JPH0372177B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a rotating anode type X-ray tube that increases X-ray output at ultra-high speed rotation. [Technical background of the invention and its problems] In general, a rotating anode X-ray tube has an anode target mounted on a cylindrical (rotor) support column that is rotatably supported by at least one ball bearing provided at a predetermined interval. is fixed, and the anode target is rotated at a high speed of, for example, 9000 revolutions per minute. The ball bearing not only enables this high-speed rotation, but also functions as a path for the anode current. For this reason, conventional ball bearings generally consist of a metal inner ring, outer ring, and a large number of balls.In order to suppress wear between these balls, conductive materials such as Pb and Ag are coated on the surfaces of the balls. A solid lubricant is attached. During X-ray tube operation, the ball bearings reach a high temperature of several hundred degrees Celsius due to conduction heat from the anode target, and since this is in a vacuum, the lubricant in the ball bearings evaporates in a relatively short period of time. There is a risk of deterioration of rotational performance. Of the pair of ball bearings, the one that is closer to the anode target in terms of thermal path tends to be about 100°C or more hotter than the one that is farther away. When a ball bearing reaches a high temperature of 500°C or higher, during high-speed rotation, the frictional heat between the balls and the inner and outer rings or between the balls and other balls that make up the ball bearing is superimposed, causing the surface temperature of the balls to become extremely high. The solid lubricant adhering to the surface of the anode target runs out in a relatively short period of time, making it easy for an accident in which the anode target stops due to so-called lubrication failure. Furthermore, even when the temperature is relatively low, the thin film of solid lubricant attached to the balls or the inner and outer rings may peel off or be pushed to areas other than the rolling surfaces of the balls due to the load applied to the ball bearings. Similar problems often occurred. In particular, when rotating at high speeds of 20,000 rpm or more, the service life was generally extremely short due to the above-mentioned problems. In general, to prevent such inconveniences, measures are taken such as minimizing the input to the anode target to suppress the rise in ball bearing temperature, or limiting the rotation speed of the anode target to a low value. The reality is that it is true. [Object of the Invention] An object of the present invention is to provide a rotating anode type X-ray tube having an extremely long-life rotating mechanism in which ball bearings exhibit almost no deterioration in high-speed rotation performance even at high temperatures. [Summary of the Invention] The present invention provides a rotating anode type X-ray tube in which a lubricant supply ball made of a self-lubricating sliding material and a load receiving ball made of metal or ceramic or both are mixed as balls of a ball bearing. It is. [Embodiments of the Invention] The rotating anode type X-ray tube of the present invention is shown in FIGS. 1 to 4.
It is constructed as shown in the figure, and includes an eccentric cathode 3 and a rotatable substantially umbrella-shaped anode target 4 in a vacuum envelope 1.
are arranged facing each other at a predetermined interval. The anode target 4 is fixed to a support column 5, and the support column 5 coaxially and integrally protrudes from one end (lid portion) of a covered cylinder (rotor) 6. A rotating shaft 8 is fixed coaxially to the inside of this cylinder 6. In this case, a disk 8a is integrally formed at one end of the rotating shaft 8, and this disk 8a is fixed to the inner surface of the lid portion of the cylinder 6. Further, a stator 10 in the shape of a cylinder with a bottom is inserted between the rotary shaft 8 and the cylinder 6, and the stator 10 is connected to the vacuum envelope 1 through sealing rings 12 and 11. is fixed. A pair of ball bearings 13 and 14 , which will be described later, are arranged between the stator 10 and the rotating shaft 8. Further, in order to keep the distance between the inner rings of each ball bearing 13 , 14 constant, a rotating shaft sleeve 15 is provided on the outer periphery of the rotating shaft 8. or,
A stator sleeve 16 is provided while pressing the outer ring of the ball bearing 13 on the anode target 4 side against the stator 10. This stator sleeve 1
Two steps are provided on the ball bearing 14 side of 6, and a movable sleeve 17 having an L-shaped cross section is disposed between one step and the ball bearing 14 . A spring 18 is provided between one end of the letter and the other step. This spring 18 is connected to the sleeve 1
This is to apply pressure to spread the ball bearings 6 and 17 in opposite directions, and to apply thrust preload to both ball bearings 13 and 14 from the outer rings. Here, the ball bearings 13 and 14 will be explained .
is constructed as shown in FIGS. 2 and 3 and is of an angular contact type. That is, each ball bearing 13 , 14 consists of an outer ring 22, an inner ring 23, and two types of balls 24, 25 interposed between the outer rings 23, 22 in large numbers and alternately arranged. The inner and outer rings 23 and 22 are both made of metal such as high-speed steel.
Further, one ball 24 is for receiving a load,
Made of metal, such as high-speed steel, or wear-resistant ceramic. This ceramic is selected from among alumina (Al ₂ O ₃ ), silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), or cermet, and formed into a spherical shape. A solid lubricant such as Pb, Ag, molybdenum sulfide (MoS ₂ ), or an alloy thereof is further adhered to the surface of the ball 24 . Another ball 25 is disposed between these load receiving balls 24, and this ball 25 is for supplying lubricant, and has a diameter slightly smaller than the load receiving balls 24, and Made of self-lubricating sliding material. Molybdenum sulfide, such as MoS ₂ alloy, is particularly suitable as the self-lubricating sliding material. For example, MoS ₂ 30%, WS ₂ 30%, Ta 20%, Cu
A MoS ₂ alloy containing 20% has a friction coefficient of 0.13 in a vacuum at 800°C and a compressive strength of 27 Kg/mm ² or more. Also, the friction coefficient is 0.1 from 0℃ to 800℃.
It only changes from 0.13 to 0.13. in this way,
A self-lubricating sliding material is a material that adheres to surrounding bearing components and performs a lubricating function as it wears out very gradually. In addition, outer ring 2
2, a preload F is applied via the sleeve 16. Further, the space between the ball bearing 13 on the side of the anode target 4 and the disc 8a of the rotating shaft 8 is as shown in FIG. 4 when shown in detail in an enlarged manner. That is, a ring 19 is disposed on the anode target 4 side in contact with the outer ring 22 of the ball bearing 13 . This ring 19 is used to fix the outer ring 22 of the bearing 13 and to prevent fine powder generated by the bearing 13 from coming out of the cylinder 6. The ring 19 has a substantially S-shaped cross section and the outer periphery of the sleeve 16 ( Or it is fixed to the stator 10). One end contacts the outer ring 22 of the bearing 13 , and the inner periphery 26 faces the sleeve 21 inserted into the outer periphery of the rotating shaft 8 with a wide surface, forming a small gap passage 27. This small gap passage 27 is as small as possible (preferably 0.1
mm) is set. Between this ring 19, the stator 10, and the disk 8a of the rotating shaft 8, a dustproof ring 20 has a substantially U-shaped cross section, and one end is in contact with the sleeve 21 and fixed to the rotating shaft 8, and the other end is in contact with the sleeve 21 and fixed to the rotating shaft 8. The free end faces the outer surface of the ring 19 with a small gap (preferably 0.1 mm) 29 therebetween. Therefore,
The free end of the ring 19, that is, one end 28 of the small gap passage 27 is located inside the dustproof ring 20. The dustproof ring 20 rotates together with the rotating shaft 8 during operation, and is used to press the fine powder that has passed through the small gap passage 27 against its inner wall 30 by centrifugal force and prevent it from coming out of the cylinder 6. be. In addition, in order to fix the inner ring 23 of the ball bearing 13 to the rotating shaft 8 together with the dustproof ring 20,
A sleeve 21 is inserted around the outer periphery of the rotating shaft 8. A stator 7 is disposed outside the vacuum envelope 1 in correspondence with the cylinder 6, and during operation drives the cylinder 6 and the rotating shaft 8 to rotate the anode target 4. The rotating anode X-ray tube configured as described above is
In its operation, high-speed rotation performance can be maintained extremely stably for a long period of time. That is, the ball 2 that receives the load
4, as mentioned above, does not lose strength even when using hard metals such as high-speed steel or at high temperatures of 800 to 1000 degrees Celsius.
They are made of ceramics such as Si ₃ N ₄ and have solid lubricants such as Pb, Ag, and MoS ₂ attached to their surfaces. and MoS ₂ (molybdenum disulfide)
In this case, the ball 24 or the inner ring 23, the outer ring 22
It is effective to form a spatter film on the surface. These solid lubricants serve to provide sufficient lubrication to ball bearings in their initial state. These pre-attached thin film solid lubricants either become high temperature and evaporate due to frictional heat during high-speed rotation or conductive heat from the anode target 4, or are moved to other parts due to pressure. The lubricating effect will be lost in a relatively short period of time. However, in the rotary anode type X-ray tube of the present invention, the lubricant supply ball 25 made of a self-lubricating sliding material
is provided between the load-receiving balls 24, and due to friction between these balls 24 and 25, a portion of the self-lubricating sliding material is applied to the surface of the load-receiving balls 24 and the rolling surfaces of the inner and outer rings. Transferred to 1μm
Forms the following thin and highly adhesive film.
Since the films that are strongly transferred to the mating surface slide against each other, the coefficient of friction is lowered and a good lubrication effect is exhibited. In addition, since the lubricant supply ball 25 made of a self-lubricating sliding material has a small coefficient of friction with the transferred film, it has good wear resistance despite being made of a relatively soft material and can operate for a long time. can withstand. When the transfer film reaches a certain lifespan, it falls off and becomes abrasion powder, but a new film is immediately supplied from the lubricant supply ball 25 made of a self-lubricating sliding material, so a good lubrication effect is constantly obtained. be able to. The above-mentioned fallen wear powder is removed from the ball bearing 1 .
A ring 19, a dustproof ring 20, and a sleeve 21 provided on the target side of the cylinder 3 prevent the particles from scattering outside the cylinder 6. Since the small gap passage 27 is narrow and long, this small gap passage 2
The amount of wear powder that escapes from 7 is extremely small. A small amount of wear powder that escaped from this small gap passage 27 is removed from the opening end 2.
At 8, the dust particles are blown away in the radial direction by centrifugal force due to the high speed rotation of the shaft, and adhere to the inner wall 30 of the rotating dustproof ring 20. In addition, since the opening of the retention space, that is, the small gap 29, is sufficiently small, the amount of fine particles going out to the outside of the cylinder 6 can be sufficiently reduced, and problems such as poor withstand voltage of the rotating anode type X-ray tube will not occur. do not. [Effects of the Invention] According to the present invention, a sufficiently small coefficient of friction can always be maintained in vacuum and at high temperatures.
Moreover, since the self-lubricating material itself has wear resistance,
The lubricating properties can be kept constant even during extremely long periods of operation. Therefore, it is possible to provide a long-life rotating anode type X-ray tube that has stable rotational characteristics. Also, when performing ultra high speed rotation,
Since no collision occurs between the load receiving balls 24,
Since the balls 24 rotate regularly and the coefficient of friction between the inner ring 23, the outer ring 22 and the balls 24 is always kept small, noise and vibration can be suppressed. In this case as well, since the lubricant is automatically supplied, it goes without saying that the service life will be dramatically extended. This means that in an X-ray tube with a long microfocus,
In order to suppress the temperature rise at the point on the anode target 4 where the electrons are incident, the
This means that it is possible to provide a rotating anode type X-ray tube that rotates the anode target 4 at 30,000 rpm or more.
And compared to the previous case of 10000 rpm rotation, √3
Since the input can be doubled, it is possible to maintain a sufficient amount of X-ray output, which was previously insufficient with ultra-fine focusing tubes. This means that while conventional X-ray tubes can only image objects that are small and have a small X-ray absorption coefficient, such as breasts, other parts of the human body can be imaged with high resolution. This means that it has revolutionary meaning in terms of diagnostics. Furthermore, if the load receiving balls 24 of the ball bearing 13 , which are close to the anode target 4 in terms of thermal path, are made of ceramic such as Si ₃ N ₄ as described above, the temperature of the ball bearing 13 will rise to ~1000°C. No change in hardness occurs. Furthermore, if MOS ₂ alloy is used for the lubricant supply ball 25, the lubricating properties will not deteriorate up to 850℃, so the temperature of the ball bearing 13 , which conventionally operates at around 400℃, can be raised to, for example, 600℃. It becomes like this. In other words, a large amount of heat is allowed to flow from the anode target 4 to the ball bearing 13 , providing the following two advantages. One of them is to set the operating temperature of the anode target 4, for example.
300℃, which means that the heat radiation from the anode target 4 to the outside can be increased by (1300/1000) ⁴ = 2.86 times, making it possible to provide a rotating anode X-ray tube with a high cooling rate. can. Another advantage is that the thermal path between the anode target 4 and the ball bearing 13 can be shortened, and an extremely compact rotating anode X-ray tube can be provided. In addition, the load receiving ball 2 of the ball bearing 13
4 is made of ceramic, the load receiving bearing 24 of the ball bearing 14, which is farther away from the anode target 4 in terms of thermal path, is made of a metal such as high-speed steel than expected for electrical conduction by the lubricant supply ball 25 . It is preferable for the current to be stably supplied to the anode target 4. The ball bearing is preferably of the angular contact type as in the above embodiment (FIGS. 2 and 3), but may be of the deep groove type as shown in FIGS. 5 and 6. In this case, it is preferable to provide notches 31 and 32 in the inner ring 23 and outer ring 22, or one of them, as shown in the figure, and insert the balls 24 through the notches 31 and 32. Further, in the above embodiment, the load receiving balls 24 and the lubricant supply balls 25 made of self-lubricating material are installed alternately, but this is not necessarily necessary, and at least one lubricating ball 25 made of self-lubricating material is installed alternately. A similar effect can be obtained if the material supply ball 25 is attached. Further, in the above embodiment, the diameter of the lubricant supply ball 25 is made smaller than the diameter of the load receiving ball 24, but the same effect can be expected even if this is not necessarily the case. Further, in the above embodiment, a thrust preload is applied to the outer ring 22 of the ball bearing 13 by the spring 18, but it goes without saying that a structure in which the preload is applied from the inner ring 23 may also be used. Furthermore, it is also possible to apply no preload. Since the operating temperature of the ball bearing 14 , which is thermally distant from the target 4, is low, conventionally used metal lubricants (such as Pb,
Ball bearings coated with Ag) may also be used. Further, in the above embodiment, the dustproof ring 20 and the ring 19 are used to prevent wear particles from coming out of the cylinder 6, but these have the same effect between the cylinder 6 and the stator 10. It may be modified as follows.
If a particularly long life is not expected, all or part of these can be omitted. A similar effect can be obtained by forming a maze of these dustproof rings as shown at 33 and 34 in FIG. 7. Further, the lubricant supply ball 25 made of the self-lubricating sliding material described above does not necessarily have a spherical shape, but even if it has corners, or even if it is a ball with poor sphericity, the same effect can be produced.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a rotating anode type X-ray tube according to an embodiment of the present invention, FIG. 2 is a plan view showing an enlarged main part of FIG. 1, and FIG. - A longitudinal cross-sectional view taken along the line A' and seen in the direction of the arrow;
FIG. 6 is a plan view showing another embodiment of the present invention, FIG. 6 is a sectional view taken along the line B-B' in FIG. 5 and viewed in the direction of the arrow, and FIG. FIG. DESCRIPTION OF SYMBOLS 1... Vacuum enclosure, 3... Cathode, 4... Anode target, 5... Support column, 6... Cylinder (rotor), 7... Stator, 8... Rotating shaft, 10...
Stator, 13 , 14 ...Ball bearing, 15
... Sleeve for rotating shaft, 16 ... Sleeve for stator, 17 ... Movable sleeve, 18 ... Spring, 19 ... Ring, 20 ... Dust-proof ring, 21
... Sleeve, 22 ... Outer ring, 23 ... Inner ring, 2
4...Load receiving ball, 25...For lubricant supply,
27...Small gap passage, 29...Small gap.

Claims (1)

[Claims] 1. A rotating part connected to an anode target, a fixed part disposed coaxially with the rotating part, and a ball bearing interposed between the rotating part and the fixed part. In the rotating anode type X-ray tube, the ball bearing is characterized by a mixture of lubricant supply balls made of a self-lubricating sliding material and load receiving balls made of ceramic or metal or both. Rotating anode type
wire tube. 2. The rotary anode X-ray tube according to claim 1, wherein the ball bearing has lubricant supply balls and load receiving balls arranged alternately. 3. The rotating anode X-ray tube according to claim 1, wherein the ball bearing is configured such that the diameter of the lubricant supply ball is smaller than the diameter of the load receiving ball. 4 Balls for supplying lubricant to ball bearings are
The rotating anode type X-ray tube according to claim 1, which is a molybdenum sulfide alloy. 5. A pair of rings 19, 20, 33, 34, which form a booth passage for preventing lubricant scattering, are fixed to the rotating part and the fixed part in the vicinity of the ball bearing. Rotating anode type X-ray tube. 6. The rotating anode X-ray tube according to claim 5, wherein the ring 20 fixed to the rotating part has a U-shaped half-section forming an annular retention space.