JPS5971241A - Rotary anode x-ray tube - Google Patents

Abstract

PURPOSE:To obtain excellent rotating characteristics and improve a rotating life by inserting a sleeve with low thermal conductivity and low coefficient of friction into a rotor, rotatably supporting it on a stationary shaft through ball bearings on both ends of the sleeve, and further fitting a spring pre-loading an outer ring of a ball bearing to the rotor end. CONSTITUTION:A sleeve 9 made of a material with low thermal conductivity and low coefficient of friction is inserted into a rotor 2, ball bearings 3, 4 are coupled with both ends of a stationary shaft 7 fixed to a vacuum housing through a inner rings respectively, and the outer rings of the ball bearings 3, 4 are inserted inside the sleeve 9. In addition, the sleeve 9 is pressed by a snap ring 6, which is fixed to the rotor 2 with a screw 8. A Belleville spring 5 is fitted between the snap ring 6 and ball bearing 4, the Belleville spring is compressed and the compression load is applied to the outer ring of the ball bearing 4 so as to maintain the gap between the ball bearings 3, 4 at zero at all times.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotating anode X-ray tube that has a lower bearing temperature and a bearing outer ring that is axially preloaded by a spring to extend its rotational life.

In a rotating anode X-ray tube, the target temperature is over 1,000°C, and the temperature of the rotor that rotates it is also 600"C.
Conventionally, ball bearings that support rotating systems such as targets and rotors are used to reduce heat generated in the radial direction between the outer ring, which is heated to a high temperature by heat conduction from the rotor, and the relatively low-temperature inner ring. It has not been possible to prevent short life due to the effects of expansion differences and axial thermal expansion differences between the rotor and the low-temperature fixed shaft that supports the inner ring. This is because if the clearance in the bearing increases, vibration will occur as the bearing rotates, and the shock caused by the vibration will raise the temperature to a high temperature, damaging materials with reduced fatigue strength. In the past, there were few rotating anode X-ray tubes in which the entire tube became unusable due to the bearing becoming defective (its rotational life had ended) even though the parts other than the bearing were in good condition for use. There wasn't.

An object of the present invention is to provide a rotating anode X-ray tube with a long rotational life.

In order to achieve the above object, in the present invention, a sleeve made of a material with low thermal conductivity and a low coefficient of friction is fitted inside the rotor, and an outer ring is fitted at both ends of the sleeve so as to be able to freely slide against the inner surface of the sleeve. The rotating part is rotatably supported by a fixed shaft fixed to the vacuum envelope via a ball bearing, and a spring is attached to the end of the rotor to always press the ball bearing outer ring with an appropriate pressure in the axial direction. Because the sleeve has low thermal conductivity,
Conventionally, the rise in temperature of the ball bearing outer ring, which has become hot, is suppressed by heat conduction from the highly heated rotor.

Therefore, no abnormally large difference in radial thermal expansion occurs between the inner and outer rings of the ball bearing. Furthermore, since the ball bearing outer ring is always properly pressed down by the spring, even if there is a difference in axial thermal expansion between the rotor and the fixed shaft, the clearance between the ball bearings will not become abnormally large. After all, the gap between the ball bearings is maintained by the spring even when the rotor is at a high temperature, so the gap is always maintained at zero and rotational vibrations do not occur. For example, boron nitride may be used as the sleeve material with low thermal conductivity and low coefficient of friction.

FIG. 1 is a sectional view of a main part of an embodiment of the present invention.

The target 1 is fixed to a rotor 2 via a support 1a, and a sleeve 9 is fitted inside the rotor 2. Ball bearings 3.4 are fitted to both ends of a fixed shaft 7 fixed to a vacuum envelope (not shown) via inner rings, respectively.
The outer ring of the ball bearing 3.4 is fitted inside the sleeve 9. The sleeve 9 is held down by a bearing valve valve 6, and the bearing valve valve 6 is fixed to the rotor 2 with a screw 8. Bearing valve plate 6
A disc spring 5 is installed between the ball bearing 4 and the disc spring 5, and the disc spring 5 is compressed, and the compressive load acts on the outer ring of the ball bearing 4, so that the gap between the ball bearings 3 and 4 is always zero. (Although not shown, a lubricant film is interposed between the nine balls of the inner and outer rings).

When target 1 is irradiated with an electron beam to generate X-rays, only a few percent of the energy is converted into X-ray energy, and the rest is all heat, increasing the temperature of the target, and this temperature is 1. ,000C or more. Although this heat is radiated to the outside from the target 1, a part of it is conducted to the rotor 2 via the support column 1a, so that the temperature of the rotor 2 also reaches around 6000. Even if heat-resistant steel is used as the material for the ball bearing 3.4, the upper limit of its operating temperature is about 500C.

Since the rotor 2 and the fixed shaft 7 have different temperatures and are made of different materials, their axial thermal expansions also differ. For this reason, if ball bearings 3 and 4
The inner and outer rings of shaft 7. If it were fixed to the rotor 2, the relative positions of the inner and outer rings would shift and the clearance between the ball bearings would fluctuate. If the sleeve 9 is not inserted and the ball bearing 3
．． If the outer ring of No. 4 were in direct contact with the inner surface of the rotor, a large temperature difference would occur between the inner and outer rings of the bearing as described above, and therefore a large difference in thermal expansion would also occur in the radial direction, increasing the gap between the ball bearings. The ball bearing 3.4 must always have a clearance greater than O in order for it to rotate, so it is necessary to set the bearing dimensions taking into account temperature differences and fluctuations in the clearance.
The maximum value of the clearance of a ball bearing that corresponds to a temperature range exceeding 0C is very large, and therefore rotational vibration is also large, which adversely affects the performance of the rotating anode and the life of one rotation.

To prevent this, vibrations are reduced and smooth rotation is achieved by applying an appropriate load to the ball bearings 3 and 4 in the axial direction and rotating the inner and outer rings while keeping them in contact with each other through a lubricant film.

This is the effect of spring 5. In the embodiment of the present invention, the ball bearing 3
, 4 and a low thermal conductivity sleeve 9 between the outer ring and the rotor 2.
Because of this, the temperature of the outer ring of the bearing is significantly lower than in the past, and the difference in thermal expansion in the radial direction between the inner and outer rings is reduced. Furthermore, if the temperature of the outer ring decreases, its material strength will also improve. Further, since the sleeve 9 has a low coefficient of friction, the bearing outer ring can easily slide in the axial direction within the sleeve, and the spring 5 acts reliably. For example, if boron nitride is used as the material for the sleeve 9, the thermal conductivity is only a few times lower than that of metal, and the inner surface of the sleeve made of boron nitride and the outer ring of the ball bearing made of heat-resistant steel are in contact with each other in a high temperature and high vacuum. Unlike metals, they do not stick together and can slide smoothly with extremely low friction.

As explained and described above, according to the present invention, the temperature of the outer ring of the ball bearing is lowered, the decrease in material fatigue strength due to temperature is prevented and damage is less likely to occur, and the outer ring of the ball bearing is preloaded. There is no unnecessary gap between the inner ring and the outer ring, and vibrations and associated shocks are no longer generated.
A rotating anode X-ray tube with good rotation characteristics and a long rotation life can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Target, 2... Rotor, 3.4... Ball bearing, 5... Belleville spring, 7... Fixed shaft, 9... Sleeve. 7- Figure 1

Claims (1)

[Claims] A sleeve made of a material with a low coefficient of friction and low thermal conductivity is fitted inside the rotor that drives the target via the strut, and ball bearings are fitted at both ends of this sleeve so that the outer ring can slide freely against the inner surface of the sleeve. A rotary system such as the target and rotor is rotatably supported on a fixed shaft fixed to the vacuum envelope through the vacuum envelope, and a spring is installed at the end of the rotor to preload the ball bearing outer ring in the axial direction. A rotating anode X-ray tube featuring: