Patent Application
20230253135
The present invention relates to a magnetorheological fluid and a manufacturing method thereof. More particularly, the present invention relates to a magnetorheological fluid which includes a dispersion medium, a magnetic particle, and a thixotropic agent and includes a predetermined viscoelastic property to have enhanced dispersion stability and sedimentation stability, and a manufacturing method thereof.
A magnetorheological fluid (MRF), as a suspension in which micro-sized micro magnetic particles sensitive to a magnetic field are mixed in a dispersion medium such as oil or water, is one of smart materials of which flow characteristics can be controlled in real time by application of an external magnetic field.
The magnetorheological fluid exhibits a magnetorheological phenomenon in which a rheological behavior and electrical, thermal, and mechanical properties are changed according to the external magnetic field. In general, the magnetorheological fluid has a Newtonian fluid property when the external magnetic field is not applied, but has a property of a Bingham fluid which has a shear force which hinders a flow of a fluid or a resistance to the flow by forming a chain structure in a direction parallel to a magnetic field to which the magnetic particle is applied therein and generates a constant yield stress without a shear strain when the external magnetic field is applied.
Since the magnetorheological fluid has the resistance to the flow, a rapid response speed, and a reversible characteristic, there is a high applicability to various industrial fields such as a vibration control device such as a damper, a clutch of a vehicle, a brake, etc.
In order for the magnetorheological fluid to be effectively utilized, the magnetorheological fluid should have a high yield stress, and the viscosity of the fluid must be sufficiently low so that the magnetorheological fluid can be quickly restored to an original state thereof when the magnetic field is removed again after the magnetic field is applied, and the magnetic particles inside the magnetorheological fluid should be evenly distributed in the dispersion medium.
However, since the density of the magnetic particles constituting the magnetorheological fluid (for example, tap density of iron particles of 3.9 to 4.1 g/cm3) is still larger than the density (for example, in the case of silicone oil, approximately 0.8 to 1.0/cm3 at room temperature) of the dispersion medium, the magnetic particles are sedimented by gravity in the dispersion medium, thereby reducing the dispersion stability of the magnetorheological fluid. Therefore, when the user uses the magnetorheological fluid, the user suffers from inconvenience that the magnetic particles and the dispersion medium sedimented and separated in a container should be remixed or redispersed, and the physical properties of the magnetorheological fluid may be changed during the remixing/redispersing process.
In order to solve the problem, in the case of Korean Patent Application No. 2000-0025029, the dispersion stability was improved by the interaction with water droplets in the emulsion by adsorbing a water-affinity surfactant on the surface of magnetic particles, but this is difficult to maintain stability for a long time. In addition, in the case of U.S. Pat. No. 5645752, a thixotropic network was formed using colloidal silica and silicon oligomer to achieve the dispersion stability, but there was a problem in that redispersion was difficult due to agglomeration of particles during long-term storage.
On the other hand, in the prior art, the dispersion stability is attempted to be improved by further mixing or reacting a specific substance with a magnetorheological fluid, but there is no definite standard for improving dispersion or sedimentation stability, so that research thereon is required.
Accordingly, the present invention is contrived to solve the problems in the related art and the present invention has been made in an effort to provide a magnetorheological fluid and a manufacturing method thereof which can improve the degree of sedimentation of magnetic particles in a dispersion medium.
The present invention has been made in an effort to provide a magnetorheological fluid and a manufacturing method thereof which present physical property criteria that can improve dispersion stability and sedimentation stability.
The present invention has been made in an effort to provide a magnetorheological fluid having enhanced dispersion stability and sedimentation stability and having a high yield stress, and a manufacturing method thereof.
However, such a problem is exemplary and the scope of the present invention is not limited thereto.
An object of the present invention is achieved by a magnetorheological fluid including: a dispersion medium; magnetic particles; and a thixotropic agent, in which the magnetorheological fluid has viscoelasticity, and when shear stress τ of the viscoelasticity of the magnetorheological fluid is τ = τ0sin(wt) and shear strain γ is γ = γ0sin(wt + δ) = G′sin(wt) + G″cos [G′ is referred to storage modulus and G″ is referred to as loss modulus], when a magnetic field is not applied, the slope of G″ is equal to or less than 0 for the range from 0.01% shear strain applied to the magnetorheological fluid to the shear strain value satisfying tan δ = G″ / G′= 1.
According to an embodiment of the present invention, as the content of the thixotropic agents increases, the shear strain value satisfying tan δ = G″ / G′= 1 may increase.
According to an embodiment of the present invention, as the content of the magnetic particles increases, formation of a three-dimensional network by the thixotropic agent is weakened and the shear strain value satisfying tan δ = G″ / G′= 1 may decrease.
According to an embodiment of the present invention, as the content of the thixotropic agent increases, the three-dimensional network by the thixotropic agent is strengthened and the viscosity of the magnetorheological fluid may increase.
According to an embodiment of the present invention, when the magnetic field is not applied, G′ may be at least greater than 250 Pa in an initial linear region and G″ may be at least greater than 75 Pa in the initial linear region.
According to an embodiment of the present invention, when the magnetic field is not applied, a flow point (τf) value may be at least greater than 10 Pa.
According to an embodiment of the present invention, when the magnetic field is applied, for the section from 0.01% shear strain applied to the magnetorheological fluid to the shear strain value that satisfies tan δ = G″ / G′= 1, before the values of G′ and G″ become equal to each other, the section may include at least one portion in which the slope of G″ changes from positive to negative.
According to an embodiment of the present invention, as the intensity of the applied magnetic field increases, the shear strain value corresponding to the portion where the slope of G″ changes from positive to negative may increase before the G′ and G″ values become equal to each other.
According to an embodiment of the present invention, as the content of magnetic particles increases, an integral value of G″ may increase for a section in which the value of shear strain applied to the magnetorheological fluid is in the range of 0.01% to 100%.
According to an embodiment of the present invention, as the intensity of the applied magnetic field increases, the integral value of G″ may increase for the section in which the value of shear strain applied to the magnetorheological fluid is in the range of 0.01% to 100%.
According to an embodiment of the present invention, the applied magnetic field intensity and the bump area have a linear relationship y = ax + b [x represents the magnetic field intensity, y represents the bump area], and a = 73.1 ± 2.0.
According to an embodiment of the present invention, when the shear strain value satisfying tan δ = G″ / G′= 1 is 15% or more and 35% or less, the sedimentation rate S is at least greater than 80%, and a sedimentation rate S is measured by naturally sedimenting the magnetorheological fluid in a measuring cylinder for 60 days, the sedimentation rate S is at least greater than 80% and S(vol%)=100 - [(ΔS) / (h)] X 100 [ΔS corresponds to the height of a supernatant liquid after a certain time after filling a cylinder with the magnetorheological fluid, and h corresponds to the initial height of the cylinder with the magnetorheological fluid].
According to an embodiment of the present invention, the thixotropic agent may contain at least a silicone or clay component.
Another object of the present invention is achieved by a method for manufacturing a magnetorheological fluid, including a dispersion medium; magnetic particles; and a thixotropic agent, in which the magnetorheological fluid has viscoelasticity, and when shear stress τ of the viscoelasticity of the magnetorheological fluid is τ = τ0sin(wt) and shear strain γ is γ = γ0sin(wt + δ) = G′sin(wt) + G″cos [G′ is referred to storage modulus and G″ is referred to as loss modulus], when a magnetic field is not applied, the slope of G″ is equal to or less than 0 for the range from 0.01% shear strain applied to the magnetorheological fluid to the shear strain value satisfying tan δ = G″ / G′= 1.
According to an embodiment of the present invention, as the content of the thixotropic agents increases, the shear strain value satisfying tan δ = G″ / G′= 1 may increase.
According to an embodiment of the present invention, as the content of the magnetic particles increases, formation of a three-dimensional network by the thixotropic agent is weakened and the shear strain value satisfying tan δ = G″ / G′= 1 may decrease.
According to an embodiment of the present invention, as the content of the thixotropic agent increases, the three-dimensional network by the thixotropic agent is strengthened and the viscosity of the magnetorheological fluid may increase.
According to an embodiment of the present invention, when the magnetic field is applied, for the section from 0.01% shear strain applied to the magnetorheological fluid to the shear strain value that satisfies tan δ = G″ / G′= 1, before the values of G′ and G″ become equal to each other, the section may include at least one portion in which the slope of G″ changes from positive to negative.
According to an embodiment of the present invention, as the intensity of the applied magnetic field increases, the shear strain value corresponding to the portion where the slope of G″ changes from positive to negative may increase before the G′ and G″ values become equal to each other.
According to an embodiment of the present invention, as the content of magnetic particles increases, the integral value of G″ may increase for the section in which the value of shear strain applied to the magnetorheological fluid is in the range of 0.01% to 100%.
According to an embodiment of the present invention, as the intensity of the applied magnetic field increases, the integral value of G″ may increase for the section in which the value of shear strain applied to the magnetorheological fluid is in the range of 0.01% to 100%.
According to an embodiment of the present invention, the applied magnetic field intensity and the bump area have a linear relationship y = ax + b [x represents the magnetic field intensity, y represents the bump area], and a = 73.1 ± 2.0.
According to the present invention configured as described above, there is an effect of improving the degree of sedimentation of magnetic particles in the dispersion medium of the magnetorheological fluid.
According to the present invention, there is an effect of presenting a physical property standard that can improve the dispersion stability and sedimentation stability of the magnetorheological fluid.
According to the present invention, there is an effect that the magnetorheological fluid has a high yield stress while improving the dispersion stability and the sedimentation stability.
Of course, the scope of the present invention is not limited by such an effect.
The following detailed description of the present invention will be made with reference to the accompanying drawings which illustrate a specified embodiment in which the present invention may be implemented as an example. The embodiment will be described in enough detail so that those skilled in the art are able to embody the present invention. It should be understood that various embodiments of the present invention are different from each other and need not be mutually exclusive. For example, specific shapes, structures, and characteristics described herein may be implemented in other embodiments without departing from the spirit and scope of the present invention in relation to one embodiment. In addition, it is to be understood that the location or arrangement of individual components within each disclosed embodiment may be changed without departing from the spirit and scope of the present invention. Accordingly, the detailed description to be described below is not intended to be taken in a limiting sense, and the scope of the present invention, if properly described, is limited only by the appended claims, along with all scopes equivalent to those claimed by the claims. In the drawings, similar reference numerals refer to the same or similar functions over various aspects, and the length, area, thickness, and the like and the form may be exaggerated for convenience.
In the present specification, it should be understood that the term “include” or “have” indicates that a feature, a number, a step, an operation, a component, a part or the combination thereof described in the specification is present, but does not exclude a possibility of presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof, in advance.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.
According to an embodiment of the present invention, a magnetorheological fluid may have a phase in which a liquid phase and a solid phase are converted or the liquid phase and the solid phase are mixed according to an external magnetic field. Magnetic particles included in the magnetorheological fluid may form a chain according to the external magnetic field, and thus exhibit properties similar to solids.
According to an embodiment of the present invention, the magnetorheological fluid may include a mixture of a dispersion medium, magnetic particles, and a thixotropic agent.
The dispersion medium is a material that allows a magnetic powder composite to be dispersed to form a suspension, and has a polar or non-polar property, and a low viscosity is preferable for a maximum magnetorheological effect.
For example, the dispersion medium may be at least one selected from the group consisting of silicone oil, mineral oil, paraffin oil, corn oil, hydrocarbon oil, castor oil, and vacuum oil. In addition, the dispersion medium may have a kinematic viscosity of 40° C. in the range of approximately 5 to 300 mm2/s. If the kinematic viscosity is lower than the range, there may be a problem of lowering a sedimentation property, and if the kinematic viscosity is higher than the range, there may be a problem of lowering the fluidity, so it is preferable that the kinematic viscosity is included in the range.
The magnetic particles may be at least one selected from iron, carbonyl iron, iron alloy, iron oxide, iron nitride, carbide iron, low carbon steel, nickel, cobalt, and mixtures thereof or alloys thereof. The average particle diameter of the magnetic particles may be approximately 1 to 100 µm. Further, the magnetic particles may be uncoated magnetic particles or magnetic particles coated with an organic resin.
For example, the magnetic particles may be included in an amount of approximately 65 to 85 wt% in the magnetorheological fluid. If the magnetic particles are included in a lower content than the above content, a shear stress may be lowered, and if the magnetic particles are included in a higher content than the above content, a fluidity problem may appear, and as a result, it is preferable that the content is included within the above range.
As the thixotropic agent is mixed and dispersed in the magnetorheological fluid, a known thixotropic agent may be used that causes the magnetorheological fluid to exhibit thixotropy.
Besides, the magnetorheological fluid may further include a dispersing agent, an antifriction agent, an antioxidant, and a corrosion inhibitor as conventional additives.
In the present invention, viscoelasticity is presented as a means for measuring properties similar to solids of the magnetorheological fluid. As for elastic, a shear stress-shear strain curve indicates linearity. The viscoelasticity exhibits hysteresis in the shear stress-shear strain curve, which is due to energy loss when an external force is applied.
Referring to
Here, (i) when δ = 0, the magnetorheological fluid is an elastic material, (ii) when δ = π/2, the magnetorheological fluid is a viscous material, and (iii) when 0 < δ < π/2, the magnetorheological fluid is a viscoelastic material.
Here, G′ is referred to as a storage modulus and G″ is referred to as a loss modulus.
With a linear viscoelastic region test of the magnetorheological fluid, three parameters such as storage modulus G′, loss modulus G″, crosspoint, and flow point τf may be measured. After arranging the magnetorheological fluid on a fixed base, a viscoelasticity test may be performed by a method for measuring torque by rotating the magnetorheological fluid while compressing the magnetorheological fluid from the top with a pressing means. In one embodiment, at a temperature T = 25° C., it is possible to measure G, G″, cross point, and flow point by adjusting the angular velocity ω = 10 rad/s of the compressing means.
Referring to
From
The thixotropic agent may form a three-dimensional network structure within the magnetorheological fluid over time. In
Referring to
Here, ΔS corresponds to the height of a supernatant liquid after a certain time after filling a cylinder with the magnetorheological fluid, and h corresponds to the initial height of the cylinder filled with the magnetorheological fluid. The supernatant liquid refers to the upper layer layer-separated by the sedimentation of the magnetic particles in the magnetorheological fluid.
For example, the magnetorheological fluid may be filled in a container that is maintained horizontally, and the degree of the sedimentation may be measured at every set time by setting a state in which no sedimentation occurs as 100%.
In the present invention, the measurement was performed with 7 types of samples. Samples in which the content of the magnetic particles, the types of thixotropic agent, and the content of the thixotropic agent were changed were prepared. Silicon-based thixotropic agents are typically fumed silica, and clay-based thixotropic agents representatively include Bentonite clay, Smectite clay, Montmorillonite clay, and Hectorite clay, and specific commercial products include claysClaytone AF, Bentone®, Baragel®, and Nykon®.
A magnetorheological fluid containing 70 to 80 wt% of magnetic particles, 1 to 5 wt% of thixotropic agent 1, and the dispersion medium and an additive as a balance was used. Thixotropic Agent 1 is a thixotropic agent based on a silicone component.
A magnetorheological fluid was used, which includes magnetic particles in the same content as Sample 1, contains thixotropic agent 2 by 10% less than Sample 1, and contains the dispersion medium and additives as the balance. Thixotropic Agent 2 is an Organophilic Phyllosilicate based thixotropic agent with a clay based density of 1.5 g/ml.
A magnetorheological fluid was used, which includes magnetic particles in the same content as Sample 1, contains thixotropic agent 2 in the same content as Sample 1, and contains the dispersion medium and additives as the balance.
A magnetorheological fluid was used, which includes magnetic particles in the same content as Sample 1, contains thixotropic agent 3 by 10% more than Sample 1, and contains the dispersion medium and additives as the balance. Thixotropic agent 3 is a clay-based Bentonite based thixotropic agent.
A magnetorheological fluid was used, which includes magnetic particles by 5% less than Sample 1, contains thixotropic agent 3 in the same content as Sample 1, and contains the dispersion medium and additives as the balance.
A magnetorheological fluid was used, which includes magnetic particles in the same content as Sample 1, contains thixotropic agent 3 in the same content as Sample 1, and contains the dispersion medium and additives as the balance.
A magnetorheological fluid was used, which includes magnetic particles by 5% more than Sample 1, contains thixotropic agent 3 in the same content as Sample 1, and contains the dispersion medium and additives as the balance.
When the magnetic field of each sample is not applied, the values of G′ and G″ in the initial linear region when the magnetic field is applied, the crosspoint, and the flow point (τf) values are respectively shown in the table below.
Referring to
It can be seen that when comparing Samples 2 and 3, the crosspoint and the viscosity of Sample 3 are high, and when comparing Samples 4 and 6, the crosspoint and the viscosity of Sample 4 are high. That is, it can be seen that even in the same thixotropic agent, as the content of the thixotropic agent increases, the three-dimensional network in the magnetorheological fluid is strengthened and the crosspoint and the viscosity increase.
In contrast to Samples 5 to 7, it can be seen that the viscosity increases but the crosspoint decreases from Sample 5 to Sample 7. That is, it can be seen that as the content of the magnetic particles increases, the viscosity of the magnetorheological fluid increases due to the increased amount of the magnetic particles, but the increased magnetic particles hinder forming of the 3-dimensional network by the thixotropic agent, and as a result, the degree to which G″ rises is larger than the degree to which G′ rises, thereby eventually reducing the crosspoint.
Referring to
In Samples 4 to 7, it can be seen that when the magnetic field is not applied, G′ appears to be greater than 250 Pa preferably 250 Pa or more and 450 Pa or less, and when the magnetic field is applied, G′ appears to be greater than 1,000 kPa, preferably 1,000 kPa or more and 1,200 kPa or less.
In Samples 4 to 7, it can be seen that when the magnetic field is not applied, the value of the flow point Ó is greater than 10 Pa, preferably 10 Pa or more and 12 Pa or less.
As shown in
On the other hand, as shown in
The bump area may correspond to a force that breaks the chain structure of magnetic particles formed when the magnetic field is applied to the magnetorheological fluid.
Referring to
Referring to
According to an embodiment, the loss modulus (G″) plot may be quantified by the following equation.
However, the method of simulating the plot is not particularly limited to the Gaussian method, and a known method may be used.
Next, referring to
Referring to
Referring to
The relationship between the magnetic field intensity and the bump area may be expressed as a linear function (dotted line in
As described above, the present invention proposes a physical property standard that can improve the dispersion stability and sedimentation stability of the magnetorheological fluid, and there is an effect of improving the degree of sedimentation of magnetic particles in the dispersion medium of the magnetorheological fluid. In addition, in the magnetorheological fluid according to the present invention, there is an effect that the magnetorheological fluid has a high yield stress while improving the dispersion stability and the sedimentation stability.
Although the present invention has been shown and described with reference to a preferred embodiment as described above, the present invention is not limited to the above embodiment, and within the scope without departing from the spirit of the present invention, various modifications and changes can be made by those skilled in the art. It should be considered that such modification example and change example belong to the scopes of the present invention and the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2020-0143043 | Oct 2020 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2020/015488 | 11/6/2020 | WO |
