US2573553A - Overlapping header for radio tubes - Google Patents

Description

R. F. DORAN OVERLAPPING HEADER FOR RADIO TUBES Filed Sept. 28, 1946 l I I INVENTO \J r L I? f?aberi 007 2 172 L J I A "av W M MQN Patented Oct. 30, 1951 OVERLAPPING. HEADER FOR'RADIO TUBES Robert F. Doran, Floral Park, N. Y., assignor to Sylvania ElectricProducts, Inc., a corporation of Massachusetts Application September 28, 1946, SerialNo. 699,978

1 Claims.

This invention relates to headers for electron tubes and the like and to a method for sealing them into a glass envelope.

As the diameter of the envelope enclosing an electrode assembly is decreased the wall thickness of the envelope becomes critical because'space economics require that a minimum amount of the total envelope space be dissipated in glass wall thicknessv Because of this fact it has been found desirable to use a bulb having as thin a wall as can be handled in the tube making process in making the smaller type tube such as those which have a 4; or 4 diameter. It has been found. possible in commercial practice to reduce the envelope wall thickness to approximately .012" and still obtain a good seal to a header having a thickness of .080" or greater.

A reduction of the header thickness below .080" increases the danger of leakage due to insufficient length of glass-to-metal seal. The problem has therefore arisen of sealing a .012" wall bulb to a .080" header in such manner as to obtain satisfactory glass distribution at the seal point and at the same time prevent stem distortion or lead displacement as may be caused by the softening of the mass of glass in the stem. This latter point becomes particularly troublesome because as the tube diameter is decreased it becomes more and more desirable to maintain maximum pin circle diameter. This necessarily locates the pin circle very close to the inside of the bulb and adjacent to the hot sealing zone, thus complicating the sealing problem. These two'problems seriously interfere with commercial tube production andhave made otherwise eflicient methods of manufacture unsatisfactory.

It is therefore a general object of thisinvention to improve the sealin technique now in use in manufacturing electron tubes and the like.

A further object is to provide a method of seal ing a glass header to a bulb which lends itself to sufficient working of the stem glass and bulb glass to form good seals even under thoseexacting conditions in which the glass header is several times as thick as the tube wall to which it is to be sealed.

A further object is to provide a method of accomplishing a satisfactory seal in close proximity t -a lead circle without distortion of either the leads or the main section of the stem glass previously molded to the shape preferred in the finished tube.

In accordance with my invention these and other advantages which are incidental to its application can be obtained by providingthe header disc with a relatively thin and large diameter flange which extends an appreciable distance beyond the bulb diameter, and by placing the header of this construction on a bulb whose mouth is uppermost where the adjoining edges are sealed by means of a hot flame.

In the accompanying drawings which illustrate the preferred form of header of this invention and the method of sealing it to the bulb:

Fig. 1 is a side elevation partly in section showing the header and tube assembly before sealing, mounted in a spindle carrying holder.

Fig. 2 is a plan view of the header end ofthe tube showing the manner in which the sealing flres are applied.

Fig. 3 is a longitudinal central sectional View of the tube showing the manner in which the thin glass flange reacts to early sealing fires.

Fig. 4 is a sectional view of the tube being sealed-in just as it is entering the shaping position.

Fig. 5 is a view similar tothat shown in Fig. 4 showin the roller as-moved to operative position and the seal as completed.

Fig. 6 is a side elevation of the finished tube as drawn to actual size.

Fig. '7 is a plan view of a sector of an intermittently rotating table showing two separate positions.

The header IQ of the invention as shown in Fig. 1, consists of a wafer type disc of glass having a relatively thick stem portion l2 through which the metal leads- [8- project and a relatively thin large diameter flange [4 which has been molded so as to extend an appreciable distance beyond the main stem portion. In a preferred embodiment of the header of this invention the stem portion should be at least .080" in thickness. However, any thickness of glass may be used which will insure a good vacuum tight glass-tometal seal between the stem and any wire lead passing therethrough. In the preferred headers it has furthermore been found possible and even desirable to maintain a minimum ratio of approximately 1 :4 between the flange thickness and stem thicknesswhere the glass-to-metal seal is made. In the assembly, as shown in Fig. l, a slight inner edge It is'provided on the inside of the header which serves to locate the header more readily on the open mouth of the bulb at the time it is being placed on the bulb for assembly. The need for such a locating edge is of course optional. It does, however, serve as a convenient and time saving method of insuring proper locating of the header on the bulb with the least possible effort and a maximum assurance that the electrodes and mount assembly are properly centered within the envelope.

When the wafer type header of this invention is located on the open end of the bulb mounted on spindle carrying holder 25 as shown in Fig. 1, the slight inner edge 16 abuts the inner side walls of the open end of the tube 20 and the thin large diameter flange 14 projects an appreciable distance beyond the bulb diameter.

As the turntable 30, a portion of which is shown in Fig. 7, revolves and brings the spindle carrying holder 25 and the assembled parts shown in Fig. 1 to the station at which the heating fires are applied as shown in Fig. 2 the small sharp tangential oxygen-hydrogen fires 3| are directed onto the flange I4 of the header by nozzles 32 while the tube carrying holder 25 is being revolved in a counter-clockwise direction as indicated by the arrow in Figs. 2 and '7. The heat applied in this manner is highly localized and thus makes it possible to locally melt the flange exposed to heat from top, bottom, and periphery as shown in Fig. 2. In this manner it is possible to develop a rather molten ring of glass in which the surface tension forces serves to draw the softened glass into a ring having slightly ellipsoidal cross sectional shape without appreciable distortion or melting of the very thin bulb glass 20 and without softening of the main section of the stem of the header. The glass ring so formed with its slightly ellipsoidal cross sectional shape is clearly illustrated in Fig. 3 of the drawing. As the heating progresses it tends to melt the top edge of the bulb enabling the very hot and fluid glass flange to unite readily to the bulb glass. At this time it can be blown to the shape shown in Fig. 4 by forcing a neutral gas up through the tubulation 22.

When the viscosity of the glass has been sufficiently lowered by the applied heat at station (a) to cause fusion between the glass flange of the header and the open section of the bulb to fuse the glass the turn table and the spindle carrying holder is rotated to the next station (1)) where a pair of graphite rollers 40 and H are located. These rollers may be suspended by levers 42 and 43 from hinges 44 and 45 attached to stationary rods 59. Automatic means (not shown) operated by the indexing control are provided to separate the rollers 48 and 4! so as to provide a clear path for the bulb 20 and header between the rollers as shown in Fig. 4. As soon as the turn table 30 is at rest again after completion of the indexing motion the rollers 40 and 4| close into the position shown in Fig. and their weight works the hot glass from the outside whereby a perfectly smooth transition between the cylindrical part of the bulb and the header is obtained. By properly locating hinges 42 and 43 and by proper choice of the diameter of the rollers 40 and M the straightness of the seal as shown in Fig. 5 between the cylindrical bulb and the header can easily be insured. The proper amount of radially inward and upward pressure exerted by the rollers on the soft glass seal can easily be adjusted by counterweights 46 and 41 threaded to horizontal rods 48 and 49 which form bell cranks with arms 42 and 43. It will be observed that the hinges or pivots l and 45 are located considerably above the softened sealed portion and are located outside the boundary of the bulb 20. Consequently as the rollers 40 and 4! swing inwardly towards the bulb, they describe a circular arc directed up- 4 wardly towards the header l0. Furthermore, the rollers and 4| are considerably longer than the length of the softened area so that their inward movement is limited by their respective engagements with the unsoftened portion of the bulb 20.

The above described wafer type header lends itself readily to use with thin walled bulbs to form a tube envelope in spite of the differences in thickness because it permits thin thickness of glass to be heated by precisely located small and intense flames thereby enabling small areas of the assembly to become locally soft without distortion of i the major body of the stem or bath. This is clearly illustrated in Fig. 3 where the uniformly fluid condition of the flange l4 permits the surface tension forces to ball up the glass. It is therefore possible to obtain completed seals of relatively thick headers to thin walled bulbs at commercial speeds and still obtain a good glass distribution at the seal and a square undistorted stem base as shown in Fig. 5.

While the above description and drawings submitted herewith disclose preferred and practical embodiments of the wafer type header of my invention and the method of sealing it to a bulb, it will be understood by those skilled in the art that the specific details of construction and arrangement of parts, as shown and described are by way of illustration and are not to be construed as limiting the scope of the invention. 7

What I claim is:

i. A header for radio tubes or the like comprising a glass disc with metal leads projecting therethrough said disc being approximately .080 inch thickness to permit a good vacuum tight glass-to-metal seal between it and the metal leads and being further provided with a relatively thin tapered large diameter flange of approximately one fourth the thickness of the main portion of the disc.

2. The method of sealing a header with a large diameter flange to the bulb of a radio tube or similar device which comprises supporting the bulb with its mouth uppermost, resting the header on the open mouth with the flange edges extending an appreciable distance beyond the bulb and heating the extending flange portion of the header by localized heat to locally melt the flange prior to the melting of the glass of the bulb, continue the heating until the hot fluid glass of the heated flange unites with the adjacent portion of the bulb.

3. The method of sealing-in a header with a large diameter flange to the bulb of a radio tube or similar device which comprises supporting the bulb with its mouth uppermost, resting the header on the open mouth with the flange edges extending an appreciable distance beyond the bulb, heating the extending flange portion of the header by localized heat to locally melt the flange prior to the melting of the glass of the bulb, continue the heating until the hot fluid glass of the heated flange unites with the adjacent portion of the bulb and subjecting the heated portion of the bulb and header to an inwardly directed force applied by spaced rollers.

4. In the method of sealing-in a header with a thin peripheral extension to the bulb of a radio tube or similar device the steps comprising locating the header on the mouth of the bulb with the thin peripheral extension projecting to a substantial distance beyond the walls of the bulb, heating the thin peripheral edge by localized heat until the thin glass becomes fiuid, continuing the heat until the fluid glass flange unites with the adjacent tube wall, subjecting the molten regions to a pressure from within the bulb to form a bulge and subsequently subjecting the bulged regions to an inwardly directed force by means of a pair of spaced rollers.

ROBERT F. DORAN.

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

UNITED STATES PATENTS Number Name Date Vello May 31, 1932 Malloy et al. June 25, 1935 Rose June 8, 1937 Thomas Oct. 4, 1938 Schoonenberg Aug. 29, 1939 Steimel June 25, 1940 Freeman Sept. 24, 1940 Miller July 22, 1941 Barber Mar. 10, 1942 Perkins Nov. 9, 1943 McGowan June 13, 1944

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