EP1308984A1 - Vacuum tube having getter layer of high thermal emissivity - Google Patents

Abstract

The vacuum tube has a coating (30) provided in the inner space (5) of the tube, the outer and inner side of the rotor jacket and inner walls of the metal housing (12) which serves as a getter. The coating has a thickness such that it has a thermal emissive power, adequate for cooling.

Description

The invention relates to a vacuum tube for processing or converting electrical Services, such as an X-ray tube or a traveling wave tube, that at least a surface to be cooled in the operating state by thermal emission and a getter to avoid an undesirable increase in pressure.

To maintain the operating characteristics and reliability of such vacuum tubes Two factors are particularly important over the longest possible service life special meaning

The conversion of electrical power into electromagnetic radiation is due physically unavoidable losses with the generation of large amounts of heat different parts or surfaces connected inside the tube. These amounts of heat must, if necessary after temporary storage in a material with high thermal capacity, be removed by a heat dissipation device. In many cases, For example, with rotating anode X-ray tubes, this device is predominantly or too essentially formed by a heat-radiating surface.

In order to be able to radiate a certain amount of heat at the lowest possible temperature, the highest possible specific emission coefficient of the heat radiation emitting or receiving surface.

High temperatures are undesirable because they damage the tube or restrict it the permissible operating parameters through direct temperature influence, however also by outgassing the materials and an associated increase in pressure in the Can lead tube. The production of surfaces with sufficient thermal Emissivity requires complex and expensive operations, such as one galvanic coating or reactive sputtering of the surfaces concerned, such as for Example is described in JP-07134958A.

To maintain the vacuum with one for safe tube operation sufficiently low pressures must also generally be gas consuming Materials (getters) are introduced into the tube. From WO 99/05694 for Example of a miniaturized X-ray source for insertion into the body of a Known patient, which has a cold cathode made of getter material. The Getter serves as a trap for binding gas molecules that are released over time Outgass anode material or other sources and contaminate the vacuum. Getter materials can then be zirconium, aluminum, vanadium, iron and / or Contain titanium and for example by an alloy of vanadium, iron and Zirconium can be formed.

A problem related to the use of the getter is that of this must be introduced into the tube in an initially inactive form, since otherwise it surrounding atmosphere would react and become unusable, and that it only after the generation of a sufficient vacuum may be activated by heating.

For activation, such getters typically have to reach 800 ° C for a few minutes 900 ° C to be heated. When activated, they diffuse on the surface of the getter bound atoms (mainly carbon, oxygen and nitrogen) into the interior of the Materials and leave a metal surface that is receptive to gases. The degree of activation is a function of time and temperature, with a sufficiently high activation even at significantly lower temperatures and correspondingly longer times can be achieved.

In high-performance vacuum tubes, the getter is generally in one with the getter pot connected to the evacuated tube interior, the getter for activation can be heated by means of a resistance heating wire.

The disadvantage here is that additional components and at least one for the getter pot Carrying out through the tube wall into the vacuum are required. In addition, must an electrical line for supplying the electrical current to the heating wire from the outside through the wall of the getter pot.

All of this, on the one hand, requires relatively complex manufacturing steps, which cause additional costs. On the other hand, any such implementation involves the risk of leakage a total failure of the tube. Finally, the absorption capacity of the Getters due to its small size relatively small, so the result is the maximum Tube life is also limited.

Overall, therefore, ensuring adequate heat dissipation and avoidance a pressure increase in the vacuum has a significant cost impact and at the same time, it is of crucial importance with regard to the operating characteristics that Reliability and the lifespan of vacuum tubes.

An object on which the invention is based is therefore a vacuum tube to create the type mentioned, which is much cheaper to produce without that disadvantages in terms of operating characteristics, reliability and durability the tube must be accepted.

Furthermore, a vacuum tube of the type mentioned is to be created, in which the Activation of the getter in a relatively simple manner and without special additional devices can be carried out.

Furthermore, a vacuum tube of the type mentioned is to be created, in which the Activation of the getter at almost any time during or after manufacture the tube can be made.

Furthermore, a vacuum tube of the type mentioned is to be created, in which the The effectiveness and capacity of the getter is significantly increased.

The task is solved with a vacuum tube of the type mentioned at the beginning Claim 1 characterized in that the getter in the form of a coating in whole or in part such a thickness is applied to the surface of the tube to be cooled that the coating has sufficient thermal emissivity for cooling.

Thus, one layer has both the function of the getter and the heat dissipation fulfilled, there is not only a simplified construction and cost advantages with the Manufacture of the tube. In particular, this also enables a getter structure with a particularly large area be realized, which has a correspondingly high absorption capacity and insofar as the lifespan or service intervals are significantly extended.

The dependent claims contain advantageous developments of the invention.

The embodiment according to claim 2 has the advantage that none to activate the getter separate heating devices and no electrical lines are required to An electrical heating current can be fed through a wall of the tube would.

Another advantage of this solution is that there is an option to getter also in later operation, for example as part of maintenance - if necessary reactivate. This can be controlled from a remote location. Changes in System architecture is not required and the life of the tube can be extended by one getters that are always kept optimally effective.

The embodiment according to claim 3 has the advantage that the activation to a desired Time can be made during the manufacture of the tube. This can do that Manufacturing processes can be designed optimally, saving time and costs.

With the embodiment according to claim 4, these advantages can also be achieved if the activation temperature and the activation time are higher on certain surfaces have to be.

In claims 5 to 10 are particularly preferred material compositions for the Coating specified.

Fig 1 einen schematischen Längsschnitt durch eine erfindungsgemäße Röntgenröhre; und

Fig. 2 einen schematischen Längsschnitt durch einen Teil der in Figur 1 gezeigten Röhre.

Further details, features and advantages of the invention will become apparent from the following description of a preferred embodiment with reference to the drawing.

1 shows a schematic longitudinal section through an X-ray tube according to the invention; and

Fig. 2 is a schematic longitudinal section through part of the tube shown in Figure 1.

Figure 1 shows the essential parts of a rotating anode X-ray tube 1 in longitudinal section. On Vacuum chamber 5 is of an essentially cylindrical glass bulb 11, which is expanded at one end, and enclosed an adjoining metal housing 12. In the vacuum space 5 there is an anode plate 21 which is provided by one Anode style 22 is held. The anode style 22 is attached to a rotor 23 which is connected to a bearing sleeve 24 rotatably on a bearing element 25 provided with spiral groove bearings 251 is stored. The bearing element 25 serves to hold the X-ray tube 1 while the bearing sleeve 24 shows the rotor of a motor that is outside the X-ray tube in the area of the Glass bulb 11 is arranged and with which the anode plate 21 is rotated. For storage of the rotor 23 in the axial direction is a first at its lower end in the illustration Ring magnet 252 attached between two second ring magnets 253, which on the Bearing element 25 are attached is held

On the front side of the metal housing 12 there is a cathode 3 with a heating wire, of which an electron beam onto the inclined, radially outer region of the anode plate 21 is directed so that it excites x-rays that enter the x-ray tube exit through an exit window 13 present in the metal housing 12.

During operation of the X-ray tube, the anode plate 21 and in particular in its radially outer area, in which the X-rays are excited, is high Heat loss generated. This heat is thermal on the one hand by the anode plate 21 radiated on the other hand, however, spreads considerably over the anode style 22 onto the rotor 23 and is also emitted there. Even if the rotor 23 only on its upper end in the illustration is connected to the bearing sleeve 24 is about however, this connection also heats the bearing sleeve 24 and the bearing element 25. One too however, a sharp increase in temperature, in particular of these parts, is undesirable since this causes may result in increased bearing wear and possibly bearing damage.

FIG. 2 schematically shows the rotor 23 with the first ring magnet in an enlarged representation 252 and part of the anode stem 22. By extending over the anode stem 22 spreading heat becomes the upper part 2311 of the rotor 23, which is shown in the illustration extends up to the dashed line A, particularly strongly heated, while the lower Part 2312 due to the heat radiation from the entire outer surface 231 of the rotor generally has a significantly lower temperature. The upper part 2311 For example, in normal operation, temperatures of up to 500 ° C can occur for a few minutes reach while the lower part 2312 cools to temperatures of about 300 ° C. Has.

As already mentioned at the beginning, it is for reliable and permanent operation a vacuum tube required that - on the one hand - especially with moving tubes Share - adequate heat dissipation is ensured and that, on the other hand, the vacuum is maintained with a sufficiently low pressure and not through outgassing materials is polluted.

This problem is solved according to the invention with a coating 30 in the interior 5 Tube solved, which has both the function of a getter, and an increased thermal Has emissivity.

For example, those surfaces in the tube are provided with the coating, which are blackened in known tubes or which are cooled by thermal emission In the case of the X-ray tube shown in FIG. 1, the outside in particular is preserved and the inside of the rotor shell 231 and the inside wall of the metal housing 12 the coating 30. Furthermore, the coating can also be applied to at least part of the cathode 3 be applied.

To further improve the specific heat radiation and getter effect the areas to be coated can be enlarged by initially grooving or Grooves can be screwed or milled into these surfaces or the surfaces by blasting be roughened before the coating is applied

The coating 30 contains at least two materials from the group titanium, zirconium and vanadium. The selection and the proportions of the materials are chosen so that there is a getter activation temperature for a tube with the temperature ranges mentioned above of about 400 ° C and a getter activation time of between is about 0.2 and an hour.

The temperature required for activation can then either for the required time during the manufacture of the tube (for example step by step) to one or more optimal or suitable times are generated by heat supplied from the outside. On the other hand, it is also possible to activate all or part of the activation by appropriate Commissioning or individual or several normal operating phases of the tube. This can also be done by the customer after completion of the tube corresponding initial commissioning. If coated parts in the normal Operation does not operate at the required activation temperature or does not operate for a sufficiently long time can achieve the coating through one or more controlled short-term overload operating phases the tube or by additional external heat. In no case, however, are separate passages through the wall of the tube required, that contain the risk of leakage mentioned at the beginning.

Suitable material combinations for the coating for an activation temperature of about 400 ° C and an activation time of between about 0.2 and one hour Example about 20 to 50% vanadium and 80 to 50% titanium; still a composition from about 10 to 30% vanadium and 90 to 70% zirconium; as well as a composition from about 20 to 80% zirconium and 80 to 20% titanium.

Furthermore, it has a composition of about 70 to 90% zirconium and 30 to 10 % Titanium and vanadium have been found to be suitable, the proportion of titanium being relative to that Vanadium content is between about 5 and 95%.

Finally, there is also a composition of about 60 to 90 percent titanium and 40 to 10% zirconium and vanadium are suitable, the zirconium proportion relative to that Vanadium content is between about 5 and 95 percent.

The coating can be applied by sputtering, either a corresponding one Mix of the starting materials or three individual sputtering targets with the respective Starting materials can be used. But there are also other well-known ones Coating processes can be used, such as plasma spraying or vapor deposition.

In addition to the getter capacity, the thickness of the coating also determines the achievable specific heat radiation ("degree of blackening"). For a coated surface of at least about 100 cm ^2, it should therefore be at least 1 µm, but preferably be significantly larger than the wavelength maximum at the desired operating temperature (approx. 3.5 µm at 550 ° C, approx. 6 µm at 200 ° C) of the coated part. Depending on the operating temperature, the preferred layer thickness is therefore between approximately 1 and approximately 20 μm, preferably between approximately 5 and approximately 20 μm.

Such a coating could then step by step in the course of the manufacturing process after process progress - also automatically - activated so that during high-voltage conditioning a good (low) tube pressure is always ensured. To can also use coatings made of different material compositions that have different activation temperatures.

In another embodiment of the invention, the rotor jacket 231 with a Coating with a combination of the materials titanium, zirconium and vanadium provided that an activation time of 0.2 to at a temperature above 600 ° C. has an hour. Such a coating can be activated specifically by the Rotor 23, for example, by selective heating from the outside to a higher than that normal operating temperature is brought up Various other easily implementable processes such as heating by induction heating (especially in the case of Glass tubes) as well as series connection of several start-up / braking processes using of eddy current losses, or a combination of these methods with the normal heating during operation or a brief overload operation of the Tube. At the same time, other parts, such as the housing, can be specifically cooled.

In this embodiment, activation or reactivation of the getter layer can also be carried out at the customer, for example by choosing a special one Operating mode of the tube or triggered by an automatic or remote control Maintenance process to restore the vacuum quality after long operation of the Tube.

The optimal operating temperature and thus the composition of the coating is the permissible operating temperatures of the corresponding component and the manufacturing process adapt.

Claims (10)

Vacuum tube for processing or converting electrical power at least one surface to be cooled in the operating state by thermal emission, and includes a getter to avoid an undesirable increase in pressure, in which the Getters in the form of a coating (30) in whole or in part with such a thickness on the Surface of the tube (1) to be cooled is applied so that the coating is used for cooling has sufficient thermal emissivity. Vacuum tube according to claim 1,
characterized in that the material for the coating (30) is selected such that the activation temperature and the activation time of the getter can be achieved by one or more normal operating phases or one or more short-term overload operating phases of the vacuum tube. Vacuum tube according to claim 1,
characterized in that the material for the coating (30) is selected such that the activation temperature and the activation time of the getter can be achieved by temperatures occurring during the manufacture of the vacuum tube. Vacuum tube according to claim 2 or 3,
characterized in that the activation temperature and the activation time of the getter can be achieved by additional external heat. Vacuum tube according to claim 1,
characterized in that the coating (30) has at least two of the three materials vanadium, zirconium, titanium. Vacuum tube according to claim 5,
characterized in that the coating (30) has about 20 to 50% vanadium and 80 to 50% titanium. Vacuum tube according to claim 5,
characterized in that the coating (30) has about 10 to 30% vanadium and 90 to 70% zirconium. Vacuum tube according to claim 5,
characterized in that the coating (30) has about 20 to 80% zirconium and 80 to 20% titanium. Vacuum tube according to claim 5,
characterized in that the coating (30) has approximately 70 to 90% zirconium and 30 to 10% titanium and vanadium, the titanium proportion relative to the vanadium proportion being between approximately 5 and 95%. Vacuum tube according to claim 5,
characterized in that the coating (30) has about 60 to 90 percent titanium and 40 to 10% zirconium and vanadium, the zirconium portion relative to the vanadium portion being between about 5 and 95%.

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