JP2988107B2 - Magnetic fluid sealing device and magnetic fluid composition used therein - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic fluid sealing device and a magnetic fluid composition used for the same (hereinafter, also simply referred to as a magnetic fluid).
As described above, splash (scatter) of the magnetic fluid when rotating at high speed is effectively prevented.

[0002]

2. Description of the Related Art As a conventional magnetic fluid sealing device in which splash prevention measures are taken into consideration, Japanese Patent Application Laid-Open No. 3-163271 is known.
There is one shown in Japanese Patent Publication No. In this device, splash is prevented by devising the shape and arrangement of the pole piece and the permanent magnet, which are components of the sealing device. That is, in general, a magnetic fluid sealing device has two annular pole pieces sandwiching a permanent magnet disposed in a cylindrical space between a shaft and a housing. , Forming a magnetic circuit that returns to the permanent magnet via the other pole piece, and closes the ring-shaped gap by holding the magnetic fluid injected into the gap between the inner peripheral edge of each pole piece and the outer peripheral surface of the shaft by its magnetic force Like that. However, when a magnetic body such as a rolling bearing is disposed between the shaft and the housing in the vicinity of one of the pole pieces (inside), a part of the magnetic flux of the magnetic circuit may cause a part of the rolling bearing. The magnetic flux existing between the inner peripheral edge of one of the pole pieces and the outer peripheral surface of the shaft decreases. As a result, the amount of the magnetic fluid held in the clearance of the other pole piece (outside) having a higher magnetic flux density increases and swells, and as a result, the magnetic fluid scatters outside due to centrifugal force generated by the relative rotation of the shaft or the housing. Easy to do. As a countermeasure, Japanese Patent Application Laid-Open No. 3-163271
In the device shown in the above publication, a second permanent magnet is further disposed between one of the pole pieces and the rolling bearing, thereby increasing the magnetic flux flowing toward the one of the pole pieces. In addition, the amount of magnetic fluid that is excessively held in the clearance between the inner peripheral edge of the other pole piece and the outer peripheral surface of the shaft is suppressed to prevent splash.

[0003]

However, in the above-described splash prevention technology in the conventional magnetic fluid sealing device, the high speed outer ring rotation (the outer ring of the rolling bearing) in which the peripheral speed of the rotation of the seal portion is increased to reach 2 m / sec or more. Side, i.e., the housing rotates at a high speed), the centrifugal force cannot maintain the magnetic fluid and a splash occurs. Therefore, there is a problem that the function as a dust-proof seal cannot be performed, such as generation of dust due to the ferromagnetic fine particles in the scattered magnetic fluid and a decrease in the seal strength due to a shortage of the magnetic fluid in the seal portion.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and a magnetic fluid which does not cause a splash of a magnetic fluid even at a high speed rotation of the seal portion at a peripheral speed of 2 m / sec or more. An object of the present invention is to provide a fluid seal device and a magnetic fluid composition used for the fluid seal device.

[0005]

According to a first aspect of the present invention, two permanent magnets are provided in a tubular space formed between a shaft and a housing which is rotatably fitted to the shaft. A magnetic circuit forming member sandwiched between the ring-shaped pole pieces is disposed, and a gap is formed between one of the inner and outer end faces of the pole piece and the outer peripheral surface of the shaft or the inner peripheral surface of the housing. The present invention relates to a magnetic fluid sealing device in which a magnetic circuit is formed with a magnetic fluid interposed therebetween and a magnetic fluid is injected into the gap, wherein the viscosity of the magnetic fluid is 150 to 6 at 40 ° C.
It is in the range of 00 cP.

The second invention of this application relates to a magnetic fluid composition used for the magnetic fluid sealing device of the first invention, and has a low-volatile organic solvent as a carrier and an affinity for the organic solvent. A dispersant having a lipophilic group, and ferromagnetic fine particles whose surface is coated with the dispersant and dispersed in the low-volatile organic solvent, wherein the low-volatile organic solvent is octadecyldiphenyl ether and ditetradecyltetra It is characterized by comprising a mixture with phenyl ether.

[0007]

When the magnetic fluid composition having the above viscosity range is used, splash can be effectively prevented by countering the centrifugal force at a peripheral speed of the seal portion of 2 m / sec or more with a high viscosity. The ferrofluid composition having the above viscosity range suppresses evaporation loss by using a low-volatile organic solvent prepared by mixing a low vapor pressure of octadecyl diphenyl ether and ditetradecyl tetraphenyl ether at a predetermined ratio as a carrier. Can extend the life of the seal. It can also be suitably used for high vacuum devices.

Hereinafter, the present invention will be described in more detail. As the low volatile organic solvent of the magnetic fluid composition of the present invention, poly-α-
Preferred are olefin oils, alkyl diphenyl ethers, alkyl naphthalenes, dialkyl tetraphenyl ethers, alkyl triphenyl ethers, fatty acid ester oils, or mixtures of these oils. Further, in addition to hydrocarbon oils, silicone oils such as dimethylpolysiloxane and fluorine oils such as perfluoropolyether may be used.

The viscosity of the magnetic fluid of the present invention is 15 at 40 ° C.
Although it is 0 to 600 cP, good splash resistance is obtained particularly in the range of 150 to 400 cP. In order to adjust the viscosity to a predetermined value, it is preferable to mix the above low-volatile organic solvents in various combinations, and a mixture of octadecyl diphenyl ether and ditetradecyl tetraphenyl ether is particularly preferable because the vapor pressure is low. is there.

The applicant of the present invention has disclosed in Japanese Patent Application No. 3-23262, which was previously filed by the present applicant, with any of the above-mentioned low-volatile organic solvents or a mixture obtained by combining the above-mentioned low-volatile organic solvents. The viscosity may be adjusted within the above range by adding the proposed polymer additive. In this case, the polymer additive is preferably polybutene succinic acid or sodium polybutene sulfonate, and a magnetic fluid composition having high water resistance and heat resistance can be obtained.

The viscosity of the magnetic fluid of the present invention at 40 ° C. is 15
If it is less than 0 cP, the force of the magnetic fluid to maintain the clearance between the shaft and the pole piece due to viscosity is weak,
Splashes cannot withstand the centrifugal force of high-speed rotation.
On the other hand, if the viscosity of the magnetic fluid is greater than 600 cP at 40 ° C., the surface wave of the magnetic fluid in the seal portion generated by the high-speed rotation at a peripheral speed of 2 m / sec or more becomes large, and the rising portion of the surface wave is affected by the centrifugal force. The phenomenon that splash receives more and can be considered.

Further, the viscosity of the magnetic fluid at 40 ° C. is 600 c.
If it is larger than P, the swelling at the time of injecting the magnetic fluid becomes large, the force for holding the swelled portion by the magnetic force is weakened, and at the same time, the effect of the large centrifugal force generated by the high-speed rotation of the peripheral speed of 2 m / sec or more. A phenomenon that receives a large amount of splash and can be considered. The saturation magnetic flux density of the magnetic fluid of the present invention is set to 250 Gauss in order to oppose the centrifugal force at high speed rotation of the seal portion at a peripheral speed of 2 m / sec or more.
s or more is required.

[0013]

The present invention will be described in more detail with reference to the following examples. [Example 1] Example of adjusting viscosity of magnetic fluid composition: First, a magnetite colloid liquid was produced by a known wet method.

The magnetite colloid solution is mixed with 3N H
After adding Claq to adjust the pH to 3, a synthetic sodium sulfonate was added as a dispersant thereto, and
For 30 minutes to adsorb the dispersant on the surfaces of the magnetite fine particles. Thereafter, the mixture is allowed to stand, and the magnetite fine particles in the liquid are aggregated and settled, and the supernatant is discarded. Further, add fresh water, stir and let stand, and discard the supernatant. This washing was repeated several times to remove the electrolyte in the aqueous solution, followed by filtration, dehydration and drying to obtain powdery magnetite fine particles whose surface was coated with a surfactant.

Next, hexane was added to the magnetite powder as a low-boiling organic solvent and shaken sufficiently to obtain an intermediate medium in which magnetite particles were dispersed in hexane. Methanol, which is a low-boiling-point polar organic solvent, is added to the colloidal solution to coagulate and precipitate particles once, and the supernatant is discarded. As a result, extra dispersants other than the dispersant adsorbed on the fine particles by a single molecule are removed. Thereafter, the precipitated fine particles are dispersed again in hexane to obtain an intermediate medium.

The intermediate medium is centrifuged at 800
The mixture is centrifuged under a centrifugal force of 0 G for 30 minutes to settle and remove relatively large particles of magnetite dispersed particles having poor dispersibility. Then, the supernatant liquid in which the magnetite fine particles remaining without settling were dispersed was transferred to a rotary evaporator, and the low-boiling organic solvent component, that is, hexane was removed by evaporation at 90 ° C. to obtain lipophilic magnetite fine particles.

The steps so far are substantially the same as those described in, for example, Japanese Patent Application Laid-Open No. 3-139596 filed earlier by the present applicant. Next, 5 g of the magnetite fine particles were collected and redispersed in hexane, and octadecyl diphenyl ether and ditetradecyl tetraphenyl ether as carriers were mixed in the six kinds shown in Table 1.

[0018]

[Table 1]

The mixed solution was transferred to a rotary evaporator and kept at 90 ° C. to remove the low-boiling organic solvent components, ie, hexane, by evaporation. As a result, the magnetite fine particles disperse in the carrier. This is further centrifuged, and 8
The mixture was treated under a centrifugal force of 000 G for 30 minutes to remove non-dispersed solids, and six types of magnetic fluids were obtained. Next, 0.5 g of polybutene succinic acid (average molecular weight 1100) was added as an additive to the magnetic fluid, and the mixture was stirred well at a liquid temperature of 100 ° C. to dissolve the polybutene succinic acid in the magnetic fluid. Was obtained. Table 1 also shows the results of measuring the viscosity of these magnetic fluids.

Example 2 A seal device using the above-described six types of magnetic fluid compositions was used.
A comparison test of the state of the splash at / sec was performed. FIG. 1 is a sectional view of a main part of a high-speed outer ring rotating splash tester to which a magnetic fluid sealing device is attached.

A shaft 1 made of a magnetic material is fixed to a gantry 2 and stands upright. A housing 3 is fitted to the shaft 1 via a cylindrical space 4 and is rotatably supported by a ball bearing 5. A belt groove 6 is provided on the outer peripheral surface of the housing 3, and the housing 3 is rotated at an arbitrary speed by belting between the belt groove 6 and a pulley of a drive motor (not shown). The magnetic fluid sealing device 10 is disposed in the space 4 between the shaft 1 and the upper part of the housing 3. The magnetic fluid sealing device 10 includes a magnetic circuit forming member 13 formed by magnetizing an annular permanent magnet 11 in the thickness direction and sandwiching the annular permanent magnet 11 between two annular pole pieces 12. Is fixed to the inner peripheral surface of the housing 3 to form a magnetic circuit that rotates with the permanent magnet 11, the one pole piece 12, the shaft 1, the other pole piece 12, and the permanent magnet 11. Then, a magnetic fluid 15 is injected into a gap between the inner peripheral surface of each pole piece 12 and the outer peripheral surface of the shaft 1 and is held by magnetic force, thereby closing and sealing the annular clearance.

This high-speed outer ring rotating splash tester is
And one drive motor with speed control (not shown) were prepared, and the pulley attached to the motor output shaft and the belt groove 6 of each test machine were connected by a belt, and eight test machines were simultaneously operated at the same speed. To rotate. For all testing machines,
A magnetic fluid sealing device 10 using the same magnetic fluid (for example, No. 1) was mounted as a subject, and the peripheral speed of the sealing portion was kept constant at 3 m / sec and operated at room temperature for 5 minutes. Was measured and recorded, and the results of magnetic fluids No. 1 to No. 6 of the subject were compared. The saturation magnetic flux density of the magnetic fluid used was 310 Gauss.

The results are shown in Table 2.

[0024]

[Table 2]

As is clear from Table 2, when the saturation magnetic flux densities are the same, the magnetic fluids No. 2 to No. 5 having a viscosity of 150 to 600 cP at 40 ° C. are magnetic fluids outside the range.
Excellent splash resistance compared to No.1 and No.6. Example 3 A comparative test similar to that of Example 2 was performed on a sealing device using the above-described six types of magnetic fluids No. 1 to No. 6, and the peripheral speed of the sealing portion was changed to 1.0 m / sec, 1.5 m / sec. sec, 2.0m / se
c, 2.5 m / sec and 3.0 m / sec were set at each stage.

The results are shown in Table 3.

[0027]

[Table 3]

As apparent from Table 3, when the peripheral speed of the seal portion is 1.0 m / sec or 1.5 m / sec, which is smaller than 2.0 m / sec,
No difference in splash resistance due to the viscosity of the magnetic fluid is observed. On the other hand, when the peripheral speed of the seal portion is 2.0 m / sec or more, the magnetic fluids No. 2 to No.
Showed almost no splash and was found to be excellent in splash resistance.

Although the above embodiment has been described only for the case of the inner peripheral seal for sealing between the inner peripheral surface of the pole piece and the shaft, the present invention is not limited to this, and the present invention is not limited to this. The present invention can also be applied to an outer peripheral seal for sealing between the housing and the housing.

[0030]

As described above, according to the first invention of this application, the viscosity of the magnetic fluid of the magnetic fluid sealer is set to be in the range of 150 to 600 cP at 40 ° C. However, even at a high speed rotation of 2 m / sec or more, the splash of the magnetic fluid can be suppressed, and the effects such as the generation of dust and the reduction of the sealing strength can be prevented, and the effect that the dustproof sealing function can be completed can be obtained.

According to the second invention, the low-volatile organic solvent of the magnetic fluid composition used in the magnetic fluid sealing device of the first invention is a low-vapor-pressure octadecyldiphenyl ether and a ditetradecyltetraphenyl. Since it is composed of a mixture with ether, the effect of preventing the splash, extending the life of the seal by suppressing the evaporation loss, and applying to a high vacuum apparatus can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part of a high-speed outer ring rotating splash tester to which a magnetic fluid sealing device is attached.

[Explanation of symbols]

 Reference Signs 1 shaft 3 housing 10 magnetic fluid sealing device 11 permanent magnet 12 pole piece 13 magnetic circuit forming member 15 magnetic fluid (composition)

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Claims (2)

(57) [Claims] 1. A magnetic circuit comprising: a permanent magnet sandwiched between two annular pole pieces in a tubular space formed between a shaft and a housing which is rotatably fitted to the shaft. A forming member is disposed, a magnetic circuit is formed by interposing a clearance between one of the inner and outer end surfaces of the pole piece and an outer peripheral surface of the shaft or an inner peripheral surface of the housing, and a magnetic circuit is formed in the clearance. In a magnetic fluid sealer in which a fluid is injected, the viscosity of the magnetic fluid is 40 ° C.
Wherein the magnetic fluid sealing device is in the range of 150 to 600 cP. 2. A low-volatile organic solvent as a carrier, a dispersant having a lipophilic group having an affinity for the organic solvent, and a surface coated with the dispersant and dispersed in the low-volatile organic solvent. 2. The magnetic fluid composition according to claim 1, further comprising ferromagnetic fine particles, wherein the low-volatile organic solvent comprises a mixture of octadecyl diphenyl ether and ditetradecyl tetraphenyl ether. Stuff.