KR101757727B1 - Magnetorheological fulids with improved re-dispersibility and method for evaluating re-dispersibility of magnetorheological fluids - Google Patents

Abstract

Disclosed is a method for evaluating the redispersibility of a magnetorheological fluid and a magnetorheological fluid. The magnetorheological fluid according to the present invention is a magnetorheological fluid containing magnetic particles, a dispersion medium and an additive, wherein all the solids in the magnetorheological fluid are recovered and the particle size distribution is measured to obtain a span value defined as follows (D ₉₀ - D ₁₀ ) / D ₅₀ , and the span value is 1.3 or more. The present invention also provides a method for evaluating redistribution of a magnetorheological fluid, comprising the steps of: providing a transparent container containing a magnetorheological fluid; irradiating near infrared rays while rotating the transparent container by a centrifugal separator; A step of measuring a primary dispersion stability, a step of applying an external force to the magnetorheological fluid to redisperse the centrifugally separated solid material in the dispersion medium, and the transparent container containing the magnetorheological fluid to which the solid content is redispersed, And irradiating near infrared rays to measure the amount of light transmitted through the transparent container (measurement of secondary dispersion stability).

Description

TECHNICAL FIELD The present invention relates to a method for evaluating the redispersibility of a magnetorheological fluid and a magnetorheological fluid having improved redistribution properties, and a method for evaluating the redispersibility of a magnetorheological fluid and a magnetorheological fluid,

The present invention relates to a magnetorheological fluid, and more particularly, to an evaluation method capable of quantitatively evaluating the redispersibility of a magnetorheological fluid and a magnetorheological fluid having improved redispersibility.

A magnetorheological fluid is a suspension of micro-sized magnetic particles, such as iron powder, which is sensitive to a magnetic field, in a non-magnetic fluid such as oil or water. It is a smart material capable of controlling its flow characteristics in real time through application of an external magnetic field smart material.

Generally, magnetorheological fluids contain magnetic particles in a volume ratio of about 20 to 50 percent, and basically have Newtonian fluid properties, but when an external magnetic field is applied, the magnetic particles migrate and move in a direction parallel to the applied magnetic field , It has the property of Bingham fluid which has shear force and flow resistance and generates constant yield stress without shear strain.

Magneto-rheological fluids are used in dampers, clutches, brakes, etc. due to their resistance to flow, and are also used for polishing due to their shear-strength properties.

In order for the magnetorheological fluid to be effectively applied to various systems, it is necessary to have a high yielding stress, to disperse the magnetic particles uniformly in the dispersion medium, to quickly recover to its original state when removed after application of the magnetic field The viscosity of the fluid and the residual magnetization value should be low.

However, the density of the magnetic particles constituting the magnetorheological fluid (for example, 7.86 g / cm ^{3 in} the case of iron powder) is much higher than the density of the dispersion medium (for example, 0.95 g / cm ^{3 in} the case of silicone oil) . Therefore, even after the preparation of the magnetorheological fluid, even if the dispersibility is excellent, the precipitation of the internal solids can not be completely prevented over time. For this reason, it is very important to ensure the redispersibility of the precipitated solid component, which is a property of redispersing the precipitated solid component again in the dispersion medium, for use in a device such as a linear type damper.

In the case of US 6203717B1 of the prior art, a magnetorheological fluid is prepared by changing the content of magnetic particles, the type of carrier fluid (oil), additives, clay, and the like in order to improve redispersibility, The compressive strength is measured and the redistribution property is evaluated by the strength of the force applied to the load cell.

However, since the USP 6203717B1 is not a redispersion property of a magnetorheological fluid itself but a thermosetting, i.e., a primary processed fluid, a compression strength of the fluid is measured to evaluate the redispersibility of the magnetorheological fluid. It is difficult to see that it is redispersed or that it directly evaluates the redispersibility of the magnetorheological fluid itself.

In addition, since factors such as the type of dispersion medium, additives, and clay are used as variables at the same time as the content of magnetic particles, it is difficult to know the factors affecting the redispersibility.

In the case of US7297290B2, which is another prior art, the magnetic particle size was reduced to nano size, and the redispersibility of the magnetorheological fluid was improved. In the evaluation method of the redispersibility, the experiment was performed by using the spatula Method, it is not possible to obtain the quantified result and the reliability of the result is not high.

Therefore, the method for evaluating the redistribution property of the magnetorheological fluid proposed so far has a problem that it can not be relied on only as a result of qualitative analysis.

DISCLOSURE OF THE INVENTION The present invention is to solve problems such as improvement of redispersibility of a magnetorheological fluid and reliability of an evaluation method. It is a method of quantitatively evaluating redispersibility, which is one of important characteristics of a magnetorheological fluid, To improve the redispersibility and to provide a magnetorheological fluid produced thereby.

A magnetorheological fluid according to an embodiment of the present invention is a magnetorheological fluid including magnetic particles, a dispersion medium, and an additive. After recovering all the solids in the magnetorheological fluid, the particle size distribution is measured and a span value (D ₉₀ - D ₁₀ ) / D ₅₀ , where D _{90 ,} D ₁₀ and D ₅₀ are respectively 90%, 10% and 50% relative to the maximum in the cumulative distribution of solid fractional granularity, %), And the span value is 1.3 or more.

Also, the magnetorheological fluid according to an embodiment of the present invention is a magnetorheological fluid including magnetic particles, a dispersion medium, and an additive. After recovering all the solids in the magnetorheological fluid, the particle size distribution is measured to obtain D ₉₀ / D ₁₀ (Where D ₉₀ and D ₁₀ are particle sizes corresponding to 90% and 10%, respectively, with respect to the maximum value in the cumulative distribution of solid particle sizes), and D ₉₀ / D ₁₀ is 3 or more.

All the solids in the magnetorheological fluid are 20 to 50 volume percent (vol%) of the magnetorheological fluid, and the additive may be 1 to 30 volume percent (vol%) relative to the magnetic particles.

Wherein the magnetic particles are selected from the group consisting of iron, nickel, cobalt, iron-cobalt alloys, iron-aluminum alloys, iron-silicon alloys, iron-nickel alloys, iron-vanadium alloys, iron-molybdenum alloys, Iron-copper alloy, carbonyl iron, chromium dioxide, stainless steel, silicon steel, manganese-zinc ferrite, chromium oxide, iron nitride, iron oxide, iron carbide, ferrite- Zinc ferrite, ferrite (Fe ₃ O ₄ ), and mixtures thereof.

The dispersion medium may be selected from the group consisting of water, ethanol, silicone oil, mineral oil, vacuum oil, castor oil, hydraulic oil, lubricant oil, saturated hydrocarbon oil, unsaturated hydrocarbon oil, synthetic hydrocarbon oil, cycloparaffin oil, ethylene glycol, (PAO), transformer oil, transformer-sealing solution, halocarbon oil, paraffin oil, mineral oil (mineral oil), and the like. ), Olive oil, corn oil, soybean oil, vegetable oil, and mixtures thereof.

The additive may be at least one selected from the group consisting of chemical additives, metal oxides, organic clay and inorganic clay, which are used for dispersion stability, thixotropy, abrasion resistance, chemical stability, antioxidation purpose in a magnetorheological fluid.

The method for evaluating the redispersibility of a magnetorheological fluid according to another embodiment of the present invention comprises the steps of measuring the primary dispersion stability of a magnetorheological fluid using infrared rays, applying an external force to the magnetorheological fluid to redisperse the magnetorheological fluid, Measuring the secondary dispersion stability of the fluid using the infrared; and comparing the primary dispersion stability measurement to the secondary dispersion stability measurement.

A method for evaluating redistribution of a magnetorheological fluid according to another embodiment of the present invention includes the steps of providing a transparent container containing a magnetorheological fluid, irradiating near infrared rays while rotating the transparent container with a centrifuge, A step of measuring the amount of light (primary dispersion stability measurement), a step of re-dispersing the centrifugally separated solid matter in the dispersion medium by applying an external force to the magnetorheological fluid, and a step of re-dispersing the transparent vessel containing the magnetorheological fluid And irradiating near infrared rays while rotating by a centrifugal separator to measure the amount of light transmitted through the transparent container (measurement of secondary dispersion stability).

The first and second dispersion stability measurement values may be represented by respective instability indexes.

The measurement of the amount of light can be performed by measuring 999 transmissivity profiles at intervals of 150 seconds with respect to the near-infrared rays irradiated in a state where the rotation speed of the centrifuge is 4,000 rpm.

According to the present invention, it is possible to provide a measurement method capable of quantifying and evaluating the redispersibility of a magnetorheological fluid by itself, and a magnetorheological fluid with improved redispersibility can be provided through the above method, A clear criterion for the factor can be given.

In addition, by providing a re-dispersibility evaluation method capable of quantitatively evaluating the redispersibility of a magnetorheological fluid, a method for rapidly and reliably redispersing the magnetorheological fluid in the field of manufacturing and utilizing magnetorheological fluid can be extended .

The method for the evaluation of redispersibility according to the present invention measures the redispersibility of magnetorheological fluid depending on the influence of all the solids including the magnetic particles contained in the magnetorheological fluid as well as the organic and inorganic additives used for improving the properties of the magnetorheological fluid can do.

Further, the magnetorheological fluid having improved redispersibility according to the present invention is applicable to various linear type dampers and rotary type dampers applied to passenger cars, commercial vehicles, railroad cars, two-wheel vehicles, and shock absorbers in the military industry It can be extended to various dampers, bridges and building damper, and vibration control dampers of household appliances.

1 is a process diagram for a method for evaluating the redispersibility of a magnetorheic fluid according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of a profile used in calculating instability index of a magnetorheological fluid according to an embodiment of the present invention. FIG.
3 is a graph showing the results of primary dispersion stability measurement on specimens in the evaluation of redispersion of a magnetorheological fluid according to an embodiment of the present invention.
FIG. 4 is a graph showing the results of secondary dispersion stability measurement on specimens in the evaluation of redispersibility of a magnetorheological fluid according to an embodiment of the present invention. FIG.
FIG. 5 is a graph showing the relationship between the rate of change in instability index and the span value of the results of the primary dispersion stability measurement and the secondary dispersion stability measurement in the evaluation of the redispersibility of the magnetorheic fluid according to an embodiment of the present invention. FIG.
6 is a graph showing the relation between the change rate of the instability index of the result of measurement of the primary dispersion stability and the result of measurement of the secondary dispersion stability and D ₉₀ / D _{10 in} the evaluation of the redispersibility of the magnetorheological fluid according to an embodiment of the present invention FIG.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims. Like reference numerals refer to like elements throughout the specification.

Hereinafter, a magnetorheological fluid according to a preferred embodiment of the present invention will be described.

A magnetorheological fluid according to an embodiment of the present invention is a magnetorheological fluid including magnetic particles, a dispersion medium, and an additive, wherein all the solids in the magnetorheological fluid are recovered to measure the particle size, and all solids in the magnetorheological fluid When the span value is defined as follows, the span value is 1.3 or more.

Span value = (D ₉₀ - D ₁₀ ) / D ₅₀ ;

(Where D _90, D ₁₀ and D ₅₀ are respectively the particle sizes corresponding to 90%, 10% and 50% of the maximum value in the cumulative distribution of the solid particle size)

Generally, even though the sedimentation stability is ensured after the preparation of the magnetorheological fluid, the sedimentation of the solid content (solid particles such as magnetic particles and additives) occurs over time. Therefore, in order to be used in a device such as a linear type damper, It is very important to secure acidity.

The re-dispersibility refers to a property of returning to a state before separation by an external force applied by a solid content that has been sedimented or separated under the action of gravity or centrifugal force.

In the prior art, by measuring and evaluating the redistribution property of the primary processed fluid by thermosetting the magnetorheological fluid, rather than the magnetorheological fluid itself, for the redistribution of the magnetorheological fluid, the precipitated solids in the magnetorheological fluid Or the direct redistribution of the magnetorheological fluid itself, and the effect of the solids present in the magnetorheological fluid on the redispersion could not be confirmed.

That is, although the redispersibility of the magnetorheological fluid is obviously affected not only by magnetic particles but also by other solids in the fluid, it is evaluated based on all the solids such as magnetic particles and organic additives contained in the magnetorheological fluid Until now, it can be said that it is in no condition.

Accordingly, in the present invention, by changing the size and the width of the particle size distribution of all the solid components (all the solid components including magnetic particles, surface-modified magnetic particles, various organic and inorganic additives, etc.) contained in the magnetorheological fluid, Based on this evaluation, we developed a magnetorheological fluid with improved redistribution.

More specifically, in order to improve the redispersibility of a magnetorheological fluid, a fluid is prepared in consideration of D ₁₀ , D ₅₀ , D _90, and span value of all the solids contained in the magnetorheological fluid.

The span value is a method in which the particle size distribution width of the solid content can be known. The span value is a value obtained by dividing the magnetic particle size Based on the values for all solids in the rheological fluid.

In the present invention, it is preferable that the span value of the magnetorheological fluid is at least 1.3 or more so as to have good redispersibility. When the span value is less than 1.3, the redispersibility is remarkably reduced.

Further, a magnetorheological fluid having improved redispersibility according to a preferred embodiment of the present invention is a magnetorheological fluid containing magnetic particles, a dispersion medium, and an additive, wherein all the solids in the magnetorheological fluid are recovered and the particle size distribution is measured D ₉₀ / D ₁₀ (where D ₉₀ and D ₁₀ are respectively the particle size corresponding to 90% and 10% of the maximum value in the cumulative distribution of solid particle size), and D ₉₀ / D ₁₀ 3 or more.

Further, in the magnetorheological fluid according to the embodiment of the present invention, all the solids in the magnetorheological fluid are 20 to 50 volume percent (vol%) of the magnetorheological fluid, and the additive is 1 to 30 And a volume percentage (vol%).

In the present invention, not only the magnetic particles but also all of the solid components including the additives added to the magnetorheological fluid are used as criteria for the re-dispersibility evaluation, so that the magnetic particles, the surface-modified magnetic particles, So that the original redispersibility of the magnetorheological fluid itself can be considered.

Wherein the magnetic particles are selected from the group consisting of iron, nickel, cobalt, iron-cobalt alloys, iron-aluminum alloys, iron-silicon alloys, iron-nickel alloys, iron-vanadium alloys, iron-molybdenum alloys, Iron-copper alloy, carbonyl iron, chromium dioxide, stainless steel, silicon steel, manganese-zinc ferrite, chromium oxide, iron nitride, iron oxide, iron carbide, ferrite- Zinc ferrite, ferrite (Fe ₃ O ₄ ), and mixtures thereof.

In the present invention, metal powders such as iron (Fe), nickel (Ni), cobalt (Co), and carbonyl iron powder having a large saturation magnetization are preferably used as magnetic particles. Shape.

In order to secure the sedimentation stability of the magnetorheological fluid, metal oxide particles having a relatively small particle size and a low density as compared with the metal particles can be used. These metal oxide particles have a relatively low saturation magnetization.

The magnetic particles used in the magnetorheological fluid may be a mixture of two or more materials having different particle sizes and properties.

The dispersion medium may be selected from the group consisting of water, ethanol, silicone oil, mineral oil, vacuum oil, castor oil, hydraulic oil, lubricant oil, saturated hydrocarbon oil, unsaturated hydrocarbon oil, synthetic hydrocarbon oil, cycloparaffin oil, ethylene glycol, (PAO), transformer oil, transformer-sealing solution, halocarbon oil, paraffin oil, mineral oil (mineral oil), and the like. Olive oil, corn oil, soybean oil, vegetable oil, and a mixed oil thereof. [0029] The term " oil "

The additive may be at least one selected from the group consisting of chemical additives, metal oxides, organic clays and inorganic clays which are used for the purposes of dispersion stability, thixotropy, abrasion resistance, chemical stability and oxidation resistance in a magnetorheological fluid.

Accordingly, all solids of the magnetorheological fluid may include magnetic particles as well as organic or inorganic clays of the additive.

More specifically, the additives include inorganic clays, dispersants, surfactants, corrosion inhibitors, lubricants, antiwear additives, antioxidants, thixotropic agents and conventional suspension agents.

As the inorganic clay, bentonite, hectorite, montmorillonite or a similar inorganic clay having a lamina structure and a polar surface is used.

Dispersing agents include oleic acid, fatty acid metal soap, polyalcohols, ammonium salts, fatty acids, compounds such as polyethylene oxide, phosphates, phosphonates, and mixtures thereof.

Surfactants include, but are not limited to, sulfonates, phosphate esters, stearic acid, glycerol monooleate, sorbitan sesquioleate, laurates, fatty acids, fatty alcohols, Fluoroaliphatic polymeric esters, and titanates, aluminates and zirconate coupling agents and other surface active agents. Also included are polyalkenediol and partially esterified polyols.

Corrosion inhibitors include sodium nitrite, sodium nitrate, sodium benzoate, borax, ethanolamine phosphate and mixtures thereof, and the anti-wear additive includes molybdenum disulfide, zinc phosphate, triaryl phosphate, triphenylphosphorothio Compounds such as sodium carbonate, sodium carbonate, sodium carbonate, sodium carbonate, sodium carbonate, sodium carbonate, sodium carbonate, sodium carbonate and sodium carbonate.

The method for evaluating the redispersibility of a magnetorheological fluid according to another embodiment of the present invention comprises the steps of measuring the primary dispersion stability of a magnetorheological fluid using infrared rays, applying an external force to the magnetorheological fluid to redisperse the magnetorheological fluid, Measuring the secondary dispersion stability of the fluid using the infrared rays, and comparing the primary dispersion stability measurement value and the secondary dispersion stability measurement value.

In order to evaluate the redispersibility of the magnetorheological fluid in the present invention, the dispersion stability of the magnetorheological fluid was measured by dividing the dispersion stability of the magnetorheological fluid by two times using infrared rays. After the primary dispersion stability was measured, the magnetorheological fluid was re- The dispersion redistribution of the magnetorheological fluid can be quantitatively evaluated by measuring the dispersion stability of the secondary and comparing the primary and secondary dispersion stability measurements.

As shown in FIG. 1, the method for evaluating redistribution of a magnetorheic fluid according to another embodiment of the present invention includes the steps of providing a transparent container containing a magnetorheological fluid, rotating the transparent container by a centrifuge, A step of measuring the amount of light transmitted through the transparent container (primary dispersion stability measurement), applying an external force to the magnetorheological fluid, redispersing the centrifugally separated solid into a dispersion medium, Irradiating near infrared rays while rotating the transparent container containing the fluid by a centrifugal separator, and measuring the amount of light transmitted through the transparent container (measuring the secondary dispersion stability).

The magnetorheological fluid is prepared by fixing the solid components (the magnetic particles, the surface-modified magnetic particles, additives, etc.) constituting the magnetorheological fluid to the same weight and changing the D ₁₀ , D ₅₀ , D ₉₀ and span values .

As described above, the solid content is fixed at a constant weight, and the magnetorheological fluid having the particle size and the particle size distribution width of the solid content is charged in the transparent container (the light of constant wavelength can be transmitted) in the same amount.

The transparent container filled with the magnetorheological fluid is mounted on a centrifuge and rotated, and the magnetorheological fluid is separated into a dispersion medium and a solid component. While the solid component is separated by centrifugal force, light is irradiated on the transparent container to transmit the transparent container. And detects light (amount of light).

At this time, it is preferable that the amount of transmitted light of the dispersion medium is 40% or more, because the instability index value is low when the transmission rate of the dispersion medium is less than 40%. In particular, less than 40% of the permeability may be seen when the particles are not precipitated or when a deeply colored oil is used.

The light detection is performed by disposing the light detecting sensor at a position opposite to the light emitting point, that is, at a point symmetrical with the light emitting point about the transparent container.

And then an external force is applied to the sedimented solid portion so that redispersing is performed on the dispersion medium.

It is preferable to apply an external force to the solid portion by using a vibration exciter capable of rapid energy transfer. It is preferable to use a vortex mixer as a vibration exciter.

The redispersibility refers to a property of returning to a state before solidification is performed by applying an external force to sediments or solids separated from the dispersion medium under the action of gravity or centrifugal force.

The transparent container containing the re-dispersed magnetorheological fluid is rotated again in the above centrifugal separator to centrifuge the magnetorheological fluid and simultaneously transmit the same light to detect transmitted light.

The light used in the irradiation of the light is preferably a near infrared ray.

The redistribution property of the magnetorheological fluid is evaluated by comparing the first dispersion stability measurement value based on the first transmission light amount and the second dispersion stability measurement value based on the second transmission light amount.

With respect to the above dispersion stability, the term "dispersion" refers to floating of another material in a state of fine particles in one material, and the property of maintaining such state is called dispersion stability.

The first and second dispersion stability measurement values can be represented by respective instability indexes.

The instability index indicating the dispersion stability means that the dispersion stability is better as the value is closer to 0, and as the value is closer to 1, the dispersion stability is worse.

Instability index should be not less than 0.3. If the magnetorheological fluid with a viscosity of less than 0.3 is a high-viscosity, high-concentration magnetorheological fluid, or if the calculation formula is different (when the setting of n is different) Lt; / RTI > Thus, differences in instability index values before and after redispersion may appear differently. Therefore, it is preferable that the primary dispersion stability and the secondary dispersion stability are calculated by setting the same calculation method.

A schematic diagram of the profile is shown in Fig. The position of the horizontal axis (x-axis) indicates the position in the transparent container for centrifugal separation, and the position toward the right side means the outer side of the transparent container. That is, it means that the precipitate layer accumulates. Transmission of the longitudinal axis (y-axis) means that near-infrared rays are transmitted through a transparent container containing fluid and light is detected. As the centrifugation proceeds (as precipitation proceeds), the profile gradually moves from the first to the last. Where n is the number of the profile.

The measurement of the amount of light is performed by measuring 999 transmissivity profiles at intervals of 150 seconds with respect to the near-infrared rays irradiated while the rotation speed of the centrifuge is 4,000 rpm.

Hereinafter, a method of evaluating the redispersibility of a magnetorheic fluid according to the present invention will be described in detail with reference to examples. The following examples are illustrative of the present invention only and are not intended to limit the scope of the present invention.

<Examples>

A magnetorheological fluid was prepared by fixing all the solids of the magnetorheological fluid to the same weight and then combining different D ₁₀ , D ₅₀ , D ₉₀ and span values of the solids.

Then, all the solid components contained in the magnetorheological fluid were recovered using a centrifuge, washed, and then D ₁₀ , D ₅₀ , D ₉₀ and span values were obtained using a particle size analyzer as shown in Table 1 below.

&Lt; Particle size distribution of solid content contained in magnetorheological fluid > Example D ₁₀ (占 퐉) D ₅₀ (占 퐉) D ₉₀ (占 퐉) D ₉₀ / D ₁₀ span value  No 1 (# 1) 1.884 6.490 15.520 8.238 2.008  No 2 (# 2) 1.952 4.260 7.810 4.001 1.375  No 3 (# 3) 4.470 8.050 16.220 3.629 1.460  No 4 (# 4) 2.831 4.160 6.680 2.360 0.925  No 5 (# 5) 3.980 5.560 8.550 2.148 0.822  No 6 (# 6) 6.000 9.470 16.540 2.757 1.113  No 7 (# 7) 3.330 5.260 8.700 2.613 1.021  No 8 (# 8) 2.537 6.820 16.180 6.378 2.000  No 9 (# 9) 3.940 6.650 12.710 3.226 1.319  No 10 (# 10) 2.319 5.580 11.170 4.817 1.586

The ultrasonic treatment of the particle size analyzer should be performed within 5 minutes. For the particle size analysis, water and ethanol were used as the dispersion medium.

In the present invention, the dispersion stability before and after redispersion according to the difference of the solid particle size and the span value in the magnetorheological fluid was measured and compared using the method of measuring the dispersion stability of the magnetorheological fluid as a method of evaluating the redispersibility of the magnetorheological fluid.

For the measurement of the dispersion stability, the LUMi series of L.U.M GmbH (Germany) was used, and the dispersion stability was measured by measuring the dispersion stability of the solids in the real time sedimentation rate while centrifuging.

For measurement of dispersion stability, centrifugation was carried out while rotating at a speed of 4000 rpm, and near infrared rays were irradiated to the specimen and 999 transmission profiles were measured at intervals of 150 seconds.

The redispersibility was evaluated by comparing the D ₁₀ , D ₅₀ , D ₉₀ and span values of the solids of the magnetorheological fluid by measuring the dispersion stability before and after re-dispersion as described above and calculating the dispersion stability difference.

In the results of the dispersion stability measurement, the instability index is closer to 0 and the dispersion stability is better. When the instability index is 1, the dispersion stability is worst. This instability index is an index that numerically represents dispersion stability.

The sedimented sediment in the magnetorheological fluid was redispersed by the rotation of the centrifuge using the vortex mixer for the same time (10 minutes) for all specimens under the same conditions.

The redispersed magnetorheological fluid was subjected to light irradiation while conducting centrifugation under the same method (conditions) as above, and the amount of transmitted light was measured.

FIGS. 3 and 4 show results of instability index before and after re-dispersion for each magnetorheological fluid.

Comparing the amounts of change in the instability index before and after re-dispersion in FIGS. 3 and 4 can be used as an indicator of the redispersibility of the magnetorheological fluid.

3 and 4, in the relation between the rate of change of the instability index before and after redispersion and the span value, when the span value is 1.3 or more, the rate of change of the instability index before and after redispersion is 5% , And the value of the instability index rapidly increased to 8.22% or more for a specimen having a span value of less than 1.3.

FIG. 5 is a table showing the relationship between the change rate and the span value of the instability index before and after re-dispersion according to the measurement of the primary and secondary dispersion stability, and the dotted line shows the good redispersibility of the specimen.

The increase in the instability index means that the precipitated solids are differently redispersible under the same dispersion conditions and do not completely redisperse, but remain in aggregated or precipitated state with each other.

Therefore, according to the test results of the present invention, it can be seen that redispersions are performed more satisfactorily when the particle size distribution width of the solid particles in the magnetorheological fluid is wide, that is, when the span value is 1.3 or more.

FIG. 6 is a table showing the relationship between the change rate of the instability index and the D ₉₀ / D ₁₀ before and after re-dispersion according to the measurement of primary and secondary dispersion stability, and the dotted line shows the good redispersibility of the specimen.

As shown in FIG. 6, when the D ₉₀ / D ₁₀ value was 3 or more, the rate of instability index change before and after redispersion was 4.01%, which was less than 5%, and the D ₉₀ / D ₁₀ value was less than 3 In the sample, the rate of change of the instability index was greatly increased by 8.22% or more.

In summary, it can be seen that the redispersibility of the magnetorheological fluid is greatly improved when the value of D ₉₀ / D ₁₀ is 3 or more.

The method of evaluating the redispersibility disclosed by the prior art includes a method of measuring the compressive strength after thermally curing the magnetorheological fluid, a method of manually measuring the rotational resistance of the spatula, a method of vigorously shaking the magnetorheological fluid, However, these methods have difficulty in quantifying the re-dispersion result and have a disadvantage in that an error of a person who performs the test is inevitable.

In the present invention, the dispersion stability of the magnetorheological fluid is measured, and it is possible to quantitatively evaluate the dispersion stability before and after the redispersion by comparing the size, span value, and particle size distribution of all the solids in the magnetorheological fluid. .

Furthermore, it may be a standard for quantitatively evaluating the redispersibility of the magnetorheological fluid based on the method of measuring the redispersibility of the present invention.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

Claims (6)

In a magnetorheological fluid comprising magnetic particles, a dispersion medium and an additive,
Wherein the magnetorheological fluid comprises at least one additive in the form of a solid,
When all the solids in the magnetorheological fluid are recovered and the particle size distribution is measured to obtain the span value defined below,
Span value = (D ₉₀ - D ₁₀ ) / D ₅₀ ;
(Where D _90, D ₁₀ and D ₅₀ are respectively the particle sizes corresponding to 90%, 10% and 50% of the maximum value in the cumulative distribution of the solid particle size)
The span value is not less than 1.3 and not more than 2.0,
When the dispersion stability of the magnetorheological fluid is measured before and after re-dispersion to obtain the rate of change of the instability index,
Wherein the absolute value of the rate of change of the instability index is less than 5%.
In a magnetorheological fluid comprising magnetic particles, a dispersion medium and an additive,
Wherein the magnetorheological fluid comprises at least one additive in the form of a solid,
When all the solids in the magnetorheological fluid are recovered and the particle size distribution is measured to obtain D ₉₀ / D ₁₀ ,
(Where D ₉₀ and D ₁₀ are respectively the particle size corresponding to 90% and 10% of the maximum value in the cumulative distribution of the solid content)
Wherein D ₉₀ / D ₁₀ is in the range of 3.226 to 8.238,
When the dispersion stability of the magnetorheological fluid is measured before and after re-dispersion to obtain the rate of change of the instability index,
Wherein the absolute value of the rate of change of the instability index is less than 5%.
3. The method according to claim 1 or 2,
Wherein all solids in said magnetorheological fluid are 20 to 50 volume percent (vol%) of said magnetorheological fluid,
Wherein the additive is 1 to 30 volume percent (vol%) of the magnetic particles.
3. The method according to claim 1 or 2,
Wherein the magnetic particles are selected from the group consisting of iron, nickel, cobalt, iron-cobalt alloys, iron-aluminum alloys, iron-silicon alloys, iron-nickel alloys, iron-vanadium alloys, iron-molybdenum alloys, Iron-copper alloy, carbonyl iron, chromium dioxide, stainless steel, silicon steel, manganese-zinc ferrite, chromium oxide, iron nitride, iron oxide, iron carbide, ferrite- Zinc ferrite, ferrite (Fe ₃ O ₄ ), and mixtures thereof.
3. The method according to claim 1 or 2,
The dispersion medium may be selected from the group consisting of water, ethanol, silicone oil, mineral oil, vacuum oil, castor oil, hydraulic oil, lubricant oil, saturated hydrocarbon oil, unsaturated hydrocarbon oil, synthetic hydrocarbon oil, cycloparaffin oil, ethylene glycol, (PAO), transformer oil, transformer-sealing solution, halocarbon oil, paraffin oil, mineral oil (mineral oil), and the like. ), Olive oil, corn oil, and soybean oil, vegetable oil, and mixtures thereof. The magnetorheological fluid according to claim 1,
3. The method according to claim 1 or 2,
Wherein the additive is at least one selected from the group consisting of chemical additives, metal oxides, organic clays and inorganic clays used for the purpose of dispersion stability, thixotropy, abrasion resistance, chemical stability, antioxidation in a magnetorheological fluid, Magnetorheological fluid.

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