JPS61236971A - Sealing method for magnetic fluid seal - Google Patents

Abstract

PURPOSE:To make it possible to prevent the occurrence of spike-shaped leakage to use a multistage magnetic fluid seal under a superhigh-vacuum condition by previously exhausting air in a space formed by the first stage seal part on the vacuum side of the multistage magnetic fluid seal to reduce its pressure lower than the proof pressure in the first stage seal part. CONSTITUTION:A multistage magnetic fluid seal is composed of the first stage seal part 5a, the second stage seal part 5b or the like which are arranged in order from the vacuum side of the seal. A space 11 formed by the first stage seal part 5a is connected with an exhaust pump 13. Consequently, this exhaust pump 13 can previously reduce the pressure in the space 11 lower than the proof pressure in the first stage seal part 5a.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for sealing a magnetic fluid seal used in a vacuum, particularly a multi-stage magnetic fluid seal.

[Prior Art] In general, when a magnetic fluid seal is adopted as a seal mechanism for a movable shaft, it has many advantages such as low frictional resistance and no wear of the seal portion, and has been put into practical use in many fields.

When using such a magnetic fluid seal in a sealing mechanism for a movable shaft that introduces power from the outside into a vacuum, the maximum pressure resistance is approximately 0.2 atmospheres if there is only one seal part, that is, one stage. Therefore, a plurality of seal portions, that is, multiple seal portions are provided in order to improve pressure resistance.

The structure of such a multistage magnetic fluid seal for vacuum is shown in Figure 4~
It is shown in FIG. That is, the magnetic fluid 101 is attached to the movable shaft 10
3 and the pole piece 105 by the magnetic flux of a permanent magnet 107, and a magnetic fluid seal made up of these members is attached to a housing (not shown).

Then, when the vacuum chamber is evacuated, the first stage seal part 1 on the vacuum side
01a is destroyed and the pressure in the cavity @109 formed by this seal part 101a becomes approximately equal to the withstand pressure value of the first stage seal part 101a, this tenth stage seal part 101a is formed. In addition, the sealing portions of the second and subsequent stages shown in □ are also configured to be once destroyed when the vacuum chamber is evacuated, and then stably maintained at a constant pressure according to the withstand pressure value of each stage.

Note that the symbol @111 in FIG. 6 is a non-magnetic material,
Also, the same components in each section are given the same reference numerals.

When these multi-stage magnetic fluid seals are used under ultra-high vacuum, there is a concern that the vacuum chamber may be contaminated due to evaporation of the magnetic fluid, and this evaporation increases the viscosity of the magnetic fluid, causing deterioration of sealing characteristics such as increased torque. There is a fear. However, these problems can be solved to some extent by using a magnetic fluid with a low vapor pressure, and in particular, if a magnetic fluid with a low vapor pressure such as bar 70 polyether or triester is used, it can be used under a vacuum of up to 10'Torr. It becomes possible.

[Problems to be Solved by the Invention] However, such conventional magnetic fluid seals are
When used in an ultra-high vacuum of over 1000 yorr, when analyzing the residual gas in the vacuum chamber with a quality 1 analyzer, a spike-like leak was observed from the first stage seal close to the vacuum side. However, this is because the temperature rise due to the viscous torque of the magnetic fluid increases the pressure in the space formed by the first stage seal, and the pressure difference with the vacuum chamber side increases, causing the first stage This is thought to be due to the fact that the seal part could no longer withstand the damage, and this seal part broke.

As described above, the seal portions at each stage in this magnetic fluid seal are slightly stabilized at a constant pressure according to their respective withstand pressures, so when such pressure fluctuations occur, spike-like leaks are likely to occur.

This leak not only deteriorates the characteristics of various analytical instruments, thin film forming equipment, and various testing equipment used in ultra-high vacuum conditions, but also causes a significant drop in reliability due to contamination inside the equipment. This has become a problem. Therefore, at present, magnetic fluid seals are not often used under ultra-high vacuum conditions of 1 (18 Torr or higher).

This invention was made by focusing on the conventional problems as described above, and it is a magnetic fluid seal that can be used even under ultra-high vacuum of 10°s'rorr or more by suppressing the occurrence of spike-like leaks. intended to provide.

[Means for Solving the Problems] In order to achieve this object, the present invention sets the pressure in the space formed by the seal portion of the first stage on the vacuum side of the multistage magnetic fluid seal to The exhaust pressure is lower than the withstand pressure of the eye seal.

[Example] Hereinafter, an example of the present invention will be described in detail based on FIGS. 1 to 3.

FIG. 1 is a cross-sectional view of a magnetic fluid seal which is an embodiment of the present invention. In the minute gap between the movable shaft 1 and the pole piece 3 that covers the outer periphery of the movable shaft 1, there is a magnetic fluid with a low vapor pressure. 5 is held by the magnetic flux of a permanent magnet 7 interposed between each pole piece 3.

These magnetic fluid seals consisting of the pole piece 3, magnetic fluid 5, permanent magnet 7, etc. are attached to a housing 9, and the left side of the housing 9 in the figure □ is the vacuum side.This vacuum side The seal portion 5a is the first seal portion, and from this seal portion 5a to the right is the second seal portion 5b.
, the third stage seal portion 5C...

The space 11 between the first-stage seal part 5a and the second-stage seal part 5b and the exhaust pump 13 communicate with each other through a pipe 15 provided through the permanent magnet 7 and the housing 9. As a result, this space 11 can be evacuated to a pressure significantly lower than the withstand pressure of the first stage seal portion 5a. □ For this reason, the temperature rise during rotation of movable shaft 1 causes space 1 to
Even if the pressure inside 1 rises to some extent, the seal portion will not be destroyed and no sudden spike-like leaks will occur.

In addition, in this embodiment, even if the seal portion 5b of the second stage is destroyed, the space 11 has a structure with sufficient volume, so that the pressure is stabilized in the seal portion of each stage. However, the first @th seal portion 5a on the vacuum side will not be destroyed.

In this embodiment, the exhaust pump was provided separately from the exhaust pump for the vacuum chamber, but the exhaust pump for the vacuum chamber was also used to tighten the pulp in the piping communicating with the space 11 after evacuating the space 11. You can also do this.

FIG. 2 shows another embodiment. In this embodiment, the same components as in the previous embodiment are given the same reference numerals to simplify the explanation. This is applied to the inner peripheral side of the permanent magnet 7 provided between the pole piece 3 forming the first stage sealing part 5a on the vacuum side and the pole piece 3 forming the second stage sealing part 5b. An electromagnet 17 is provided.

This electromagnet 17 acts to cancel the magnetic flux of the permanent magnet during evacuation, and seals the first and second stage seal portions 5a.
and 5b, the magnetic flux density of the minute gap in which the magnetic fluid is sealed is reduced. This allows the first stage and second stage to be
The seal portions 5a and 5b of the tiers are destroyed and the space 11 is evacuated to the vacuum side. After that, when the air fm11 is evacuated to a pressure sufficiently lower than the seal pressure, when the power supply to the electromagnet 7 is stopped, the magnetic flux by the permanent magnet 7 is restored in the minute gap between the broken seal parts 5a and 5b. The magnetic fluid is replenished from a storage portion (not shown), and the first-stage seal portion 5a and the second-stage seal portion 5b are formed again.

In this embodiment as well, since the pressure applied to the first stage seal portion 5a is small, sudden spike-like leakage does not occur even under ultra-high vacuum. Also,
The electromagnet 17 is energized only during evacuation, and does not need to be energized while the movable shaft 1 is rotating, that is, when a device (not shown) that is linked to the movable shaft 1 is operating, so the power consumption becomes large enough to become a problem. There isn't.

Note that the pole piece 3 forming the first stage sealing part 5a and the pole piece 3 forming the second stage sealing part 5b
Only an electromagnet may be provided without providing a permanent magnet between the two. However, in this case, since the seal portion is formed by an electromagnet, it is necessary to keep the electromagnet energized at all times while the movable shaft 1 is rotating.

Figure 3 shows a magnetic fluid seal 1 as shown in each of the above embodiments.
9 is attached in a housing 25 attached to the vacuum chamber wall 23 side by a flange 21. The magnetic fluid seal 19 is disposed on the vacuum side of a bearing 27 that is provided in the housing 25 and supports the movable shaft 1, thereby preventing contamination of the inside of the vacuum chamber by grease or the like on the bearing 27. Further, an annular cooling water passage 29 is formed in the housing 25 around the magnetic fluid seal 19, and a cooling water inlet 31 that communicates with this passage 29 and projects to the outside of the housing 25 is installed. .

That is, by supplying cooling water to the cooling water passage 29, the seal portion is cooled and the amount of evaporation of the magnetic fluid can be reduced, and this cooling also prevents the magnetic fluid from heating up and deteriorating, allowing baking of the vacuum chamber. is possible. Note that a cover may be provided on the side of the vacuum chamber to prevent the vapor of the magnetic fluid from directly flying into the vacuum chamber.

[Effects of the Invention] As described above, according to the present invention, the pressure applied to the first stage magnetic fluid seal on the vacuum side can be set to be lower than the seal pressure resistance, thereby preventing the occurrence of sudden spike-like leaks. It becomes possible to use the magnetic fluid seal under an ultra-high vacuum of 1QJvorr or more without causing problems.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a magnetic fluid seal according to one embodiment of the present invention, FIG. 2 is a cross-sectional view of another embodiment, FIG. 3 is a cross-sectional view showing an application example of these magnetic fluid seals, and FIG. 6 are cross-sectional views of conventional magnetic fluid seals. 5...Magnetic fluid, 5a...First stage seal part, 5b...Second stage seal part, 11...Space! Fig. 2 Fig. 8

Claims (1)

[Claims] A magnetic fluid seal characterized in that the pressure in the space formed by the first stage seal portion on the vacuum side of the multistage magnetic fluid is evacuated in advance to a pressure lower than the withstand pressure of the first stage seal portion. Sealing method.