RU2530533C1 - Cathode of x-ray tube - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: cathode of X-ray tube comprises a cathode cup, an emission unit consisting of two current leads and emitter fixed at them, and isolators. Each isolator is composite and is made of ceramic bushing and metal latch placed at one of butt ends of the ceramic bushing. Free end of the ceramic bushing is placed at the mounting seat made in the cathode cup for each isolator. Fixation of the isolator in the cathode cup is made by fullering technique. The emitter current leads are set in the isolators and fixed by laser welding with metal latches.

EFFECT: improving accuracy of the emitter setting in the location slot, reducing time for assembly operations, improving reliability of the cathode design.

3 cl, 2 dwg

Description

The invention relates to x-ray technology, namely, to the cathodes of x-ray tubes.

An X-ray tube cathode is known in the prior art, in which a regulating part is introduced between each emitter current lead and a ceramic insulator, and a transition metal sleeve is installed between the insulator and the cathode cup by soldering. The regulating part is made in the form of a tube made of metal with various cross-sections along the length and hemispherical thickening in the middle part. The emitter current lead is fixed at the bottom of the tube by soldering. The upper part of the tube is made of a slightly larger diameter than the diameter of the current lead, which makes it possible to change the position of the current lead in the radial direction. The change in the position of the current lead in the axial direction is provided by the deformation of the spherical section of the tube. US Patent 5526396, H01J 35/06, 06/11/1996.

A serious drawback of this design is the need for subsequent fixation of the position of the movable regulatory part for each emitter current lead in a predetermined position, which requires the introduction of additional parts into the cathode design and, therefore, increases the assembly time, and there is a risk of the regulatory part being displaced from a given position.

Soldering the emitter current lead in the regulating part can cause mechanical stresses in other nearby soldered seams of the cathode structure and lead to deformation of the assembly parts due to the high temperature at which the soldering operation occurs and the difference in the thermal expansion coefficients of the materials used. So, in the case of silver solder, it can reach over 800 ° C. Also, the presence of a large number of soldered joints reduces the reliability of the structure, especially if it is necessary to have a two or three-focal cathode, when the number of soldered joints increases two or three times, respectively.

An x-ray tube cathode is known in which a common insulator is used to isolate emitters from the cathode cup, and the emitter legs are mounted directly into the insulator through metal bushings. US Patent 5515413, H01J 35/14, 05/07/1996.

A significant drawback of this design is that when the emitter is installed in the mounting groove of the cathode cup in the absence of current leads, the risk of marriage associated with the breakdown of the emitter, which is usually made of tungsten, which has low mechanical properties, increases.

The disadvantage of this design is also the difficulty in ensuring the given accuracy of the emitter installation and the insufficient reliability of the fastening of the current leads under the conditions of the x-ray tube.

The closest to the claimed technical solution is the cathode of the x-ray tube, in which a metal sleeve is located between each current lead and the ceramic insulator, and a transverse flange is made in its central part, and the insulator is located directly in the body of the cathode cup. Each emitter current lead is fixed in a metal sleeve by soldering, and each metal sleeve is fixed in the insulator on both sides, and from the location of the conductive busbars, the sleeve is soldered to the insulator through a transverse flange. US patent 3943393, H01J 35/02, 09/09/1976.

The disadvantage of this design is the difficulty of manufacturing a metal sleeve and its installation in a ceramic insulator with a given accuracy.

The emitter temperature at operating conditions can reach 2500 ° C, which leads to its intense evaporation. Therefore, during prolonged use of the device, it is possible to deposit emitter material on the unshielded surfaces of ceramic insulators, which makes them conductive. The design of this cathode does not provide protection against the sprayed material of the emitter, and the current leads are located quite close to the conductive surfaces of the cathode cup. During the operation of the X-ray tube, this can cause short circuits between the cathode cup and the emitter unit or cause sparking, which will negatively affect the stability of the emission current, X-ray optical parameters and the final resource of the product.

The authors were faced with the task of creating an x-ray tube cathode, devoid of these drawbacks and distinguished by good reliability, as well as allowing for high assembly accuracy and reduce the time to complete this operation.

The problem is solved due to the fact that the proposed cathode of an x-ray tube, the design of which includes a cathode cup, an emitter unit, consisting of two current leads and an emitter fixed to them, insulators, each insulator made of a ceramic sleeve and a metal retainer placed on one of the ends of the ceramic sleeve by soldering, and the free part of the ceramic sleeve is placed in the seat, made in the cathode cup for each insulator, and fixed in it by chapping the edges of the annular grooves made around the seats, and the emitter current leads are located in insulators, and the current leads are fixed by laser welding of metal clamps with current leads. As the material of the fixing element of the insulator, either copper, or nickel, or titanium, or their alloys can be used.

The introduction of a metal retainer at the end of the ceramic sleeve into the design of the insulator makes it possible to simplify the design of the fixing element, reduce the assembly time of the insulator, and increase the accuracy of the emitter in the mounting groove of the cathode cup. The use of a metal clamp makes it possible to simplify the operation of exposing the emitter in the cathode cup due to the possibility of preliminary fixing the current leads in metal clamps by crimping them. The insulator enters the assembly operation already as part of two parts brazed together, namely a ceramic sleeve and a metal retainer, which allows, on the one hand, to completely eliminate their heating during this operation and, on the other hand, to accelerate the assembly process.

The choice of laser welding as the method of the final fastening of current leads in metal clamps is due to the simplicity of this method, which reduces the cathode assembly time and eliminates overheating of closely located cathode structure elements.

The choice of caulking as a method of fixing the insulator in the cathode cup is due to several factors. Mechanical fastening eliminates the heating of the structure during assembly, which can lead to oxidation of the heated surfaces, which will require further cleaning and, therefore, increase the duration of the process. Also, heating can cause mechanical stresses in nearby soldered joints found in insulators. During operation of the x-ray tube, the cathode is subject to constant thermocyclic loads, which can cause the destruction of soldered joints between the insulator and the cathode cup. Mechanical fastening eliminates the occurrence of such situations and, therefore, increases the reliability of the cathode design. The cathode assembly time is also reduced.

The invention is illustrated in FIGS. 1-2. Figure 1 shows the design of the two-focus cathode of the x-ray tube, where 1 is the cathode cup, 2 are the mounting grooves, 3 are emitters, 4 are current leads, 5 are insulators, 6 are ceramic bushings, 7 are metal clips. Figure 2 shows the cross-section of the cathode made in the plane AA along the installation groove, where 8 are the seats of the insulators, 9 are the edges, 10 are the annular grooves, 11 is the centering collar of the metal retainer.

Implementation example

The cathode of the x-ray tube (Fig. 1) is bi-focal and consists of a cathode cup 1, in the mounting grooves 2 of which emitters 3 are located on the current leads 4. The current leads 4 are made of molybdenum and placed in insulators 5, consisting of ceramic bushings 6 and metal clips 7, made of copper and soldered. The insulators 5 are installed in the seats 8 (figure 2), made in the cathode cup 1, and are fixed by chapping the edges 9 of the annular grooves 10 made around the seats 8. In order to improve the accuracy of the assembly, centering collars 11 are made in the metal clips 7.

The introduction of this design significantly reduced the cathode assembly operation time and increased the accuracy of the emitter installation in the cathode cup, and the experience of using this cathode design in x-ray tubes showed high reliability of their operation in the operating conditions of the device.

Claims (3)

1. The cathode of an X-ray tube, consisting of a cathode cup, an emitter placed in the mounting groove of the cathode cup and mounted on the current leads, the current leads being installed in insulators, and the insulators are placed in the seats made in the cathode cup, characterized in that, in order to increase reliability of the cathode design, reduction of the assembly operation time and ensuring the given accuracy of emitter alignment, ring slots are made around the seats for insulators on the back of the cathode cup, and the fixation is isolate The ditch in the cathode cup is carried out by chipping the edges of the annular grooves, each insulator made of a ceramic sleeve and a metal retainer placed on the free end of the ceramic sleeve and connected to it by soldering, and each metal retainer is made with a centering shoulder under the ceramic sleeve. 2. The cathode of the x-ray tube according to claim 1, characterized in that the fixation of the current leads in the metal retainer is carried out either by laser welding, or by contact welding, or crimping. 3. The cathode of the x-ray tube according to claim 1, characterized in that as the material of the metal retainer can be used either copper, or nickel, or titanium, or their alloys.

Images