JPH0540663U - Magnetic fluid sealing device - Google Patents

Abstract

(57) [Summary] [Purpose] To reduce the thickness and make it compact, and to secure sufficient sealing performance. [Structure] The maximum energy product of a permanent magnet 7 constituting a magnetic fluid seal device used adjacent to a magnetically permeable bearing is set to 3 MG · Oe or more. Further, the density of the magnetic flux existing in the gap 10 corresponding to the inner peripheral edge of the pole piece 8 on the bearing side is set to 1 in the space corresponding to the inner peripheral surface of the permanent magnet 7 of the magnetic flux density of the portion in contact with this inner peripheral surface. 3 times or more.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The magnetic fluid seal device according to the present invention is used when, for example, a portion where a hard disk drive shaft incorporated in a computer or the like penetrates a wall surface of a casing is kept airtight.

[0002]

[Prior Art]

 It is necessary to provide a seal device at the part where the drive shaft of the motor for hard disk storage device built into a computer or the like penetrates the wall surface of the casing containing the hard disk to prevent foreign matter such as dust from passing through. A magnetic fluid seal device disclosed in Japanese Patent Laid-Open No. 62-110080 has been generally used as a seal device installed in such a portion to prevent passage of dust and the like. There is.

The structures of conventionally known magnetic fluid sealing devices differ in detail, but basically they have the structures shown in FIGS. In FIG. 1, reference numeral 1 denotes a housing having an inner peripheral surface made of a non-magnetic material such as aluminum or synthetic resin, which is fixed to, for example, the wall surface of the casing. Reference numeral 2 is a shaft made of a magnetic material such as iron, and the magnetic fluid seal device main body 3 is installed in a cylindrical space 6 between the inner peripheral surface 4 of the housing 1 and the outer peripheral surface 5 of the shaft 2. To be done.

The magnetic fluid seal device main body 3 has a pair of circular ring-shaped permanent magnets 7 magnetized in the axial direction (left and right direction in FIG. 1) and made of a magnetic material. It is sandwiched between pole pieces 8 and 9, and magnetic fluids 11 and 11 are placed in the gaps 10 and 10 between the inner peripheral edges of the pole pieces 8 and 9 and the outer peripheral surface 5 of the shaft 2, respectively. It is composed by being held by force. The main body 3 of the magnetic fluid sealing device is fixed to the inner peripheral surface 4 of the housing 1 by internal fitting, adhesion or the like.

The magnetic fluid seal device body 3 is configured as described above, and is mounted between the inner peripheral surface 4 of the housing 1 and the outer peripheral surface 5 of the shaft 2 to configure the magnetic fluid seal device as described above. Therefore, regardless of the rotation of the shaft 2 inside the housing 1 or the rotation of the housing 1 around the shaft 2, the outer peripheral surface 5 of the shaft 2 and the inner peripheral edges of the pole pieces 8, 9 are The magnetic fluids 11, 11 held in between hold the sealing property between the inner peripheral surface 4 of the housing 1 and the outer peripheral surface 5 of the shaft 2.

As shown in FIG. 2, the outer peripheral surface 5 of the shaft 2 is made of a non-magnetic material and the inner peripheral surface 4 of the housing 1 is made of a magnetic material, and the permanent magnet 7 and a pair of pole pieces are formed. 8 and 9 are externally fitted and fixed on the outer peripheral surface 5 side of the shaft 2, and the magnetic fluids 11 and 11 are retained between the outer peripheral edges of the respective pole pieces 8 and 9 and the inner peripheral surface 4 of the housing 1. Fluid seal devices are also known in the art.

[0007]

[Problems to be solved by the device]

By the way, due to the recent miniaturization of hard disk storage devices and the like, there is a demand for reducing the thickness dimension (the dimension in the left-right direction in FIGS. 1 and 2) of the magnetic fluid seal device configured and used as described above. Is coming out. When thinning the magnetic fluid sealing device, it is necessary to use a permanent magnet 7 having a large magnetic force, that is, a large maximum energy product BH _{max in} order to secure the holding force of the magnetic fluids 11, 11. Occurs.

For this reason, the present inventor conventionally used the permanent magnet 7 having a maximum energy product of about 2 MG · Oe, while the permanent magnet 7 having a maximum energy product of 3 MG · Oe or more was used. , The magnetic fluid sealing device was studied.

However, in the case of the conventional permanent magnet 7 having a maximum energy product of up to about 2 MG · Oe, the magnetic flux mainly comes in and goes out from both axial end surfaces of the permanent magnet 7, which causes a particular problem. Although it does not occur, in the case of a permanent magnet 7 having a maximum energy product of 3 MG · Oe or more, since the magnetic flux goes in and out not only from both end surfaces of this permanent magnet 7 but also from the peripheral surface, the magnetic fluids 11, 11 described above However, this tends to be attracted to the peripheral surface of the permanent magnet 7, and the amount of the magnetic fluid 11, 11 existing in the gaps 10, 10 tends to be insufficient.

In particular, when a magnetic fluid seal device is adjacent to a magnetically permeable bearing (not shown) provided between the housing 1 and the shaft 2, a part of the magnetic flux emitted from the permanent magnet 7 is generated by this bearing. And the density of the magnetic flux existing in the gap 10 between the peripheral edge of the pole piece 8 (or 9) on the bearing side and the outer peripheral surface 5 of the shaft 2 (or the inner peripheral surface 4 of the housing 1) becomes low. End up.

As a result, the magnetic fluid 11 to be retained in the gap 10 is attracted by the magnetic flux flowing in and out from the peripheral surface of the permanent magnet 7, and is sandwiched between the pair of pole pieces 8 and 9. It moves to the pocket 12 facing the peripheral surface of the permanent magnet 7, and the amount of the magnetic fluid 11 existing in the gap 10 is insufficient. If it is significant, the seal of the gap 10 cannot be performed. .

The magnetic fluid sealing device of the present invention eliminates the above-mentioned inconvenience.

[0013]

[Means for solving the problem]

 The magnetic fluid sealing device of the present invention is configured, for example, as shown in FIGS. 1 and 2, like the conventional magnetic fluid sealing device described above.

The shaft 2 or the housing 1 which is the first member made of a magnetic material has an outer peripheral surface 5 or an inner peripheral surface 4 which is a cylindrical peripheral surface. The second member, the housing 1 or the shaft 2, is provided concentrically with the first member, the shaft 2 or the housing 1, and rotates relative to the shaft 2 or the housing 1. The permanent magnet 7 magnetized in the axial direction has a size such that it can be inserted into a cylindrical space 6 between the inner peripheral surface 4 of the housing 1 and the outer peripheral surface 5 of the shaft 2. It is formed in a ring shape. A pair of pole pieces 8 and 9 fixed to both side surfaces of the permanent magnet 7 are formed in a circular ring shape having a size that can be inserted into the cylindrical space 6. The magnetic fluids 11 and 11 are placed in the gaps 10 and 10 between the inner peripheral edge or outer peripheral edge of the pole pieces 8 and 9 and the outer peripheral surface 5 of the shaft 2 or the inner peripheral surface 4 of the housing 1, respectively. It is held by the magnetic force of the permanent magnet 7. A bearing (not shown) having magnetic permeability is provided between the outer peripheral surface 5 of the shaft 2 and the inner peripheral surface 4 of the housing 1 to allow relative rotation between the shaft 2 and the housing 1. . The main body 3 of the magnetic fluid sealing device including the permanent magnet 7 and the pole pieces 8 and 9 is used in a state of being adjacent to the bearing.

Further, in the magnetic fluid sealing device of the present invention, the maximum energy product of the permanent magnet 7 is set to 3 MG · Oe or more. At the same time, the density of the magnetic flux existing in the gap 10 corresponding to the inner peripheral edge or the outer peripheral edge of the bearing-side pole piece 8 (or 9) is determined by comparing the inner peripheral surface or the outer peripheral surface of the permanent magnet 7 with the shaft 2 1.3 times or more the density of the magnetic flux existing in the space between the outer peripheral surface 5 or the inner peripheral surface 4 of the housing 1 and in the portion in contact with the inner peripheral surface or the outer peripheral surface of the permanent magnet 7. It is characterized by what was done.

[0016]

[Action]

 In the case of the magnetic fluid sealing device of the present invention configured as described above, the density of the magnetic flux existing in the gap 10 corresponding to the peripheral edge of the pole piece 8 (or 9) on the bearing side is determined by the magnetic flux density of the permanent magnet 7. In the space corresponding to the surface, the density of the magnetic flux existing in the portion in contact with the peripheral surface is set to 1.3 times or more, so that the space in the gap 10 is sufficient regardless of the magnetic flux in the portion in contact with the peripheral surface. A quantity of ferrofluid 11 will be retained. As a result, the sealing property of the gap 10 portion is secured. The density of the magnetic flux existing in the gap 10 corresponding to the peripheral edge of the pole piece 9 (or 8) on the side opposite to the bearing is necessarily higher than the density of the magnetic flux existing in the gap 10 on the bearing side. A sufficient amount of the magnetic fluid 11, 11 is retained also in the gaps 10, 10.

In order to make the density of the magnetic flux existing in the gap 10 portion higher than the density of the magnetic flux existing in the portion in contact with the peripheral surface, the dimension of the gap 10 in the radial direction is changed, Alternatively, the thickness of the pole piece 8 (or 9) is changed. The smaller the radial dimension of the gap 10, the higher the density of the magnetic flux existing in the gap 10, so that the above-mentioned gap 10 can be sufficiently secured in the range where the amount of the magnetic fluid 10 retained in the gap 10 can be sufficiently secured. Reduce the radial dimension of 10. Further, as the thickness of the pole piece 8 (or 9) is made smaller (thinner), by concentrating the magnetic flux, the density of the magnetic flux existing in the gap 10 can be made higher, so that the pole piece 8 (or 9). The thickness of the pole piece 8 (or 9) is reduced within the range where the magnetic flux is not saturated. When the magnetic flux is saturated, the magnetic flux existing in the gap 10 decreases, which is not preferable. Changing the thickness of the permanent magnet 7 also relates to the density of the magnetic flux existing in the gap 10 portion in relation to the density of the magnetic flux existing in the portion in contact with the peripheral surface. Since it is premised that the thickness dimension is made as small as possible, it is not appropriate to adjust the magnetic flux density by adjusting the thickness dimension of the permanent magnet 7. Note that these values can be determined while measuring the magnetic flux of each part with a measuring instrument, but if they are determined by analysis by the finite element method, the decision operation can be performed efficiently.

[0018]

[Effect of the device]

 Since the magnetic fluid seal device of the present invention is constructed and operates as described above, the thickness dimension can be reduced and the size can be reduced, and the sealing performance can be sufficiently ensured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a first example of the basic structure of a magnetic fluid sealing device which is the subject of the present invention.

FIG. 2 is a sectional view showing the second example.

[Explanation of symbols]

 1 Housing 2 Shaft 3 Magnetic Fluid Sealing Device Main Body 4 Inner Surface 5 Outer Surface 6 Space 7 Permanent Magnet 8 Pole Piece 9 Pole Piece 10 Gap 11 Magnetic Fluid 12 Pocket

Claims (1)

[Scope of utility model registration request] 1. A first member made of a magnetic material having a cylindrical peripheral surface, a second member concentric with the first member and rotating relative to the first member; A permanent magnet, which is formed in a ring shape having a size that can be inserted into a cylindrical space between the peripheral surface of the two members and the peripheral surface of the first member, and is magnetized in the axial direction, A pair of pole pieces formed in a circular ring shape having a size that can be inserted into the cylindrical space and fixed to both side surfaces of the permanent magnet, the periphery of each pole piece and the peripheral surface of the first member. In the gap between and, consisting of a magnetic fluid held by the magnetic force of the permanent magnet,
In a magnetic fluid seal device used in a state of being adjacent to a magnetically permeable bearing provided between the first member and the second member, the maximum energy product of the permanent magnet is 3MG.O.
e and the density of the magnetic flux existing in the gap corresponding to the peripheral edge of the pole piece on the bearing side, in the space between the peripheral surface of the permanent magnet and the peripheral surface of the first member, and A magnetic fluid seal device characterized in that the density of magnetic flux existing in the portion in contact with the peripheral surface is 1.3 times or more.