Rotating anode type x-ray tube

Abstract

A rotating anode type X-ray tube is provided with: a cathode (60) that emits electrons; an anode target (50) which receives the electrons and generates X-rays; a sliding bearing (3) having a rotating body (20) connected to the anode target (50) and extending along a rotation axis (a), a fixed shaft (10) rotatably supporting the rotating body (20), and a lubricant held between the rotating body (20) and the fixed shaft (10); and a vacuum tube case (70) which accommodates the cathode (60) and the anode target (50) and fixes the fixed shaft (10), the rotating body (20) is provided with a bearing member (21) which is formed so as to extend along the rotation axis (a) and which is positioned so as to surround the fixed shaft (10), and at least one of the fixed shaft (10) and the bearing member (21) is formed of tungsten carbide, silicon carbide, or titanium carbide.

Description

Technical Field

[0001] Embodiments of the present invention relate to a rotating anode type X-ray tube. Background Art

[0002] Generally, in medical devices and / or industrial devices that use X-rays to diagnose a subject, an X-ray tube device is used as an X-ray generation source. The X-ray tube device is installed in an X-ray CT device and rotates around the subject. As the X-ray tube device, a rotating anode type X-ray tube device including a rotating anode type X-ray tube (hereinafter also referred to as "rotating anode type X-ray tube") is known. Prior Art Documents Patent Documents

[0003] Patent Document 1: Japanese Patent Laid-Open No. 9-115467 Patent Document 2: Japanese Patent Laid-Open No. 2000-353485 Summary of the Invention Technical Problem to be Solved by the Invention

[0004] The present embodiment provides a rotating anode type X-ray tube capable of maintaining good rotation of a rotating body. Technical Solution for Solving the Technical Problem

[0005] A rotating anode type X-ray tube according to an embodiment includes: a cathode that emits electrons; an anode target that receives the electrons and generates X-rays; a sliding bearing having a rotating body, a fixed shaft, and a lubricant, the rotating body being connected to the anode target and extending along a rotation axis, the fixed shaft supporting the rotating body so as to be rotatable, the lubricant being held between the rotating body and the fixed shaft; and a vacuum tube housing that houses the cathode and the anode target and fixes the fixed shaft, the rotating body having a bearing member formed to extend along the rotation axis and located at a position surrounding the fixed shaft, at least one of the fixed shaft and the bearing member being formed of tungsten carbide, silicon carbide, or titanium carbide. Brief Description of the Drawings

[0006] Figure 1 is a perspective view showing the appearance of an X-ray CT device. Figure 2 is showing along Figure 1 a cross-sectional view of the X-ray CT device taken along line A-A. Figure 3 is showing Figure 2 a front view of the rotating gantry, X-ray tube device, cooling unit, and X-ray detector shown in Figure 4 is a cross-sectional view showing an X-ray tube device according to an embodiment. Figure 5 is a side view showing Figure 4 a part of the fixed shaft shown. Figure 6 is a cross-sectional view showing a modified example of the X-ray tube device of the above-described embodiment. Detailed Embodiment

[0007] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the disclosure is only an example, and appropriate changes that can be easily conceived by those skilled in the art while maintaining the gist of the present invention are naturally included in the scope of the present invention. Further, for clearer illustration and description, the width, thickness, shape, etc. of each part may be schematically shown compared to the actual form, but this is only an example and does not limit the interpretation of the present invention. In addition, in this specification and each drawing, for elements that are the same as those previously described in the existing drawings, the same reference numerals may be given and detailed description may be appropriately omitted. Next, a rotating anode type X-ray tube according to an embodiment will be described in detail with reference to the drawings.

[0008] First, the basic concept of the embodiment of the present invention will be described. The X-ray CT apparatus includes a gantry and an X-ray tube device, etc. The X-ray tube device has a rotating anode type X-ray tube and rotates together with the gantry. The rotating anode type X-ray tube has a cathode, an anode target, a fixed shaft, a rotating body, etc. Currently, in an X-ray CT apparatus for the heart, the high-speed rotation of the gantry is being promoted. Specifically, an X-ray CT apparatus that rotates the gantry at 0.2 s / r (5 rps) is being developed. When the rotating gantry rotates at 0.2 s / r, the X-ray tube device generates a centrifugal acceleration (centrifugal force) of about 70 G. Conventionally, the gantry rotates at 0.35 s / r (about 2.8 rps). At this time, the centrifugal acceleration generated by the X-ray tube device is 23 G. That is, in the X-ray CT apparatus under development, the X-ray tube device needs to withstand about three times the centrifugal acceleration. Specifically, when the X-ray tube device generates a high centrifugal acceleration, the fixed shaft may be deformed and come into contact with the rotating body.

[0009] In addition, the rotating anode type X-ray tube generates X-rays by causing electrons generated by the cathode to collide with the anode target at high speed. At this time, the X-ray generation efficiency is about 1%, and the remaining energy is heat. For example, when the input power obtained by multiplying the tube voltage that determines the speed of electrons by the tube current that determines the amount of electrons is 100 kW, when electrons are incident on the anode target for 4 seconds, the electron incident surface of the anode target is locally heated to nearly 3000 °C. Before the temperature of the anode target drops to a certain level, the rotating anode type X-ray tube cannot be used, so it is desired to quickly release heat from the rotating anode type X-ray tube.

[0010] To solve the above problems, an X-ray tube with a conduction cooling method that transfers the heat of the anode target to the refrigerant flowing through the fixed shaft by heat conduction is being developed, but there are the following two problems. 1. The heat of the anode target is transferred to the circulating water through the bearing surface, so the bearing surface is also heated. As a result, sometimes the rotating body expands in a direction away from the fixed shaft, the gap between the rotating body and the fixed shaft becomes larger, and stable rotation of the rotating body cannot be obtained. 2. In a rotating anode type X-ray tube with high input, a liquid metal of gallium tin indium alloy (Galinstan) is usually used as a lubricant for the bearing. Therefore, when the rotating body is heated, a chemical reaction occurs between the bearing surfaces of the rotating body and the fixed shaft and the lubricant, and a compound is generated on the above-mentioned bearing surfaces. The gap between the fixed shaft and the rotating body is narrowed due to this compound, and finally the fixed shaft contacts the rotating body. Therefore, in the embodiment of the present invention, this problem is improved, and a rotating anode type X-ray tube capable of maintaining good rotation of the rotating body can be obtained.

[0011] First, refer to Figures 1 to 3 to describe the structure of the X-ray CT apparatus 80. Figure 1 is a perspective view showing the appearance of the X-ray CT apparatus 80. Figure 2 is a sectional view of the X-ray CT apparatus 80 taken along line A-A of Figure 1 . Figure 3 is a front view showing the rotating gantry 84, the X-ray tube device 86, the cooling unit 87, and the X-ray detector 88 shown in Figure 2 . As shown in Figures 1 to 3 , the X-ray CT apparatus 80 includes a housing 81, a base portion 82, a stationary gantry 83, a rotating gantry 84, a bearing member 85, an X-ray tube device 86, a cooling unit 87, and an X-ray detector 88.

[0012] The housing 81 houses the stationary gantry 83, the rotating gantry 84, the bearing member 85, the X-ray tube device 86, etc. The housing 81 has an exhaust port 81a, an intake port 81b, and an introduction port 81c. The external air inhaled from the intake port 81b is discharged from the exhaust port 81a. The introduction port 81c is provided for introducing the subject. Although not shown, the X-ray CT apparatus 80 further includes a platform for placing the subject.

[0013] The stationary gantry 83 is fixed to the base portion 82. The rotating gantry (also referred to as a "gantry") 84 is supported by the stationary gantry 83 via the bearing member 85 so as to be rotatable. The rotating gantry 84 can rotate about the central axis C1 of the rotating gantry 84. The rotating gantry 84 has an annular frame portion 84a located at the outermost periphery.

[0014] The X-ray tube device 86, the cooling unit 87, and the X-ray detector 88 are mounted on the rotating gantry 84 and rotate together with the rotating gantry 84. Thus, the X-ray tube device 86 generates a centrifugal acceleration CA. The X-ray tube device 86 and the cooling unit 87 are mounted on the inner wall of the frame portion 84a. The X-ray tube device 86 exchanges heat with the cooling unit 87 via the circulation path 89. The X-ray tube device 86 functions as an X-ray generator and emits X-rays. The X-ray detector 88 detects the X-rays emitted from the X-ray tube device 86 and transmitted through the subject, and converts the detected X-rays into an electrical signal. The X-ray CT apparatus 80 is configured as described above.

[0015] Figure 4 It is a cross-sectional view showing the X-ray tube device 86 of one embodiment. As Figure 4 shown, the X-ray tube device 86 includes a rotating anode type X-ray tube 1 and a stator coil 2 as a coil for generating a magnetic field, etc. The rotating anode type X-ray tube 1 includes a sliding bearing 3, an anode target 50, a cathode 60, and a vacuum tube envelope 70. The sliding bearing 3 has a fixed shaft 10, a rotating body 20, and a liquid metal LM as a lubricant.

[0016] The fixed shaft 10 is formed in a cylindrical shape, extends along the rotation axis a, and has radial bearing surfaces S11a, S11b formed on the outer peripheral surface and a heat transfer portion 10a. The fixed shaft 10 supports the rotating body 20 so as to be rotatable. The fixed shaft 10 is composed of a large diameter portion 11, a first small diameter portion 12, and a second small diameter portion 13. The large diameter portion 11, the first small diameter portion 12, and the second small diameter portion 13 are formed integrally and coaxially.

[0017] Hereinafter, Figure 5 the details of the large diameter portion 11 of the fixed shaft 10 will be described. Figure 5 It is a side view showing Figure 4 a part of the fixed shaft 10 shown. As Figure 5 shown, the large diameter portion 11 has radial bearing surfaces S11a, radial bearing surface S11b, concave surfaces S11c, S11d, and S11e respectively located on the outer peripheral surface. In addition, the large diameter portion 11 has a thrust bearing surface S11i at one end and a thrust bearing surface S11j at the other end. The radial bearing surface S11a and the radial bearing surface S11b are respectively formed over the entire circumference on the outer peripheral surface of the large diameter portion. The concave surfaces S11c, S11d, and S11e are respectively formed over the entire circumference on the outer peripheral surface of the large diameter portion 11.

[0018] The radial bearing surfaces S11a and S11b are positioned at intervals in the direction of the rotation axis a. The concave surface S11c is located between the radial bearing surface S11a and the radial bearing surface S11b, adjacent to the radial bearing surface S11a and the radial bearing surface S11b respectively. The concave surface S11d is located at a position from the concave surface S11c towards beyond the radial bearing surface S11a, adjacent to the radial bearing surface S11a. The concave surface S11e is located at a position from the concave surface S11c towards beyond the radial bearing surface S11b, adjacent to the radial bearing surface S11b.

[0019] The radial bearing surface S11a has a smooth (plane) surface Sa and a plurality of pattern portions Pa. The smooth surface Sa has a smooth outer peripheral surface. The plurality of pattern portions Pa are formed by recessing the smooth surface Sa. Each pattern portion Pa extends and is arranged obliquely with respect to the circumferential direction. The plurality of pattern portions Pa are formed at intervals in the direction of the rotation axis a. Additionally, the plurality of pattern portions Pa may also be connected in the direction of the rotation axis a.

[0020] The radial bearing surface S11b has a smooth surface Sb and a plurality of pattern portions Pb. The smooth surface Sb has a smooth outer peripheral surface. The plurality of pattern portions Pb are formed by recessing the smooth surface Sb. Each pattern portion Pb extends and is arranged obliquely with respect to the circumferential direction. The plurality of pattern portions Pb are formed at intervals in the direction of the rotation axis a. Additionally, the plurality of pattern portions Pb may also be connected in the direction of the rotation axis a. Each pattern portion Pa and each pattern portion Pb are formed by grooves having a depth of several tens of μm. The plurality of pattern portions Pa and the plurality of pattern portions Pb respectively form herringbone parallel patterns. Therefore, the radial bearing surfaces S11a, S11b are respectively uneven surfaces, capable of sucking in the liquid metal LM, and capable of easily generating hydrodynamic pressure based on the liquid metal LM.

[0021] The concave surfaces S11c, S11d, S11e are respectively smooth outer peripheral surfaces, which are smooth surfaces. The concave surface S11c, the concave surface S11d, and the concave surface S11e are formed to be recessed more than the radial bearing surface S11a and the radial bearing surface S11b. In other words, on the fixed shaft 10, the outer diameter DO2 of the section where the concave surfaces S11c, S11d, S11e are formed is smaller than the smallest outer diameter DO1 of the outer diameters of the sections where the radial bearing surfaces S11a, S11b are formed.

[0022] In the direction perpendicular to the rotation axis a, the gap between the concave surfaces (concave surfaces S11c, S11d, S11e) and the rotating body 20 is greater than the gap between the radial bearing surface S11a (smooth surface Sa) and the rotating body 20, and greater than the gap between the radial bearing surface S11b (smooth surface Sb) and the rotating body 20. The spaces between the concave surfaces S11c and the rotating body 20, between the concave surfaces S11d and the rotating body 20, and between the concave surfaces S11e and the rotating body 20 can function as reservoirs for containing the liquid metal LM. Since the liquid metal LM can be supplied to the radial bearing surfaces S11a and S11b from adjacent sides, depletion of the liquid metal LM in the bearing clearance can be suppressed.

[0023] As Figure 4 shown, the first small-diameter portion 12 is formed in a cylindrical shape with an outer diameter smaller than that of the large-diameter portion 11 and extends from one end of the large-diameter portion 11. The first small-diameter portion 12 is located on the side closer to the rotation axis a than the thrust bearing surface S11i. The second small-diameter portion 13 is formed in a cylindrical shape with an outer diameter smaller than that of the large-diameter portion 11 and extends from the other end of the large-diameter portion 11. The second small-diameter portion 13 is located on the side closer to the rotation axis a than the thrust bearing surface S11j.

[0024] The heat transfer portion 10a transfers heat to the refrigerant flowing through the inside by forced convection. The refrigerant is, for example, the coolant L. The cooling rate of the anode target 50 of the rotating anode type X-ray tube 1 can be increased by water cooling or oil cooling (insulating oil). In addition, the refrigerant can be air, and the cooling rate of the anode target 50 can also be increased by air cooling. Preferably, the heat transfer portion 10a is at least located in the region A opposite to the anode target 50. Thereby, the portion of the fixed shaft 10 that is likely to transfer heat from the anode target 50 can be cooled. In addition, the method of releasing heat from the fixed shaft 10 to the outside of the rotating anode type X-ray tube 1 is not limited to the above heat transfer from the heat transfer portion 10a to the refrigerant. For example, the heat inside the fixed shaft 10 can be released by cooling a heat exchanger on the outer peripheral surface of the first small-diameter portion 12 with the heat exchanger. In this case, the rotating anode type X-ray tube 1 can be configured by removing the heat transfer portion 10a and the refrigerant (coolant L).

[0025] The rotating body 20 is connected to the anode target 50 and extends along the rotation axis a. The rotating body 20 has a bearing member 21, a first support member 22, a second support member 23, and a cylindrical portion 24. The bearing member 21 extends along the rotation axis a, is formed in a cylindrical shape, and is located to surround the fixed shaft 10. The bearing member 21 has a bearing member main body 21a and convex portions 21b and 21c. The bearing member main body 21a has a uniform inner diameter and outer diameter throughout the circumference and includes a radial bearing surface S21 on the inner peripheral surface.

[0026] The convex portions 21b and 21c are formed by extending in a direction away from the rotation axis a at both ends of the bearing member main body 21a. The convex portions 21b and 21c have an annular shape. The convex portions 21b and 21c may be formed integrally with the bearing member main body 21a without being continuous, for example, they may be fixed to the outer peripheral surface of the bearing member main body 21a by welding or screws.

[0027] At least one of the fixed shaft 10 and the bearing member 21 is formed of tungsten carbide (WC), silicon carbide (SiC), or titanium carbide (TiC). When the fixed shaft 10 and the bearing member 21 are not formed of tungsten carbide, silicon carbide, or titanium carbide, for example, they are formed of alloy tool steel, namely SKD11, specified by JIS (Japanese Industrial Standards) G4404. In addition, the material of the fixed shaft 10 and the material of the bearing member 21 may be the same. For example, both the fixed shaft 10 and the bearing member 21 may be formed of tungsten carbide. The Young's modulus of tungsten carbide is about 600 GPa. The Young's modulus of silicon carbide is about 450 GPa. The Young's modulus of titanium carbide is about 450 GPa. The Young's modulus of SKD11 is about 200 GPa. That is, the Young's modulus of tungsten carbide, the Young's modulus of silicon carbide, and the Young's modulus of titanium carbide are about 400 to 600 GPa, approximately twice the Young's modulus of SKD11.

[0028] In addition, the linear expansion coefficient of tungsten carbide is 5×10 -6 / K or so. The linear expansion coefficient of silicon carbide is 4×10 -6 / K. The linear expansion coefficient of titanium carbide is 7×10 -6 / K. The linear expansion coefficient of SKD11 is 12×10 -6 / K. That is, the linear expansion coefficient of tungsten carbide, the linear expansion coefficient of silicon carbide, and the linear expansion coefficient of titanium carbide are about half of that of SKD11. Tungsten carbide with a thermal conductivity of about 120 W / mK and silicon carbide with a thermal conductivity of about 200 W / mK have also been developed. The thermal conductivity of SKD11 is about 20 W / mK. That is, the thermal conductivity of tungsten carbide and the thermal conductivity of silicon carbide are greater than the thermal conductivity of SKD11. Tungsten carbide, silicon carbide, and titanium carbide have electrical conductivity. Therefore, even when the fixed shaft 10 and the bearing member 21 are made of tungsten carbide, silicon carbide, or titanium carbide, tube current can flow through.

[0029] The first support member 22 has an annular shape and is fixed to one end of the bearing member 21. The first support member 22 is formed of a metal such as an Fe alloy or an Mo alloy. The first support member 22 includes a thrust bearing surface S22 that faces the thrust bearing surface S11i of the fixed shaft 10 in the direction along the rotation axis a. The thrust bearing surface S22 is located on the inner peripheral side of the first support member 22 and has an annular shape. The clearance between the first support member 22 and the fixed shaft 10 (the first small-diameter portion 12) is set to a value that can maintain the rotation of the rotating body 20 and suppress the leakage of the liquid metal LM. For the above reasons, the above clearance is small, and the first support member 22 functions as a labyrinth seal ring.

[0030] The second support member 23 has an annular shape and is fixed to the other end of the bearing member 21. The second support member 23 is formed of a metal such as an Fe alloy or an Mo alloy. The second support member 23 includes a thrust bearing surface S23 that faces the thrust bearing surface S11j of the fixed shaft 10 in the direction along the rotation axis a. The thrust bearing surface S23 is located on the inner peripheral side of the second support member 23 and has an annular shape. The clearance between the second support member 23 and the fixed shaft 10 (the second small-diameter portion 13) is set to a value that can maintain the rotation of the rotating body 20 and suppress the leakage of the liquid metal LM. For the above reasons, the above clearance is small, and the second support member 23 functions as a labyrinth seal ring. The cylindrical portion 24 is joined to the outer peripheral surface of the convex portion 21b of the bearing member 21. The cylindrical portion 24 is formed of a metal such as copper (Cu) or a copper alloy. However, if there are differences in the thermal expansion rates among the bearing member 21, the first support member 22, and the second support member 23, an undesired clearance may sometimes occur between the fixed shaft 10 and the rotating body 20. To suppress or prevent the generation of the above undesired clearance, the first support member 22 and the second support member 23 may be formed of the same material as the bearing member 21. In this case, the first support member 22 and the second support member 23 are formed of tungsten carbide, silicon carbide, or titanium carbide.

[0031] A lubricant (liquid metal LM in the present embodiment) is held between the rotating body 20 and the fixed shaft 10. More specifically, the liquid metal LM is filled in the clearance between the fixed shaft 10 (the large-diameter portion 11), the bearing member 21, the first support member 22, and the second support member 23. The liquid metal LM can use materials such as a GaIn (gallium indium) alloy or a GaInSn (gallium indium tin) alloy. During the rotation of the rotating body 20, the liquid level on the rotation axis a side of the liquid metal LM is located at a position closer to the rotation axis a than the radial bearing surfaces S11a and S11b. Thereby, the exhaustion of the liquid metal LM in the bearing clearance can be suppressed. The liquid metal LM and the bearing surfaces of the fixed shaft 10 and the rotating body 20 together form a hydrodynamic sliding bearing.

[0032] The anode target 50 is formed in an annular shape and is coaxially arranged with the fixed shaft 10 and the bearing member 21. In one example, the anode target 50 is located in a position opposite to the radial bearing surfaces S11a and S11b of the fixed shaft 10 in a direction orthogonal to the rotation axis a. In other words, a part of the radial bearing surfaces S11a and S11b is located in the area A opposite to the anode target 50. The anode target 50 has an anode target body 51 and a target layer 52 provided on a part of the outer surface of the anode target body 51. The anode target body 51 is formed in an annular shape. The anode target body 51 surrounds the outer circumference of the bearing member 21 and is fixed to the bearing member 21.

[0033] The anode target body 51 is formed of molybdenum, tungsten, or an alloy using them. The melting point of the metal forming the target layer 52 is the same as or higher than the melting point of the metal forming the anode target body 51. For example, the anode target body 51 is formed of a molybdenum alloy, and the target layer 52 is formed of a tungsten alloy.

[0034] The anode target 50 can rotate together with the rotating body 20. When electrons collide with the target surface S52 of the target layer 52, a focal point is formed on the target surface S52. Thus, the anode target 50 emits X-rays from the focal point. That is, the anode target 50 receives electrons and generates X-rays. The cathode 60 is spaced apart from the target layer 52 of the anode target 50 and is disposed opposite to the target layer 52. The cathode 60 is mounted on the inner wall of the vacuum tube housing 70. The cathode 60 has a filament 61 as an electron emission source, and the electron emission source emits electrons that irradiate the target layer 52.

[0035] The vacuum tube housing 70 is formed in a cylindrical shape. The vacuum tube housing 70 is formed of glass, ceramic, and metal. In the vacuum tube housing 70, the outer diameter of the portion opposite to the anode target 50 is larger than the outer diameter of the portion opposite to the cylindrical portion 24. The vacuum tube housing 70 has openings 71 and 72. The vacuum tube housing 70 is sealed, houses the anode target 50 and the cathode 60, and fixes the fixed shaft 10. The inside of the vacuum tube housing 70 is maintained in a vacuum state (reduced pressure state).

[0036] In order to maintain the airtight state of the vacuum tube housing 70, the opening 71 is hermetically joined to one end portion (the first small-diameter portion 12) of the fixed shaft 10, and the opening 72 is hermetically joined to the other end portion (the second small-diameter portion 13) of the fixed shaft 10. The vacuum tube housing 70 fixes the first small-diameter portion 12 and the second small-diameter portion 13 of the fixed shaft 10. That is, the first small-diameter portion 12 and the second small-diameter portion 13 function as double-end support portions of the bearing. In addition, Figure 4 The rotating anode type X-ray tube 1 of the illustrated embodiment is configured with a double-end structure in which both ends of the fixed shaft 10 are fixed, but it may also be configured with a cantilever structure in which only one end of the fixed shaft 10 is fixed.

[0037] The stator coil 2 is arranged to face the outer peripheral surface of the rotating body 20, more specifically, the outer peripheral surface of the cylindrical portion 24, and surround the outside of the vacuum tube housing 70. The shape of the stator coil 2 is annular. The stator coil 2 generates a magnetic field applied to the cylindrical portion 24 (rotating body 20), causing the rotating body 20 and the anode target 50 to rotate. As described above, an X-ray tube device including the rotating anode type X-ray tube 1 is formed.

[0038] In the operating state of the above X-ray tube device, since the stator coil 2 generates a magnetic field applied to the rotating body 20 (especially the cylindrical portion 24), the bearing member 21 rotates. As a result, the bearing member 21 and the anode target 50 also rotate together. In addition, a current is applied to the cathode 60 and a negative voltage is applied, while a positive voltage is applied to the anode target 50 relatively. Thereby, a potential difference is generated between the cathode 60 and the anode target 50. The filament 61 emits electrons. These electrons are accelerated and collide with the target surface S52. Thereby, a focal spot is formed on the target surface S52, and X-rays are emitted when the focal spot collides with electrons. The electrons (hot electrons) colliding with the anode target 50 are converted into X-rays, and the rest are converted into heat energy. In addition, the electron emission source of the cathode 60 is not limited to the filament, and for example, it may also be a planar emitter.

[0039] The heat generated by the anode target is transferred from the target surface S52 to the inside of the target layer 52, the anode target body 51, the bearing member 21, the liquid metal LM, and the fixed shaft 10 in sequence. The heat transferred to the fixed shaft 10 is transferred from the heat transfer portion 10a of the fixed shaft 10 to the coolant L and released to the outside of the sliding bearing 3 together with the coolant L.

[0040] When the temperatures of the bearing member 21, the liquid metal LM, and the fixed shaft 10 rise, a chemical reaction occurs between the bearing surfaces (radial bearing surfaces S11a, S11b, S21) and the liquid metal LM. Thereby, a compound is generated on the bearing surface. In addition, the generation rate of the compound of SKD11 and the liquid metal LM is about 0.3 μm / h at 300 °C, and the generation rate of the compound of tungsten carbide and the liquid metal LM is about 0.003 μm / h at 300 °C. That is, when at least one of the fixed shaft 10 and the bearing member 21 is formed of tungsten carbide and the lubricant is a gallium-indium alloy or a gallium-indium-tin alloy, the generation of the compound can be suppressed. In addition, when emphasizing the suppression of the generation of the compound, it is preferable that both the fixed shaft 10 and the bearing member 21 are formed of tungsten carbide.

[0041] In addition, when the temperature of the bearing member 21 rises, it expands in a direction away from the fixed shaft 10, and the gap between the fixed shaft 10 and the bearing member 21 increases. When the gap between the fixed shaft 10 and the bearing member 21 increases, the bearing load decreases, and the risk of vibration and cavitation increases. In addition, the X-ray tube device rotates together with the rotating gantry 84 and is subjected to a centrifugal acceleration CA in a direction orthogonal to the rotation axis a. When the Young's modulus of the fixed shaft 10 is low, the fixed shaft 10 bends and deforms in the same direction as the centrifugal acceleration CA.

[0042] Hereinafter, the effects of the rotating anode type X-ray tube 1 of the above-described embodiment will be described. According to the rotating anode type X-ray tube configured as described above, the rotating anode type X-ray tube 1 includes: a cathode 60; an anode target 50; a sliding bearing 3 having a fixed shaft 10 and a rotating body 20; and a vacuum tube shell 70. The rotating body 20 has a bearing member 21 located at a position surrounding the fixed shaft 10. At least one of the fixed shaft 10 and the bearing member 21 is formed of tungsten carbide, silicon carbide, or titanium carbide. Thereby, when the fixed shaft 10 is formed of tungsten carbide, silicon carbide, or titanium carbide, compared with the case where the fixed shaft 10 is formed of SKD11, bending deformation of the fixed shaft 10 caused by the centrifugal acceleration CA can be suppressed.

[0043] In addition, when the bearing member 21 is formed of tungsten carbide, silicon carbide, or titanium carbide, compared with the case where the bearing member 21 is formed of SKD11, an excessive gap between the fixed shaft 10 and the bearing member 21 can be suppressed. Thereby, the occurrence of vibration and cavitation during rotation of the rotating body 20 can be suppressed. In addition, since more heat can be transferred from the bearing member 21 to the fixed shaft 10, cooling of the rotating anode type X-ray tube 1 can be promoted.

[0044] When the materials of the fixed shaft 10 and the bearing member 21 are the same, since the linear expansion coefficients can be made the same, as long as the temperatures of the fixed shaft 10 and the bearing member 21 are substantially the same, the gap between the fixed shaft 10 and the bearing member 21 can be maintained at a certain size. When at least one of the fixed shaft 10 and the bearing member 21 is formed of tungsten carbide and the lubricant is a gallium-indium alloy or a gallium-indium-tin alloy, generation of compounds can be suppressed. For the above reasons, according to the present embodiment, a rotating anode type X-ray tube capable of maintaining good rotation of the rotating body 20 can be obtained.

[0045] (Modification example) Next, a modification example of the rotating anode type X-ray tube 1 of the above-described embodiment will be described. The rotating anode type X-ray tube 1 is configured in the same manner as the above-described embodiment except for the structure described in this modification example. Figure 6 It is a cross-sectional view showing a modification example of the rotating anode type X-ray tube of the above-described embodiment. As Figure 6As shown, the anode target 50 is located at a position surrounding the rotating body 20 (more specifically, the bearing member 21). The anode target 50 has: an anode target body 51; and a target layer 52 provided on the outer surface of the anode target body 51 and facing the cathode 60. The anode target body 51 is formed of the same material as the bearing member 21 and is continuously formed integrally therewith. In other words, the anode target body 51 and the bearing member 21 are not joined. The integral body of the bearing member 21 and the anode target body 51 can be manufactured by methods such as casting or cutting. According to a modification of the rotating anode type X-ray tube 1 of the above-described embodiment configured as described above, the anode target body 51 is integrally formed with the bearing member 21. Thus, compared with the case where the anode target body 51 and the bearing member 21 are joined, more heat generated by the anode target 50 can be transferred to the fixed shaft 10.

[0046] The embodiments of the present invention have been described above, but the above embodiments are merely examples and do not represent a limitation of the scope of the invention. The above new embodiments can also be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope or gist of the invention and are included in the invention described in the claims and the scope equivalent thereto.

Claims

1. A rotating anode type X-ray tube, characterized in that, Comprising: A cathode (60) that emits electrons; An anode target (50) that receives the electrons to generate X-rays; A sliding bearing (3) having a rotating body (20), a fixed shaft (10), and a lubricant, wherein the rotating body (20) is connected to the anode target (50) and extends along a rotation axis (a), the fixed shaft supports the rotating body (20) so as to be rotatable, and the lubricant is held between the rotating body (20) and the fixed shaft (10); and A vacuum tube housing (70) that houses the cathode (60) and the anode target (50) and fixes the fixed shaft (10), The rotating body (20) has a bearing member (21) formed to extend along the rotation axis (a) and located at a position surrounding the fixed shaft (10), At least one of the fixed shaft (10) and the bearing member (21) is formed of tungsten carbide, silicon carbide, or titanium carbide.

2. The rotating anode type X-ray tube according to claim 1, wherein The anode target (50) is located at a position surrounding the bearing member (21), has an anode target body (51), and a target layer (52) provided on an outer surface of the anode target body (51) and facing the cathode (60), The anode target body (51) is formed of the same material as the bearing member (21) and is continuously formed integrally with the bearing member (21).

3. The rotating anode type X-ray tube according to claim 1, wherein The material of the fixed shaft is the same as the material of the bearing member.

4. The rotating anode type X-ray tube according to claim 3, wherein The anode target (50) is located at a position surrounding the bearing member (21), has an anode target body (51), and a target layer (52) provided on an outer surface of the anode target body (51) and facing the cathode (60), The anode target body (51) is formed of the same material as the bearing member (21) and is continuously formed integrally with the bearing member (21).

5. The rotating anode type X-ray tube according to claim 1, wherein The lubricant is a gallium-indium alloy or a gallium-indium-tin alloy.

6. The rotating anode type X-ray tube according to claim 5, wherein The anode target (50) is located at a position surrounding the bearing member (21), has an anode target body (51), and a target layer (52) provided on an outer surface of the anode target body (51) and facing the cathode (60), The anode target body (51) is formed of the same material as the bearing member (21) and is continuously formed integrally with the bearing member (21).

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