US1953516A - X-ray part - Google Patents

Description

X-RAY PART Filed DGO. l, 1951 Patented Apr. 3, 1934 Westinghouse Lamp Company,

Pennsylvania a corporation of Application December 1, 1931, Serial No. 578,244

Claims.

This invention relates to electrical discharge devices and more particularly to devices of this character employed. for the production of X-rays and commonly termed X-ray tubes. In its more g specific aspect the invention is directed to the provision of electrical discharge devices and especially IST-ray tubes which during construction or operation will not fail because ci envelope puncture caused by electrical stresses.

An X-ray tube design which has found application in a number of different fields generally comprises an elongated envelope having a plurality of oppositely disposed electrodes therein. '111e envelope is composed of glass or the like and consists of a cylindrical body portion having a generally hemispherical upper end and a lower end with a reentrant tube extending upwardly therewithin and spaced from the interior thereof. The free end of the reentrant tube is sealed to a tubular metallic and generally copper sleeve carrying the anode and also serving as a means of electrical connection by means of an anode extension connected thereto. Within said envelope and fused thereto is a Second reentrant tube hav- I ing a major portion spaced from the sides thereof and extending upwardly in the envelope, spaced from and surrounding the anode.

Tubes ci this character require a great deal of care and time in practical production. The anode, cathode, X-ray screen and a portion of the metallic cap as weil as the interior of the envelope and the reentrant tubes are carefully cleaned before the tube assemblage. The sealing operation of the metallic tubular sleeve to the upper portion i oi' the reentrant tube generally results in the outer surface thereof, or what is the surface thereof located within the completed tube, becoming covered with a layer or coating of metallic oxides or other compounds.

A portion of said area may be readily freed from said coating by either chemical or mechanical means, but it is not generally feasible to remove the coating in close proximity of the metallic-glass seal without either puncturing the '51 metallic sleeve or breaking the seal which must be kept air tight. In the course of practical operation or seasoning of tubes of this character it sometimes has been found that the tube punctured at that or in proximity to the place of ring 50 fusion or seal.

l"The basis reason for this puncturing I believe is due primarily tol the oxides, other compounds or impurities on the metallic sleeve. One explanation at which I have arrived is that when a high voltage, within the operating voltages and normal (Cl. Z-35) surge voltages, are applied to the terminals oi the tube, the anode as well as the sleeve is heated and particles of matter which I believe to be positive ions are expelled from the coating and deposited on the inner wall or the envelope. These par-4 ticles of matter build up a charge on the inner wall o1" the tube at the areas of deposition and thereby increase the liability of puncture at these areas, which puncture does sometimes occur.

In order to obviate this diiiiculty and to thus minimize the liability of envelope puncturing clue to electrical stresses, I have developed the following invention which in its briefest aspect comprises shielding the envelope and especially the seal of the second reentrant tube from those por- 7 tions oi its internal structure which are not clean surfaced, and particularly from the coating at the seal of the reentrant tube and metallic sleeve. For this purpose I may employ a simple expedient in the form of a shielding skirt. 7

This shield is spaced from, surrounds the metallic sleeve-glass seal and serves as a barrier to prevent most if not all of the impurities such as the metallic compounds or other impurities at or y Y adjacent the seal from traveling to and deposit- 80 ing on the envelope and especially at or adjacent the place of union ci the envelope and second reentrant tube.

An object of my invention is to provide an electrical discharge tube which will withstand comparatively high voltages without envelope puncture.

Another object of my invention is to provide an X-ray tube having a simple expedient incorporated therein which serves to minimize the danger of its envelope puncture.

Another object of my invention is tor provide an X-ray tube capable of operating at the practical voltages encountered in tube operation without puncturing of the envelope.

Other objects and advantages of my invention will become apparent from the following specification and appended drawing wherein,

Fig. 1 represents a longitudinal cross sectional View with some of the parts in elevation of an X-ray tube having a part broken away and embodying my invention.

Fig. 2 is a cross sectional view of Fig. 1 along the line II--II in the direction of the arrows.

According to my invention the X-ray tube 105,

and has a major portion of its wall spaced from and surrounded by the body portion. To this reentrant tube is hermetically sealed a tubular metallic and preferably copper sleeve or support coupling 14.

This sleeve has a thin annular portion to which the upper end of the reentrant tube 13 is hermetically sealed by following the common process generally employed for this purpose.

This sleeve or support coupling 14 has a threaded recess in which is screwed a metallic and preferably a copper rod 15 which functions as an anode extension and serves as a heat and electrical conducting element. The outer portion of said sleeve or support coupling 14 is also threaded and is secured thereat to an anode 16. This anode 16 may be of any suitable metallic material and preferably copper, extending upwardly within the envelope and along the longitudinal axis thereof. The upper or free end (not shown) of the anode has a target of suitable material, such as tungsten or the like embedded therein and serving as an X-ray emitting material upon bombardment thereof by the electrons from a suitable filamentary cathode (not shown).

Disposed around and having its interior wall spaced from the free end of the anode 16 is an X-ray screen 18 consisting of nickel-iron. This X-ray screen houses the cathode and a focusing cup (both not shown). The cathode is electrically connected to a plurality of conductors 19 and 20 which are hermetically sealed to the envelope 10 and electrically secured to contact caps 21 and 22 respectively. Surrounding this metallic screen and functioning to provide a screen supporting and shock absorbing means are a plurality of resilient plates 23 which bear against the outer surface of said screen and the interior of the envelope.

Located within the envelope and extending upwardly therewithin is a second reentrant tube 24 surrounding and spaced from the tubular sleeve 14 and the anode 16.

This reentrant tube is of a material length and has its lower edge fusedly united with the envelope at about the lowermost quarter length of the envelope and as shown slightly below the seal of the first reentrant tube 13 and the tubular sleeve 14.

Spaced around said anode 16 and bearing thereagainst are a plurality of resilient supporting and shock absorbing plates 25. The plates 25 function as frictional bearing resilient elements bearing against the outer surface of the anode 16 and the inner surface of the reentrant tube 24 to provide a rugged structure.

In the course of production of electrical discharge devices and especially X-ray tubes of this character it is advisable to surface clean as much as possible all of the internal parts of the tube. In practice, any impurities, such as dirt, oxide films or the like are removed from the cathode leads, the cathode, the anode, the screen and the resilient plates before assembly thereof. The tubular sleeve or support 14 is freed as nearly as possible from any of the oxides, other compounds or impurities thereon which may have been produced during the sealing of the reentrant tube 13 with the tubular sleeve 14. As heretofore stated, it is possible to so treat the major portion of said sleeve 14 by either a mechanical or chemical process to provide it with a clean surface, but it is not feasible to clean either chemically or mechanically the seal per se or that area immediately adjacent the seal, the latter of which generally is of a darker hue than the cleaned portion and indicated by the reference character A.

With a construction of this character I have observed that when a voltage is applied between the anode and the cathode that sometimes the envelope punctures at or in proximity of the area of ring fusion of the second reentrant tube 24 and the envelope 10.

In order to avoid this difficulty and in further accordance with my present invention, there is provided a shielding means 30 around the tubular sleeve 14 to prevent any impurities in the form of uncharged particles or positive ions from going directly to the envelope in the vicinity of the fusion ring of the reentrant tube 24 and the envelope 10. This shielding means 30 may be composed of a dielectric and preferably a conducting material such as copper, and may be in the form of a cup having a suitably sized opening in its base adapted to accommodate the upper threaded portion of the tubular sleeve 14. This cup shaped copper shielding means 30 may be expeditiously manufactured at a comparatively low cost by a simple drawing operation. Thereafter this cup may be readily cleaned by a mechanical and preferably a chemical process to remove all impurities such as oxides, other compounds or other impurities from the surface thereof.

The shielding means 30 is appropriately dimensioned so that upon assembly thereof with the other elements of the tube, it rests on the shoulder portion of the tubular sleeve and extends therearound and downwardly at least as far as and preferably materially below the seal of the tubular sleeve 14 and the reentrant tube 13.

As is apparent from the drawing this shielding means 30 may be readily applied by simply projecting the upper threaded end of the sleeve 14 through the opening in the base of the shielding means. The anode 16 is thereafter screwed on to said end to provide an even bearing between the lower end of the anode 16 and the upper surface of the bottom of the cup, and the lower surface of the bottom of the cup and the shoulder of the tubular sleeve.

Besides improving the electrical characteristics of the tube, this shielding means 30 imparts to the tube as a whole a finer and cleaner appearance because it shields from view the seal as well as the tubular sleeve having a portion thereof which appears to have been overlooked in the cleaning operation.

What is claimed is:

1. An electrical discharge device comprising a gas tight dielectric envelope, a plurality of electrodes therein, said envelope having a reentrant tube in the lower portion thereof, an electrode supporting member forming a hermetic seal with the upper end of the reentrant tube and having impurities on the surface thereof adjacent said seal, one of said electrodes being electrically connected to said supporting member and a shielding means depending from said supporting member, spaced from and surrounding a portion of said supporting member and said seal.

2. An electrical discharge device comprising a gas tight dielectric envelope, a plurality of electrodes therein, said envelope having a reentrant tube in the lower portion thereof and a second reentrant tube fusion ring sealed to the interior of said envelope, an electrode supporting member forming a hermetic seal with the upper end of said rst mentioned reentrant tube and having impurities on the surface thereof adjacent said seal, one of said electrodes being electrically connected to said supporting member and shielding means spaced from and surrounding a portion of said supporting member and said seal, said shielding means also supported by said supporting member, said second reentrant tube also supporting said electrode connected to said supporting member.

3. An X-ray tube comprising a dielectric gas tight envelope, a supporting member, a plurality of electrodes therein, one of said electrodes connected to the supporting member forming a hermetic seal with a portion of the envelope and having impurities on the surface thereof adjacent said seal, and shielding means within the envelope located between said supporting member and the envelope, said shielding means having a portion thereof located between said electrode and said supporting member.

4. An X-ray tube comprising a gas tight dielectric envelope, a supporting member, a plurality of electrodes therein, said envelope having a reentrant tube in the lower portion thereof and a second reentrant tube fusion ring sealed to the interior of said envelope, said supporting member forming a hermetic seal with said first mentioned reentrant tube and having impurities on the surface thereof adjacent said seal, one of said electrodes connected to said supporting member and means spaced from and shielding said seal and supporting member from the envelope, said means depending from said supporting member, said second reentrant tube also supporting said electrode connected to said supporting member.

5. An X-ray tube comprising a gas tight dielectric envelope, a plurality of electrodes therein, said envelope having a reentrant tube in the lower portion thereof, a supporting member hermetically sealed to said first mentioned reentrant tube and having impurities thereon adjacent said seal, a second reentrant tube fusion ring sealed to the interior of said envelope and extending upwardly

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