JPS6324196B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A shaft sealing device for a rotating shaft can be obtained using a magnetic fluid in which ferrite or other magnetic powder is dispersed in a liquid such as hydrocarbon, fluorocarbon, or fatty acid. However, when the rotational speed of the shaft exceeds 10,000 revolutions per minute, the circumferential speed of the shaft becomes extremely high, so that the flow of the magnetic fluid becomes intense and air bubbles are likely to flow. Therefore, when such a shaft sealing device is used to seal between a high vacuum chamber and an atmospheric pressure part, the degree of vacuum becomes unstable, and sometimes magnetic fluid scatters into the vacuum chamber and contaminates it. In severe cases, the shaft sealing function is completely lost. In addition, as a countermeasure, if the viscosity of the magnetic fluid is increased or the density of the magnetic flux used to constrain the magnetic fluid is increased, the heat of stirring the magnetic fluid will increase, and the binder liquid will evaporate with that heat, causing the magnetic The fluid dries and the shaft sealing function disappears. The present invention provides a shaft sealing device that can rotate a shaft at high speed without having such drawbacks.

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention, and FIG. 2 is a partially enlarged view of FIG. 1. That is, a disk-shaped X-ray target 2 is provided in a vacuum-tight housing 1, and a cathode 3 for projecting an electron beam onto the target is provided on the circumferential side of the target. A wire extraction window 4 is provided. In such a rotating anticathode X-ray tube, the shaft 5 of the target 2 is disposed coaxially with a cylindrical bearing 6 protruding from the housing 1 and supported by ball bearings 7 and 8, and the shaft 5 is supported by ball bearings 7 and 8 (not shown). 5, for example, several thousand to one per minute.
It is connected to a rotary drive source that rotates 10,000 revolutions. Further, a magnetic fluid shaft sealing element 9 is provided at the base of the bearing portion 6, and an appropriate solid shaft sealing element 10 is provided between this shaft sealing element and the bearing 7. The formed annular sealed chamber 11 is passed through a conduit 13 to a vacuum pump 12 such as an oil rotary pump for obtaining a relatively low vacuum of, for example, about 10 ^-2 Torr.
It is connected with. The pump 12 is further connected to a high vacuum pump 14 such as a turbo molecular pump or an oil diffusion pump, and this pump pumps the housing 1.
is evacuated to a high vacuum of, for example, 10 ^-6 Torr or higher.

The magnetic fluid shaft sealing element 9 is shown in FIG.
As shown in , annular magnets 15, 15... magnetized in the axial direction and annular magnetic poles 16, 16... are arranged alternately, and the inner periphery of the knife-edge magnetic pole is covered with a magnetic material. The magnetic fluid 17, 1 as described above is placed in the gap between
7... is held in an annular shape. In addition, the solid shaft sealing element 10 has an inner circumferential portion of V, for example, as shown in the figure.
A rubber ring 18 formed in the shape of a letter is fitted onto the shaft 5 and tightened by a spiral metal spring 19, and its sliding portion is coated with lubricating oil. However, as this solid shaft sealing element 10, for example, a mechanical seal formed only of metal parts or any other shaft sealing device formed only of solid materials such as metal or rubber can be used.

As described above, in the present invention, a solid shaft sealing element 10 is further provided on the atmospheric pressure side of the magnetic fluid shaft sealing element 9, and the annular sealed chamber 11 therebetween is evacuated by a low vacuum pump 12. So atmospheric pressure 760mm
Almost all of the Hg is retained by the solid sealing element 10, and the pressure applied to the magnetic fluid sealing element 9 is only about 10 ^-3 to 10 ^-2 mmHg. Therefore, there is no need to increase the viscosity of the magnetic fluid or to significantly increase the density of the magnetic flux passing through the magnetic fluid 17 in FIG.
A high vacuum inside can be easily maintained. Therefore, even when the shaft 5 is rotated at a high speed of 10,000 revolutions per minute, the amount of heat generated by stirring the magnetic fluid is small, and shortening of the life of the magnetic fluid due to evaporation of the binder is also prevented. Moreover, since the air pressure applied to the first stage magnetic fluid 17 in FIG. 2 is extremely small, the amount of gas leakage due to air bubbles flowing through this fluid is also significantly reduced. Therefore, the housing 1
The degree of vacuum inside has also been improved by more than an order of magnitude than before, making it easier to
A high vacuum of 10 ^-7 Torr or higher can be obtained.

Furthermore, when the shaft 5 starts rotating after the housing 1 is evacuated to a high vacuum, the pressure difference on both sides of the shaft sealing element 9 is created by the first or second stage magnetic fluid 17 on the vacuum side before the rotation. However, after the shaft 5 rotates, gas leaks through the magnetic fluid, so that the pressure difference is almost equally divided and maintained by the magnetic fluids 17, 17, . . . in each stage. In other words, when the shaft 5 starts rotating, the magnetic fluid 1 close to the vacuum side
The gas trapped between 7 and 17 leaks into the vacuum chamber all at once, resulting in the above-mentioned state, and as a result, the air pressure inside the housing 1 temporarily decreases. However, in the conventional device, the pressure difference between both sides of the magnetic fluid shaft sealing element was 1 atm, but in the device of the present invention, this is less than 10 ^-2 Torr, so the above-mentioned temporary decrease in the degree of vacuum is extremely small. become. Furthermore, if the magnetic fluid shaft sealing element 9 is broken for some reason, the lubricating oil from the ball bearings 7, 8, etc. will enter the housing 1 all at once and contaminate the interior of the conventional device. , the device of the present invention can prevent this by the solid shaft sealing element 10.

As described above, the present invention can improve the ultimate vacuum degree of the vacuum chamber by more than one order of magnitude, especially when the shaft is rotated at high speed, and can extend the life of the magnetic fluid shaft sealing element. Further, there are excellent effects such as a temporary decrease in the degree of vacuum at the time of startup is significantly reduced, and contamination of the vacuum chamber by oil is also prevented.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention, and FIG. 2 is an enlarged view of a part of FIG. 1. In the figure, 5 is a magnetic rotating shaft, 9 is a magnetic fluid shaft sealing element, 10 is a solid shaft sealing element, 15 is a magnet, 16 is a magnetic pole, 17 is a magnetic fluid, and 12 is a vacuum pump.

Claims (1)

[Claims] 1 A ring-shaped magnetic pole excited by a magnet is fitted to the high vacuum side of a rotating shaft of a magnetic body that passes between the high vacuum chamber and the atmospheric pressure part, and the magnetic pole and the rotating shaft are connected using a magnetic fluid. A magnetic fluid shaft sealing element is provided which seals the high vacuum chamber, and an annular solid shaft sealing element is provided which slides into contact with the atmospheric pressure side of the rotating shaft, and the magnetic fluid shaft sealing element and the solid shaft sealing element are connected to each other. A high-vacuum shaft sealing device using a magnetic fluid, characterized in that it is equipped with a vacuum pump that evacuates an annular sealed chamber formed between the two to a relatively low-vacuum state.