JPS63124352A - X-ray tube target - Google Patents

Abstract

PURPOSE:To enable the manufacture of a target which resists high-speed rotation and has high performance and high efficiency by forming a X-ray target in a X-ray CT device so that it is composed of graphite/carbon fiber composite/ graphite. CONSTITUTION:Graphite 1, ceramics 3, a carbon fiber composite 2, ceramics 3, and graphite 1 are incorporated serially inside a metallic mold 4, and they are molded with a molding pressure 500 kg/cm<2> in order to uniformalize the thickness of the ceramics 3. Then the thickness after the sintering of the ceramics 3 is made 0.5 mm to 1 mm or so. This molded composite target is sintered by a hot press. The sintering conditions are as follows; this target is heated for about 15 min. until its temperature rises up to 1900 deg.C from a room temperature, and pressure 300 kg/cm<2> is applied to the target at 1900 deg.C, and moreover the target is heated up to 2150 deg.C at the rate of 10 deg.C/min, and after the target is held at 2150 deg.C for 30 min., it is cooled, and the pressure is released at 1500 deg.C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an X-ray tube target for an X@CT device,
In particular, in order to be suitable for high-speed rotation, a high-strength carbon fiber composite material is used in the middle part to reinforce the graphite material on the front and back surfaces.
This article relates to an X-ray tube target that has high strength, is lightweight, and is suitable for high-speed rotation.

[Conventional technology]

Whole-body X-ray CT systems that combine X-ray photography and computer imaging are in demand as medical diagnostic equipment, and are desired to have improved diagnostic efficiency and image quality.

To improve diagnostic efficiency (shorten imaging time), it is necessary to increase the heat storage capacity of the X-ray tube target (rotating anode).

On the other hand, in order to improve image quality (highly clear images), a large current is input to the target to increase the amount of X-rays, which increases the circumferential speed of the electron irradiation surface of the target, which requires high-speed rotation.

Heat capacity is calculated as the product of specific heat, specific gravity, and temperature. Metal materials are suitable for increasing heat capacity, have high X-ray generation efficiency, and are heated (1200℃ to 1200℃) during target operation.
(300°C), a material with a high melting point and excellent heat resistance is required. W, Mo, etc. have been selected so far, but their specific gravity greatly overlaps, and when rotating at high speed, the life of the bearing will be shortened.

In order to solve these problems, bonding graphite to a metallic target, or using graphite alone has been considered.

As mentioned above, a target made of graphite bonded to metal is heavy and has a short bearing life. In addition, graphite alone had the disadvantage of low strength and inability to rotate at high speeds. Therefore,
An X-ray tube target has been developed that is a composite of ceramic, a lightweight, high-strength material, and a graphite plate. Ceramic multilayer targets require thicker ceramic to reinforce graphite. A graphite/ceramic/graphite composite target is produced using hot pressing, but when the ceramic is made thicker, minute changes in the thickness of the ceramic and minute cracks occur.

Voids are more likely to occur when rotating at high speed.

The problem was that the target could be destroyed due to unbalance, or the rotational stress could concentrate on minute cracks or voids, causing the target to be destroyed, resulting in a lack of stability. In order to reduce these defects, the problem is being solved by making the ceramic thinner or by using ceramic as a bonding material for graphite materials. In other words, by making the ceramic thinner, the gas contained therein is released more easily, and fewer voids occur inside the ceramic. In addition, the temperature difference between the center and outer periphery that occurs during hot pressing is small, and cracks due to thermal stress are less likely to occur. On the other hand, since ceramic is used to bond graphite materials, it is much thinner than conventional thicknesses, and there is little non-uniformity in thickness. However, as mentioned above, if the ceramic is made thinner, it becomes impossible to reinforce the graphite.

[Means for solving problems]

In order to make ceramic thin and to reinforce it with graphite, a material with high strength, stability under high temperatures, and low specific gravity is required. Therefore, we focused on carbon fiber composite materials that have both of these properties. Carbon fiber composite materials have high strength and are stable even when used at high temperatures.Furthermore, they have a lower specific gravity than ceramics, making them lighter and less likely to damage bearings even when rotating at high speeds. Further, the carbon fiber composite material is made of graphite and can be easily joined by hot pressing using ceramics containing nitrides, borides, carbides, and oxides. Moreover, since it is used as a bonding material, there is no problem even if the thickness of the ceramic is made thin. On the other hand, since the ceramic is thinner, processing is easier than processing a target with a conventional ceramic sandwich structure, and a stable target with fewer cracks and cracks during processing can be obtained, reducing work time. Become.

[Effect]

By making the ceramic thinner, internal defects in the ceramic are eliminated, and high-speed rotation can be achieved by eliminating stress concentration on defective parts that occurs during rotation. Furthermore, the carbon fiber composite material that reinforces the graphite material is easy to process, and ceramic is thin, which shortens processing time and prevents cracks and breaks during processing.

〔Example〕

Since the xiv target rotates at high speed during operation and is irradiated with a large amount of electron beam, it is heated to about 1200° C., and the bonding material must be able to withstand this temperature and be easily bonded to the graphite material. Therefore, ceramics made by adding various sintering aids to SiC, which can withstand high temperatures, were used. Table 1 shows the ceramics and sintering aids used in the experiment.

Table 1 SiC uses α-8iC particles with an average particle size of 2 μm, and each sintering aid has a particle size of about 0.05 to 3 μm, and the amount added is 0.5 to 2% by weight. As shown in Table 1, S
3. Addition of BeO to C provides high thermal conductivity + A QzOs
, AQN has the characteristics of high strength, and 84C has the characteristics of densification of the sintered body.

Mixing of the SiC powder and each auxiliary material and granulation to make the moldability uniform are carried out by first adding 2% by weight of the sintering auxiliary material to the SiC powder, which is the main raw material, and then adding a molding binder and granulating it using a mixer. After sufficiently dispersing the sintering aid, the particles were granulated with a dry spray to an average particle size of 100 to 120 μm.

The graphite materials shown in Table 2 were used.

Table 2 The graphite material is homodisperse graphite. The strength of carbon fiber composite material is greater than that of graphite material, and it is sufficiently greater than that of ceramic material, so that it is sufficient to reinforce graphite material. Using such materials, as shown in FIG. 1, graphite/ceramic 3.
Carbon fiber composite material 2° Ceramic 3. Graphite 1 was incorporated into the entire mold, and molding was performed at a molding pressure of 5001 cg/cI# in order to make the thickness of the ceramic uniform. At this time, the thickness of the ceramic was made to be about 0.5 to 1 inch after sintering.

The shaped composite target was sintered by hot pressing. The sintering conditions were to raise the temperature from room temperature to 1900°C at a rate of about 15°C, at which point a pressure of 300 kg/d was applied, and then to raise the temperature to 2150°C at a rate of 10°C/min.
It was held for 30 minutes and then cooled. The pressure was released at a cooling temperature of 1500°C. 5 is punch.

The target after hot pressing was processed into the shape shown in FIG. With a target having a conventional structure in which ceramic 3 is sandwiched with graphite 1, machining holes is difficult or takes a long time, but in the composite target of this experiment, the ceramic 3 was thin and machining was easy. Further, even when observing the cross section after hot pressing, there was no defect in the ceramic part 3, and the bonding of graphite/carbon fiber composite material 2 and graphite 1 was good with all the sintering aids.

To irradiate a large capacity electron beam to an X-ray tube target 1
0. OOOrpm (average circumferential speed 62 m/s)
High speed rotation is required, and if the safety factor is doubled, the number of rotations at failure will be 30. Since OOO rpm or more is required, the rotation speed of the composite X-ray tube target prepared in this experiment was set to 30,
A rotation test was conducted with the goal of OOOrpm or higher. As a result, it was possible to clear the rotational speed of 30.00 Orpm. In addition, carbon fiber has a low specific gravity, making the target lightweight, less bearing damage, and a long-life target for X-ray tubes. 6 is the center hole.

〔Effect of the invention〕

According to the present invention, it is possible to produce a target that can withstand high-speed rotation, has high performance, and is highly efficient. On the other hand, carbon fiber composite materials are easier to process.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a molded structure of graphite/ceramic/carbon fiber composite material/ceramic/graphite according to an embodiment of the present invention, and FIG. 2 is a sectional view of the structure of an X-ray tube target of the present invention. DESCRIPTION OF SYMBOLS 1...Graphite, 2...Carbon fiber composite material, 3...Ceramic, 4...Mold, 5...Punch, 6...Center hole.

Claims (1)

[Scope of Claims] 1. An X-ray tube target for an X-ray CT device, characterized in that it is composed of graphite/carbon fiber composite material/graphite.
line tube target. 2. In claim 1, the fiber arrangement of the carbon fiber composite is a plain woven fabric arranged at equal intervals vertically and horizontally, and the stacking angle of one sheet or two or more sheets is from 5 degrees to 90 degrees. An X-ray tube target characterized by overlapping layers. 3. The X-ray tube target according to claim 1, wherein the fibers of the fiber composite are arranged in a spiral shape. 4. An X-ray tube characterized in that graphite/carbon fiber composite material/graphite is bonded using ceramics, and the ceramics are ceramics containing 0.5 to 2% by weight of oxides, carbides, borides, and nitrides. target.