JPS63160142A - Rotary target for x-ray tube - Google Patents

Abstract

PURPOSE:To generate strong X-rays by providing a chamfering section at a corner section formed by the inner face of the center hole of a ceramic plate and the outer face facing a metal layer. CONSTITUTION:A hole is bored at the center section of a laminated body made of a graphite plate 1 and a ceramic plate 3, i.e., a target, and a rotary shaft 5 is inserted into this center hole 4. The rotary shaft 5 and the target are fixed by a collar 7 provided on the rotary shaft 5, a washer 8, and a screw 9, and a fastening body fixing the target to the rotary shaft 5 is formed with the collar 7, washer 8, and screw 9. A chamfering section 10 is provided at the corner section formed by the inner face of the center hole 4 of the ceramic plate 3 and the outer face facing a metal layer 2. This chamfering section 10 could be either flat or polygonal, but a curved surface shape is preferable. Accordingly, the stress concentration caused by the temperature gradient generated at the time of the high-speed rotation or when a strong electron beam is radiated to the metal layer can be mitigated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a rotating target for an X-ray tube used in an X@CT device, etc., and particularly to a rotating target for a large-capacity xlIIAw suitable for obtaining powerful X-rays. Concerning rotating targets.

[Conventional technology and its problems]

Medical equipment such as X-ray CT uses an X-ray system that generates X-rays by rotating a target on top of a rotating shaft at high speed and irradiating the surface of this target with electron beams emitted from a hot cathode. A wire tube is used. In recent years, with the rapid advancement of medical equipment, there is a need for powerful, large-capacity X-ray tubes to increase throughput (the number of patients per unit time) and to obtain clear information. As a result, a large-diameter, high-speed rotation type is required.

Traditionally, rotating targets have been made of metal such as tungsten (W) plates or W alloy plates, but these targets are heavy and put a strain on the rotating shaft, making it difficult to increase diameters and rotate at higher speeds. It was difficult.

As an alternative target, targets in which a W or W alloy layer is formed on a graphite plate using methods such as chemical vapor deposition (CVD) are beginning to be used, but in this case, the strength of graphite is low, so high-speed rotation is required. It has the disadvantage of lack of reliability over time.

In order to deal with these problems, patent application No. 58-69941
No. 59-102574 and No. 59-187743
In this issue, a composite target of ceramics and graphite is proposed. This target has the advantage of being suitable for high-speed rotation because the high-strength ceramics bear the centrifugal stress during rotation. However, as a result of experimenting with a prototype target of this structure, it was found that when irradiated with a powerful electron beam, a large thermal stress is generated in the ceramic due to the thermal gradient inside the ceramic, causing the target to break from the ceramic part. Ta.

In this way, conventional rotating targets for X-ray tubes are lightweight, large-diameter, capable of high-speed rotation, and
However, it did not satisfy all the conditions for enabling strong electron beam irradiation.

The object of the present invention is to eliminate the drawbacks of the prior art and provide a powerful
The object of the present invention is to provide a rotating target suitable for a large-capacity X-ray tube capable of generating rays.

[Means and effects for solving the problem] The present invention provides a chamfered portion at the corner formed by the inner surface of the center hole of the ceramic plate and the outer surface facing the metal layer.
The chamfered portion alleviates stress concentration caused by temperature gradients that occur during high-speed rotation or when a strong electron beam is irradiated onto the metal layer.

〔Example〕

Hereinafter, the present invention will be explained using the drawings. In FIG. 1, 1 is a graphite plate with a metal layer 2 provided on its surface. metal layer 2
Generally, W or a W alloy is used as the material, and X-rays are generated by irradiating this with an electron beam. Further, 3 is a ceramic plate, which is joined to the graphite plate 1 to form a laminate. That is, the target 6 is formed of this laminate. As a ceramic, RaC has high strength, high Young's modulus, and good bondability with graphite.
, S j , C, VC, Ti C, etc. are used, and B 4 Cp S j-C is preferable because it is lightweight, and S 3. C is particularly desirable.

A hole is provided in the center of the laminate of the graphite plate 1 and the ceramic plate 3, that is, the target 6, and a rotating shaft 5 is inserted through the center hole 4. The rotating shaft 5 and the target 6 are fixed by a collar 7, a washer 8, and a screw 9 provided on the rotating shaft 5. The collar 7, washer 8, and screw 9 form a fastening body that fixes the target 6 to the rotating shaft 5. A chamfered portion 10 is provided at a corner formed by the inner surface of the center hole 4 of the ceramic plate 3 and the outer surface facing the metal layer 2. The chamfered portion 10 may have either a planar shape or a polygonal shape, but is preferably curved.

Next, the effect will be explained. First, for comparison, a conventional structure without a chamfered portion 10 will be described with reference to FIG. As a result of various studies, the inventors of the present invention found that when the metal layer 2 is irradiated with an electron beam, this part momentarily reaches a temperature of about 2,000 degrees Celsius, and on average rises to 1.
As a result of being heated to a temperature exceeding OOO'C, a temperature gradient occurs in which during use, the outside of the target 6 on the rotation axis 5 side, that is, the outside is hotter than the inside, and the upper surface is hotter than the bottom surface away from the metal layer 2. I understand. For this reason,
Stress that pulls outward and stress that bends from the upper side to the lower side act on the target 6, and due to the superposition of these two stresses, the largest stress is applied to the portion of the ceramic plate 3 where the chamfered portion 10 of the present invention is provided, Stress is concentrated on the acute corner portion of this portion, and the ceramic plate 3 is likely to be damaged. In addition, the Young's modulus of graphite plate 1 is generally 84c, Si, C, V
Since the thermal stress is 1/40 to 1/10 that of ceramics such as C and TiC, the thermal stress generated in the graphite plate 1 is small, and there is little possibility that the graphite plate 1 will be destroyed by electron beam irradiation.

In contrast, in the structure of the present invention, since the chamfered portion 10 is provided, this stress concentration is alleviated and damage to the ceramic plate 3 can be prevented.

When the chamfered portion 10 has a curved shape, the larger the radius, the greater the effect of alleviating stress concentration, and in fact, 0.3 + n
It was confirmed that if it is at least m, it works sufficiently effectively to relieve stress during heating.

Further, as shown in FIG. 1, the graphite plate 1 is generally provided with a taper on its outer periphery, and a metal layer 2 is provided on this tapered portion. The electron beam is normally irradiated onto the center of the metal layer 2, and the thickness of the graphite plate 1 in this area is preferably about 3 m or more. If the thickness of the graphite plate 1 is thin, the effect of thermal distortion due to ON and OFF of electron beam irradiation is applied to the joint between the graphite plate 1 and the ceramic plate 3, and this part tends to peel off.

FIG. 2 shows another embodiment of the invention. In the same figure, the first
Components that are the same as those in the drawings are given the same reference numerals and their explanations will be omitted. In the figure, a graphite layer 11 is interposed between the ceramic plate 3 and the rotating shaft 5. This graphite layer 1 and graphite plate 1 are formed separately. In this embodiment, since the graphite layer 11 with a small Young's modulus is interposed between the rotating shaft 5 and the ceramic plate 3, the stress applied to the ceramic plate 3 due to the expansion and contraction of the rotating shaft 5, which has a different coefficient of thermal expansion than the ceramic layer, is This can prevent the ceramic plate 3 from being damaged due to expansion and contraction of the rotating shaft 5. Since the rotating shaft 5 is generally made of Mo, W, Ta, etc., which have high heat resistance, this graphite layer 11 is particularly suitable when SiC or B10, which has a relatively small coefficient of thermal expansion, is used as the ceramic. It is valid.

FIG. 3 shows yet another embodiment of the invention. As shown in the figure, the graphite plate 1 and the graphite layer 11 can be integrated.

In this case, the number of parts is reduced compared to the case where they are separated as shown in Fig. 2, and manufacturing is easier, and the reliability is improved compared to the case where the graphite plate 1 and the graphite layer 11 are joined. It has the advantage of being expensive.

The outer diameter of the graphite layer 11 is desirably smaller than the outer diameters of the collar 7 and washer 8 . That is, it is desirable that the outer diameter (radius) of the collar 7 and the washer 8 be larger than the distance from the center of the target 6 to the inner surface of the center hole 4 of the ceramic plate 3. In this case, the ceramic plate 3 is tightened by the stress tightened by the screw 9 through the washer 8, so the strength and rigidity of the ceramic plate 3 work effectively against the centrifugal stress during rotation, and the target 6 rotates at high speed. It is also highly reliable.

In the same figure, another graphite plate 12 is provided below the target 6, and the ceramic plate 3 is bonded to both graphite plates 1 and 12 and has a structure in which it is sandwiched between the graphite plates. are doing. In this case, since the upper and lower outer surfaces of the target 6 are formed of graphite layers with high thermal emissivity, the target 6
This has the advantage of making cooling easier and increasing the capacity of the chassis. In addition, a graphite plate 12 is provided between the collar 7 and the ceramic plate 3.
is present, it is possible to prevent the ceramic plate 3 from being cracked due to local stress being applied to the ceramic plate 3 when the screw 9 is tightened, and the reliability of the target 6 is improved.

Further, the target 6 of the present invention is shown in FIGS. 4(a) and (b) (
Fill the graphite mold shown in c) with ceramics 13 (
This can be easily manufactured by pot press sintering to sinter the ceramic plate 3 and bonding it to the graphite plate 1 (see figure (b)), followed by processing (see figure (a)). C)). If there is a chamfered portion 10 in advance, the stress applied to that portion during hot pressing is alleviated, and there is also the advantage that breakage of the graphite during hot pressing can be prevented. here,
14 is a graphite die.

<Example>> A target 6 consisting of a laminate of a graphite plate 1- and a ceramic plate 3 was produced according to the method shown in FIG. The surface hot lead plates 1 and 12 have a tensile strength of 2.5 to 3 kg.
/ mm2. Specific gravity approximately 1.8. Thermal expansion coefficient 4.5-5
x 10''/'C was used. ceramic powder 1
For 3, a mixed powder of 5 α-8iC particles with a particle size of 1 to 2 μm and 1% Be0 particles or AQ, N particles was used, and the mixture was heated in vacuum at a temperature of 2000 to 2200'C1-axial pressure of 300.
Hot press sintering was performed under the conditions of kg/* to obtain a laminate of graphite plates 1 and 12 and SjC ceramic plate 3.

Next, after machining this, a Re and W-Re alloy layer is applied to the inclined part of the upper graphite plate 1 to a thickness of about 300 μm.
Targetera 1- having the structure shown in FIG. 3 was obtained. The size of the obtained target 6 is 140 mm in outer diameter and 11 mm in inner hole diameter.
n, the maximum thickness is 28 m (the target thickness for tightening the rotating shaft 5 is 20 mm), the thickness of the SiC ceramic plate 3 is 5 + m +, 1500XO, 7X 10'j
It has a large heat capacity greater than that of ole.

The obtained rotating target was set in a tubular shape and heated at 11,000 yen.
While rotating at a speed of 0 rpm, the voltage is 120 kW and the current is 60 kW.
As a result of generating X-rays by applying an electron beam for 9 seconds each for a total of 180,000 seconds under the conditions of 0 mA, pulse width of 2.2 m seconds, and pulse number of 134 times/second, a chamfer with a radius of 0.3 + a or more was formed on the SiC ceramic plate 3. ] If there is 0,
There was no problem that the target 6 was damaged due to thermal gradients caused by electron beam irradiation. Note that this result is based on the SiC
The same result was obtained when the experiment was conducted by changing the thickness of the ceramic plate 3 from 3 to 11 mm.

In this case, the thickness of the graphite plate under the metal layer 2] is related to reliability improvement, and the thickness of the electron beam irradiation part (usually the graphite plate under the metal layer 2) is related to improving reliability.
When the thickness of the lower graphite plate (at the center of The results showed that such problems did not occur.

In addition, in this example, as seen in FIG.
There is a thickness of approximately 5rLrrl between the rotating shaft 5 and the ceramic plate 3.
A graphite layer 11 is interposed therebetween. Therefore, even if the rotating shaft 5 (MO is used in this embodiment) thermally expands, the influence of the thermal expansion is alleviated by the graphite layer 11, and it is possible to prevent large stress from being applied to the ceramic plate 3. In fact, even when the target 6 having the structure shown in FIG. 3 was subjected to repeated thermal cycles at room temperature and -1200° C., no problems such as breakage occurred.

Furthermore, in this embodiment, since the outer diameter of the washer 8 (Tail) is located 5 m outside the graphite layer 11, the tightening force by the washer 8 is applied to the ceramic plate 3 via the graphite plate 1°12. The reliability of the rotating body can be improved. This target 6 is rated at 1-0000 rpm
Even when rotated at 20,000 rpm, which is twice the speed of A Si layer 15 is provided on the surface of the
The graphite plate 1 and the ceramic plate 3 were joined by hot pressing (FIG. 2(b)). Next, this was machined to produce a target 6 having the structure shown in FIG. 6(c).

In this case, the ceramic plates 3 are 84C and C.
A pressureless sintered SiC ceramic to which was added as an auxiliary agent was used, and the chamfered portion 10 thereof had a curved shape with a radius of 0.3 m or more.

In this example, since the ceramic plate 3 is thicker on the inner hole side where the rotational stress is greater, the reliability as a rotating body is particularly high.

〔Effect of the invention〕

As explained above, since the target of the present invention has a chamfered part, it has high reliability against high-speed rotation and powerful electron beam irradiation, and can be used to create a large-capacity X-ray tube that can generate powerful X-rays. can be realized.

[Brief explanation of the drawing]

1 to 3 are sectional views showing different embodiments of the present invention, FIG. 4 is an explanatory diagram of the manufacturing process of the target shown in FIG. 3, and FIG. 5 is an explanatory diagram of the manufacturing process of a different target. 1.12... Graphite plate, 2... Metal layer, 3... Ceramic plate, 4... Center hole, 5... Rotating shaft, 6...
・Target, (7, 8, 9)... fastener, 10...
- Chamfered portion, 11... graphite layer.

Claims (1)

[Claims] 1. The target is formed as a laminate of a graphite plate with a metal layer on its surface and a ceramic plate, and a rotating shaft is inserted into a central hole penetrating both plates of the target. In the fixed rotating target for an X-ray tube, a chamfered portion is provided at a corner formed by an inner surface of the center hole of the ceramic plate and an outer surface facing the metal layer.
Rotating target for wire tube. 2. The rotating target for an X-ray tube according to claim 1, wherein the chamfered portion has a curved shape and a radius of 0.3 mm or more. 3. A rotating target for an X-ray tube according to claim 1 or 2, in which a graphite layer is interposed between the ceramic plate and the rotating shaft. 4. A rotating target for an X-ray tube according to claim 3, wherein the graphite layer and the graphite plate are integrally molded. 5. A rotating X-ray tube according to claim 3 or 4, wherein the radius of the fastening body that tightens and fixes the target to the rotating shaft is larger than the distance from the shaft center to the inner surface of the center hole of the ceramic plate. target. 6. Claims 1, 2, 3, 4, or 5, for an X-ray tube in which an outer surface of a ceramic plate facing the metal layer and an opposite outer surface are sandwiched between graphite plates. rotating target. 7. Claims 1, 2, 3, 4,
In item 5 or 6, the ceramic plate is SiC,
B_4C, VC or TiC rotating target for X-ray tubes. 8. The rotating target for an X-ray tube according to claim 1, wherein the electron beam irradiation part of the graphite plate provided with the metal layer has a thickness of 3 mm or more.