US2799422A - Cathode-ray tube having a glass cone - Google Patents

Description

y 6, 1957 Y I T.-HAGENBERG 2,799,422

CATHODE-RAY TUBE HAVING A GLASS CONE Filed June 24, 1955 INVENTOR THEODORUS HAGENBERG AGENT United States Patent 6 CATHODE-RAY TUBE HAVING A GLASS CONE Theodorus Hagenberg, Eindhoven, Netherlands, assignor, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware The invention relates to a cathode-ray tube, more particularly a television tube, having a rectangular glass window and a glass cone, the seal between window and cone being reinforced by means of a metal ring. Particularly with large-sized cathode-ray tubes entirely made of glass the glass, particularly that of the window, must have a large thickness or this window must be strongly curved. In the first case the weight of such tubes is great, whilst the image is deformed owing to the large thickness of the glass or the strong curvature of the window. With such tubes it is moreover difiicult to manufacture the window free from inperfections. Moreover, it is diflicult to seal such a thick glass window to the glass cone, since the thickness of the glass at the area of the seal must be still larger.

It is known that these disadvantages may be avoided for the major part, if the transition zone or the sealing edge between window and cone is reinforced by means of a metal ring, which may be sealed wholly or partly in the glass wall. This ring had a circular, elongated or Z-shaped cross section.

In this case the thickness of the glass may be smaller and the window may be manufactured from plate glass, which is completely free from imperfections.

In practice, however, it is found to be very difficult to perform a seal with such a ring. If use is made of a fiat, Z-shaped ring, it may be clamped in the cold state between the glass parts during heating the edges of window and cone are sealed each to the ring. This method has, however, a limitation in that on the inner side of the bulb the ring remains uncoated and can therefore be struck by electrons. Thus the ring may assume a high potential, which gives rise to serious danger. Moreover, the metal of the ring may be affected during the chemical cleaning of the bulb or the settling of the fluorescent screen.

A seal with which the ring is coated on the inner side of the tube is obtained only with difficulty. If the glass parts are positioned one upon the other in the cold state, the ring surrounding them, the ring will become hot first when heated by means of burners or high-frequency currents and owing to the expansion it will get loose from the glass parts. Therefore the heating of the glass parts throughout their thickness will give rise to difficulties and a complete sealing will practically not occur, particularly since we are concerned with glass parts having a fairly large wall thickness (6 to 8 mms.). It is found thatthe glass nearest the ring melts, flows along the ring around the seam between the glass parts and screens off this scam to a greater or smaller extent from the hot ring, so that on the inner side of the tube the seam subsists and the glass parts are not satisfactorily sealed to one another. Moreover, such a ring contributes comparatively little to the rigidity of the sealing zone, since the glass is subjected not only to pressure, but also to off-setting and bending. It is furthermore a problem how to support the ring during the sealing operation.

In accordance with the invention the said disadvantages may be completely obviated with a cathode-ray tube comprising a glass window and a glass, cone, which are sealed together, the sealing edge being reinforced by means of a metal ring, it the metal ring has a cross section in the shape of a T, the leg of which is completely sealed in the glass and is shorter than the thickness of the glass wall of the. cone at that area.

This shape of the ring has various great advantages.

Both for circular and rectangular. windows the ring may be made by bending a rod having a T profile, the ends of which can be welded to one another by the material itself in a reducing or inert atmosphere for example by means of an argon are weld.

The ring and the glass parts the other in the cold state, so supported separately.

During the heating, when the outer edge from the glass parts, the sealing edges remain always in contact with the leg of the T, so that these edges'are satisfactorily heated.

The glass of the edge of the window melts to the ring and flows finally smoothly over the inner edge of the leg of the T down to mix with the hot edge of the cone. The metal of the ring on the inner side of the tube is thus completely coated.

Since the glass parts are held in gaps, they are subjected practically only to pressure by the ring, so that the risk of cracks is materially reduced.

The ring may be made of comparativlcy thin material, since the fairly thick glass layer coating the inner side of the ring has great rigidity.

The invention will be described more fully with reference to a drawing, in which:

Fig. l is a sectional view of the seal prior to the sealing operation,

Fig. 2 is a sectional view of the seal subsequent to the sealing operation, and

Fig. 3 is a lateral view of a cathode-ray tube according to the invention.

Referring to the figures, reference numeral 1 designates the glass window, preferably made of plate glass, 2 designates the glass cone and 3 the supporting ring according to the invention. In the cold state these component parts are positioned one upon the other as is illustarted in Fig. 1. The edges of the cone and the window are adjacent the inner edge or leg 4 of the T-shaped profile of the ring 3, which includes a top portion surrounding and abutting the junction of the conical and window portions. If the ring 3 expands during heating, the edges of the window 1 and the cone 2 remain in contact with the edge 4, so that an eliicient heating of the glass edges is realized. Since the edge 4 forms gaps with the ring 3, in which gaps the glass is collected during melting, a saitsfactory seal of this glass to the ring is obtained. Since the leg 4 has a smaller length than the thickness of the cone wall at this area, the liquid glass of the window is capable of sealing completely with that of the cone, as is shown in uninterrupted glass layer contributes materially to the rigidity of the sealing Zone, so that the ring 3, which is preferably made of ferrochromium, need exhibit only a small wall thickness and may thus be cheap. Since the ring may be made from a rod having a T-profile, both for tubes having circular windows or rectangular windows, substantially no material is wasted.

It is found to be advantageous, if the upright edge of the ring tapers from the inner side to the outer side, for example by 3 and if itjexhibits rounded-oft edges. Since the metal ring 3 is coated on the inner side of the tube, there is no risk of a charge or of corrosion during the operation, the cleaning of the bulb or the manufacture of the screen.

Fig. 3 shows the finished tube.

The thickness of the window may be approximately may be placed one upon that the ring need not be ring gets loose at its Fig. 2. The thick,

equal to that of the cone wall, i. e. 6 to 8 mms. with tubes having a diameter of about 40 to 60 cms.

What is claimed is:

1. A cathode-ray tube having an envelope constituted of a glass, window portion and a glass, substantially conical portion sealed together at their junction, said conical portion having a given Wall thickness at its junction with the window portion, and a metal ring having a T-shaped cross-section and including a top portion surrounding the junction of the sealed glass portions and a leg portion sealed between the window and conical portions, said leg portion having a shorter length than said given thickness of said conical wall portion at the junction, said leg portion being completely covered by glass sealing together sadi window and conicalportions and thus said metal ring being inaccessible from the interior of said envelope.

2. A cathode-ray tube having an envelope constituted of a glass, window portion and a glass, substantially conical portion sealed together at their junction, said conical portion having a given wall thickness at its junction with the window portion, and a thin metal ring having a T- shaped cross-section and including a top portion surrounding and abutting the junction of the sealed glass portions and a leg portion sealed between the window and conical portions, said leg portion having a shorter length than said given thickness of said conical wall portion at the junction, said leg portion being completely covered by glass sealing together said Window and conical portions and thus said metal ring being inaccessible from the interior of said envelope.

3. A cathode-ray tube as set forth in claim 2 wherein the portion of said ring top portion adjacent the window portion is tapered.

References Cited in the file of this patent (2nd addition to No. 1,005,363)

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