Magnetic fluid seal device

Abstract

To provide a magnetic fluid seal device which can inhibit extension of a device configuration in an axial direction.SOLUTION: A magnetic fluid seal device of the invention includes: a shaft body extending in a predetermined direction; a cylindrical housing which encloses the shaft body around an axis of the shaft body; a flange part which extends from one of the shaft body and the housing to the other in a plane shape intersecting with the axis of the shaft body in the housing; and a seal mechanism being a structure in which a cylindrical first pole piece which encloses the shaft body around the axis in the housing, a magnetic body magnetized in an axial direction, and a second pole piece are stacked in the axial direction and one of these members is fixed to the other of the shaft body and the housing through a member formed of a non-magnetic material in a state where the first pole piece is directed to the flange part side.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a magnetic fluid sealing device. [Background technology]

[0002] Magnetic fluid seal devices have been used to maintain airtightness on one end of a shaft that rotates inside a housing relative to the other end. This device achieves both rotation of the shaft and airtightness by using a sealing mechanism that magnetically holds a magnetic fluid between the outer circumferential surface of the shaft and the inner circumferential surface of a pole piece that surrounds the shaft around its axis (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-179613 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the magnetic fluid seal device described above, due to the structure in which individual seals made up of the pole piece tips and the magnetic fluid surround the shaft around the axis, there is a problem in that the device configuration required to ensure the required airtightness tends to become long in the axial direction.

[0005] For example, in applications where the pressure difference between the other end of the shaft and one end is large, such as when the other end is placed in a reduced pressure environment such as a vacuum chamber, it is necessary to provide multiple stages of individual seals in the sealing mechanism in the axial direction to improve pressure resistance, but the device configuration becomes longer in the axial direction depending on the number of stages.

[0006] Depending on the installation location of the magnetic fluid sealing device, it may not be possible to ensure sufficient space in the axial direction, in which case it may not be possible to achieve a device configuration that ensures the required airtightness.

[0007] The present disclosure has been made to solve such problems, and its purpose is to provide a magnetic fluid sealing device that can prevent the device configuration from becoming long in the axial direction. [Means for solving the problem]

[0008] In order to solve the above problem, a magnetic fluid sealing device according to a first aspect of the present invention is a structure comprising a shaft extending in a predetermined direction, a cylindrical housing surrounding the shaft around its axis, a flange portion extending in a plane intersecting the axis of the shaft from one side of the shaft and the housing to the other side inside the housing, and a cylindrical first pole piece, a magnet body, and a second pole piece each surrounding the shaft around its axis inside the housing, stacked in the axial direction, and with the first pole piece facing the flange portion side, any one of the members is fixed to the other of the shaft and the housing via a member made of a non-magnetic material. and a seal mechanism, in which the magnet body is magnetized in the axial direction of the shaft body, the first pole piece has a plurality of concentric annular protrusions formed on the end face on the flange portion side, each centered on the axis of the shaft body, and a magnetic fluid is filled between the tip side of the annular protrusions and the flat surface of the flange portion, and the magnetic fluid is magnetically held between the annular protrusions and the flange portion by a magnetic circuit formed along a route from the magnet body via the second pole piece, one of the shaft body and the housing, the flange portion, the first pole piece, and back to the magnet body, or the reverse route.

[0009] In this aspect of the magnetic fluid seal device, the shaft can be rotated while maintaining airtightness on one end side of the housing relative to the other end side, thanks to a sealing mechanism in which individual seals made of the annular protrusion of the first pole piece and the magnetic fluid are concentrically arranged along the plane of the flange portion.

[0010] Here, the individual seals formed by the annular projections and the magnetic fluid are concentrically arranged along the plane of the flange, i.e., the plane intersecting the axis of the shaft, so even if the number of seal stages is increased depending on the required airtightness, the device configuration does not become longer in the axial direction regardless of the number of stages. Thus, with the magnetic fluid sealing device of the above aspect, it is possible to prevent the device configuration from becoming longer in the axial direction.

[0011] The above aspect may also be implemented as the second aspect described below.

[0012] In a second aspect, the first pole piece surrounds the shaft in a positional relationship in which a predetermined seal gap g is formed between the flat surface of the flange portion and the annular protrusion, and a first distance r1 that exceeds the seal gap g is formed as the radial distance between one of the shaft and the housing and the side surface of the first pole piece, and the second pole piece surrounds the shaft in a positional relationship in which a predetermined second distance r2 is formed as the radial distance between one of the shaft and the housing and the side surface of the second pole piece, and a distance d that exceeds the second distance r2 is formed between the first pole piece and the second pole piece in the axial direction of the shaft.

[0013] With this magnetic fluid seal device, it is possible to prevent the formation of unintended magnetic circuits by arranging the gaps between each part of the seal mechanism and the shaft and flange portion so that the parts that should be the route of the magnetic circuit are close together and separating the parts that should not be formed, making it possible to easily maintain the magnetic holding force of the magnetic fluid.

[0014] Furthermore, each of the above aspects may be configured as in the third aspect shown below.

[0015] In the magnetic fluid seal device of the third aspect, the flange portion extends in a plane from the shaft body toward the housing, and the seal mechanism is fixed to the housing via a member formed of a non-magnetic material, with the first pole piece, the magnet body, or the second pole piece, and the end of the housing on the second pole piece side being placed in a reduced pressure environment, and the end of the housing on the first pole piece side being placed in an atmospheric pressure environment.

[0016] In a magnetic fluid seal device configured as described above, the magnetic fluid filled between the annular protrusion of the first pole piece and the surface of the flange portion is easily displaced outward due to the centrifugal force caused by the rotation of the shaft. Therefore, in order to maintain airtightness, it is necessary to use the device under conditions that prevent the magnetic fluid from displacing significantly outward.

[0017] In this regard, in the third aspect, the effect of centrifugal force on the magnetic fluid can be counteracted by the pressure difference caused by the placement of the housing, making it possible to use the device even under conditions where a stronger centrifugal force is generated.

[0018] Specifically, inside the housing, the end of the housing facing the second pole piece is placed in a reduced-pressure environment, while the end of the housing facing the first pole piece is placed in an atmospheric-pressure environment. This means that the air pressure in the vacuum space between the inner surface of the seal mechanism and the outer surface of the shaft is lower than the atmospheric-pressure space between the outer surface of the flange and the inner surface of the housing. This pressure difference acts to draw the magnetic fluid from the atmospheric-pressure space toward the vacuum space, that is, from the outside toward the inside. This cancels out the effect of centrifugal force on the magnetic fluid.

[0019] Furthermore, each of the above aspects may be modified as in the following fourth aspect: In the magnetic fluid seal device of this aspect, the side surface of the first pole piece facing one of the shaft body and the housing is chamfered so that the closer it is to the second pole piece along the axis of the shaft, the further it is from one of the shaft body and the housing.

[0020] In the magnetic fluid seal device of this aspect, the side surface of the first pole piece facing either the shaft or the housing is chamfered, which prevents this side surface from forming an unintended magnetic circuit between the second pole piece or the shaft, making it easier to maintain the magnetic holding force of the magnetic fluid. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a front cross-sectional view of a magnetic fluid sealing device according to a first embodiment of the present disclosure. [Figure 2] FIG. 1 is an enlarged front cross-sectional view of a main part of a magnetic fluid sealing device according to a first embodiment of the present disclosure. [Figure 3] FIG. 10 is an enlarged front cross-sectional view of a main part of a magnetic fluid sealing device according to a second embodiment of the present disclosure. [Figure 4] FIG. 10 is an enlarged front cross-sectional view of a main part of a magnetic fluid sealing device according to another embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (1) First embodiment

[0023] As shown in Figure 1, the magnetic fluid sealing device 1 of this embodiment comprises a shaft 10 extending in a predetermined direction (up and down in the figure), a cylindrical housing 20 surrounding the shaft 10 around its axis 11, a flange portion 30 extending in a plane intersecting the axis 11, a sealing mechanism 40 surrounding the shaft 10 around the axis 11 inside the housing 20, and a bearing 50 that holds the shaft 10 rotatably relative to the housing 20.

[0024] The magnetic fluid sealing device 1 of this embodiment is used with one end (upper end in the figure) of the housing 20 placed in a reduced pressure environment and the other end (lower end in the figure) placed in an atmospheric pressure environment. Specifically, one end of the housing 20 is connected to an opening of a vacuum chamber (not shown) via an O-ring 21 that surrounds the end face around the axis 11.

[0025] The shaft body 10 is a member made of a magnetic material.

[0026] The housing 20 is a cylindrical member made of a non-magnetic material.

[0027] Flange portion 30 extends inside housing 20 in a plane that intersects with axis 11 from one of shaft body 10 and housing 20 to the other. In this embodiment, flange portion 30 extends from a region of shaft body 10 that is located inside housing 20 toward housing 20. This flange portion 30 is integrally molded from the same magnetic material as shaft body 10.

[0028] The sealing mechanism 40 is a structure in which a cylindrical first pole piece 41, a magnetic body 43 and a second pole piece 45, each of which surrounds an area of ​​the shaft body 10 located inside the housing 20 around its axis 11, are stacked in the direction of the axis 11.

[0029] In this sealing mechanism 40, one of the members is fixed to the other of the shaft body 10 and the housing 20 via a non-magnetic material, with the first pole piece 41 facing the flange portion 30 side (the lower side in FIG. 1). In this embodiment, the outer peripheral surfaces of the first pole piece 41 and the second pole piece 45 of the sealing mechanism 40 are fixed to the inner peripheral surface of the housing 20 via a cylindrical holder 23 made of a non-magnetic material. An O-ring 25 is disposed on the outer peripheral surface of the first pole piece 41 at a location where it comes into contact with the housing 20.

[0030] 2, the first pole piece 41 has a plurality of concentric annular protrusions 47 formed on the end face (the lower end face in the figure) on the flange portion 30 side, each of which is centered on the axis 11. A predetermined seal gap g is formed between the annular protrusions 47 and the flat surface of the flange portion 30, and a magnetic fluid 49 is filled in this seal gap g.

[0031] This first pole piece 41 surrounds the shaft body 10 over a wider range inside and outside than the magnet body 43 in a positional relationship where a first interval r1 greater than the seal gap g is formed as the radial interval between its side surface (inner peripheral surface) and the outer peripheral surface of the shaft body 10 (r1 > g).

[0032] Furthermore, the side surface (inner peripheral surface) of the first pole piece 41 facing the shaft body 10 is chamfered in a planar shape so as to move away from the shaft body 10 as it approaches the second pole piece 45 along the axis 11.

[0033] This first pole piece 41 has a side surface (inner peripheral surface) side facing the shaft body 10 that extends toward the second pole piece 45 and overlaps a part of the side surface of the magnet body 43 in the inner - outer direction, and the overlapping region is chamfered so as to move away from the shaft body 10 as it approaches the second pole piece 45.

[0034] Also, the second pole piece 45 surrounds the shaft body 10 in a positional relationship where a predetermined second interval r₂ is formed as the radial interval between its side surface (inner peripheral surface) and the outer peripheral surface of the shaft body 10. In the present embodiment, the second pole piece 45 surrounds the shaft body 10 over a wider range inside and outside than the magnet body 43 in a positional relationship where a second interval r₂ less than the first interval r₁ is formed (r₂ < r₁).

[0035] This second pole piece 45 has a side surface (inner peripheral surface) side facing the shaft body 10 that extends toward the first pole piece 41 and overlaps a part of the side surface of the magnet body 43 in the inner - outer direction.

[0036] Also, the first pole piece 41 and the second pole piece 45 are arranged in a positional relationship where an interval d greater than the second interval r₂ is formed in the direction of the axis 11 of the shaft body 10 (r₂ < d). In the present embodiment, in the first pole piece 41 and the second pole piece 45, the side surface (inner peripheral surface) side that is closest in the direction of the axis 11 forms the interval d.

[0037] Furthermore, magnet body 43 is a magnet that is magnetized in the direction of axis 11 (the vertical direction in FIGS. 1 and 2). This magnet body 43 surrounds shaft body 10 in a positional relationship where a third distance r3 that is greater than or equal to first distance r1 is formed as a radial distance between its side surface (inner peripheral surface) and shaft body 10 (r3≧r1). In this embodiment, magnet body 43 surrounds shaft body 10 in a positional relationship where a third distance r3 that is greater than first distance r1 is formed (r3>r1).

[0038] The bearing 50 is attached between the outer periphery of the flange portion 30 and the inner periphery of the housing 20, and rotatably holds the shaft body 10 via the flange portion 30.

[0039] In the magnetic fluid sealing device 1 described above, the magnetic fluid 49 is magnetically held between the annular protrusion 47 and the flange portion 30 by a magnetic circuit formed along a route from the magnet body 43 through the second pole piece 45, the shaft body 10, the flange portion 30, the first pole piece 41, and back to the magnet body 43 (see the arrow in Figure 2), or along the reverse route.

[0040] In the above embodiment, the shaft body 10 is made of a magnetic material. However, the shaft body 10 need not necessarily be made entirely of a magnetic material as long as a magnetic circuit can be formed along its outer circumferential surface. For example, the shaft body 10 may be made of a non-magnetic material, but the outer circumferential surface thereof may be coated with a magnetic material, or only the area of ​​the shaft body 10 that is to form the magnetic circuit may be made of a magnetic material.

[0041] (2) Second embodiment As shown in FIG. 3, the magnetic fluid sealing device 1 of this embodiment has the same components as those of the first embodiment, but the details of the components are different, so the following description will focus on these differences.

[0042] The magnetic fluid sealing device 1 of this embodiment is used with one end (upper end in the figure) of the housing 20 placed in an atmospheric pressure environment and the other end (lower end in the figure) placed in a reduced pressure environment.

[0043] The housing 20 is a cylindrical member formed of a magnetic material.

[0044] The flange portion 30 extends from the inner peripheral surface of the housing 20 toward the shaft body 10. Here, the flange portion 30 is integrally formed of the same magnetic material as the housing 20.

[0045] The seal mechanism 40 is fixed to the shaft body 10 through a non-magnetic material with one of the members facing the flange portion 30 side (the lower side in FIG. 3). In the present embodiment, among the seal mechanism 40, the first pole piece 41 and the second pole piece 45 are fixed to the outer peripheral surface of the shaft body 10 through a cylindrical holder 27 formed of a non-magnetic material. Note that an O-ring 25 is disposed at a contact location with the shaft body 10 side on the inner peripheral surface of each of the first pole piece 41 and the second pole piece 45.

[0046] Among these, a predetermined seal gap g is formed between the annular protrusion 47 of the first pole piece 41 and the plane of the flange portion 30, and the seal gap g is filled with magnetic fluid 49.

[0047] The first pole piece 41 surrounds the shaft body in a positional relationship (r1 > g) where a first interval r1 exceeding the seal gap g is formed as a radial interval between its side surface (outer peripheral surface) and the inner peripheral surface of the housing 20.

[0048] Furthermore, the side surface (outer peripheral surface) of the first pole piece 41 facing the inner peripheral surface of the housing 20 is chamfered in a planar shape so as to move away from the inner peripheral surface of the housing 20 as it approaches the second pole piece 45 along the axis 11.

[0049] Also, the second pole piece 45 surrounds the shaft body in a positional relationship (r2 < r1) where a second interval r2 less than the first interval r1 is formed as a radial interval between its side surface (outer peripheral surface) and the inner peripheral surface of the housing 20.

[0050] Furthermore, the magnetic body 43 surrounds the shaft body 10 in a positional relationship where a third distance r3 that is equal to or greater than the first distance r1 is formed as a radial distance between its side surface (outer peripheral surface) and the inner peripheral surface of the housing 20 (r3≧r1). In this embodiment, the magnetic body 43 surrounds the shaft body 10 in a positional relationship where a third distance r3 that is greater than the first distance r1 is formed (r3>r1).

[0051] In the magnetic fluid sealing device 1 of this embodiment, the magnetic fluid 49 is magnetically held between the annular protrusion 47 and the flange portion 30 by a magnetic circuit formed along a route from the magnetic body 43 through the second pole piece 45, the housing 20, the flange portion 30, the first pole piece 41 and back to the magnetic body 43 (see the arrow in Figure 3), or along the reverse route.

[0052] In the above embodiment, the housing 20 is made of a magnetic material. However, the housing 20 does not necessarily have to be made entirely of a magnetic material as long as a magnetic circuit can be formed along its inner circumferential surface. For example, the housing 20 may be made of a non-magnetic material, but the inner circumferential surface may be coated with a magnetic material, or only the area of ​​the housing 20 that will form the magnetic circuit may be made of a magnetic material.

[0053] (3) Variations Although the embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to the above-described embodiments and can take various forms as long as they fall within the technical scope of the present invention.

[0054] For example, in the above embodiment, the magnetic fluid sealing device 1 is exemplified as being used with one end of the housing 20 placed in one of a reduced pressure environment and an atmospheric pressure environment, and the other end placed in the other of a reduced pressure environment and an atmospheric pressure environment. However, the magnetic fluid sealing device 1 may be used with both ends of the housing 20 placed in an atmospheric pressure environment or a reduced pressure environment, as long as the magnetic fluid sealing device 1 is used to ensure airtightness of one end of the shaft 10 rotating within the housing 20 relative to the other end.

[0055] In the above embodiment, the magnet body 43 surrounds the shaft body 10 in a positional relationship where a third interval r3 greater than the first interval r1 is formed (r3>r1). However, as shown in FIG. 4(a), the magnet body 43 may be configured in a positional relationship where a third interval r3 equal to the first interval r1 is formed (r3=r1). In this case, the position of the side surface of the first pole piece 41 (the inner peripheral surface in the figure) on one side of the shaft body 10 and the housing 20 coincides with the side surface of the magnet body 43 in the radial direction.

[0056] In the above embodiment, a configuration has been exemplified in which the side surface of the first pole piece 41 facing either the shaft body 10 or the housing 20 is chamfered into a flat shape. However, it is sufficient that the side surface of this first pole piece 41 is configured so that it becomes more distant from either the shaft body 10 or the housing 20 as it approaches the second pole piece 45 along the axis 11. The side surface of the first pole piece 41 may be configured, for example, so that it is chamfered into a curved shape, or so that it has multiple surfaces that gradually become more distant from either the shaft body 10 or the housing 20 as it approaches the second pole piece 45. In this latter configuration, as shown in FIG. 4(b), the side surface of the first pole piece 41 may be configured with two surfaces that gradually become more distant from either the shaft body 10 or the housing 20 as it approaches the second pole piece 45, so that the surface facing the second pole piece 45 (the upper surface in the same figure) is also distant from the second pole piece 45.

[0057] In the above embodiment, the side surface (inner peripheral surface) of the first pole piece 41 facing the shaft body 10 extends toward the second pole piece 45 and overlaps in the inward and outward direction with a portion of the side surface of the magnetic body 43. However, the side surface facing the shaft body 10 may be configured not to overlap in the inward and outward direction with a portion of the side surface of the magnetic body 43, as shown in FIG.

[0058] In the above embodiment, the side surface (inner peripheral surface) of the second pole piece 45 facing the shaft body 10 extends toward the first pole piece 41 and is configured to overlap in the inward and outward direction with a part of the side surface of the magnetic body 43. However, this side surface facing the shaft body 10 may be configured not to overlap in the inward and outward direction with a part of the side surface of the magnetic body 43, as shown in FIG.

[0059] (4) Action and effect In the magnetic fluid sealing device 1 of the above-described embodiment, the seal mechanism 40, in which individual seals made of the annular protrusion 47 of the first pole piece 41 and the magnetic fluid 49 are concentrically arranged along the plane of the flange portion 30, allows the shaft 10 to rotate while maintaining airtightness on one end side of the housing 20 relative to the other end side.

[0060] Here, the individual seals formed by the annular projections 47 and the magnetic fluid 49 are arranged concentrically along the plane of the flange portion 30, i.e., the plane intersecting the axis 11, so even if the number of seal stages is increased depending on the required airtightness, the device configuration does not become longer in the axial direction regardless of the number of stages. In this way, the magnetic fluid sealing device 1 can prevent the device configuration from becoming longer in the axial direction.

[0061] Furthermore, with the magnetic fluid sealing device 1 of the above embodiment, it is possible to prevent the formation of unintended magnetic circuits by bringing the locations that should be the route of the magnetic circuit closer together and separating the locations that should not be formed among the distances between each part of the sealing mechanism 40 and the shaft 10 and the flange portion 30. This makes it easy to maintain the magnetic holding force of the magnetic fluid 49.

[0062] Furthermore, in the magnetic fluid sealing device 1 configured as in the above embodiment, the magnetic fluid 49 filled between the annular protrusion 47 of the first pole piece 41 and the surface of the flange portion 30 is easily displaced outward due to the centrifugal force that accompanies the rotation of the shaft body 10. Therefore, in order to maintain airtightness, it is required to use the device under conditions that prevent the magnetic fluid from being displaced outward significantly.

[0063] In this regard, in the magnetic fluid sealing device 1 of the above embodiment, the pressure difference caused by the arrangement of the housing 20 cancels out the effect of centrifugal force on the magnetic fluid, making it possible to use the device under conditions where a stronger centrifugal force is generated.

[0064] In the first embodiment, inside the housing 20, the end on the second pole piece 45 side is placed in a reduced pressure environment, and the end on the first pole piece 41 side is placed in an atmospheric pressure environment, so that the air pressure in the vacuum space sandwiched between the inner circumferential surface of the seal mechanism 40 and the outer circumferential surface of the shaft 10 is lower than the atmospheric pressure space sandwiched between the outer circumferential surface of the flange portion 30 and the inner circumferential surface of the housing 20. In the second embodiment, inside the housing 20, the end on the second pole piece 45 side is placed in an atmospheric pressure environment, and the end on the first pole piece 41 side is placed in a reduced pressure environment, so that the air pressure in the vacuum space sandwiched between the inner circumferential surface of the flange portion 30 and the inner circumferential surface of the shaft 10 is lower than the atmospheric pressure space sandwiched between the outer circumferential surface of the seal mechanism 40 and the inner circumferential surface of the housing 20.

[0065] These pressure differences act to pull the magnetic fluid 49 in the direction from the atmospheric pressure space to the vacuum space, that is, from the outside to the inside, thereby canceling out the effect of centrifugal force on the magnetic fluid 49.

[0066] Furthermore, according to the magnetic fluid sealing device 1 of the above embodiment, the side surface of the first pole piece 41 is chamfered, which prevents this side surface from forming an unintended magnetic circuit between the second pole piece 45 and the shaft body 10. This makes it easier to maintain the magnetic holding force of the magnetic fluid 49. [Explanation of symbols]

[0067] 1...magnetic fluid seal device, 10...shaft body, 11...axis line, 20...housing, 21...O-ring, 23...retainer, 25...O-ring, 27...retainer, 30...flange portion, 40...seal mechanism, 41...first pole piece, 43...magnet body, 45...second pole piece, 47...annular protrusion, 49...magnetic fluid, 50...bearing.

Claims

1. a shaft extending in a predetermined direction; a cylindrical housing that surrounds the shaft around its axis; a flange portion extending in a plane intersecting the axis of the shaft from one side of the shaft and the housing to the other side inside the housing; a structure in which a cylindrical first pole piece, a magnet body, and a second pole piece, each of which surrounds the shaft around its axis inside the housing, are stacked in the axial direction, and the first pole piece is facing the flange portion, and a sealing mechanism is provided in which one of the members is fixed to the other of the shaft and the housing via a member made of a non-magnetic material, The magnet body is magnetized in the axial direction of the shaft body, The first pole piece has a plurality of concentric annular protrusions, each centered on the axis of the shaft, formed on an end face of the flange portion side, and a magnetic fluid is filled between the tip end side of the annular protrusions and the flat surface of the flange portion, the magnetic fluid is magnetically held between the annular protrusion and the flange portion by a magnetic circuit formed along a route from the magnet body through the second pole piece, one of the shaft body and the housing, the flange portion, the first pole piece, and back to the magnet body, or along the reverse route. Magnetic fluid sealing device.

2. the first pole piece surrounds the shaft in a positional relationship such that a predetermined seal gap g is formed between a flat surface of the flange portion and the annular projection, and a first gap r1 that is greater than the seal gap g is formed as a radial gap between one of the shaft and the housing and a side surface of the first pole piece, the second pole piece surrounds the shaft in a positional relationship in which a predetermined second distance r2 is formed as a radial distance between one of the shaft and the housing and a side surface of the second pole piece, Between the first pole piece and the second pole piece, a distance d greater than the second distance r2 is formed in the axial direction of the shaft. The magnetic fluid seal device according to claim 1 .

3. The flange portion extends in a plane from the shaft body toward the housing, the sealing mechanism is configured such that any one of the first pole piece, the magnet body, and the second pole piece is fixed to the housing via a member made of a non-magnetic material; The housing has an end portion on the second pole piece side that is placed in a reduced pressure environment, and an end portion on the first pole piece side that is placed in an atmospheric pressure environment. The magnetic fluid seal device according to claim 1 .

4. a side surface of the first pole piece facing one of the shaft body and the housing is chamfered so that the closer the first pole piece is to the second pole piece along the axis of the shaft, the further it becomes from one of the shaft body and the housing; The magnetic fluid sealing device according to claim 2 or 3.

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