Rotary anode type x-ray tube device

Abstract

To provide a rotary anode type X-ray tube device capable of making a liquid metal which is captured in a recess of a seal part efficiently reflow into a bearing.SOLUTION: A rotary body 14 has a main body part 30 which is disposed around a large diameter part 22 of a stationary shaft 13, and a seal part 31 which is provided in an end of the main body part 30 and disposed around a small diameter part 23 of the stationary shaft 13. The seal part 31 has a thrust bearing surface 34 which is opposed to an end face of the large diameter part 22, a seal surface 35 which is opposed to an outer peripheral surface of the small diameter part 23, a recess 36 which is provided on the seal surface 35 and captures a liquid metal 40, and a through hole 44 which communicates the recess 36 and the thrust bearing surface 34. The through hole 44 has a first opening 45 which is opened in the recess 36, and a second opening 46 which is opened in the thrust bearing surface 34, the second opening 46 is positioned on an outer diameter side rather than the first opening 45, and a hole diameter on the side of the second opening 46 is smaller than a hole diameter on the side of the first opening 45.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a rotating anode X-ray tube assembly. [Background technology]

[0002] In X-ray tubes, X-rays are generated by bremsstrahlung radiation, which occurs when electrons emitted from a cathode collide with an anode target. The conversion efficiency is approximately 1%, with the remaining 99% converted into heat. This results in a temperature rise in the target. To obtain higher-power X-rays, more electrons must be bombarded onto the target, which significantly increases the target's temperature. The target temperature must be kept below its melting point, and a rotating anode X-ray tube is commonly used to prevent localized temperature rises. A hydrodynamic sliding bearing with a liquid metal lubricant is widely used to rotate the target. A hydrodynamic sliding bearing consists of two elements: an inner fixed shaft and an outer rotor containing the target. The rotor's bearing against the fixed shaft consists of a radial bearing that supports the circumferential (radial) load perpendicular to the axial direction of the rotor, and a thrust bearing that supports the axial load of the rotor. A disk-shaped seal (hereafter referred to as a thrust ring) that also functions as a thrust bearing is provided at one or both ends of the rotor. There is a gap between the inner circumferential surface of the center of the thrust ring and the outer circumferential surface of the fixed shaft, and this gap seals the liquid metal, preventing it from leaking out of the bearing. It functions as a seal because the surface tension of the liquid acts in a direction that pushes it out of the gap. If the fluid pressure of the liquid metal exceeds this surface tension, the seal breaks down and the liquid metal leaks out of the bearing.

[0003] If liquid metal leaks outside the bearing, it can cause discharges when X-rays are generated (due to the electron beams used to generate X-rays and the leaked liquid metal), or it can cause the bearing to seize due to a lack of lubrication inside the bearing. Therefore, preventing liquid metal from leaking outside the bearing is extremely important for maintaining the performance of the X-ray tube.

[0004] To prevent liquid metal leakage, multiple recesses are sometimes provided along the axial direction on the inner circumferential surface of the thrust ring center (the sealing surface that seals with the fixed shaft) as traps to capture liquid metal. When liquid metal breaks through the seal and reaches a recess, it is trapped within the recess by the centrifugal force of the rotating body, preventing it from leaking outside the bearing. However, once liquid metal reaches the recess, it cannot return to the bearing, and so this is not expected to be effective in preventing bearing seizure due to insufficient lubrication within the bearing.

[0005] Therefore, it is necessary to efficiently return the liquid metal trapped in the recesses of the thrust ring back into the bearing. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2023-96523 Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to provide a rotating anode X-ray tube assembly that can efficiently circulate liquid metal trapped in the recess of the seal portion back into the bearing. [Means for solving the problem]

[0008] The rotating anode X-ray tube assembly of this embodiment includes a fixed shaft having a large-diameter section and a small-diameter section at the end of the large-diameter section, the small-diameter section being smaller in diameter than the large-diameter section; a rotor on which a target is mounted and which rotates around the fixed shaft; and liquid metal sealed between the fixed shaft and the rotor and forming a bearing together with the fixed shaft and the rotor. The rotor has a main body section disposed around the large-diameter section and a seal section disposed at the end of the main body and around the small-diameter section. The seal section has a thrust bearing surface facing the end face of the large-diameter section, a seal surface facing the outer circumferential surface of the small-diameter section, a recessed portion disposed in the seal surface for capturing the liquid metal, and a through hole communicating with the recessed portion and the thrust bearing surface. The through hole has a first opening that opens into the recessed portion and a second opening that opens into the thrust bearing surface. The second opening is located radially outward of the first opening, and the diameter of the second opening side is smaller than the diameter of the first opening side. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view of a rotating anode X-ray tube assembly showing an embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of a seal portion of the rotating anode X-ray tube assembly. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment will be described below with reference to FIGS.

[0011] 1 shows a schematic cross-sectional view of a rotating anode X-ray tube device 10. The rotating anode X-ray tube device 10 includes a vacuum envelope 11, a cathode 12, a fixed shaft 13, a rotor 14, a target 15, a rotor 16, and a stator coil 17. The cathode 12, the fixed shaft 13, the rotor 14, the target 15, and the rotor 16 are arranged inside the vacuum envelope 11, and the stator coil 17 is arranged outside the vacuum envelope 11.

[0012] The inside of the vacuum envelope 11 is maintained at a vacuum. The vacuum envelope 11 is provided with an X-ray transmission window at a position corresponding to the target 15, through which X-rays generated by the target 15 pass.

[0013] The cathode 12 emits electrons toward the target 15 .

[0014] The fixed shaft 13 is cylindrical, with its axial direction parallel to the direction of gravity. The fixed shaft 13 is roughly cylindrical, with one end fixed to the vacuum envelope 11. A cooling passage 21 is formed inside the fixed shaft 13, through which a refrigerant 20, which is a cooling liquid for cooling, passes. The refrigerant is circulated between the cooling passage 21 and the heat exchanger by a cooling device equipped with a heat exchanger (not shown).

[0015] The fixed shaft 13 has a large diameter portion 22 and small diameter portions 23 provided at both ends of the large diameter portion 22 and having a smaller diameter than the large diameter portion 22. A radial bearing surface (fixed shaft-side radial bearing surface) 24 is provided on the outer peripheral surface of the large diameter portion 22, a thrust bearing surface (fixed shaft-side thrust bearing surface) 25 is provided on the axial end surface of the large diameter portion 22, and a seal surface (fixed shaft-side seal surface) 26 is provided on the outer peripheral surface of the small diameter portion 23.

[0016] The rotor 14 is cylindrical and rotatably disposed around the fixed shaft 13 via a gap 29. The rotor 14 includes a cylindrical main body 30 disposed around the large-diameter portion 22 and cylindrical seal portions 31 provided at both ends of the main body 30 and disposed around the small-diameter portion 23. The seal portions 31 also function as thrust bearings and are hereinafter referred to as thrust rings 32. The inner circumferential surface of the main body 30 is provided with a radial bearing surface (rotor-side radial bearing surface) 33 that faces the radial bearing surface 24 of the large-diameter portion 22 via a gap 29. The thrust ring 32 includes a thrust bearing surface (rotor-side thrust bearing surface) 34 that faces the thrust bearing surface 25 on the end face of the large-diameter portion 22 via the gap 29, a seal surface (rotor-side seal surface) 35 that faces the seal surface 26 on the outer circumferential surface of the small-diameter portion 23, and a recess 36 that is a space provided in the seal surface 35 and serves as a trap for capturing liquid metal. One or more recesses 36 are provided in the axial direction of the seal surface 35. The recesses 36 are recessed from the seal surface 35 into the thrust ring 32 and are provided in the shape of continuous annular grooves along the circumferential direction of the seal surface 35.

[0017] The rotating body 14 is rotatably supported by a bearing 37 relative to the fixed shaft 13. The bearing 37 includes a hydrodynamic sliding bearing 38, which is a radial bearing that supports the radial load of the rotating body 14 relative to the fixed shaft 13, and a thrust bearing 39 that supports the axial load of the rotating body 14 relative to the fixed shaft 13.

[0018] The hydrodynamic sliding bearing 38 is composed of a radial bearing surface 24 of the large diameter portion 22 of the fixed shaft 13, a radial bearing surface 33 of the rotating body 14, and a liquid metal 40 as a lubricant sealed in the gap 29 between these radial bearing surfaces 24, 33.

[0019] The thrust bearing 39 is composed of the thrust bearing surface 25 of the fixed shaft 13, the thrust bearing surface 34 of the thrust ring 32, and a liquid metal 40 sealed in the gap 29 between these thrust bearing surfaces 25, 34.

[0020] There is a minute seal gap 41 between the seal surface 35 of the thrust ring 32 (other than the recess 36) and the seal surface 26 of the fixed shaft 13, and the surface tension of the liquid metal 40 prevents the liquid metal 40 from leaking from the seal gap 41 to the outside of the bearing 37. If the pressure of the liquid metal 40 inside the bearing 37 exceeds the sealing force caused by the surface tension of the liquid metal 40, the liquid metal 40 will break through the seal gap 41, but at that time the liquid metal 40 is captured in the recess 36, which prevents it from leaking to the outside of the bearing 37.

[0021] The liquid metal 40 is a fluid lubricant material such as a gallium-indium (Galn) alloy or a gallium-indium-tin (GaInSn) alloy, and is sealed in the gap 29 between the fixed shaft 13 and the rotor 14.

[0022] The target 15 is provided in a disk shape and protrudes from the outer circumferential surface of the rotor 14. The target 15 is provided with an anode 15a on the surface facing the cathode 12, which generates X-rays when electrons emitted from the cathode 12 collide with the anode 15a. The anode 15a is made of a heavy metal with a high melting point, such as molybdenum (Mo), tungsten (W), or an alloy of these.

[0023] The rotor 16 is cylindrical and is provided around the rotating body 14 .

[0024] The stator coil 17 is disposed in a position facing the rotor 16 across the vacuum envelope 11, and generates a magnetic field that rotates the rotor 16.

[0025] Next, FIG. 2 shows a schematic cross-sectional view of the thrust ring 32 which is the seal portion 31.

[0026] The thrust ring 32 has a through hole 44 that connects the recess 36 closest to the thrust bearing surface 34 to the thrust bearing surface 34. The through hole 44 may be provided at only one location on the thrust ring 32, or at multiple locations around the circumference of the thrust ring 32.

[0027] The through hole 44 has a first opening 45 that opens into the recess 36 and a second opening 46 that opens into the thrust bearing surface 34. The first opening 45 opens into the outer peripheral surface, which is the outermost diameter position of the recess 36. The second opening 46 is located on the outer diameter side of the first opening 45, at or near the outermost diameter portion of the thrust bearing surface 34. Therefore, the through hole 44 is provided obliquely with respect to the axial and radial directions of the thrust ring 32. Furthermore, the through hole 44 is provided in a conical cylindrical shape such that the hole diameter on the second opening 46 side is smaller than the hole diameter on the first opening 45 side, and the hole diameter decreases from the first opening 45 to the second opening 46.

[0028] By providing the through hole 44, there is a possibility that the liquid metal 40 in the gap 29 of the bearing 37 may flow back through the through hole 44 toward the recess 36. However, by reducing the diameter of the second opening 46, a force (sealing force) that inhibits the backflow occurs due to the surface tension of the liquid metal 40, preventing the liquid metal 40 in the gap 29 of the bearing 37 from flowing back toward the recess 36 through the through hole 44. Since the sealing effect due to the surface tension of the liquid metal 40 contributes more significantly as the diameter of the second opening 46 is smaller, it is desirable to have a smaller diameter for the second opening 46 in order to prevent the backflow of the liquid metal 40 in the gap 29 of the bearing. On the other hand, the first opening 45 is formed with a diameter large enough that the surface tension of the liquid metal 40 does not act, allowing the liquid metal 40 in the recess 36 to flow into the through hole 44.

[0029] In the rotating anode X-ray tube assembly 10, a minute seal gap 41 is formed between the seal surface 35 of the thrust ring 32 and the seal surface 26 of the fixed shaft 13, and the surface tension of the liquid metal 40 prevents the liquid metal 40 from leaking out of the bearing 37 through the seal gap 41.

[0030] If the pressure of the liquid metal 40 inside the bearing 37 exceeds the sealing force due to the surface tension of the liquid metal 40 in the seal gap 41, the liquid metal 40 will break through the seal gap 41, but at that time the liquid metal 40 will be captured in the recess 36 and prevented from leaking outside the bearing 37.

[0031] Rotating body 14 rotates at a high speed of about 6,000 to 10,000 rpm, and is subjected to centrifugal force due to the rotation. The centrifugal force causes liquid metal 40 trapped in recess 36 to move from recess 36 toward thrust bearing surface 34 through through-hole 44, allowing it to return to the interior of bearing 37. Because the diameter of second opening 46 of through-hole 44 is small, a sealing force due to surface tension acts on liquid metal 40 moving from through-hole 44 to the interior of bearing 37. However, because the centrifugal force is greater than the sealing force due to the surface tension of liquid metal 40, liquid metal 40 can be returned to the interior of bearing 37.

[0032] While the rotor 14 is rotating at high speed, centrifugal force causes the liquid metal 40 captured in the recess 36 to flow back into the bearing 37 through the through-hole 44. However, when the effect of centrifugal force decreases, such as when the rotor 14 is decelerating or after it has stopped rotating, the liquid metal 40 inside the bearing 37 may flow back through the through-hole 44 toward the recess 36. By reducing the diameter of the second opening 46, a force that inhibits backflow (a sealing force) acts due to the surface tension of the liquid metal 40, preventing the liquid metal 40 inside the bearing 37 from flowing back through the through-hole 44 toward the recess 36.

[0033] The second opening 46 of the through hole 44 is located on the outer diameter side of the first opening 45 and at or near the outermost diameter part of the thrust bearing surface 34, so that the liquid metal 40 can be returned to the hydrodynamic sliding bearing 38 side of the bearing 37 and the liquid metal 40 can be prevented from reaching the sealing surfaces 26, 35 side.

[0034] Since the first opening 45 of the through hole 44 is provided on the outer peripheral surface, which is the outermost diameter part of the recess 36, the centrifugal force of the rotating body 14 can be used most effectively to push the liquid metal 40 out of the through hole 44 and into the inside of the bearing 37.

[0035] By providing a plurality of through holes 44 in the recess 36, the liquid metal 40 captured in the recess 36 can be efficiently returned to the inside of the bearing 37.

[0036] As in the above embodiment, the liquid metal 40 trapped in the recess 36 of the thrust ring 32 can be efficiently returned to the inside of the bearing 37, which can contribute to improving the performance of the bearing 37 of the rotating anode X-ray tube assembly 10.

[0037] In addition, a connecting portion such as a hole or groove may be provided at the outermost diameter portion between the recess 36 connected to the through hole 44 and another recess 36, so that the liquid metal 40 trapped in the other recess 36 can be taken into the recess 36 connected to the through hole 44 and circulated.

[0038] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0039] 10 Rotating anode X-ray tube device 13 Fixed axis 14 Rotating body 22 Large diameter section 23 Small Diameter 30 Main body 31 Seal part 34 Thrust bearing surface 35 sealing surface 36 Recess 37 Bearings 40 liquid metal 44 through holes 45 First opening 46 Second Opening

Claims

1. a fixed shaft having a large diameter portion and a small diameter portion provided at an end of the large diameter portion with a diameter smaller than that of the large diameter portion; a rotor on which a target is disposed and which rotates around the fixed axis; a liquid metal sealed between the fixed shaft and the rotating body, which forms a bearing together with the fixed shaft and the rotating body; Equipped with the rotating body has a main body portion disposed around the large diameter portion, and a seal portion provided at an end of the main body portion and disposed around the small diameter portion, the seal portion has a thrust bearing surface facing an end face of the large diameter portion, a seal surface facing an outer circumferential surface of the small diameter portion, a recess provided in the seal surface for capturing the liquid metal, and a through hole communicating between the recess and the thrust bearing surface, The through hole has a first opening that opens into the recess and a second opening that opens into the thrust bearing surface, the second opening being positioned on the outer diameter side of the first opening, and the hole diameter on the second opening side being smaller than the hole diameter on the first opening side. A rotating anode X-ray tube device characterized by:

2. The first opening of the through hole is open to the outer circumferential surface of the recess.

2. The rotating anode X-ray tube assembly according to claim 1.

3. The second opening of the through hole is provided with a hole diameter that prevents the liquid metal from flowing back from the thrust bearing surface side into the through hole due to surface tension of the liquid metal.

3. A rotating anode X-ray tube assembly according to claim 1 or 2.

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