US2178826A - Closure member for electric discharge tubes and the like - Google Patents

Description

R. M. BOWIE Nov. 7, 1939.

CLOSURE MEMBER FOR ELECTRIC DISCHARGE TUBES AND THE LIKE Filed March 31, 1937 INVENTOR ATTORNEY Patented Nov. 7, 1939 PATENT, OFFICE CLOSURE IMEMBEB. FOR ELECTRIC DIS- CHARGE TUBES AND THE LIKE Robert M. Bowie, St. Marys, Pa., assignor to Hygrade Sylvania Corporation, Salem, Mass, a. corporation of Massachusetts Application March 31, 1937, Serial No. 134,059

4 Claims. (01. 250-164) This invention relates to closures for electric discharge tubes and more particularly to such devices of the vacuum or low pressure type.

, The invention is in the nature of an improvement on the type of closure member disclosed in application Serial No. 82,742, filed June 1, 1936.

A principal object of the invention is to provide an electron discharge tube of the composite metal-glass evacuated envelope type having a vitreous window or closure member which is supported around its periphery against atmospheric pressure, by a member which is not sealed into the said vitreous member.

A feature of the invention relates to an evacuated envelope having its main body portion of metal which is sealed to a vitreous closure member by an intermediate ring or frame of metal, a portion of the envelope being provided with a peripheral seat or ridge to support the vitreous member against atmospheric pressure without affecting the eflicacy of the seal.

Another feature relates to the means for supporting a metal-framed vitreous closure member for the metal wall of an evacuated enclosing envelope, so that the frame can be welded or otherwise fastened to the metal wall without damaging the seal between the frame and the vitreous member.

A further feature relates to an evacuated envelope having a main body portion of metal with a relatively massive vitreous member at the end, the arrangement being such that the mechanical supporting of the vitreous member against atmospheric pressure is borne substantially entirely by end thrust of the vitreous member directly against the end of the envelope. As a result of this feature the sealing ring or frame is used substantially entirely to eifect a vacuum tight seal between the vitreous member and the metal envelope and therefore it may be of relatively thin metal strip. Since the sealing strip must be of a special alloy the cost thereof is materially reduced while at the same time enabling a more reliable and satisfactory seal to be achieved. The use of such thin metal strip for the sealing ring or frame has the pronounced advantage that if the vitreous member is sealed thereto by a press molding operation, as described for example in said application Serial No. 82,742, there is less chance of a defective seal existing than is the case where the frame is of relatively heavy gauge sheet metal stock.

A still further feature relates to an improved cathode ray tube of the composite metal-glass env p p While the invention will be described herein as applied to a cathode ray tube such as is employed in television and similar receiving sys-- tems, it will be understood that the invention is equally well applicable to similar devices such as radio tubes, light sensitive devices, oscillograph tubes for television or picture analysis, for example tubes known in theart as iconoscopes", dissector tubes and the like. In fact the invention is applicable to any evacuated device in which a vitreous closure member of large surface extent is required to be sealed in a vacuum tight manner to an enclosing envelope. Furthermore, merely for purposes of explanation, the invention will be disclosed as embodied in a cathode ray tube of the rectangular end or window type, but it will be obvious that it is applicable to other shapes such as round, oval or the like. It will be understood that while the invention is illustrated in connection with a device having a window at one end thereof, this window may be located at any other part of the device, for example in one of the side walls. Likewise only sufficient parts of the cathode ray tube structure are shown to enable the invention to be understood. Accordingly in the drawing,

Fig. 1 is a longitudinal plan view, partly in section, of a cathode ray tube embodying the invention.

Fig. 2 is a left-hand end view of Fig. 1.

Fig. 3 is a sectional view of Fig. 1 taken along the line 3-3 thereof and viewed in the direction of the arrows.

Fig. 4 shows a modification of the invention.

Fig. 5 is another view of the modification of Fig. 4.

Fig. 6 shows the invention embodied in a radio tube of the metal envelope type.

Fig. 7 is a modification of Fig. 6.

Referring to Fig. 1, there is shown partly in section and partly in dotted outline, a typical cathode ray tube comprising an elongated neck portion I of glass or other suitable material. The main body 2 of the tube is in the form of a frustum of a cone of a suitable metal such for example as steel. In order to insure a vacuumtight seal between the portions I and 2 there is provided a special sealing ring 3 of an alloy which has substantially the same coefiicient of expansion as the glass I. Preferably the flare 4 of the neck is of Coming 705AJ" glass and the ring 3 is of kovar, an alloy consisting of approximately 18% cobalt, 28% nickel and 54% iron. While any known manner of effecting the union between members 3 and 4 may be emdeflecting means are also provided. For a detailed description of a typical electrode structure reference may be had to' application Serial No. 95,970, filed August 14, 1936. r

As shown clearly in Fig. l, the metal portion 2 is welded or otherwise hermetically" fastened to the ring I, and said body'portion'terminates at its enlarged open end in aflange comprising a shoulder 5 and a rim 8, the latter prefer- I ably, although not necessarily, extending at right angles to the longitudinal axis of the tube. The enlarged end of the tube body 2 is closed by means of a relatively :massive rectangular transparent vitreous member I of such dimensions that it fits snugly in the shoulder. 6, and for this purpose preferably the said member'l is provided with a rim 8 where it contacts with the shoulder 5.

In order. to provide a vacuum-tight seal between the closure member and the tube proper the said closure member has sealed into and 1 around the edge thereof .ametal frame 9 having an integral flat rim ll joined thereto by a curved portion H. The rim 10 preferably extends parallel to the member I and is di" oned so that when the rim 8 is in'contact with shoulder 5,

the parts 6 and III are likewise in contact. In

other words, the weight of the member I is borne substantially entirely by the shoulder i. It will be understood of course that the inner surface of member I is provided with a suitable coating of material or materials which become fluorescent when struck by the electron beam, asindicated by the stippling in Fig. 3. When the member I has been positioned on the end of the tube the parts 6 and Ill may be hermetically sealed as by welding, brazing and the like and thereafter the tube may be evacuated and processed in the manner well-known in the electron tube art.

I have found that with the particular manner of supporting the member 1 as described, it is possible to use relatively thin metal strip stock for the frame 9 since this frame is employed merely to provide a vacuum tight seal between the rim 6 and the glass 1. Heretofore it has been proposed to employ relatively heavy gauge metal sheet for the frame 9 since this frame was required not only to effect the necessary vacuumtight seal but also to carry the entire weight of the member I and also the force of the atmospheric pressure on said member. Apart from the difficulty of welding a relatively massive metal frame to the rim 6, there was always the possibility that during the welding of the parts 8 and ill, the seal between the glass 1 and the frame 9- might be destroyed. I have found that the use of light gauge metal strip for the frame as is rendered possible by the present disclosure, not only facilitates the welding of the parts 6 and ill but also reduces the chance of destroying the seal.

In addition to the advantages of providing a more reliable seal is the economic advantage that considerably less material is required for the frame 9. When it is considered that a special alloy must be used for the said frame it a once fective seals and defective windows.

duces the cost of the finished tube. For example with the arrangement as described I have fcund it possible to employ for the frame 9, kovar of the order of 0.0075 inch in thickness, whereas to produce a satisfactory seal with the prior method it was necessary to use an alloy of the order of 0.03 inch in thickness.

In addition to improving the seal and reducing the cost of assembling. the tube. the use of the thin gauge metal frame also reduces the cost of 'sealing'in the said-frame tothe glass 1. This is particularly true where the frame 9 is sealed into the glass 1 by apressure molding operation such for example as disclosed in said application Serial No.'82,742. When relatively heavy gauge metal strip is employed in the frame, as a result of the scaling in process it is necessary carefully to anneal the frame and the seal area so as to avoid warping of the glass due possibly to slight differences in-the. rates of cooling of the glass and metal, or to avoid distortion of the frame. This annealing operation not only increased the cost .and time; of manufacturing the framed' window, but also increased'the percentage of de- I have found that by mechanically supporting the window on the shoulder 5, againsthtmospheric, pressure, enabling theuse of the thin gauge metal for the frame, the costly annealing operation referred tois obviated or at least the same degree of care and-control is not necessary when sealing the frame 9 into the glass I. The above noted disadvantages of the prior tubes made with heavy gauge metal for the frame 9 are particularly noticeable when the window is non-circular in shape. Forexample in the case of rectangular windows as shown in the drawing, the use of heavy gauge metal for the frame very frequently caused the glass to crack, particularly at the corners, during the seam welding of the parts 6 and I0. If with the prior construction the frame 9 were made sufllciently thin to avoid this cracking during the seam welding, it would then be too thin to support the window against the atmospheric pressure on the outside thereof.

Preferably, in order to avoid trapping of air between the contacting surfaces of the rim 8 and shoulder 5 during the evacuation of the tube, the said rim 9 is provided with one or more grooves II. It will be obvious however that instead of providing these grooves in the rim 9, the shoulder 5 where it contacts with the rim Smay be grooved or corrugated to avoid this trapping of air.

While the drawing shows the window I supported on the shoulder 5 throughout its entire periphery, it will be understood that this is not necessary. Thus there is shown in Figs. 4 and 5 an arrangement wherein the window I is spaced throughout the major portion of its periphery from the shoulder 5. In this embodiment the corners of the shoulder 5 are provided, with projections l3 such for example as embossings or the like, to engage and support the window 1. With the arrangement of Fig. 4, therefore the window is out of contact with the member 2 except at the points of support l3. Instead of providing the spacing and supporting lugs on the shoulder 5, these lugs may be formed as integral projections from the corners of the glass 1. Various other manners of supporting the window against the end of the tube portion 2 will be clear from the foregoing descriptions of typical embodiments.

While the invention has been described as applied to cathode ray tubes it is also applicable to 30 rim '1.

electron discharge tubes such as radio tubes, light-sensitive cells, and the like. Thus there is shown in Fig. 6 a typical radio tube comprising an enclosing envelope l5 of a metal such as steel 5 or other metal ordinarily employed in metal radio tubes. The envelope I5 is provided with a flange comprising the'shoulder l6 and the flat rim I1. Adapted to be seated against the shoulder I6 is a closure member l8 of glass or other 10 suitable insulating material such as ceramic or the like and into which are sealed in a vacuumtight manner the wire prongs l9- Suitably supported from the member l8 and within the envelope I5 is any well-known form of radio tube mount indicated generally by the numeral 20,

it being understood that this mount may be insulatingly spaced at its upper end from the metal wall Hi. In order to seal the member l8 to the member 15 in a vacuum-tight manner, the said member I 8 has sealed therein around the edge thereof a thin metal ring or frame 2| corresponding to the frame 9 of Fig. 1, it being understood that the ring 2| is of a suitable metal capable of being sealed in a vacuum-tight manner to the member I8, and having substantially the same coefficient of expansion as said member Ill. The member l8 carrying the ring 2| and the electrode mount is assembled against the end of tube I5 and the flat rim 22 is seam welded to the The tube may thereupon be evacuated through the exhaust tubulation in the wellknown manner, after which this tubulation may be sealed off as indicated by the numeral 23.

Instead of providing the rims I! and 22 ex- 5 tending outwardly relatively to the vertical axis of the tube, these rims may be turned downwardly as indicated in Fig. 7. Various changes and modifications may be made without departing from the spirit and scope of the invention. By the expression "permanently evacuated" as employed in the claims is meant a device such as a cathode-ray tube which has been evacuated and has been permanently sealed-oi, to distinguish from an arrangement where the parts are not 5 sealed together in a vacuum-tight manner and require evacuation during the operation of the device.

What I claim is:

1. An electron discharge tube having a body portion in the form of a metal tube, a flange at the end of said body portion defining a peripheral seat, a vitreous closure member for said tube said closure member being supported from said 5 flange by a plurality of spaced projections, a metal frame sealed in a vacuum-tight manner into and around said closure member, said frame being fastened to the end of said tube in a vacuum-tight manner. 10

2. A cathode ray tube having a glass neck joined to a flared metal tubular member, a vitreous plate closing off the enlarged end of said tubular member, a peripheral shoulder in said enlarged end to receive said plate, a thin metal 15 frame sealed into and around the edge of said plate, said frame being welded to the flared end of said tubular member.

3. A cathode ray tube comprising a glass neck sealed to a flared metal body portion, a flange at 20 the end of said body portion and extending substantially perpendicularly to the axis thereof, a peripheral seat in said flange, a relatively massive vitreous plate conforming in shape to said seat and lying thereon, a thin metal frame sealed 25 into the edge of said plate and having a flange extending parallel to the first-mentioned flange, both of said flanges being fastened together in a vacuum-tight manner.

4. An electron discharge tube having a metal tubular body portion, a peripheral flange at one end of said body portion and provided with a peripheral shouldered recess, an insulating closure member in the form of a substantially flat glass member lying in said recess, said recess receiving substantially the entire thrust of said glass member underoutside atmospheric pressure, a plurality of lead-in wires sealed directly through said glass member, an electrode mount supported from said closure member within said tubular body, a thin metal frame having one peripheral margin sealed directly in a vacuumtight manner into and around the margin of said glass member and its other peripheral margin sealed directly to the peripheral flange on a said body portion.

ROBERT M. BOWIE.

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