JPS58225273A - Rotary sealing device using magnetic fluid - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sealing device using a magnetic fluid for sealing a rotating shaft.

In conventional devices of this type, a ferrofluid or magnetic liquid O-ring seal is mounted around a shaft in one or more stages (see, for example, U.S. Pat.
620,584 (see the multi-stage rotary shaft seal using magnetic fluid).

Single-stage and multi-stage seals using magnetic fluids have been used as isolation seals to protect the environment or space on one side of the shaft from contaminants in the environment or space on the other side of the shaft. A magnetic fluid-based isolation seal is specifically installed on the spindle of a computer disk drive to protect the storage disk area KMWO? ij? m"5~6-2-"61
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Useful.

The standard ferrofluidic barrier seal currently used in the computer field consists of an annular ring-shaped permanent magnet configured to surround the spindle axis and two equal parts sandwiching the magnet.
a pole piece member, the outer diameter of the pole piece member being arranged to contact and be flux-associated with each pole tip of the permanent magnet, and the inner diameter of the pole piece member being arranged to be in flux relation with each pole tip of the permanent magnet. A magnetic fluid is placed in the gap formed by the insertion of the shaft or spindle in close proximity to the surface of the shaft or spindle in a non-contact manner, and is held magnetically by one or more liquid O-rings. Form a tier. This forms a magnetic fluid isolation seal around the shaft.

A variety of magnetic materials can be used to form permanent magnets. A commonly used material is sintered or bonded ceramic building material having a longitudinal thickness of about 8'0 to 1150 mils. The pole piece members are comprised of a magnetically permeable material, such as magnetic stainless steel (eg, 400 series), approximately 25 to 80 mm thick. Depending on the customer's requirements, standard isolation seals may be installed as described above, or they may be made of non-magnetic materials such as aluminum or stainless steel (eg 300 series), for example by laminating or staking assembly techniques.・It is placed inside Uzing.

The isolation seal is formed by placing a precise, optimal amount of ferrofluid in the annular gap region between the inner diameter of the pole piece and the main shaft. Typically, the magnetic fluid is
Low vapor pressure carrier liquids, such as fluorocarbons, polyphenyl ethers, hydrocarbons, liquid Contains diesters and similar low vapor pressure liquids. For example, standard ferrofluidic seals typically operate at spindle speeds of 360Qrp for common computer disk drives at moderate temperatures.
m and within about 1.8 inches of shaft diameter, only a few years of life can be expected.

The viscosity and saturation magnetization of the magnetic fluid used may generally vary within the range of 20 to 50 Q epl and 100 to 400 Gauss, respectively.

Extending the useful service life of isolation seals using magnetic fluids, especially when the ambient temperature is higher, e.g. higher than 50'C, and when the spindle speed is higher than 360 Orpm;
It is desirable to extend the useful life of isolation seals when the shaft diameter is larger or when these conditions overlap.

The present invention provides a long-life rotating shaft seal using magnetic fluid;
and a method of manufacturing and using such a sealing device. More particularly, the present invention relates to a magnetic fluid barrier seal that is particularly effective for long-term sealing of spindles of computer disk drives.

Standard ferrofluidic seal design requires consideration of two basic factors. One is the magnetic component, which determines the seal pressure,1 and the other is heat generation, which determines the expected service life of the seal.

Typically, the total pressure capacity of a single service ferrofluidic seal corresponds to approximately 30 to 60 inches of water approximately equally divided between the two pole pieces.

When used in a disk drive, the pressure required is only 5 inches of water. Therefore, the safety factor of the seal with respect to pressure is high. That is, the required pressure capacity can be exceeded by simply installing one O-ring type seal. However, current standard designs use two pole pieces to complete the flux circuit.

It is known that temperature gradients occur within O-ring ferrofluid seals as a result of heat generation due to viscous shear of the ferrofluid between the rotating spindle shaft and the inner diameter of the stationary pole piece. These heats are effectively dissipated by conduction between the pole pieces and the spindle shaft. Therefore, the temperature of the ferrofluid during operation depends on the material of the seal and the ability of the structure to dissipate heat as a heat sink. The temperature of this ferrofluid determines the evaporation rate of the ferrofluid and thus the life of the seal. When both gap regions are filled with magnetic fluid, the temperature of the fluid during operation is 1. higher than when one stage is filled with magnetic fluid and the other stage is an air gap. This is because each gap region filled with magnetic fluid acts as a heat source, raising the temperature of the seal structure more than if only one stage was filled with magnetic fluid.

Therefore, 1. The sealing pressure is, when both stages are used,
In contrast, seal life is extended when only one gap is filled with ferrofluid than when both or multiple gap areas are filled with ferrofluid. Ru. Ideally, therefore, only one pole piece would act as a ferrofluidic seal, with the second pole piece forming the air gap having only the function of completing the magnetic circuit. In this case, the air gear knob may facilitate evacuation of the cavity between the pole pieces. But two people,
With current seal installation techniques, such a situation cannot be achieved because if the ferrofluid is injected into the magnet region, the ferrofluid will migrate into both gap regions upon insertion of the spindle shaft.

It has been found that the life of a ferrofluid seal can be extended by increasing the radial extent of the gap from the usual 4-6 mils to 12-24 mils or more. Extending seal life by utilizing a wider than normal gap range is based on Petrov's equation (Pet
According to Roff'@equatlon), this is thought to be based on the fact that the energy loss associated with the viscosity of the magnetic fluid is smaller, and if this loss is reduced, the amount of heat generated is reduced, and the temperature of the magnetic fluid during operation is lower. As a result, the evaporation rate of the ferrofluid is lower υ, and the life of the seal is extended. The maximum gap range will be such that the spacing and submergence are such that a pressure-induced seal will not occur due to lack of subfocal force. Experiments using the same ferrofluid show that a 24 mil gap (
(approximately 4 times the normal 6 mil gap), 3600r
Using a 1.8 inch diameter spindle shaft operating at pm reduces the ferrofluid temperature by 5°C and seal life by 5°C.
It increased by about 0%. During operation, no ferrofluid droplets were observed even when the ferrofluid reached magnetic saturation levels as low as 100 Gauss.

The present invention provides a magnetic flow J having different widths or dimensions and a cohesive length, extending the service life.
Consists of a rotary seal device using a body.

In the simplest embodiment of a two pole piece ferrofluidic seal, one pole piece is configured to provide a typical to standard gap width of 2 to 6 mils, and the other or opposite pole piece is configured to provide a typical gap width of 2 to 6 mils. The piece may have a weight of, for example, 10 to 8 Gf, in particular about 12
An enlarged larger gap width of ~iI4 mils is configured to be formed.

When a shaft member is inserted and an isolation seal is constructed by forming an O-ring seal of ferrofluid in each gap, rotation of the shaft member results in a more rapid flow preferentially in the smaller gaps of the seal. This causes an increase in temperature and faster vaporization of the ferrofluid. When the O-ring seal of the ferrofluid disappears in this small gap, the gap that was filled by the vaporized ferrofluid becomes an air gap, while the other larger ferrofluid gap is filled with ferrofluid, especially for computer disk drives. Pressure seals required for the spindle of the mechanism 1
Continue to provide functionality. By increasing the width of the ferrofluid gap that performs the pressure seal function, the life of the seal can be extended even if the two pole pieces have the same size or length and the same gap width is typically between 2 and 6 mils. It may be more extended than similar sealing devices configured to form.

In a multi-stage ferrofluid seal, the dimensions or lengths of the plurality of pole piece members can be varied as desired from a size that forms the smallest gap to a size that forms the widest gap to obtain a reliable sealing function by the ferrofluid. You can leave it there.

In this case, the ferrofluid changes its width from the smallest gap to the largest gap by vaporization from the gap? It disappears continuously and gradually. Therefore, when the sealing pressure requirements are not so severe and the seal life is more important, such as in the operation of the spindle of a computer digital drive mechanism, this sealing device, on the other hand, gradually reduces the sealing pressure characteristics of the seal. The life of the seal is extended.

When thermally conductive non-magnetic materials such as stainless steel, copper or aluminum are used in accordance with the disclosure of U.S. Patent Application No. 208,289, referenced herein,
That is, a non-magnetic material is brought into contact along the pole pieces with a larger gap, conducting away heat from the ferrofluid in this gap, thereby lowering the temperature of the ferrofluid, reducing the rate of vaporization, and sealing. In this case, the seal life of the shutoff seal of the present invention is further extended.

The invention will be described below with reference to the drawings for the purpose of illustrating only particularly preferred embodiments. It will be apparent, however, that one skilled in the art may make various changes and modifications to the described embodiments without departing from the spirit and scope of the invention.

FIG. 1 shows an extended life isolation seal device 10. The device 10 includes a ring-shaped permanent magnet 14 with opposing magnetic poles N and S, and magnetically permeable pole pieces 16 and 18 respectively disposed on either side of the magnet 140 and associated in terms of magnetic flux with the magnet 14. It has a non-magnetic housing 12. Pole pieces 16 and 18 have different dimensions or lengths such that the end of pole piece 16 cooperates with the magnetically permeable rotating shaft 300 surface to form a gap 22 of approximately 2 to 6 mils. The pole piece 18, on the other hand, cooperates with the shaft 300 surface to form a larger gap 20 of 12 to 24 mils.

A magnetic fluid 26 such as a diester type magnetic fluid fills the gap 2.
2 and the larger gap 20 to form an O-ring shaped ferrofluidic seal 34, respectively. The closed circuit magnetic flux path 32 is illustrated schematically by dotted lines, and the two O-rings 34 formed by the magnetic fluid 26 are shown by parallel dotted lines below each gap 20 and 22.

In some cases, the seal also includes a sheet 28 of non-magnetic heat transfer material that is closely associated with the pole piece 18 along the outside of the pole piece 18 for heat exchange. In other words, this sheet 28 is
It is closely attached to the pole piece 18 along the outside of the pole piece 18 so that heat exchange with the pole piece 18 takes place.

The ends of the sheet-like material or member 18 extend approximately to the ends of the pole pieces 18 forming the gap 20. Preferably, the sheet material 28 is an integral part of the metal housing 12, as shown, or
in contact with the ferrofluid 26 of the gear 20 to form a larger heat sink for conducting heat away from the magnetic fluid 26 of the gear 20.

In the sealing device 10, the pole pieces 16.18 are e.g.
The housing 12 and heat transfer material 28 may be of equal width or thickness of 50 mils, and for example from 5 to 30 mils, may be formed integrally or separately, and may be made of aluminum, copper, etc. Alternatively, it may be made of metal such as non-magnetic stainless steel. Shaft 30 may be, for example, the shaft of a 1.8 inch diameter computer disk drive operating at 3600 rpm.

In operation, as the shaft 30 rotates, the ferrofluid in the gap 22 is blown preferentially or before the ferrofluid seal in the larger gap 20.

The ferrofluidic seal in the gap 20 is caused by the large width of the gap 20 and by the sheet-like material 28.
Since the temperature of the magnetic fluid 26 is lower because heat is conducted and removed from the magnetic fluid 26, it vaporizes much more slowly or slowly.

FIG. 2 shows the shielding seal device 10 of FIG. 1 with magnetic fluid 2.
The gap 22 is shown as an air gap due to the vaporization of the magnetic fluid 2 in the gap 20.
6 provides an O-ring type seal for extended seal life, increasing seal life by 25-50L4.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing a rotary seal device using a magnetic fluid according to a preferred embodiment of the present invention at the start of operation, and FIG. Figure 1 is a schematic cross-sectional view showing the isolation sealing device. 10...Break seal device, 12...Using, 14...Ring-shaped permanent magnet, 16
．． 18... Magnetic pole piece, 20, 22... Gap, 26... Magnetic fluid, 28...
... Sheet material, 30 ... Rotating shaft (shaft), 32 ... Magnetic flux path, 34 ...0
Ring-shaped seal. Attorney Patent Attorney Imamura Moto Procedural Amendment August 10, 1980 Commissioner of the Patent Office Kazuo Wakasugi 1, Indication of Case Patent Application No. 109113 of 1982
No. 2, Title of the invention Rotary seal device 3 using magnetic fluid
, Relationship with the case of the person making the amendment Patent applicant name: Ferrofluidics Corporation 4, agent: Yamada Building, 1-1-14 Shinjuku, Shinjuku-ku, Tokyo, Japan

Claims (1)

[Claims:] a permanent magnet; first and second magnetically permeable pole piece members flux-related to each end of the permanent magnet, each pole piece member having one end; and the other end thereof, and is configured to surround the rotating shaft to be sealed, and the one end of each pole piece member is configured such that a gap is formed between the one end and the surface of the shaft to be sealed. the two pole piece members have lengths different from each other at the one end so as to extend in close proximity to the surface in a non-contact manner, and to form a first gap having a smaller dimension than the second gap. During rotation of the shaft, the magnetic fluid placed and held in the first gap and the second gap to form an O-ring magnetic seal around the shaft evaporates preferentially from the first gap, and A rotary seal device that uses a magnetic fluid and has a long seal life, and is capable of forming a seal device that has a long seal life and has a first gap and a second gap that is a gap sealed by the magnetic fluid. 2. The sealing device of claim 1, wherein the length of the first pole piece is selected to create a first gap of about 2 to 6 mils. (3) The length of the second pole piece is about 12 to 24 mils.
3. A sealing device according to claim 1, wherein the sealing device is selected to form a gap. (4) Any one of claims 1 to 3, including a non-magnetic thermally conductive material capable of conducting heat from the second magnetic pole piece to reduce the temperature of the magnetic fluid in the second gap. The sealing device described in . (6) The thermally conductive material is a sheet-like material in contact with the outer wall of the second pole piece, and one end of the sheet-like material extends to the vicinity of the one end of the second pole piece.
The sealing device described in Section. (6) The seal electrical manufacturing device according to any one of claims 1 to 5, wherein the magnetic pole pieces have the same thickness. (7) A sealing device according to claim 6, wherein the thickness of the magnetic pole piece is 80 to 5°. (8) A combination of the sealing device according to claim 1 and a rotating shaft member. and a magnetic fluid is held in at least one gap of the sealing device to seal a rotating shaft. (9) A combination in which the shaft member is a spindle shaft of a computer disk drive mechanism. The combination described in item 8. first and second magnetically permeable pole piece members associated with each other, one end of each pole piece member being in contact with the surface of the shaft to be sealed such that a gap is formed therebetween; the lengths of the two pole piece members differ from each other at the one end to form a first gap that is smaller in size than the second gap; The length is selected to form a first gap of about 2 to 6 mils, and the length of the second pole piece is selected to form a second gap of about 12 to 24 mils.
a non-magnetic thermally conductive material selected to form a gap and further including a non-magnetic thermally conductive material capable of conducting heat of the second pole piece to reduce the temperature of the magnetic fluid in the second gap; During the rotation of the shaft, the magnetic fluid placed and held in the first gap and the second gap to form an O-ring type magnetic seal around the shaft evaporates preferentially from the first gap, and the first gap becomes an air gap. A rotary seal device that uses a magnetic fluid and has a long seal life, and has a second gap that is a gap sealed by the magnetic fluid, so that an advantageous configuration with a long seal life can be formed. (1) In order to extend the seal life of a rotating shaft sealing device using magnetic fluid, when sealing a rotating shaft, a) one end and the other end are provided, and opposite magnetic poles are attached to both ends. surrounding the rotating shaft with an annular permanent magnet having b) first and second magnetically permeable pole piece members having one end and an opposite end and associated in terms of magnetic flux to each end of the permanent magnet; C) surrounding one end of each pole piece to the surface of the rotating shaft such that first and second gaps of predetermined dimensions are formed between one end of each pole piece and the surface of the rotating shaft; d) magnetically applying ferrofluid into the first and second gaps to form at least two O-ring shaped liquid seals sealing the rotating shaft to the surface of the rotating shaft; The method includes a process of preferentially evaporating magnetic fluid from a gap of one dimension by changing a predetermined dimension of the gap to form a first gap and a second gap of different dimensions. , the ferrofluid evaporates preferentially from the smallest dimension gap, and the ferrofluid in the largest dimension gap forms a seal with longer alignment compared to seals with equal and smaller gap dimensions. A method for extending the life of a seal in a rotary shaft seal device using (b) A method according to claim 11, wherein a plurality of gaps of various dimensions are formed in a multi-stage seal. (c) In order to reduce the evaporation rate of the magnetic fluid in the large gap and further extend the life of the seal, heat is dissipated from the magnetic fluid in the large gap by conduction. Method described. 64. The method of claim 13, wherein a non-magnetic thermally conductive material is used in contact with the pole pieces forming a large gap such that heat is dissipated by conduction. 60 Magnetic 15. A method according to any of claims 11 to 14, wherein the fluid has a viscosity of about 50 to 500 eps and a magnetic saturation of about 100 to 450 Gauss. 16. A method according to any of claims 11 to 15 using a spindle axis of a mechanism. Alpha force. Claim 11 wherein the leftmost gap has a dimension in the range of about 12 to 24 mils. Item to item