JPH04212247A - Lublicated bearing holder for x-ray tube - Google Patents

Abstract

PURPOSE: To reduce friction between a holder and a stem and prevent friction of bearing parts by holding one of bearings supporting a rotary shaft by a bearing holder that smoothly moves inside of an anode stem and providing a solid lubricant layer on an outside smooth movement face. CONSTITUTION: A rotary shaft 12 is surrounded by a tubular anode stem 20, a front bearing holder 30 is fixed at a front end of the stem 20, and an outer lace of the front bearing 26 is held. On the other hand, a rear bearing holder 16 is lubricantly provided at a rear end of the stem 20, and an outer lace of the rear bearing 28 is held. Therefore, the holder 16 coaxially moves inside of the stem 20 smoothly and absorbs an axial play of the bearings 26 and 28. A thin solid lubricant layer is covered on an outer face of the holder 16, and thereby friction between the holder 16 and the stem 20 is reduced. Thereby, friction between the holder 16 and the stem 20 is reduced, and friction of bearing parts due to frictional powder is prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION This invention relates to x-ray tubes having rotating anodes, and more particularly to bearing retainers for supporting bearings used in x-ray tubes.

One of the main components of conventional X-ray imaging devices and computed tomography (CT) devices is an X-ray tube for supplying X-rays. Such an X-ray tube is 10-
It has a vacuum level of 8 to 10-9 Torr and operates by accelerating a stream of electrons emitted from a heated cathode with a high voltage to collide with a target anode. The conversion efficiency of such x-ray tubes is low and therefore a large amount of heat is generated in the anode as a by-product of x-ray generation. The anode was rotated at 10,000 rpm to reduce the heat concentration in the anode.
By rotating at a speed of up to , a new cold surface is constantly directed toward the cathode. In high-performance X-ray tubes, the surface temperature of the anode can reach as high as 3200°C.
Also, the temperature of the anode region located outside the immediate target surface can rise to about 1300°C.

Much of the heat generated at the anode is radiated from the anode coating, which has a high thermal emissivity, through the glass wall of the bulb. However, the temperature of the anode shaft and bearings that support the rotating anode can reach a maximum of 450°C. It goes without saying that the anode shaft and bearing are housed inside the evacuated tube of the X-ray tube.

[0004] In order to extend the life of the bearing, it is known to preload the bearing supporting the anode shaft. Usually,
While the front bearing is fixed relative to the anode stem, the outer race of the rear bearing is held in a bearing retainer that is axially slidable within the hollow anode stem. Note that the inner race of the rear bearing is fixed to the anode shaft. As a result of the bearing retainer being able to slide along the axial direction, the bearing is not constrained even if the anode shaft expands as the temperature of the X-ray tube increases. Both bearings are preloaded by the preload spring exerting an axial force on the bearing retainer for the rear bearing. Such preload improves the motion of the balls sandwiched between the inner and outer races of the front and rear bearings, thereby extending bearing life and reducing noise.

[0005] The combined effects of high rotational speeds, high operating temperatures and vacuum environments place severe requirements on anode support bearings. As a result, bearing failure constitutes a major factor limiting the lifespan of x-ray tubes. Such failures may result from bearing "welding" (ie, the rolling parts of the bearing seize inside the race) or from increased bearing noise. In the latter case, the x-ray tube may need to be replaced despite otherwise proper operation.

[0006] Because bearing retainers and anode stems are exposed to extremely high operating temperatures and high vacuum environments, conventional organic lubricants cannot be used in such applications.

[0007]

SUMMARY OF THE INVENTION To prevent excessive radial play of the anode shaft, a sliding bearing retainer holding the rear bearing is tightly fitted within the guiding anode stem. As mentioned above, the bearing retainer is designed to allow expansion of the anode shaft as the temperature of the x-ray tube increases. Previously, it was thought that lubricating the bearing retainer was unnecessary because such movements did not occur frequently. However, it is now known that various movements of the bearing retainer during normal operation of the x-ray tube (e.g., direct impact on the anode stem wall, which can produce bearing "rattling" noises) can cause considerable wear and tear. It is thought to generate particles. Such wear particles will contaminate the bearing, thereby increasing bearing noise and wear.

In the present invention, one of the bearings supporting the rotating anode shaft of the X-ray tube is held in a bearing retainer that slides inside the hollow anode stem. The external sliding surfaces of such bearing cages are coated with a thin layer of solid lubricant. This lubricant layer provides a surface that reduces wear and suppresses the generation of wear particles between the sliding bearing retainer and the inner surface of the anode stem.

The main object of the invention is thus to reduce the wear between the sliding bearing retainer and the support-like anode stem, and thus to reduce the wear of the bearing parts caused by the generation of particles in the bearing system. X that reduces
The object of the present invention is to provide a lubrication means suitable for use in a wire tube environment.

Furthermore, it has been found that bearing failures can result from adhesive migration between the bearing retainer and the anode stem. The lubricant layer as described above is
It also helps to reduce adhesive wear between the sliding surfaces of the bearing retainer and anode stem. Such wear can increase the friction between the sliding surfaces of the bearing retainer and the anode stem, or conversely can increase the radial play of the bearing retainer within the anode stem.

[0011] Thus, another object of the present invention is to prevent changes in the sliding characteristics of the bearing retainer within the anode stem from adversely affecting the life of the bearing.

The bearing sleeve of the bearing retainer includes a flange that can be deformed by swaging to surround the bearing to securely hold the outer race of the bearing relative to the bearing retainer. To prevent unnecessary flaking of lubricant particles during swaging operations, such flanges are not lubricated.

[0013] Thus, another object of the present invention is to reduce the introduction of particles into the bearing assembly.

These and other objects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, which form a part of this specification. BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention are illustrated in the accompanying drawings. It should be noted that such embodiments do not necessarily represent the entire scope of the present invention, and the scope of the present invention should be understood to be solely defined by the scope of the claims.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning first to FIG. 1, an anode support structure for an x-ray tube is shown. As a result of the front end of the anode shaft 12 being fixed to the center of the disc-shaped anode 10, the anode 1
0 rotates as the anode shaft 12 rotates. The rear end of the anode shaft 12 is housed within a collar 25 that supports a copper rotor sleeve 24 as described below. Anode shaft 1
The rotating shaft 13 extends rearward from the collar 25 in alignment with the collar 2.

The front end of the rotating shaft 13 is supported by a front bearing 26, the inner race 46 of which is supported by the rotor sleeve 2.
4 and the front surface of the front lip 15 of the rotating shaft 13. On the other hand, the rear end of the rotating shaft 13 is supported by a rear bearing 28, of which the inner race 4
6 is captured between the rear face of a rear lip 17 provided at the rear of the rotary shaft 13 and the front face of a rear support nut 29 screwed onto the rear end of the rotary shaft 13.

The rotating shaft 13 is a tubular anode stem 2 made of copper alloy.
Surrounded by 0. A front bearing retainer 30 is secured to the front end of the anode stem 20, which coaxially retains the outer race 50 of the front bearing 26 within the anode stem 20. On the other hand, a rear bearing retainer 16 is slidably fitted within the rear end of the anode stem 20 and retains the outer race 50 of the rear bearing 28 coaxially within the anode stem 20.

In the anode stem 20, a preload spring 18 made of molybdenum coaxially surrounds the rotating shaft 13, so that the front bearing retainer 30 and the rear bearing retainer 16
is subjected to a force acting outward along the axial direction. Under the effect of such preload, the rear bearing retainer 16
coaxially sliding therein, thereby absorbing axial play between the inner and outer races of the front bearing 26 and the rear bearing 28.

Next, referring to FIG. 2, a keyway 38 is provided on the outer surface of the rear bearing retainer 16 along the axial direction. By engaging the locking screw 22 with the keyway 38 as shown in FIG.
is prevented from rotating relative to the anode stem 20.

Referring again to FIG. 1, the front bearing 2
6, the front bearing retainer 30 and the front of the anode stem 20 are coaxially surrounded by a copper tubular rotor sleeve 24. As mentioned above, the rotor sleeve 24 has a collar 2.
5 to the anode shaft 12 and the rotating shaft 13, so that it rotates together with the anode 10. Copper rotor sleeve 24 serves as the armature of an induction motor (not shown) that torques and rotates anode shaft 12 during operation of the x-ray tube.

The anode assembly as described above is housed inside a glass tube 14 whose pressure is reduced to, for example, 10 -9 Torr. A cathode (not shown) is disposed inside the glass bulb 14 facing in front of the anode 10 . Such a cathode serves to emit a stream of high energy electrons towards the front of the rotating anode 10, as is known in the art.

Referring now to FIGS. 2 and 3, aft bearing retainer 16 includes a cylindrical retainer base 34 made of 304LSS stainless steel. 304LSS
Stainless steel consists of 18% Cr, 8% Ni, up to 1% Si, 1% Mn, up to 0.08% C, and the balance Fe, expressed in weight percentages. The bearing retainer 16 has an outer diameter tolerance of 0.0005.
Machined to measure inches.

The outer surface of the cage base 34 has an X shape as described above.
Thickness 3-7μm suitable for use in line tube environment
coated with a solid lubricant layer. Suitable solid lubricants include metals such as lead and silver, tungsten disulfide (W
These include disulfides and diselenides such as tungsten diselenide (WSe2) and tungsten diselenide (WSe2), diamond and diamond-like carbon (DLC), and similar materials known in the art. These lubricants can be placed on the bearing retainer by various methods also known in the art. Useful methods include physical vapor deposition, especially plasma enhanced physical vapor deposition (PEPVD).
, as well as chemical vapor deposition, especially plasma enhanced chemical vapor deposition (
PECVD method).

The bearing retainer 16 has an inner surface 132 formed by drilling in the axial direction.
The rear part of the bearing 28 is provided with a sill that matches the outer diameter of the rear bearing 28. As a result, the bearing sleeve 3 for receiving the outer race 50 of the rear bearing 28 as shown in FIG.
6 and a radial bearing stop surface 42 are formed.

Referring again to FIG. 3, the rear end 130 of the bearing sleeve 36 has a reduced outer diameter thereby forming a flange 44. the result,
When the bearing retainer 16 is installed within the x-ray tube, the flange 44 does not contact the anode stem 20. In addition, flange 4
The outer surface of No. 4 is not coated with lubricant.

Referring to FIG. 4, after the rear bearing 28 is inserted into the bearing sleeve 36 along the axial direction, the flange 44 is deformed by swaging so as to surround the rear surface of the outer race 50 of the rear bearing 28. It will be done. As a result, the outer race 50 will be captured between the front face of the flange 44 and the bearing stop surface 42.

Although preferred embodiments of the present invention have been described above, it will be obvious to those skilled in the art that many modifications can be made without departing from the scope of the invention. For example, a slidable bearing retainer can be used for the front bearing as well as the rear bearing, or a slidable bearing retainer can be used only for the front bearing.

[Brief explanation of the drawing]

1 is a partial view of an X-ray tube showing, in partial cross-section, an anode support structure including a bearing retainer according to the invention; FIG.

FIG. 2 is an end view of the rear bearing retainer used in the X-ray tube of FIG. 1, showing the installation of a solid lubricant layer.

3 is a cross-sectional view of the rear bearing retainer of FIG. 2 taken along line 3-3 in FIG. 2;

4 is a cross-sectional view of the rear bearing retainer of FIG. 3 after the bearing has been placed in the rear bearing retainer and the flange has been deformed; FIG.

[Explanation of symbols]

10 Anode 12 Anode axis 13 Rotation axis 14 Glass tube 16 Rear bearing retainer 18 Preload spring 20 Anode stem 24 Rotor sleeve 25 Brim 26 Front bearing 28 Rear bearing 30 Front bearing retainer 34 Cage base 36 Bearing sleeve 40 Solid lubricant layer 44 Flange 46 inner race 50 outside race

Claims (6)

[Claims] 1. A hollow anode stem for use in an In the bearing cage, (a
(b) a cage base coaxially and slidably fitted within the anode stem; a bearing sleeve fixed to, and (c
) A bearing retainer, characterized in that it comprises elements of a solid lubricant applied on the outer surface of the retainer base to facilitate sliding of the bearing retainer. 2. The bearing retainer of claim 1, wherein said solid lubricant is selected from the group consisting of silver and lead. 3. The bearing retainer according to claim 1, wherein the solid lubricant is a metal disulfide. 4. The bearing retainer according to claim 1, wherein the solid lubricant is a metal diselenide. 5. The bearing retainer according to claim 1, wherein the solid lubricant is diamond-like carbon. 6. The bearing retainer according to claim 1, wherein the solid lubricant is diamond.