JP2011187972A - Magnetic fluid and damper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic fluid wherein magnetic particles never aggregate when there is no magnetic field and which has fluid characteristics having an excellent long-time stability and an excellent responsiveness to an external magnetic field, and to provide a damper which is equipped with the magnetic fluid and can correctly adjust its attenuation force over a long time. <P>SOLUTION: The damper 1 comprises: a circular cylindrical cylinder 2 with top and bottom ends closed; a piston rod 31 which penetrates a ceiling portion 21 of the cylinder 2 and is extended into the cylinder 2; a piston 3 which is disposed at the bottom end of the piston rod 31 and slides up and down inside the cylinder 2; and the magnetic fluid 10 stored in the cylinder 2. The damper 1 is also equipped with a magnetic field formation means for applying a magnetic field to the magnetic fluid 10. The magnetic fluid 10 contains Fe-based amorphous metal particles. By adjusting the existence/non-existence and the intensity of a magnetic field to be applied to the magnetic fluid 10, the attenuation force of the damper 1 can be adjusted. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a magnetic fluid and a damper.

The magnetic fluid is a functional fluid obtained by dispersing magnetic particles or ferrite particles of a ferromagnetic material whose surface is covered with a surfactant in a liquid dispersion medium. In such a magnetic fluid, even if magnetic particles or ferrite particles are magnetized, the dispersed state is maintained without aggregation of the particles. For this reason, the whole magnetic fluid can behave like a magnetic liquid.
By the way, magnetic fluid has the property that the viscosity and fluidity change according to an external magnetic field. For this reason, a damper (buffer) capable of changing the damping force by utilizing this property has been put into practical use.

  Such a damping force variable damper generally includes a cylinder that stores magnetic fluid, a piston that slides inside the cylinder, and a magnetic field forming unit that applies a magnetic field to the magnetic fluid. By adjusting the strength of the magnetic field applied to the magnetic fluid by the magnetic field forming means, the fluid properties such as the viscosity and fluidity of the magnetic fluid can be changed. When the fluid characteristic of the magnetic fluid changes, the resistance when the piston slides in the cylinder changes. As a result, the damping force of the damper can be changed.

Using such characteristics, the damping force variable damper can be used as a shock absorber for an automobile that can select an optimum damping force according to, for example, a road surface condition.
As a magnetic fluid used for such a damping force variable damper, for example, particles whose surface is coated with a surfactant and mainly containing a mixture of iron and ferrite are dispersed in a vegetable oil derivative such as castor oil. A magnetic fluid is disclosed (for example, see Patent Document 1).

  Here, when the damping force variable damper repeats the operation of absorbing the impact, external stress (for example, shearing force) by the piston or cylinder is continuously applied to the magnetic fluid. For this reason, there exists a problem that the particle | grains contained in a magnetic fluid are destroyed or cannot be lacking without enduring this external stress. When the particles in the magnetic fluid are broken or lost, the fluid characteristics of the magnetic fluid change, and an unintended change occurs in the damping force characteristics of the damping force variable damper.

Moreover, the iron powder used for the particles in the magnetic fluid has a relatively large coercive force. For this reason, the particles in the magnetic fluid are strongly magnetized by the external magnetic field, and the particles may aggregate even when there is no magnetic field.
Furthermore, in a material having a relatively low saturation magnetic flux density such as ferrite, it may take a considerable time to change the fluid characteristics of the magnetic fluid with respect to changes in the external magnetic field. In this case, it becomes difficult to control the change of the damping force characteristic with high accuracy.

JP-T-2004-511094

  The object of the present invention is to prevent magnetic particles from agglomerating in the absence of a magnetic field, to provide excellent long-term stability of fluid characteristics, and to excellent response of changes in fluid characteristics to an external magnetic field. Another object of the present invention is to provide a damper comprising such a magnetic fluid and capable of accurately adjusting a damping force over a long period of time.

The above object is achieved by the present invention described below.
The magnetic fluid of the present invention comprises magnetic particles whose surfaces are covered with a surfactant,
A liquid phase dispersion medium for dispersing the magnetic particles,
The magnetic particles are made of an Fe-based amorphous metal.
As a result, the magnetic particles can be reliably prevented from aggregating in the absence of a magnetic field, and the magnetic fluid can be obtained with excellent long-term stability of fluid characteristics and excellent response to changes in fluid characteristics with respect to an external magnetic field. .

In the magnetic fluid of the present invention, the Fe-based amorphous metal preferably contains at least one of B (boron), C (carbon), Si (silicon) and Cr (chromium) as a constituent component. .
Thereby, stability as an amorphous metal improves Fe system amorphous metal.

In the magnetic fluid of the present invention, it is preferable that the Fe-based amorphous metal contains Fe as a main component, contains Si in a content of 4 to 9 wt%, and contains B in a content of 1 to 5 wt%.
As a result, the Fe-based amorphous metal has a particularly small coercive force and a particularly large saturation magnetic flux density. For this reason, in a magnetic fluid including magnetic particles composed of such an amorphous metal, aggregation of the magnetic particles is reliably prevented when there is no magnetic field, and the fluid of the magnetic fluid according to the magnetic field applied from the outside. Responsiveness of the change in characteristics can be increased.

In the magnetic fluid of the present invention, the magnetic particles preferably have an average particle size of 0.1 to 25 μm.
Thereby, the fluid characteristics can be optimized in the magnetic fluid.
In the magnetic fluid of the present invention, when the short diameter of the magnetic particles is S [μm] and the long diameter is L [μm], the average value of the aspect ratio of the magnetic particles defined by S / L is 0. It is preferable that it is 4-1.
Thereby, since the shape of the magnetic particles becomes relatively spherical, it is more difficult to break or break due to the shape action. For this reason, the magnetic particle excellent in durability is obtained.

In the magnetic fluid of the present invention, the magnetic particles preferably have a coercive force of 5 Oe or less.
This ensures that the magnetic particles are prevented from agglomerating when there is no magnetic field.
In the magnetic fluid of the present invention, the magnetic particles preferably have a saturation magnetic flux density of 0.6 T or more.
Thereby, the magnetic particle can obtain a magnetic fluid that is excellent in the response of the change in the fluid characteristics to the change in the external magnetic field.

In the magnetic fluid of the present invention, the magnetic particles are preferably manufactured by an atomizing method.
Thereby, magnetic particles closer to a spherical shape can be obtained.
In the magnetic fluid of the present invention, the content of the magnetic particles in the magnetic fluid is preferably 50 to 95 wt%.
Thereby, while being excellent in fluidity | liquidity, the magnetic fluid which shows sufficient responsiveness with respect to the change of an external magnetic field is obtained.

In the magnetic fluid of the present invention, it is preferable that the surfactant is mainly composed of oleate.
Thereby, the magnetic fluid excellent in stability is obtained.
In the magnetic fluid of the present invention, it is preferable that the liquid phase dispersion medium is mainly composed of hydrocarbon oil, silicone oil, or fluorine oil.
Thereby, the magnetic fluid excellent in durability is obtained.

The damper of the present invention comprises a cylinder for storing the magnetic fluid of the present invention,
A piston that slides in the cylinder and divides the space in the cylinder into two;
A piston rod having one end connected to the piston and the other end located outside the cylinder;
Magnetic field forming means for forming a magnetic field so as to reach the magnetic fluid stored in the cylinder,
The damping force can be controlled by changing the fluid characteristics of the magnetic fluid by the action of a magnetic field.
Thereby, the damper which can adjust damping force correctly over a long period of time is obtained.

In the damper of the present invention, the damper is formed in the piston, and has a flow path communicating with the two spaces.
Preferably, the magnetic field forming means is provided in the vicinity of the flow path, and the damping force can be controlled by changing a fluid characteristic by forming a magnetic field so as to reach the magnetic fluid passing through the flow path. .
Thereby, the viscosity of the magnetic fluid can be adjusted more strictly.

It is a longitudinal section showing an embodiment of a damper of the present invention. It is the elements on larger scale which expand and show some dampers shown in FIG. It is a figure for demonstrating operation | movement of the damper shown in FIG. It is a figure for demonstrating operation | movement of the damper shown in FIG. It is an observation image by the scanning electron microscope of the metal powder obtained in the Example. It is an X-ray-diffraction spectrum by the X-ray-diffraction apparatus of the metal powder obtained in the Example.

Hereinafter, the magnetic fluid and damper of the present invention will be described in detail with reference to the accompanying drawings.
[Damper]
First, before describing the magnetic fluid of the present invention, the damper of the present invention will be described.
1 is a longitudinal sectional view showing an embodiment of the damper of the present invention, FIG. 2 is an enlarged partial view showing a part of the damper shown in FIG. 1, and FIGS. 3 and 4 are dampers shown in FIG. It is a figure for demonstrating operation | movement of. In the following description, the upper side in FIGS. 1 to 4 is referred to as “upper” and the lower side is referred to as “lower”.

  A damper 1 shown in FIG. 1 includes a cylindrical cylinder 2 whose upper and lower ends are closed, a piston rod 31 that extends from the outside of the cylinder 2 through the ceiling 21 of the cylinder 2 and extends into the cylinder 2, A piston 3 is provided at the lower end of the piston rod 31 and slides up and down in the cylinder 2. A magnetic fluid 10 is accommodated in the cylinder 2.

  Such a damper 1 operates to expand and contract between a member connected to the upper end of the piston rod 31 and a member connected to the lower end of the cylinder 2. For example, when the upper end of the piston rod 31 is connected to the body of an automobile and the lower end of the cylinder 2 is connected to a wheel or an axle, the damper 1 is connected to the damper 1 when the distance between the body and the wheel (axle) is expanded or contracted. Stretching force is applied.

  In the damper 1, the piston 3 slides in accordance with the expansion / contraction force applied between the members. During this sliding, the piston 3 has a resistance force in a direction that relaxes the expansion / contraction force from the magnetic fluid 10. Is granted. As a result, the piston 3 functions as a shock absorber that relaxes and attenuates the stretching force applied between the members.

The damper 1 includes a coil 4 that is provided in the piston 3 and applies a magnetic field to the magnetic fluid 10 accommodated in the cylinder 2, and a power supply circuit 5 that applies a voltage to the coil 4. . That is, the coil 4 and the power supply circuit 5 constitute magnetic field forming means for applying a magnetic field to the magnetic fluid 10.
Here, the magnetic fluid 10 will be described in detail later, but its fluid properties (viscosity, fluidity, etc.) change depending on the presence or absence and strength of the magnetic field. For this reason, the fluid characteristics of the magnetic fluid 10 can be adjusted by appropriately setting the presence or absence and strength of the magnetic field by the magnetic field forming means. By utilizing such characteristics, the damper 1 becomes a damping force variable damper capable of controlling the damping force.

Hereinafter, each part of the damper 1 will be described in detail.
The side surface of the cylinder 2 shown in FIG. 1 has a two-layer structure (double-cylinder type), and is composed of an outer outer cylinder 22 and an inner cylinder 23.
The space inside the inner cylinder 23 is divided into a rod side chamber 2 a above the piston 3 and a piston side chamber 2 b below the piston 3.

Further, a first reservoir chamber 25 is provided below the piston side chamber 2b via a base valve 24 provided so as to partition the space inside the inner cylinder 23.
The base valve 24 is provided with an orifice 241 penetrating the base valve 24, and the piston side chamber 2 b and the first reservoir chamber 25 communicate with each other through the orifice 241.

A space between the outer cylinder 22 and the inner cylinder 23 is a second reservoir chamber 26. The first reservoir chamber 25 and the second reservoir chamber 26 are adjacent to each other via the lower end portion of the inner cylinder 23.
In addition, an orifice 231 that penetrates the first reservoir chamber 25 and the second reservoir chamber 26 of the inner cylinder 23 is provided, and the first reservoir chamber 25 is connected to the inner cylinder 23 via the orifice 231. The second reservoir chamber 26 is in communication.

Such a cylinder 2 is comprised with the material excellent in the mechanical characteristic and oil resistance, for example, is comprised with various metal materials. In the present embodiment, the cylinder 2 is preferably made of a nonmagnetic material. In this embodiment, since the coil 4 for generating a magnetic field is provided in the piston 3, the magnetic field is generated in the magnetic fluid 10 at a portion other than the periphery of the piston 3 because the cylinder 2 is made of a nonmagnetic material. It is suppressed or prevented from being applied. For this reason, in the whole cylinder 2, the fluid characteristic of the magnetic fluid 10 can be made uniform.
Here, the magnetic fluid 10 is obtained by dispersing magnetic particles whose surfaces are covered with a surfactant in a liquid phase dispersion medium, and the whole behaves like a magnetic liquid. The magnetic fluid 10 will be described in detail later.

The piston rod 31 is composed of a highly rigid rod-like member, and extends through the center portion of the ceiling portion 21 of the cylinder 2 to the inside and outside of the cylinder 2.
The piston 3 is composed of a columnar member, and the outer surface thereof is in sliding contact with the inner wall surface of the inner cylinder 23 of the cylinder 2. As described above, the piston 3 partitions the space inside the inner cylinder 23 into the rod side chamber 2a and the piston side chamber 2b.
Two orifices 32 and 33 are provided so as to penetrate the piston 3. The orifices 32 and 33 communicate the rod side chamber 2a and the piston side chamber 2b.

  A valve body 34 is provided on the upper surface of the piston 3 in the vicinity of the upper end opening of the orifice 32. The valve body 34 closes the upper end opening of the orifice 32 so that the magnetic fluid 10 cannot flow through the orifice 32 (closed state), and opens the upper end opening of the orifice 32, and the magnetic fluid 10 flows through the orifice 32. It operates to take a possible state (open state). The valve body 34 is a one-way valve having a function of passing the flow of the magnetic fluid 10 from the piston side chamber 2b toward the rod side chamber 2a and blocking the reverse flow. 1 and 2 show the valve body 34 in an open state.

  The valve body 34 opens and closes using the relative flow of the magnetic fluid 10 with respect to the piston 3 generated by the sliding of the piston 3 with respect to the cylinder 2 as a driving force. In order to shift the valve body 34 from the closed state to the open state, it is necessary to apply a pressure of a predetermined magnitude or more to the valve body 34 by causing the magnetic fluid 10 to flow faster than a predetermined speed. Therefore, the valve body 34 is configured to be open only when the piston 3 slides at a speed equal to or higher than a predetermined speed. With such a valve body 34, the damping force can be varied in the damper 1 depending on whether the sliding speed of the piston 3 is low or high.

A ring-shaped coil 4 is provided inside the piston 3. A part of the outer surface of the coil 4 faces each of the orifices 32 and 33.
The coil 4 is connected to the power supply circuit 5 as described above. When a voltage is applied to the coil 4, a magnetic field is generated around the coil 4 as shown by magnetic field lines (broken lines) in FIG. 2.

The coil 4 has a ring-shaped magnetic core and a conductive wire wound around the magnetic core. The magnetic core and the conductor are electrically insulated from each other by a resin coating layer formed on the surface of the magnetic core or the surface of the conductor. Further, both ends of the conducting wire are connected to the power supply circuit 5 respectively.
The power supply circuit 5 includes a power supply and a conductive wire that connects the power supply and the coil 4. The coil 4 and the power supply circuit 5 constitute magnetic field forming means.
Although not shown, the power supply has a transformer circuit that adjusts the voltage applied to the coil 4. According to this transformer circuit, the voltage applied to the coil 4 can be changed, and the strength of the magnetic field generated by the coil 4 can be changed.

Examples of the material constituting the magnetic core include pure iron, Fe-Si alloys, Fe-Cr alloys, Fe-Ni alloys, Fe-Co alloys, amorphous metals, various soft magnetic materials such as soft ferrite, etc. Can be used.
In addition, these soft magnetic materials constitute a magnetic core in the form of, for example, a laminated body or a compacted body.

In FIG. 1, the coil 4 is provided inside the piston 3, but the installation location of the coil 4 is not particularly limited. It may be provided, and may be provided at a plurality of locations.
In FIG. 1, a magnetic field is applied to the two orifices 32 and 33 provided in the piston 3 using one coil 4, but a magnetic field is applied using each individual coil. May be. In this case, the damping force of the damper 1 can be controlled more finely and strictly by controlling the operation of each coil independently.

Next, the operation (operation) of the damper 1 shown in FIG. 1 will be described.
First, the compression process of the damper 1 will be described.
Here, as shown to Fig.3 (a), let the state which the damper 1 extended | stretched be an initial state.
When the distance between the upper member 8 connected to the upper end portion of the damper 1 and the lower member 9 connected to the lower end portion is reduced, as shown in FIG. The piston 3 slides downward in the cylinder 2.

At this time, part of the magnetic fluid 10 in the piston side chamber 2 b is pushed by the piston 3, passes through the orifice 241, and is pushed out to the first reservoir chamber 25. Accordingly, the magnetic fluid 10 filled in the first reservoir chamber 25 passes through the orifices 231 and 231 and is pushed out to the second reservoir chamber 26.
Furthermore, a part of the magnetic fluid 10 in the piston side chamber 2b passes through the orifice 33 and moves to the rod side chamber 2a.

In this way, a part of the compressive force between the upper member 8 and the lower member 9 is converted into a sliding driving force of the piston 3 or a driving force of the flow of the magnetic fluid 10, so that the damper 1 is absorbed. As a result, the compressive force can be relaxed and attenuated.
Further, when the sliding speed of the piston 3 exceeds a predetermined speed, the valve body 34 is changed from the closed state to the open state, and the flow of the magnetic fluid 10 is also formed in the orifice 231. Due to the formation of this flow, when the sliding speed of the piston 3 exceeds the predetermined speed, the degree of attenuation can be slightly reduced.

Here, when a part of the magnetic fluid 10 in the piston side chamber 2b passes through the orifices 32 and 33, a voltage is applied to the coil 4 by the power supply circuit 5, and FIG. ) Is generated.
When the magnetic field is applied, in the magnetic fluid 10 in each of the orifices 32 and 33, for example, magnetic particles (metal particles) in the magnetic fluid 10 are arranged along the magnetic field lines.
When the magnetic particles are arranged as shown in FIG. 3C, the magnetic particles obstruct the flow of the magnetic fluid 10 flowing through the orifices 32 and 33, and the viscosity of the magnetic fluid 10 increases. As a result, the damping force of the damper 1 increases.

  In this way, the fluid characteristics of the magnetic fluid 10 flowing through the orifices 32 and 33 can be changed using the coil 4 and the power supply circuit 5. And the damping force of the damper 1 can be changed. Further, by applying a magnetic field to the magnetic fluid 10 at each of the orifices 32 and 33 having a diameter smaller than that of the cylinder 2, the viscosity of the magnetic fluid 10 can be adjusted more strictly.

Next, the extension process of the damper 1 will be described.
Here, as shown in FIG. 4D, the state in which the damper 1 is compressed is set as the initial state.
As the distance between the upper member 8 and the lower member 9 increases, the piston 3 also slides upward in the cylinder 2 in the damper 1 as shown in FIG.
At this time, a part of the magnetic fluid 10 in the rod side chamber 2a is pushed by the piston 3, passes through the orifice 33, and is pushed out to the piston side chamber 2b.

As the volume of the piston side chamber 2b increases, part of the magnetic fluid 10 in the first reservoir chamber 25 passes through the orifice 241 and flows into the piston side chamber 2b.
Further, a part of the magnetic fluid 10 in the second reservoir chamber 26 passes through the orifices 231 and 231 and flows into the first reservoir chamber 25.
In this way, a part of the extension force between the upper member 8 and the lower member 9 is converted into the sliding driving force of the piston 3 or the driving force of the flow of the magnetic fluid 10, whereby the damper. 1 is absorbed. As a result, the extension force can be relaxed and attenuated.

Here, when a magnetic field is applied to the magnetic fluid 10 flowing through the orifice 33 in the same manner as in the compression process, the fluid characteristics of the magnetic fluid 10 flowing through the orifice 33 can be changed, and the damping force of the damper 1 is changed. be able to.
By continuously performing the compression process and the expansion process as described above, the damper 1 can alleviate the expansion force and the compression force generated between the upper member 8 and the lower member 9.

[Magnetic fluid]
Next, the magnetic fluid (magnetic fluid of the present invention) 10 that can be used for the damper 1 as described above will be described.
The magnetic fluid of the present invention has magnetic particles whose surfaces are covered with a surfactant, and a liquid phase dispersion medium for dispersing the magnetic particles. Among these, the magnetic particles are composed of an Fe-based amorphous metal material.

In such a magnetic fluid, the action of the surfactant prevents aggregation of magnetic particles when there is no magnetic field. For this reason, even if the magnetic particles are magnetized or charged, the state in which the magnetic particles are dispersed in the liquid phase dispersion medium is maintained. For this reason, the magnetic fluid can behave like a magnetic liquid as a whole.
As described above, in the damper 1, the damping force can be adjusted by utilizing the change in the fluid characteristics of the magnetic fluid according to the presence or absence and strength of the applied magnetic field.

Here, in conventional magnetic fluids, iron particles such as carbonyl iron, ferrite particles, and the like are used as magnetic particles.
However, when a magnetic fluid is used in a movable part such as a damper, an external stress (for example, a shearing force) is continuously applied to the magnetic fluid each time the damper repeatedly expands and contracts. For this reason, there has been a problem that the magnetic particles in the magnetic fluid are broken or broken without being able to withstand external stress. When the magnetic particles in the magnetic fluid are broken or lost, the fluid characteristics of the magnetic fluid change, and the damping force of the damper becomes unstable or deviates from the original damping force.

Carbonyl iron particles and the like have a relatively large coercive force. For this reason, there also existed a problem that the change of the fluid characteristic of a magnetic fluid was delayed with respect to the change of an external magnetic field. For this reason, the damping force of the damper 1 cannot be controlled with high accuracy.
Furthermore, since the ferrite particles have a low saturation magnetic flux density, the magnetization with respect to the external magnetic field is weak in the magnetic fluid, and the magnetization force cannot be obtained sufficiently.

Therefore, in the magnetic fluid of the present invention, as described above, particles made of an Fe-based amorphous metal material are used as the magnetic particles.
Since amorphous metal does not contain crystal grains, dislocations (displacement of atomic arrangement) and cracks at grain boundaries do not occur. For this reason, the amorphous metal has high hardness and high strength.
According to such a high-hardness amorphous metal material, it is possible to reliably prevent breakage and loss of magnetic particles. For this reason, if the magnetic fluid of this invention is used, the damping force of the damper 1 can be stably controlled over a long period of time. Magnetic particles made of such an amorphous metal material exhibit excellent soft magnetic properties.

Further, the Fe-based amorphous metal material has a particularly small coercive force. For this reason, according to the magnetic particles composed of such an amorphous metal material, a magnetic fluid excellent in response characteristics (responsiveness and magnitude of change) of fluid characteristics to changes in an external magnetic field can be obtained. can get.
Furthermore, the Fe-based amorphous metal material has a relatively large saturation magnetic flux density. For this reason, the magnetizing force with respect to the external magnetic field can be sufficiently obtained.

Hereinafter, the components of the magnetic fluid of the present invention will be described in detail.
The Fe-based amorphous metal material preferably contains at least one of B (boron), C (carbon), Si (silicon) and Cr (chromium) as a constituent element in addition to Fe. . The Fe-based alloy containing such constituent elements has improved stability as an amorphous metal by the action of these constituent elements. For this reason, even if it heat-processes etc., the Fe type amorphous metal material containing this structural element can prevent crystallization reliably.

Specific Fe-based amorphous metal materials include, for example, Fe—Si—B, Fe—B, Fe—Si—B—C, Fe—Si—B—Cr, and Fe—Si—B—Cr. Examples thereof include amorphous metals such as -C, Fe-Co-Si-B, Fe-Zr-B, Fe-Ni-Mo-B, and Ni-Fe-Si-B.
Among these, amorphous metals containing Fe and Si and B are particularly preferable.

  Such an amorphous metal preferably contains Fe as a main component, contains Si in a content of about 4 to 9 wt%, and contains B in a content of about 1 to 5 wt%, contains Fe as a main component, and contains Si. More preferably, it is contained at a content of about 4.5 to 8.5 wt%, and B is contained at a content of about 2 to 4 wt%. The Fe—Si—B based amorphous metal having such a composition has a particularly small coercive force and a particularly large saturation magnetic flux density. For this reason, in a magnetic fluid including magnetic particles composed of such an amorphous metal, aggregation of the magnetic particles is reliably prevented when there is no magnetic field, and the fluid of the magnetic fluid according to the magnetic field applied from the outside. Responsiveness of the change in characteristics can be increased.

Further, the amorphous metal containing Fe, Si and B as described above preferably further contains Cr at a content of about 1 to 3 wt%, and contains a content of about 1.5 to 2.5 wt%. Is more preferable. Since Cr forms a passive film having excellent corrosion resistance, it can improve the wear resistance and corrosion resistance of the magnetic particles.
The amorphous metal containing Fe, Si and B as described above preferably further contains C at a content of 1 wt% or less, and more preferably at a content of about 0.3 to 1 wt%.

  The average particle size of the magnetic particles is preferably about 0.1 to 25 μm, and more preferably about 1 to 10 μm. Thereby, the fluid characteristics can be optimized in the magnetic fluid. That is, when the average particle size of the magnetic particles is below the lower limit, when the viscosity of the magnetic fluid becomes too small or the viscosity of the magnetic fluid changes according to the external magnetic field, the amount of change cannot be secured sufficiently. There is a fear. On the other hand, when the average particle diameter of the magnetic particles exceeds the upper limit, the viscosity of the magnetic fluid may be too large.

The particle size distribution of the magnetic particles is preferably as narrow as possible. Specifically, when the average particle size of the magnetic particles is within the above range, the maximum particle size is preferably 50 μm or less, and more preferably 45 μm or less. By controlling the maximum particle size of the magnetic particles within the above range, a magnetic fluid having excellent fluidity can be obtained by suppressing the particle size variation of the magnetic particles.
In addition, said maximum particle size means a particle size with a cumulative weight of 99.9%.

  Further, when the short diameter of the magnetic particles is S [μm] and the long diameter is L [μm], the average value of the aspect ratio of the magnetic particles defined by S / L is about 0.4 to 1. Is preferable, and about 0.7-1 is more preferable. The magnetic particles having such an aspect ratio have a shape that is relatively close to a sphere, so that they are less likely to be destroyed or damaged by the shape action. For this reason, the magnetic particle excellent in durability is obtained.

Such magnetic particles exhibit soft magnetism as described above and have a small coercive force. Specifically, the coercive force of the magnetic particles is preferably 5 Oe or less, and more preferably 3 Oe or less. The magnetic particles having a coercive force within the above range can reliably prevent aggregation when there is no magnetic field.
The saturation magnetic flux density of the magnetic particles may be as large as possible, but is preferably 0.6 T or more, and more preferably 1 T or more. When the saturation magnetic flux density of the magnetic particles is within the above range, a magnetic fluid excellent in the response characteristics (immediate response and the magnitude of the change amount) of the fluid characteristics to the change of the external magnetic field can be obtained.

The hardness of the magnetic particles is preferably as large as possible, but preferably the Vickers hardness Hv is 650 or more, more preferably 900 or more. The magnetic particles having such hardness are particularly surely prevented from being broken or broken.
Such magnetic particles may be produced by any method, but for example, those produced by a method such as an atomizing method or a cooling roll method can be used.
Among these, the magnetic particles are preferably produced by an atomizing method.

The atomization method is a method in which a melt (molten metal) is pulverized by colliding with a cooling medium (liquid or gas). When the molten metal is sprayed or collides with a cooling medium, the molten metal becomes fine droplets, and when the droplets come into contact with the cooling medium, the molten metal is rapidly cooled and solidified. At this time, since the droplets are cooled very rapidly, each atom solidifies while maintaining the disordered atomic arrangement in the liquid state. As a result, magnetic particles (magnetic powder) composed of amorphous metal are obtained. That is, according to the atomizing method, magnetic particles made of an amorphous metal can be efficiently produced.
Further, in the atomization method, since the droplets are spheroidized by the surface tension, magnetic particles closer to a sphere can be obtained. Thereby, magnetic particles having an aspect ratio closer to 1 can be obtained.

Examples of the atomizing method include a water atomizing method, a high-speed rotating water atomizing method, a gas atomizing method, a vacuum dissolution gas atomizing method, a gas-water atomizing method, and an ultrasonic atomizing method.
Among these, as the atomizing method, it is preferable to use a water atomizing method or a high-speed rotating water stream atomizing method. According to these atomizing methods, since water having a large heat capacity is used as a cooling medium, the droplets can be cooled and solidified at a higher cooling rate. For this reason, the droplets can be made amorphous more reliably.

The surface of such magnetic particles is covered with a surfactant.
The surfactant is not particularly limited. For example, various anionic surfactants such as oleate, carboxylate, sulfonate, sulfate ester salt, phosphate ester salt, amino acid salt, Various cationic (cationic) surfactants such as quaternary ammonium salts, ester types such as glycerin fatty acid esters, ether types such as polyoxyethylene alkyl ethers and polyoxyethylene alkyl phenyl ethers, and fatty acid polyethylene glycols Examples thereof include various nonionic (nonionic) surfactants such as an ester / ether type, and various amphoteric surfactants such as alkylbetaines.
In particular, the surfactant preferably has oleate as a main component. Oleate is strongly bonded to the magnetic particles and has high dispersibility of the magnetic particles in the liquid phase dispersion medium. For this reason, the magnetic fluid excellent in stability is obtained by using an oleate as surfactant.

The surfactant has a hydrophilic part and a hydrophobic part in the molecule. For example, when oil is used as a liquid phase dispersion medium for dispersing magnetic particles, surfactant molecules are arranged along the interface between the magnetic particles and the liquid phase dispersion medium. At this time, the hydrophilic portion of the surfactant molecule is oriented to the magnetic particle side, and the hydrophobic portion is oriented to the liquid dispersion medium side.
By such an action of the surfactant, the magnetic particles can be stably dispersed in the liquid phase dispersion medium without agglomeration when there is no magnetic field.

Examples of the liquid phase dispersion medium include an aqueous dispersion medium such as water, a hydrocarbon oil, a silicone oil, a fluorine oil, an ester oil, an ether oil, and the like.
Of these, those mainly composed of hydrocarbon oil, silicone oil or fluorine oil are preferred. Since these oils are excellent in heat resistance and chemical stability, they are particularly preferably used as a liquid phase dispersion medium for magnetic fluids. That is, a magnetic fluid having excellent durability can be obtained.

The content of magnetic particles in such a magnetic fluid is preferably about 50 to 95 wt%, more preferably about 60 to 90 wt%. Thereby, while being excellent in fluidity | liquidity, the magnetic fluid which shows sufficient responsiveness with respect to the change of an external magnetic field is obtained.
As mentioned above, although the magnetic fluid and damper of this invention were demonstrated based on suitable embodiment, this invention is not limited to this.
For example, the magnetic fluid of the present invention can be used not only for the damper described above but also for a seal member of a rotating shaft, a speaker, a sensor, and the like.

Next, specific examples of the present invention will be described.
1. Production of damper (Example)
[1] First, raw materials having the following composition were melted in a high-frequency induction furnace and pulverized by a water atomization method to obtain a metal powder.

<Composition of raw materials>
・ Si: 7.5wt%
・ B: 3.8 wt%
-Fe: Remaining When the obtained metal powder was observed with a scanning electron microscope (SEM), it was found that each metal particle had a nearly spherical shape as shown in FIG.

Further, when the crystal structure of the obtained metal powder was analyzed with an X-ray diffractometer, no clear peak was observed in the X-ray diffraction spectrum shown in FIG. For this reason, it was found that the obtained metal powder was composed of an amorphous metal.
Further, when the coercive force and saturation magnetic flux density of the obtained metal powder were measured, the coercive force was 1.5 Oe and the saturation magnetic flux density was 1.3 T.

[2] Next, the obtained amorphous metal powder was coated with oleate ion (surfactant) and dispersed in isoparaffin (liquid phase dispersion medium) to obtain a magnetic fluid.
In addition, the content rate of the amorphous metal powder in a magnetic fluid was 80 wt%.
[3] Next, the obtained magnetic fluid was injected into the cylinder of the damper to produce a damper.

(Comparative Example 1)
First, raw materials having the following composition were melted in a high frequency induction furnace and pulverized by a water atomization method to obtain a metal powder.
<Composition of raw materials>
・ Si: 3wt%
・ Fe: balance

In addition, when the obtained metal powder was analyzed with the X-ray-diffraction apparatus, the X-ray-diffraction spectrum which has a clear peak was obtained. For this reason, it was found that the obtained metal powder was composed of metal crystals.
Next, the obtained metal powder was coated with oleate ions and dispersed in isoparaffin in the same manner as in the above example to obtain a magnetic fluid.
Next, the obtained magnetic fluid was injected into the cylinder of the damper to produce a damper.

(Comparative Example 2)
First, carbonyl iron (Fe (CO) ₅ ) was dispersed in isoparaffin to obtain a magnetic fluid.
Next, the obtained magnetic fluid was injected into the cylinder of the damper in the same manner as in the above example, and a damper was produced.
The carbonyl iron had a coercive force of 9.5 Oe and a saturation magnetic flux density of 2.1 T.

2. Evaluation of Damper Each of the dampers obtained in the examples and the comparative examples was expanded and contracted 10,000 times.
Thereafter, the magnetic fluid was taken out from the cylinder, and the metal powder in the magnetic fluid was observed with a scanning electron microscope.
As a result, the appearance of the metal powder (amorphous metal powder) taken out from the damper of the example was almost the same as that before evaluation. On the other hand, the metal powder (crystal metal powder) taken out from the damper of the comparative example was smaller than that before evaluation. This is probably because the metal powder was broken or partially lost.

  1 …… Damper 2 …… Cylinder 2a …… Rod side chamber 2b …… Piston side chamber 21 …… Ceiling portion 22 …… Outer cylinder 23 …… Inner cylinder 231 …… Orifice 24 …… Base valve 241 …… Orifice 25 …… No. DESCRIPTION OF SYMBOLS 1 Reservoir chamber 26 ... 2nd reservoir chamber 3 ... Piston 31 ... Piston rod 32, 33 ... Orifice 34 ... Valve body 4 ... Coil 5 ... Power supply circuit 8 ... Upper member 9 ... Lower member 10 ... Magnetic fluid

Claims (13)

Magnetic particles whose surfaces are covered with a surfactant,
A liquid phase dispersion medium for dispersing the magnetic particles,
A magnetic fluid, wherein the magnetic particles are composed of an Fe-based amorphous metal.   The magnetic fluid according to claim 1, wherein the Fe-based amorphous metal contains at least one of B (boron), C (carbon), Si (silicon), and Cr (chromium) as a constituent component.   3. The magnetic fluid according to claim 1, wherein the Fe-based amorphous metal contains Fe as a main component, contains Si in a content of 4 to 9 wt%, and contains B in a content of 1 to 5 wt%.   The magnetic fluid according to claim 1, wherein the magnetic particles have an average particle size of 0.1 to 25 μm.   The average value of the aspect ratio of the magnetic particles defined by S / L is 0.4 to 1 when the short diameter of the magnetic particles is S [μm] and the long diameter is L [μm]. The magnetic fluid according to any one of 1 to 4.   The magnetic fluid according to claim 1, wherein the magnetic particles have a coercive force of 5 Oe or less.   The magnetic fluid according to claim 1, wherein a saturation magnetic flux density of the magnetic particles is 0.6 T or more.   The magnetic fluid according to claim 1, wherein the magnetic particles are produced by an atomizing method.   The magnetic fluid according to claim 1, wherein a content ratio of the magnetic particles in the magnetic fluid is 50 to 95 wt%.   The magnetic fluid according to claim 1, wherein the surfactant is mainly composed of oleate.   The magnetic fluid according to claim 1, wherein the liquid phase dispersion medium is mainly composed of hydrocarbon oil, silicone oil, or fluorine oil. A cylinder for storing the magnetic fluid according to any one of claims 1 to 11,
A piston that slides in the cylinder and divides the space in the cylinder into two;
A piston rod having one end connected to the piston and the other end located outside the cylinder;
Magnetic field forming means for forming a magnetic field so as to reach the magnetic fluid stored in the cylinder,
A damper characterized in that a damping force can be controlled by changing a fluid characteristic of the magnetic fluid by an action of a magnetic field. A passage formed in the piston and in communication with the two spaces;
The magnetic field forming means is provided in the vicinity of the flow path, and a damping force can be controlled by changing a fluid characteristic by forming a magnetic field so as to reach the magnetic fluid passing through the flow path. The damper described in 1.

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