JPH02172205A - Magnetic fluid holding member and shaft sealing device employing it - Google Patents

Abstract

PURPOSE:To improve a force for holding magnetic fluid by a method wherein one of a pair of yokes has a smaller outer diameter than the other yoke. CONSTITUTION:A magnetic fluid holding member 7 composed of a pair of yokes 7b1 and 7b2 having shaft holes 5 which a rotary shaft 1 is inserted into and attached to and a magnet 7a provided between the yokes 7b1 and 7b2 is put into and fitted to a step part. Magnetic fluid is held between the rotary shaft 1 and the inner circumferences of the respective yoke shaft holes of the magnetic fluid holding member 7. Further, as a magnetic gap 9 is practically provided between the outer circumference of the yoke 7b1 having a smaller outer diameter than the other yoke 7b2 and the inner circumference 3b of the step part 3, a large magnetoresistance is provided between them. With this constitution, a magnetic force on the inner circumference of the magnetic fluid holding member becomes sufficiently large, so that the magnetic fluid can be held securely.

Description

【発明の詳細な説明】 〔産業上の利用分野〕 本発明は、磁性体からなる軸の外周部に磁性流体保持部
材を配置して、軸と磁性流体保持部材との間に磁性流体
を保持させる軸封装置に関するものであり、特に、磁気
回路の磁束が磁性流体保持に有効に作用するように磁性
流体保持部材の構造を改良することに関するものである
。[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a magnetic fluid holding member disposed on the outer periphery of a shaft made of a magnetic material to hold the magnetic fluid between the shaft and the magnetic fluid holding member. The present invention relates to a shaft sealing device, and particularly relates to improving the structure of a magnetic fluid holding member so that the magnetic flux of a magnetic circuit effectively acts on magnetic fluid holding.

〔従来の技術〕[Conventional technology]

最近、真空装置あるいは磁気ディスク駆動装置など数多
くの分野において、磁性流体を用いた軸封装置等が用い
られ始めている。磁性流体を用いた軸封装置は、例えば
第３図に示すように、磁性体からなる軸１の外径よりも
十分大きい径をもつ貫軸孔２を有し、貫軸孔２の少なく
とも一端部には貫軸孔の径よりも大きい外径の内周面を
有する段差部３が形成されたハウジング４と、軸１を貫
通装着するための軸孔５を有しハウジング４の段差部３
に非磁性体６を介して嵌合装着された磁性流体保持部材
７とから構成される。そして、回転軸１と磁性流体保持
部材７との間隙部分に磁性流体８を保持させて、回転軸
外周部の密封をするようにしたものである。このように
、磁性流体で密封を保つようにすれば、通常の固体シー
ル部材を使う場合のような摩擦がなく、かつ確実に密封
を保つことができるため、最近、特に注目を集めている
ものである。Recently, shaft sealing devices using magnetic fluid have begun to be used in many fields such as vacuum devices and magnetic disk drive devices. As shown in FIG. 3, for example, a shaft sealing device using a magnetic fluid has a through-shaft hole 2 having a diameter sufficiently larger than the outer diameter of a shaft 1 made of a magnetic material, and has at least one end of the through-shaft hole 2. The housing 4 has a stepped portion 3 formed thereon with an inner circumferential surface having an outer diameter larger than the diameter of the through-shaft hole, and a stepped portion 3 of the housing 4 having a shaft hole 5 for penetrating the shaft 1.
A magnetic fluid holding member 7 is fitted to the magnetic fluid holding member 7 through a non-magnetic material 6. The magnetic fluid 8 is held in the gap between the rotating shaft 1 and the magnetic fluid holding member 7 to seal the outer circumference of the rotating shaft. In this way, maintaining a seal with a magnetic fluid eliminates the friction that would occur when using a normal solid sealing material, and the seal can be maintained reliably, which is why it has been attracting particular attention recently. It is.

ところが、上記したような従来の軸封装置の場合におい
ては、磁性流体保持部材７と磁性体からなる回転軸１と
で形成する間隙部分に磁性流体を保持するための磁界を
発生させるため、磁性流体保持部材７は、通常、環状の
磁石７ａの軸方向両面に一対の等しい外径をもつ環状の
ヨーク７ｂを固着させた構成にしている。そして、磁石
から発生した磁束が、主として、磁石７ａ→一方のヨー
ク７ｂ→一方の間隙部分→回転軸１→他方の間隙部分→
他方のヨーク７ｂ−＋ｆｆｔ石７ａの経路で通り、磁性
流体保持に有効に作用するようにしている。However, in the case of the conventional shaft seal device as described above, in order to generate a magnetic field for holding the magnetic fluid in the gap formed between the magnetic fluid holding member 7 and the rotating shaft 1 made of a magnetic material, the magnetic The fluid retaining member 7 usually has a structure in which a pair of annular yokes 7b having the same outer diameter are fixed to both axial surfaces of an annular magnet 7a. The magnetic flux generated from the magnet is mainly caused by magnet 7a → one yoke 7b → one gap → rotation shaft 1 → other gap →
It passes along the path of the other yoke 7b-+fft stone 7a, and is designed to effectively hold the magnetic fluid.

〔発明が解決しようとする課題〕[Problem to be solved by the invention]

第３図にしめした従来例においては、環状の磁性流体保
持部材７と、ハウジング４の段差部３の軸方向底面３ａ
と内周面３ｂとの間にプラスチック等の非磁性体６を介
在させているが、これは、ハウジング４が磁性材から構
成されている場合には、磁性流体保持部材７の外周部か
らハウジング４に磁束が洩れるのを防止するために欠く
ことができないものである。In the conventional example shown in FIG.
A non-magnetic material 6 such as plastic is interposed between the inner circumferential surface 3b and the outer circumference of the magnetic fluid retaining member 7. This is indispensable to prevent magnetic flux from leaking to the magnetic flux.

もし、磁気的に十分な間隙を形成する厚さの非磁性体６
が無い場合には、磁束がヨーク外部に逃げるのを十分に
防止できず、磁性流体保持部材７の軸孔５の内周側の磁
力が弱まり磁性流体８を保持する力が弱まり、有用な磁
性流体シールが実現できなくなる。また、磁束が磁性体
ハウジングを通って、磁気ディスク装置の記録媒体にエ
ラーを生じさせる等、他の機器に悪影響をおよぼすこと
もある。If the non-magnetic material 6 is thick enough to form a magnetically sufficient gap,
If there is no magnetic flux, it will not be possible to sufficiently prevent the magnetic flux from escaping to the outside of the yoke, and the magnetic force on the inner circumferential side of the shaft hole 5 of the magnetic fluid holding member 7 will be weakened, and the force that holds the magnetic fluid 8 will be weakened, resulting in a loss of useful magnetic properties. A fluid seal cannot be achieved. Furthermore, the magnetic flux may pass through the magnetic housing and cause errors in the recording medium of the magnetic disk device, thereby adversely affecting other devices.

しかし、非磁性体を磁性流体保持部材とハウジングとの
間に気密状に配置するというのは、それだけ余分の部品
および工数を要し、工業的に軸封装置を製造する上で望
ましいものではない。また、非磁性体としては、通常、
プラスチック等の比較的軟らかい材料を用いているため
、磁性流体保持部材を組立る際に偏心を起こす恐れがあ
る。例えば、磁性流体を用いた軸封装置を構成する場合
、磁性流体保持部材と軸との間隙が不均一であるとギャ
ップの狭い部分に比べて広い部分の磁界が弱くなるため
、当然に磁性流体の保持力も不均一となり耐圧が弱くな
るので、偏心量は極めて小さい（数１０μｍ以下の精度
）ことが要求される。However, placing a non-magnetic material in an airtight manner between the magnetic fluid retaining member and the housing requires extra parts and man-hours, which is not desirable for industrially manufacturing shaft sealing devices. . In addition, as non-magnetic materials, usually
Since a relatively soft material such as plastic is used, eccentricity may occur when assembling the magnetic fluid holding member. For example, when configuring a shaft sealing device using magnetic fluid, if the gap between the magnetic fluid holding member and the shaft is uneven, the magnetic field will be weaker in the wide part than in the narrow part of the gap. Since the holding force becomes uneven and the withstand pressure becomes weak, the amount of eccentricity is required to be extremely small (accuracy of several tens of micrometers or less).

本発明は、上記実情に恵み、磁性流体保持部材の磁力を
有効に利用できる構造の磁性流体を使用した軸封装置を
提供することを目的とするものであり、また、容易に製
造が可能な軸封装置を提供することを目的とするもので
ある。SUMMARY OF THE INVENTION In view of the above circumstances, the present invention aims to provide a shaft sealing device using a magnetic fluid, which has a structure that can effectively utilize the magnetic force of a magnetic fluid holding member, and which can be easily manufactured. The object of the present invention is to provide a shaft sealing device.

〔課題を解決するための手段〕[Means to solve the problem]

本発明は、磁性体からなる軸を貫通装着するための軸孔
を有する少なくとも一対のヨークと、前記軸孔よりも大
きい径の孔を有し該孔が前記ヨークの軸孔とほぼ同心状
になるようにして前記一対のヨーク間に挟着された磁石
体とからなり、前記一対のヨークのうちの一方のヨーク
の外径を他方のヨークの外径より小としたことを特徴と
する磁性流体保持部材にある。The present invention provides at least a pair of yokes having a shaft hole for penetrating a shaft made of a magnetic material, and a hole having a diameter larger than the shaft hole, the hole being substantially concentric with the shaft hole of the yoke. and a magnet sandwiched between the pair of yokes in such a manner that the outer diameter of one of the pair of yokes is smaller than the outer diameter of the other yoke. Located in the fluid retaining member.

また、本発明は、貫通する軸の外径よりも十分大きい径
をもつ貫軸孔の少なくとも一端部に段差部が形成されて
いる磁性体からなるハウジングと、磁性体からなる軸を
貫通装着するための軸孔を有し前記ハウジングの段差部
に嵌合装着された磁性流体保持部材し、磁性体からなる
軸と磁性流体保持部材との間に保持される磁性流体とか
ら構成されるものであって、前記磁性流体保持部材は少
なくとも一対のヨークを有し、これらヨークの間に磁石
体が挟着されており、前記ヨークのうちの一方のヨーク
の外径を他方のヨークの外径より小さく形成することに
より、小さい方のヨーク外周面とハウジングの段差部内
周面との間隔を、他方のヨーク外周面とハウジングの段
差部内周面との間隔よりも大ならしめたことを特徴とす
る軸封装置にある。Further, the present invention provides a housing made of a magnetic material in which a stepped portion is formed at at least one end of a through-shaft hole having a diameter sufficiently larger than the outer diameter of the shaft passing through the housing, and a shaft made of the magnetic material being inserted through the housing. a magnetic fluid holding member that is fitted into the stepped portion of the housing, and the magnetic fluid is held between a shaft made of a magnetic material and the magnetic fluid holding member. The magnetic fluid holding member has at least a pair of yokes, a magnet is sandwiched between these yokes, and the outer diameter of one of the yokes is smaller than the outer diameter of the other yoke. By forming the yoke smaller, the distance between the outer peripheral surface of the smaller yoke and the inner peripheral surface of the stepped portion of the housing is made larger than the distance between the outer peripheral surface of the other yoke and the inner peripheral surface of the stepped portion of the housing. It is in the shaft sealing device.

また、本発明においては、前記磁石体の外径を小さい方
のヨークの外径以上で、かつ大きい方のヨークの外径以
下とすることにより、より好ましい特長を有する磁性流
体保持部材およびそれを用いた軸封装置を実現すること
ができる。Further, in the present invention, the outer diameter of the magnet body is set to be greater than or equal to the outer diameter of the smaller yoke and less than or equal to the outer diameter of the larger yoke. A shaft sealing device using this method can be realized.

本発明における磁性流体保持部材は、磁石の軸方向両端
面にヨークを固着して形成されるものであり、一方のヨ
ークの外径を他方のヨークの外径より小とすることによ
って、小さい方のヨークの外周面と磁性体からなるハウ
ジングの段差部内周面との間に磁気ギャップが構成され
るようにしたものである。The magnetic fluid holding member of the present invention is formed by fixing yokes to both axial end faces of a magnet, and by making the outer diameter of one yoke smaller than the outer diameter of the other yoke, the smaller one A magnetic gap is formed between the outer peripheral surface of the yoke and the inner peripheral surface of the stepped portion of the housing made of a magnetic material.

本発明においては、０．１　ｍｍ以下の磁気ギャップで
あっても、実質的に磁気抵抗を増大することができれば
有用である。しかし、加工精度上の問題もあり、十分な
磁気抵抗を安定して得るためには、上記磁気ギャップを
０．２　ｍｍ以上とすることが好ましく、特に０．５ｍ
以上であれば、実用上問題のない程度の十分な磁気抵抗
が得られる。また、本発明において、ヨーク間に挟着さ
れる磁石の外径は、大きな外径のヨークの外径と同じ大
きさから小さな外径のヨークの外径と同じ大きさの外径
まで任意に選ぶことができる。外径を大きくする（磁石
体積を大にする）と、ヨークと回転軸間に形成される間
隙部により強い磁場を生せしめることができるが、一方
、磁石の外径を小さくすることにより、より小型の磁性
流体保持部材が構成できるため、小型化・軽量化の面で
優位な軸封装置が実現できる。In the present invention, even a magnetic gap of 0.1 mm or less is useful if the magnetic resistance can be substantially increased. However, there are problems with processing accuracy, and in order to stably obtain sufficient magnetic resistance, it is preferable that the magnetic gap is 0.2 mm or more, particularly 0.5 m.
If it is above, sufficient magnetic resistance can be obtained without causing any practical problems. In addition, in the present invention, the outer diameter of the magnet sandwiched between the yokes can be arbitrarily set from the same outer diameter as the yoke with a large outer diameter to the same outer diameter as the outer diameter of the yoke with a small outer diameter. You can choose. Increasing the outer diameter (increasing the magnet volume) can generate a stronger magnetic field in the gap formed between the yoke and the rotating shaft, but on the other hand, by reducing the outer diameter of the magnet, it is possible to generate a stronger magnetic field. Since a compact magnetic fluid holding member can be constructed, a shaft sealing device that is advantageous in terms of size and weight reduction can be realized.

〔作用］ 上記手段の本発明による磁性流体を使用した軸封装置は
、磁性流体保持部材を構成する一方のヨークの外径を小
さ（し、そのヨーク外周と磁性体ハウジング内周面との
間にある程度の間隔を設けているので、磁石内周部にお
ける、磁石→一方のヨーク（小径のヨーク）→一方の間
隙部→回転軸→他方の間隙部→他方のヨーク（大径のヨ
ーク）→磁石という本来の磁路（磁性流体による軸封を
するための本来の経路）に比べ、磁石の外周部における
、磁石→小径のヨーク（一方のヨーク）→磁気ギヤツブ
→磁性体ハウジング→大径のヨーク（他方のヨーク）→
磁石という磁路は磁気抵抗が大きくなるため、洩れ磁束
が抑制される。よって、磁性流体保持部材における磁性
流体を保持する部分（ヨークの軸孔内周面と回転軸間に
形成される間隙部）の磁力を強めることができ、かつ磁
性体ハウジングを経由して洩れる磁束が少ないため他の
機器に悪影響を及ぼすことがない。[Function] The shaft sealing device using the magnetic fluid according to the present invention of the above means reduces the outer diameter of one of the yokes constituting the magnetic fluid holding member (and reduces the distance between the outer circumference of the yoke and the inner circumferential surface of the magnetic housing). Since a certain amount of space is provided between the inner circumference of the magnet, the magnet → one yoke (small diameter yoke) → one gap → the rotating shaft → the other gap → the other yoke (large diameter yoke) → Compared to the original magnetic path of the magnet (original path for shaft sealing with magnetic fluid), on the outer periphery of the magnet, the magnet → small diameter yoke (one yoke) → magnetic gear lug → magnetic housing → large diameter Yoke (other yoke) →
Since the magnetic path of a magnet has a large magnetic resistance, leakage magnetic flux is suppressed. Therefore, the magnetic force of the part of the magnetic fluid holding member that holds the magnetic fluid (the gap formed between the inner peripheral surface of the shaft hole of the yoke and the rotating shaft) can be strengthened, and the magnetic flux leaking through the magnetic housing can be strengthened. Because there is little amount of energy, there is no negative effect on other equipment.

〔実施例］ 以下、本発明を実施例に基づいて、より具体的に説明す
る。[Examples] Hereinafter, the present invention will be described in more detail based on Examples.

（実施例） 第１図は本発明による軸封装置の一実施例を示す要部断
面図である。図において、１は磁性体からなる回転軸で
あり、回転軸１は、貫軸孔２および該貫軸孔２の一端に
形成された段差部３を有する磁性体からなるハウジング
４内に装入配設されている。また、前記段差部３内には
、回転軸１を貫通装着するための軸孔５を有する一対の
ヨーク１ｂｒ、１ｂｔとの間に固着された磁石７ａとか
らなる磁性流体保持部材７が嵌合挿入され配設されてい
る。なお、磁石７ａには、前記ヨークの軸孔よりも大き
な径の孔が設けられており、該孔とヨークの軸孔とはほ
ぼ同心状になるようにして配置され、その軸方向に着磁
が施されている。(Embodiment) FIG. 1 is a sectional view of a main part showing an embodiment of a shaft sealing device according to the present invention. In the figure, 1 is a rotating shaft made of a magnetic material, and the rotating shaft 1 is inserted into a housing 4 made of a magnetic material having a through-shaft hole 2 and a stepped portion 3 formed at one end of the through-shaft hole 2. It is arranged. In addition, a magnetic fluid holding member 7 consisting of a magnet 7a fixed between a pair of yokes 1br and 1bt having a shaft hole 5 for penetrating the rotating shaft 1 is fitted into the stepped portion 3. inserted and placed. Note that the magnet 7a is provided with a hole having a larger diameter than the axial hole of the yoke, and the hole and the axial hole of the yoke are arranged so as to be almost concentric, and magnetized in the axial direction. is applied.

前記一対のヨークのうち、一方は外径の小さなヨーク７
ｂＩであり、他方は外径の大きなヨーク７ｂｚであり、
外径の大きなヨーク７ｂｚを段差部３の底面３ａおよび
内周面３ｂに当接固着した構成となっている。そして、
回転軸１と磁性流体保持部材７の各ヨーク軸孔内周面と
の間に磁性流体８を保持させた。また、外径が小さく形
成されたヨーク７ｂ、の外周面と段差部３の内周面３ｂ
との間には実質的に磁気ギャップ９が設けられ、この間
の磁気抵抗は大きなものとなる。したがって、例えば、
磁石７ａ→小径のヨーク７ｂ＋→間隙部→回転軸１→間
隙部→大径のヨーク７ｂｚ→磁石７ａに到る磁性流体に
よる軸封をするための本来の磁路に比べ、磁石７ａ→小
径のヨーク７ｂ。Among the pair of yokes, one is a yoke 7 having a small outer diameter.
bI, the other is a yoke 7bz with a large outer diameter,
The structure is such that a yoke 7bz having a large outer diameter is abutted against and fixed to the bottom surface 3a and inner circumferential surface 3b of the stepped portion 3. and,
A magnetic fluid 8 was held between the rotating shaft 1 and the inner peripheral surface of each yoke shaft hole of the magnetic fluid holding member 7. In addition, the outer circumferential surface of the yoke 7b formed with a small outer diameter and the inner circumferential surface 3b of the stepped portion 3
A magnetic gap 9 is substantially provided between them, and the magnetic resistance between them is large. Therefore, for example,
Magnet 7a→small diameter yoke 7b+→gap→rotating shaft 1→gap→large diameter yoke 7bz→magnet 7a York 7b.

→磁気ギヤツブ９→磁性体ハウジング４→大径のヨーク
７ｂｚ→磁石７ａという磁路の磁気抵抗は大きくなるの
で、相対的に洩れ磁束が抑制され磁性流体を保持する部
分の磁力が大きくなるので、より高い軸封効果が得られ
ることになる。→Magnetic gear 9→Magnetic housing 4→Large diameter yoke 7bz→Magnet 7a The magnetic resistance of the magnetic path becomes large, so the leakage magnetic flux is relatively suppressed and the magnetic force of the part that holds the magnetic fluid becomes large. A higher shaft sealing effect can be obtained.

と　じ　きざで　る　八であって　　　　の　はる゛　
上−と　　にしてハ　ヨークとハウジン磁石７ａとして
、外径１６．５　ｍｍ、内径９．４　ｍｍ、厚さ０．６
　ｍｍの環状フェライトボンド磁石を作成した。また、
外径の大なる方のヨーク７ｂ２として、磁性ステンレス
を用い、外径１６．５　ｍ、内径８．４価、厚さ０．２
　ｍｍの環状のヨーク板を作成した。さらに、外径の小
さい方のヨーク７ｂ、としては、磁性ステンレスを用い
、第１表に示すような外径を有し、内径８．４　ｍｍ、
厚さ０．２順の環状のヨーク板３種類を作成した。It's 8 and it's wide.
The upper and lower yoke and housing magnet 7a have an outer diameter of 16.5 mm, an inner diameter of 9.4 mm, and a thickness of 0.6 mm.
A circular ferrite bonded magnet with a diameter of 1 mm was created. Also,
The yoke 7b2 with the larger outer diameter is made of magnetic stainless steel, and has an outer diameter of 16.5 m, an inner diameter of 8.4 valence, and a thickness of 0.2 m.
An annular yoke plate with a diameter of mm was created. Further, the yoke 7b having a smaller outer diameter is made of magnetic stainless steel and has an outer diameter as shown in Table 1, an inner diameter of 8.4 mm,
Three types of annular yoke plates were created in order of thickness 0.2.

次に、上記ボンド磁石の両面に、上記した各々のヨーク
を、シアノアクリレート系接着剤を用いてほぼ同心状に
接着することにより本発明磁性流体保持部材（試料Ｎｏ
、　２〜４）を作製した。Next, each of the yokes described above is adhered to both surfaces of the bonded magnet in a substantially concentric manner using a cyanoacrylate adhesive to form a magnetic fluid holding member of the present invention (sample No.
, 2-4) were prepared.

これらの磁性流体保持部材を、磁性体からなる８　ｍｍ
の軸に嵌合させた状態で磁性材からなるハウジングに取
付けてから、磁性流体保持部材と軸との間隙部分に７．
５μ！の磁性流体を注入して保持させ、第１図に示す構
成の軸封装置を作製し、その耐圧力を調べた結果は第１
表に示す通りである。These magnetic fluid holding members are made of magnetic material with a diameter of 8 mm.
7. After fitting it to the shaft of the housing made of magnetic material, attach it to the gap between the magnetic fluid holding member and the shaft.
5μ! A shaft sealing device having the configuration shown in Fig. 1 was manufactured by injecting and retaining magnetic fluid, and the results of examining its withstand pressure were as follows.
As shown in the table.

尚、耐圧力は、密封容器内の圧力が５０　［Ｉｌｍ　）
ｌｚｏ／ｗｉｎの速さで加圧されるように空気を注入し
、磁性流体シール効果が破れ急激に圧力が減少し始める
直前の圧力（最大圧力）で示す。In addition, the pressure resistance inside the sealed container is 50 [Ilm]
Air is injected so as to be pressurized at a rate of lzo/win, and the pressure (maximum pressure) is shown just before the magnetic fluid sealing effect breaks and the pressure starts to decrease rapidly.

第　　　１　　　表 また、比較検討のために、上記各磁性流体保持部材を非
磁性ハウジングに装着した場合の耐圧力も調べ、同表に
示しである。さらにまた、比較例として両ヨークの外径
が等しい大きさの磁性流体保持部材を用いた場合（試料
Ｎｏ、　１　）についても検討し、同表に示しである。Table 1 In addition, for comparative study, the withstand pressure when each of the magnetic fluid holding members described above was attached to a non-magnetic housing was also investigated and is shown in the same table. Furthermore, as a comparative example, a case (sample No. 1) using a magnetic fluid holding member in which both yokes have the same outer diameter was also studied, and the results are shown in the same table.

第１表から明らかなように、本発明による磁性流体保持
部材は、非磁性材からなるハウジングに装着するよりも
、磁性体ハウジングに装着した方が高い耐圧力を得られ
ることがわかる。As is clear from Table 1, it can be seen that the magnetic fluid holding member according to the present invention can obtain a higher withstand pressure when attached to a magnetic housing than when attached to a housing made of a non-magnetic material.

また、本発明による磁性流体保持部材を、適切な設計を
行って磁性体ハウジングに取付けた場合（例えば、Ｎｏ
、　３　）には、従来方式のもの、すなわち比較例の磁
性流体保持部材を非磁性ハウジングに取付けた場合の耐
圧力（２４２ｍｌｌ□０）よりも優れた特性（２５２ｍ
ｍ　Ｈ２Ｏ）の得られることも分かる。これは、本発明
の磁性η体保持部材において、ヨークとハウジングとの
間には０．５　ｍｍ以上の間隔が存在することから、磁
性体ハウジングに取付けられた場合であっても、その部
分の磁気抵抗が大きいので、磁石から発生される磁束の
うち、ハウジング部を通って帰還してしまう分の磁束が
抑制されるためである。その結果、磁性流体を保持させ
るべき軸と磁性流体保持部材との間のギャップ部分に到
る磁束の量を相対的に増大させることが可能となるので
ある。Further, when the magnetic fluid holding member according to the present invention is installed in a magnetic housing with appropriate design (for example, No.
, 3) has better characteristics (252 m□0) than the conventional method, that is, the pressure resistance (242 m□0) when the magnetic fluid holding member of the comparative example is attached to a non-magnetic housing.
It can also be seen that m H2O) can be obtained. This is because in the magnetic η body holding member of the present invention, there is a gap of 0.5 mm or more between the yoke and the housing, so even when it is attached to the magnetic body housing, there is a gap between the yoke and the housing. This is because the magnetic resistance is large, so of the magnetic flux generated from the magnet, the amount of magnetic flux that returns through the housing portion is suppressed. As a result, it is possible to relatively increase the amount of magnetic flux that reaches the gap between the shaft where the magnetic fluid is to be held and the magnetic fluid holding member.

一方、比較例として示した両ヨークの外径が等しい大き
さの磁性流体保持部材（試料Ｎｏ、■）は、非磁性材の
ハウジングに取付けられた場合には高い耐圧力を示すも
のの、磁性材のハウジングに取付けられた場合には耐圧
力が著しく低下してしまい使用に耐えないことがわかる
。これは、磁性体ハウジングに取付けた場合には、磁石
から発生された磁束が主としてハウジングを通って磁石
に帰還してしまうために、磁性流体を保持させるべき軸
と磁性流体保持部材との間の間隙部分に到る磁束の量が
著しく減少してしまうためである。On the other hand, the magnetic fluid holding member shown as a comparative example in which both yokes have the same outer diameter (Sample No., ■) exhibits high withstand pressure when installed in a housing made of non-magnetic material, but It can be seen that when installed in a housing of This is because when it is installed in a magnetic housing, the magnetic flux generated from the magnet returns to the magnet mainly through the housing, so there is a gap between the shaft that is supposed to hold the magnetic fluid and the magnetic fluid holding member. This is because the amount of magnetic flux reaching the gap portion is significantly reduced.

本発明者等は、この様子をコンピュータを用いた磁場解
析シミュレーションにより解析した。その結果の一例を
第４図および第５図に示す。すなわち、第４図から明瞭
にわかるように、従来の構造の軸封装置においては、磁
石７ａから発生した磁束１０は、ヨーク７ｂを通って磁
性体ハウジング４にほとんど流れてしまい、磁性流体を
保持させるべき間隙部分５（すなわち、回転軸１とヨー
ク７ｂとが作る間隙）に到る磁束の量は極めて少なくな
っていることがわかる。The present inventors analyzed this situation using a magnetic field analysis simulation using a computer. An example of the results is shown in FIGS. 4 and 5. That is, as can be clearly seen from FIG. 4, in the shaft sealing device of the conventional structure, most of the magnetic flux 10 generated from the magnet 7a flows into the magnetic housing 4 through the yoke 7b, which holds the magnetic fluid. It can be seen that the amount of magnetic flux that reaches the gap portion 5 (that is, the gap formed between the rotating shaft 1 and the yoke 7b) is extremely small.

これに対し、本発明の一例として試料面、３の場合につ
いて示す第５図では、磁石７ａから発生した磁束ｌＯの
多くは、小径のヨーク７ｂ、を通って軸１の方へ流れ、
磁性流体を保持させるべき間隙部分５にも多くの磁束が
通っている。これは、ヨーク７ｂ＋　の外径が、もう一
方のヨーク７ｂ２よりも小さいので、ヨーク７ｂｚの外
径にほぼ等しい外径の段差部内周面３ｂとの間に大きな
間隙が生じ、その部分での磁束の流れが阻止されること
に基づくことがわかる。On the other hand, in FIG. 5, which shows the case of sample surface 3 as an example of the present invention, most of the magnetic flux lO generated from the magnet 7a flows toward the axis 1 through the small diameter yoke 7b.
A large amount of magnetic flux also passes through the gap portion 5 where the magnetic fluid is to be held. This is because the outer diameter of the yoke 7b+ is smaller than the other yoke 7b2, so a large gap is created between the yoke 7b+ and the stepped inner circumferential surface 3b, which has an outer diameter approximately equal to the outer diameter of the yoke 7bz, and the magnetic flux at that part is reduced. It can be seen that this is based on the fact that the flow of is blocked.

また、第１表に示した各磁性流体保持部材を磁性体ハウ
ジングに取付けて、磁性流体の注入量を変えた場合の耐
圧力の変化を第６図に示す。第６図から、磁性流体の注
入量によって一度耐圧力が小さくなる不安定領域がある
が、その後は注入量にほぼ比例して耐圧力が向上するこ
とがわかる。Furthermore, FIG. 6 shows changes in withstand pressure when each of the magnetic fluid holding members shown in Table 1 is attached to a magnetic housing and the amount of magnetic fluid injected is changed. From FIG. 6, it can be seen that there is an unstable region where the withstand pressure decreases once depending on the injection amount of magnetic fluid, but after that, the withstand pressure improves almost in proportion to the injection amount.

また、同図から、従来の磁性流体保持部材である試料Ｎ
ｏ、　１を用いた場合に比較して、本発明の磁性流体保
持部材である試料Ｎｏ、２．３．４を用いた場合には、
いずれの注入量でも高い耐圧力を示しており、本発明の
ものが優れていることが明らかである。Also, from the same figure, sample N, which is a conventional magnetic fluid holding member.
Compared to the case where Sample No. 2.3.4, which is the magnetic fluid holding member of the present invention, was used,
It is clear that the inventive method is superior as it shows a high pressure resistance regardless of the injection amount.

（実施例２） 本発明の他の実施例として、第１図に示した構成の軸封
装置において、磁石の大きさを変えた場合について説明
する。(Example 2) As another example of the present invention, a case will be described in which the size of the magnet is changed in the shaft sealing device configured as shown in FIG. 1.

磁石７として、第２表に示すような外径を有し、内径は
９．４　ｒｒｍ、厚さは０．６　＋ｎｍの環状フェライ
トボンド磁石を作成した。また、外径の大きいヨークと
して、磁性ステンレスを用いて、外径１６．５　＋＋ｏ
ｎ。As the magnet 7, an annular ferrite bonded magnet was prepared having an outer diameter as shown in Table 2, an inner diameter of 9.4 rrm, and a thickness of 0.6 + nm. In addition, as a yoke with a large outer diameter, magnetic stainless steel is used to create a yoke with an outer diameter of 16.5 ++ o.
n.

内径８．４　［１ｍ、厚さ０．２　ｍｍの環状のヨーク
を作成した。An annular yoke with an inner diameter of 8.4 m and a thickness of 0.2 mm was created.

さらにまた、小さい方のヨークとして、磁性ステンレス
を用いて第２表に示すような外径を有し、内径は８．４
　ｍｍ、厚さは０．２ｍｍの環状のヨークを作成した。Furthermore, the smaller yoke is made of magnetic stainless steel and has an outer diameter as shown in Table 2, and an inner diameter of 8.4 mm.
An annular yoke having a thickness of 0.2 mm and a thickness of 0.2 mm was prepared.

次に、上記ボンド磁石の両面に、上記各々のヨークをシ
アノアクリレート系樹脂接着剤を用いてほぼ同心状に接
着することにより、本発明の磁性流体保持部材（試料Ｎ
ｏ、　５〜７）を作製した。Next, the magnetic fluid holding member of the present invention (sample N
o, 5-7) were prepared.

これらの磁性流体保持部材を、磁性体から成る８胴の軸
に嵌合させた状態で磁性体ハウジングおよび磁性体ハウ
ジングに取付けてから、上記磁性流体保持部材と軸との
間隙部分に７．５μ！の磁性流体を注入して保持させた
ときの耐圧力を調べた。These magnetic fluid holding members are fitted to the shaft of the eight cylinders made of magnetic material and attached to the magnetic housing and the magnetic housing, and then a 7.5μ ! The withstand pressure was investigated when a magnetic fluid was injected and held.

その結果は第２表に示した通りである。The results are shown in Table 2.

実施例１で述べたように、比較例の磁性流体保持部材は
、非磁性体ハウジングに取付けられた場合には高い耐圧
力を示すが、磁性体ハウジングに取付けられた場合には
、磁性流体保持部材の磁束がハウジング部を通って帰還
してしまうため、磁性流体を保持させるべき軸と磁性流
体保持部材との間の間隙部分に到る磁束の量が減少し、
耐圧力が著しく低下してしまい使用に耐えない。As described in Example 1, the magnetic fluid retaining member of the comparative example exhibits high pressure resistance when attached to a non-magnetic housing, but when attached to a magnetic housing, the magnetic fluid retaining member exhibits high pressure resistance. Since the magnetic flux of the member returns through the housing part, the amount of magnetic flux that reaches the gap between the shaft where the magnetic fluid is to be held and the magnetic fluid holding member is reduced.
The pressure resistance has decreased significantly and it cannot be used.

これに対して、本発明の磁性流体保持部材は、磁性体ハ
ウジングに取付けられた場合には耐圧力の低下はわずか
であることが分かる。In contrast, it can be seen that when the magnetic fluid holding member of the present invention is attached to a magnetic housing, the withstand pressure decreases only slightly.

これは、本発明の磁性流体保持部材においては、磁性体
ハウジングに取付けられた場合にも、ヨークとハウジン
グとの間には０．５Ｍ以上の間隔が存在することから、
その部分の磁気抵抗が増大し、磁石から発生した磁束が
ハウジング部を通って帰還してしまうことが抑制される
ためである。その結果、磁性流体を保持させるべき軸と
磁性流体保持部材との間のギャップ部分に到る磁束の量
を相対的に増大させることが可能となり、優れた特性の
軸封装置が実現できたものである。This is because in the magnetic fluid holding member of the present invention, even when attached to a magnetic housing, there is a gap of 0.5M or more between the yoke and the housing.
This is because the magnetic resistance of that portion increases, and the magnetic flux generated from the magnet is prevented from returning through the housing portion. As a result, it became possible to relatively increase the amount of magnetic flux that reaches the gap between the shaft where the magnetic fluid is to be held and the magnetic fluid holding member, making it possible to realize a shaft sealing device with excellent characteristics. It is.

この様子は、第７図に示すコンピュータを用いた磁場解
析シミュレーションから、より明瞭に分かる。すなわち
、第゛７図は、磁石７ａから発生した磁束１０の多くは
、ヨーク７ｂ、を通って軸１の方へ流れ、磁性流体を保
持させるべき間隙部分５にも多くの磁束が通っている。This situation can be seen more clearly from the computer-based magnetic field analysis simulation shown in FIG. That is, in FIG. 7, most of the magnetic flux 10 generated from the magnet 7a flows toward the shaft 1 through the yoke 7b, and much of the magnetic flux also passes through the gap 5 where the magnetic fluid is to be held. .

これは、ヨーク７ｂ、の外径が、もう一方のヨーク７ｂ
ｚよりも小さいので、コーク７ｂｚの外径にほぼ等しい
（ｎ性体ハウジングの段差部内周壁面３ｂとの間に大き
な磁気ギャップが生じ、その部分での磁気抵抗が大きく
、磁束の流れが阻止されることに基づく。This means that the outer diameter of the yoke 7b is the same as that of the other yoke 7b.
Since it is smaller than z, it is almost equal to the outer diameter of coke 7bz (a large magnetic gap is created between the inner circumferential wall surface 3b of the step part of the n-type material housing, the magnetic resistance is large in that part, and the flow of magnetic flux is blocked. Based on that.

また、第２表の各磁性流体保持部材を磁性体ハウジング
に取付けて、磁性流体注入量を変えた場合の耐圧力の変
化を第８図に示す。第８図において、従来の磁性流体保
持部材である試料Ｎα１に比較して、本発明の磁性流体
保持部材である試料Ｎ。Further, FIG. 8 shows changes in withstand pressure when each magnetic fluid holding member shown in Table 2 is attached to a magnetic housing and the amount of magnetic fluid injected is changed. In FIG. 8, Sample N, which is a magnetic fluid holding member of the present invention, is compared to Sample Nα1, which is a conventional magnetic fluid holding member.

５．６．７は、いずれも高い耐圧力を示していることが
分かる。特に、本発明による磁性流体保持部材である試
料Ｎｏ、　７は、比較例のものに比べ、磁石体積が約半
分程度であるにもかかわらず、同等以上の耐圧力を示し
ており、本発明のものが軸封装置の小型化・高性能化に
極めて有効であることが明らかである。It can be seen that samples Nos. 5, 6, and 7 all exhibit high pressure resistance. In particular, Sample No. 7, which is a magnetic fluid holding member according to the present invention, shows a pressure resistance equal to or higher than that of the comparative example, even though the magnet volume is about half that of the comparative example. It is clear that this method is extremely effective in downsizing and improving the performance of shaft sealing devices.

（実施例３） 本発明の更に他の実施例を、第２図を参照しながら説明
する。(Embodiment 3) Still another embodiment of the present invention will be described with reference to FIG.

この実施例は、ボンド磁石７ａの両側のヨーク１ｂ＋、
１ｂｚのうち、ハウジング４に形成した段差部３の底面
３ａに対向する側のヨーク７ｂ。In this embodiment, the yokes 1b+ on both sides of the bonded magnet 7a,
1bz, the yoke 7b on the side facing the bottom surface 3a of the stepped portion 3 formed in the housing 4.

として外径の小さいヨークを用いたものであり、そのヨ
ーク７ｂ、と段差部３との間にプラスチック等の非磁性
体６を介在させて、ヨーク７ｂ＋　と磁性体ハウジング
４との間に実質的な磁気ギヤッブを形成し、磁性流体保
持部材５の外周部から磁束がハウジングに洩れるのを防
止したものである。A yoke with a small outer diameter is used as a yoke, and a non-magnetic material 6 such as plastic is interposed between the yoke 7b and the stepped portion 3, so that there is a substantial gap between the yoke 7b+ and the magnetic housing 4. A magnetic gear is formed to prevent magnetic flux from leaking into the housing from the outer circumference of the magnetic fluid holding member 5.

反対側のヨーク７ｂｚは、前記ヨーク７ｂ＋　より外径
が大きく、その外周面が磁性体ハウジング４の段差部３
に嵌合挿入され、その内周壁面３ｂに固着されており、
各ヨーク７ｂ＋、７１）ｚの軸孔と回転軸１との間に、
実施例１と同様に磁性流体３が保持させている。The yoke 7bz on the opposite side has a larger outer diameter than the yoke 7b+, and its outer peripheral surface is similar to the stepped portion 3 of the magnetic housing 4.
is fitted and inserted into and fixed to the inner peripheral wall surface 3b,
Between the shaft hole of each yoke 7b+, 71)z and the rotating shaft 1,
As in the first embodiment, the magnetic fluid 3 is used to hold it.

尚、第２図では、磁石７ａの外径が小径ヨークの外径よ
りも小さなものが示されているが、磁石の外径を小径ヨ
ークの外径よりも大きくしても良く、例えば大径ヨーク
と同じ外径としても本発明の効果が得られることは実施
例１でも述べた通りである。In addition, in FIG. 2, the outer diameter of the magnet 7a is shown to be smaller than the outer diameter of the small-diameter yoke, but the outer diameter of the magnet may be larger than the outer diameter of the small-diameter yoke. As described in the first embodiment, the effect of the present invention can be obtained even if the outer diameter is the same as that of the yoke.

第２図では、非磁性体６をヨーク７ｂ、の外周部にまで
延長させているが、必ずしもそのように延長させる必要
はない。また、第２図のような構成の場合、小径のヨー
クと段差部底面との間に非磁性体を介在させるが、本発
明では、芯だしは大径ヨーク部で行われ小径ヨーク部は
芯だしに寄与しないため、小径ヨークの挿入時に生ずる
非磁性体の変形に起因する偏心の恐れは極めて少ない。In FIG. 2, the non-magnetic material 6 is extended to the outer periphery of the yoke 7b, but it is not necessary to extend it that way. In addition, in the case of the configuration shown in Fig. 2, a non-magnetic material is interposed between the small diameter yoke and the bottom surface of the stepped part, but in the present invention, centering is performed in the large diameter yoke part, and centering is performed in the small diameter yoke part. Since it does not contribute to the deflection, there is extremely little risk of eccentricity caused by deformation of the nonmagnetic material that occurs when inserting the small diameter yoke.

また、本実施例の構造の場合には、第１図に示した構造
のものに比べ、芯だしに寄与する大径ヨーク部分は段差
部の上部（換言すれば外部側）に近い部分に嵌合される
ため、高精度の嵌めあい加工を施す部分が少なくてすみ
、加工がまた容易に嵌合できるという利点がある。Furthermore, in the case of the structure of this embodiment, compared to the structure shown in FIG. Since the parts are fitted together, there are fewer parts that require high-precision fitting processing, and there is an advantage that the fitting process can be easily performed.

外径１６．５１１１１１、内径９．４ｍｍ、厚さ０．６
印の磁石と、外径１６．５ｍｍ、内径８．４唾、厚さ０
．２　ｍｍの大径ヨークと、外径１４．５胴、内径８．
４　＋ｎｍ、厚さ０、２　ｍｍの大径ヨークとからなる
保持部材を用い、第２図の構成の軸封装置を構成した。Outer diameter 16.511111, inner diameter 9.4mm, thickness 0.6
Magnet with mark, outer diameter 16.5 mm, inner diameter 8.4 mm, thickness 0
．． 2 mm large diameter yoke, outer diameter 14.5 mm, inner diameter 8.5 mm.
A shaft sealing device having the configuration shown in FIG. 2 was constructed using a holding member consisting of a large diameter yoke with a diameter of 4 + nm and a thickness of 0.2 mm.

なお、小径ヨークと段差部底部との間隙が１．５　ｍと
なるように非磁性スペーサを設けた。得られた装置の耐
圧力は２１０　ｍｍ　ＨｚＯであり、十分実用できるも
のであった。また、このとき磁束分布をシミュレーショ
ン解析した結果を第９図に示す。この図から、本実施例
の場合にも良好な磁束分布が得られることが明らかであ
る。Note that a nonmagnetic spacer was provided so that the gap between the small diameter yoke and the bottom of the stepped portion was 1.5 m. The resulting device had a pressure resistance of 210 mm HzO, which was sufficient for practical use. Further, the results of a simulation analysis of the magnetic flux distribution at this time are shown in FIG. From this figure, it is clear that a good magnetic flux distribution can be obtained also in this example.

なお、上記実施例の説明においては、いずれも磁石とし
てボンド磁石を用い、このボンド磁石は、ナイロンにフ
ェライトあるいは希土類金属を混入させて磁力を持たせ
たものとしたが、本発明においては、ボンド磁石以外の
磁石、例えば焼結磁石等を通用することも可能である。In the description of the above embodiments, a bonded magnet was used as the magnet, and this bonded magnet was made by mixing ferrite or rare earth metal into nylon to give it magnetic force. It is also possible to use magnets other than magnets, such as sintered magnets.

「発明の効果」 以上述べたように、本発明による磁性流体保持部材ある
いはそれを使用した軸封装置は、磁石の両面に設けたヨ
ークの一方を、その外径を小さくしてヨーク外周部と磁
性体ハウジングとの間の間隔を大きくすることにより磁
路に抵抗を与え、磁束が外部に逃げることを抑止してい
るので、特に磁性体ハウジングの一部を貫通する軸に適
用された場合に、優れた効果を示すものである。また、
磁性流体保持部材の軸孔内周部の磁力は十分に強く、設
計が適切である場合には、従来の磁性流体保持用磁性流
体保持部材を非磁性ハウジングに取付けた場合の磁力を
も凌ぐものとなり、磁性流体の保持が確実となる。また
、磁束が磁性体ハウジング外部に洩れて他の機器に悪影
響を及ぼすこともない。さらには、ヨーク用材料、磁石
材料の使用量も少なくてすみ、経済的であるとともに密
封装置の軽量化にも役立つものである。"Effects of the Invention" As described above, the magnetic fluid holding member according to the present invention or the shaft sealing device using the same has the advantage of reducing the outer diameter of one of the yokes provided on both sides of the magnet to form the outer circumference of the yoke. By increasing the distance between the magnetic housing and the magnetic housing, it provides resistance to the magnetic path and prevents the magnetic flux from escaping to the outside, so this is especially true when applied to a shaft that passes through a part of the magnetic housing. , which shows excellent effects. Also,
The magnetic force at the inner periphery of the shaft hole of the magnetic fluid retaining member is sufficiently strong, and if the design is appropriate, it can exceed the magnetic force when a conventional magnetic fluid retaining member for retaining magnetic fluid is attached to a non-magnetic housing. This ensures that the magnetic fluid is retained. Furthermore, the magnetic flux does not leak to the outside of the magnetic housing and adversely affect other devices. Furthermore, the amount of yoke material and magnet material used can be reduced, which is economical and also helps to reduce the weight of the sealing device.

【図面の簡単な説明】[Brief explanation of the drawing]

第１図は本発明による軸封装置の一例を示す要部断面図
、第２図は本発明の他の実施例の一つを示す軸封装置の
要部断面図、第３図は従来の軸封装置の要部断面図、第
４図は従来の磁性流体保持用磁性流体保持部材を磁性体
ハウジングに取付けた場合についてコンピュータシミュ
レーションによる磁気解析した結果による磁束の流れ図
、第５図、第７図、および第９図は本発明の磁性流体保
持用磁性流体保持部材を磁性体ハウジングに取付けたと
きのコンピュータシミュレーションによる磁気解析した
結果による磁束の流れ図、第６図および第８図は本発明
および比較例における磁性流体の注入量と耐圧力の関係
を示す図である。 に回転軸、２：貫通孔、３：段差部、４：磁性体ハウジ
ング、５：磁性流体を保持させるべきギャップ部分、 ：非磁性体、 ：磁性流体保持 部材、 ：磁性流体、 ：磁束。 第 図 第 図 第 図 ＭＡＧＮＥＴＩＣＦＬＬＩＩＯ（＃ＪＡ）第 図FIG. 1 is a sectional view of a main part showing an example of a shaft sealing device according to the present invention, FIG. 2 is a sectional view of a main part of a shaft sealing device showing one of other embodiments of the invention, and FIG. 4 is a sectional view of the main part of the shaft sealing device, and FIG. 4 is a magnetic flux flow diagram based on the results of magnetic analysis using computer simulation when a conventional magnetic fluid holding member for holding magnetic fluid is attached to a magnetic housing. FIGS. 5 and 7 are 9 and 9 are flow charts of magnetic flux based on the results of magnetic analysis by computer simulation when the magnetic fluid holding member for holding magnetic fluid of the present invention is attached to a magnetic housing, and FIGS. FIG. 7 is a diagram showing the relationship between the injection amount of magnetic fluid and the withstand pressure in a comparative example. rotating shaft, 2: through hole, 3: stepped portion, 4: magnetic housing, 5: gap portion where magnetic fluid is to be held, : non-magnetic material, : magnetic fluid holding member, : magnetic fluid, : magnetic flux. Fig. Fig. Fig. Fig. MAGNETICFLLIIO (#JA) Fig.

Claims (3)

【特許請求の範囲】[Claims] （１）磁性体からなる軸を貫通装着するための軸孔を有
する少なくとも一対のヨークと、前記軸孔よりも大きい
径の孔を有し該孔が前記ヨークの軸孔とほぼ同心状にな
るようにして前記一対のヨーク間に挟着された磁石体と
からなり、前記一対のヨークのうちの一方のヨークの外
径を他方のヨークの外径より小としたことを特徴とする
磁性流体保持部材。(1) at least a pair of yokes each having a shaft hole for penetrating a shaft made of a magnetic material, and a hole having a diameter larger than the shaft hole, the hole being approximately concentric with the shaft hole of the yoke; and a magnetic body sandwiched between the pair of yokes as described above, wherein the outer diameter of one of the pair of yokes is smaller than the outer diameter of the other yoke. Holding member. （２）請求項１に記載の磁性流体保持部材において、前
記磁石体の外径を小さい方のヨークの外径以上で、かつ
大きい方のヨークの外径以下としたことを特徴とする磁
性流体保持部材。(2) The magnetic fluid holding member according to claim 1, wherein the outer diameter of the magnet body is greater than or equal to the outer diameter of the smaller yoke and less than or equal to the outer diameter of the larger yoke. Holding member. （３）貫通する軸の外径よりも十分大きい径をもつ貫軸
孔の少なくとも一端部に段差部が形成されている磁性体
からなるハウジングと、磁性体からなる軸を貫通装着す
るための軸孔を有し前記ハウジングの段差部に嵌合装着
された磁性流体保持部材と、磁性体からなる軸と磁性流
体保持部材との間に保持される磁性流体とから構成され
、前記磁性流体保持部材は少なくとも一対のヨーク間に
磁石体を挟着したものであって、一方のヨークの外径を
他方のヨークの外径より小さく形成することにより、小
さい方のヨーク外周面とハウジングの段差部内周面との
間隔を、他方のヨーク外周面とハウジングの段差部内周
面との間隔よりも大ならしめたことを特徴とする軸封装
置。(3) A housing made of a magnetic material in which a stepped portion is formed at least at one end of a through-shaft hole having a diameter sufficiently larger than the outer diameter of the shaft to be penetrated, and a shaft for penetrating the shaft made of a magnetic material. The magnetic fluid holding member is composed of a magnetic fluid holding member having a hole and fitted into the stepped portion of the housing, and a magnetic fluid held between a shaft made of a magnetic material and the magnetic fluid holding member. A magnetic body is sandwiched between at least a pair of yokes, and by forming the outer diameter of one yoke smaller than the outer diameter of the other yoke, the outer circumferential surface of the smaller yoke and the inner circumference of the stepped portion of the housing are A shaft sealing device characterized in that the distance between the outer circumferential surface of the other yoke and the inner circumferential surface of the stepped portion of the housing is larger than the distance between the outer circumferential surface of the other yoke and the inner circumferential surface of the stepped portion of the housing.