constructed in accordance withthe invention;

Fig. 2 is a front elevation illustrating the nature of the seal about the window member of the cathode ray tube shown in Fig. 1;

Fig. 3 is an enlarged cross-sectional view showing the nature of the seal between the window member and the metal member shown in Fig. 2;

Fig. 4 is a similar fragmentary view showing 55 the seal between the metal member and the tubular vitreous member comprising the envelope shown in Fig. 1; and

Fig. 5 is a fragmentary view showing a modified form of seal provided for the window mem- Referring now to the drawing, and particularly to Fig. 1, I 0 denotes a vitreous tubular member which has a closed reentrant end portion i I in which are sealed the conductors of a heated cathode element l2. Adjacent the cathode is 10 disposed an anode element l3 which is adapted to cooperate with the cathode element toprovlde an electron gun projecting a beam of electrons that will impinge upon a window member provided as hereinafter described. Suitable de- 16 flector plates I for the beam may also'be sealed in this portion of the device when desired.

Joined to the member i0 is a metallic member l5, this member being somewhat funnel-shaped and having its smaller end recessed, as indicated 20 at It, to provide anannular groove for receiving the open end of the vitreous member ID. The joint thus provided is sealed by inserting in the groove about the vitreous member a suitable sealing substance, as shown at it and hereinafter more fully described. The interior portions of the member l5 which overlie the edge of the member iii are preferably fluted or grooved to provide fingers, as indicated at I'I in Fig. 4, in order the better to accommodate expansion and contraction at the joint.

The metal member l5 while indicated as being preferably funnel-shaped may, of course, have any desired shape, the larger end being here shown as formed with a generally rectangular contour terminating in a recessed or grooved flange l8. About the inner side of the flange is a shoulder i9 adapted to support an inserted vitreous member 20, which is preferably transparent or translucent and designed to serve as a 40 window. Thus inserted member has a groove 2| formed about its edge for cooperating with the groove in the flange l8 and receiving the inserted sealing substance, as shown at 2 l which may be of the same character as that, inserted at it. In order to serve as a cathode ray tube adapted for oscillographic or television purposes, this window member mayhave an interior coating of a suitable fluorescent substancasuch as willemite or zinc sulphide, the presence of which is indicated on the window at 22 tallic member denoted IS. The inserted window member is indicated at and has a beveled edge'which is adapted to cooperate with the V- shaped groove formed in the flange ring I8, the

sealing substance being inserted in substantially the same manner as before.

The sealing substance of the present invention is preferably a substance that is initially plastic and dries hard at normal temperatures to become firmly'formed in place and adheres to both metal and vitreous materials, such as glass, transparent phenolic condensation products and other suitable plastics, which may be employed for the vitreous members. Certain equi-molecular mixtures of relatively complex organic constituents of low volatility are found to have the desired adhering characteristic and are suitable. For example,.a mixture of ethylene glycol with phthalic anhydride, when taken in such proportions as to provide a substantially equimolecular composition, is satisfactory because of the plastic qualities and the relatively low vapor pressure which such mixture has. The mixture is made by taking substantially 1 part by weight of ethylene glycol to 2.4 parts by weight of phthalic anhydride; the desired consistency of the sealing substance' being achieved by first mixing these constituents and then heating at a relatively high temperature for a relatively long period, for example, at 180 C. for 24 hours. The

resulting substance is plastic and may be inserted when at a temperature of 100 C. This substance also dries at 60 C., and when cold,

dry and permanently in place, has a. normal vapor pressure that is of the order of 10 mm. of mercury. v

In the event that the sealing substance becomes too dry after preparation but before insertion, it may be moistened by mixing with it a. smallportion of tricresyl phosphate; for example, the softening agent may be taken as 1 part in 200 of sealing substance.

Another sealing substance which may be employed comprises a mixture of powdered urea with furfuraldehyde. These constituents are also preferably taken in such proportions that the resulting mixture is substantially equi-molecular.

A cathode ray tube may be manufactured in accordance with the present invention by providing a glass member, such as shown at I 0, with the desired electrode parts. This is then heated and while hot,a metal member l5 and a window member 20 are put in place and the sealing material inserted to close the joints. The tube or device is, at this period, placed upon the pumps and evacuated while the parts are hot, the application of heat being kept up during the entire period of the pumping, if desired, by placing the device in a suitable oven. When the pumping is completed, the device is sealed oil in the ordinary manner, a suitable getter (not shown in the interests of clearness of illustration in the drawing) being employed when it is desired to obtain a vacuum of a relatively high order.

From the construction employed; it is seen that window members of substantially any size and configuration may readily be provided; for example, for cathode ra'y'tubes for use in television, a large, substantially plane viewing screen may be provided, of suflicient thickness to resist atmospheric pressure regardless of the degree of vacuum within the tube. The window terpreted as illustrative 2,182,788 rate ring that is welded to the body of the memember may be formed also to give desired optical effects, all undesired distortion, due to curvature in the window, being avoided by the use of independent insertable vitreous members of the character indicated.

Cathode ray tubes in which the electrodes are mounted in a metal member are thus feasible for use, the only vitreous part required being the window member, which may be inserted as provided by the invention.

The sealing substance when permanently in place in the joint about the window member is seen to project laterally both against the groove of the metal member and against the groove of the window member, whereby there is a wedging action which efl'ectually stops any tendency for relative motion between the edge of the window member and the metal groove l8 when pressure is applied to the face of the window member. The seal, once formed by the adherence of the sealing substance to both the metal and vitreous member, is thus self-preserving and is not liable to deterioration through usage.

It will be also understood that, because of the relatively low vapor pressure of the sealing substance, the vacuum within the device is not liable to substantial deterioration over relatively long periods, thereby providing. a device of the character indicated having a relatively long life.

Since certain changes may be made in the above construction and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be inand not in a limiting sense.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In an electron discharge device, the combination with electrode elements adapted to serve as cathode and anode, of an evacuated hermetically-sealed envelope comprising a vitreous member and a metal member having a joint in the form of a groove for receiving an edge of said vitreous member, and a sealing substance in said groove cooperating with said edge to close said joint consisting of a substantially equi-molecular mixture of ethylene glycol and phthalic anhydride which is adapted to be inserted while relatively hot and which dries at substantially 60 C. and has a vapor pressure when permamently in place that is in an order of 10- mm. of mercury.

2. In an electron discharge device, the combination with electrode elements adapted to serve as cathode and anode, of an evacuated hermetically-sealed envelope comprising a vitreous member. and a metal .member having a joint in the form of a groove for receiving an edge of said vitreous member, and a sealing substance in said groove cooperating with said edge to close said joint consisting of a substantially equi-molecular mixture of powdered urea and furfuraldehyde which when permanently in place adheres to both metal and the vitreous member and has a relatively low vapor pressure.

3. In a cathode ray tube, the combination witha tubular glass member closed at one end and provided with electrode elements adapted to serve as cathode and anode, of a metal member having one end recessed to provide an annular groove for receiving the open end of said tubular member, a groove formed on the other end of said metallic member and provided with a araavas supporting shoulder, a vitreous window member disposed in said groove on said shoulder, and a. sealing substance in both said annular groove and said window supporting member groove cooperating with the edges of said inserted members to close the joints and of a character when permanently in place which has a relatively low vapor pressure.

4. In a vacuum cathode ray tube, in combination, an envelope member having a metallic tubular portion provided with a supporting shoulder at the window end and an axially projecting annular ring around said shoulder, a vitreous window member supported on said shoulder, said window member being smaller than the ring,

whereby the window member may be readily positioned on said shoulder, the ring and the edge of the window member being so shaped as to provide an annular space therebetween at least part of which decreases in cross-section toward the said shoulder, and a sealing substance in said annular space adapted to hermetically seal the window member to the metallic tubular portion.

PETER C. GOLDMARK.

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