Magnetorheological fluid with excellent high and low temperature fluidity and sedimentation stability and preparation method thereof

Abstract

The invention discloses a magnetorheological fluid with excellent high and low temperature fluidity and sedimentation stability and a preparation method thereof. The magnetorheological fluid comprises the following components in percentage by mass: 70-90% of magnetic particles, 7-25.2% of an alkane carrier liquid, 0.2-0.8% of a lubricant, 0.3-1% of a surfactant, 0.5-1.5% of a dispersant and 0.5-1.5% of a thickener. The surface active agent is a lipophilic surface active agent and is HLBlt (Hydrophile Lipophile Blume); 6; the dispersing agent is one or more of fatty acid modified polyester, modified polyurethane, modified acrylate, block polyether and polymethacrylate; the thickening agent is one or more of organic bentonite, magnesium aluminum silicate and silicon dioxide. The magnetorheological fluid provided by the invention has good fluidity at high and low temperatures, and has good sedimentation stability and redispersibility at high temperature; and the resistance is small under zero field, low speed and low shear, the whole suspension cannot be harder, and the comfort level is good.

Description

Technical Field

[0001] This invention relates to the field of smart magnetic materials, specifically to a magnetorheological fluid with excellent high and low temperature fluidity and sedimentation stability, and its preparation method. Background Technology

[0002] With the development of the automotive industry and intelligent control technology, the requirements for vehicle ride comfort, handling stability, and passenger comfort are constantly increasing. Traditional passive hydraulic shock absorbers mainly rely on throttle orifices and valve systems to achieve fixed or limitedly adjustable damping force characteristics. Their damping force has limited adaptive ability to change with vehicle speed, road conditions, and load, making it difficult to balance comfort and handling. Especially under complex conditions (such as sharp turns, emergency braking, and uneven road surfaces), the vehicle's attitude control capability is insufficient.

[0003] To achieve real-time adjustable damping force in vibration dampers, various controllable vibration reduction technologies have emerged in recent years, including electrically controlled valve-type vibration dampers, variable-damping hydraulic vibration dampers, and magnetorheological vibration dampers. Among them, the magnetorheological damper (MR damper) utilizes the rapid and reversible changes in the yield stress and apparent viscosity of magnetorheological fluid under the action of a magnetic field. It can achieve continuous adjustment of damping force in milliseconds simply by adjusting the coil current. It is considered a semi-active control vibration reduction technology with fast response speed, relatively simple structure, and low energy consumption, and has gained attention in high-end passenger cars, off-road vehicles, and rail transportation.

[0004] The core working medium of a magnetorheological damper is magnetorheological fluid (MRF). A typical MRF mainly consists of soft magnetic particles (such as carbonyl iron powder, iron-cobalt alloy powder, etc.), a continuous phase base fluid (such as mineral oil, synthetic hydrocarbon oil, silicone oil, etc.), and additives such as surfactants, dispersants, thickeners, and anti-wear agents.

[0005] Magnetorheological fluids used in automotive shock absorbers still have some shortcomings. For example, the operating temperature requirement for magnetorheological shock absorbers is -40 to 130°C, but existing products on the market are all in a solidified state at -40°C, and it takes about 10 minutes for them to re-flow, which affects their practical use in low-temperature areas. Although the sedimentation stability and redispersibility are good at room temperature, they will quickly delaminate or even clump together and lose their function at high temperatures, affecting their service life. The resistance is relatively large under zero field, low speed and low shear conditions, resulting in a stiffer overall suspension and poorer comfort. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a magnetorheological fluid with excellent high and low temperature fluidity and sedimentation stability, and its preparation method, so as to achieve good fluidity at both high and low temperatures, good sedimentation stability and redispersibility at high temperatures, and low resistance under zero field, low speed and low shear conditions, which will not lead to a stiff overall suspension and better comfort.

[0007] The technical solution of the present invention is as follows: A magnetorheological fluid exhibiting excellent high and low temperature fluidity and sedimentation stability comprises the following components by mass percentage: Magnetic particles 70-90%, alkane-based carrier fluid 7-25.2%, lubricant 0.2-0.8%, surfactant 0.3-1%, dispersant 0.5-1.5%, thickener 0.5-1.5%; The surfactant is a lipophilic surfactant with HLB < 6; The dispersant is one or more of fatty acid modified polyester, phosphoric acid modified acrylate, block polyether, and polymethacrylate. The thickener is one or more of organobentonite, magnesium aluminum silicate, and silicon dioxide.

[0008] Furthermore, the magnetic particles are one or more of carbonyl iron powder, iron oxide particles, and iron alloy particles, with a particle size of 3-20 μm; preferably, they are a mixture of amorphous iron alloy and soft magnetic particles, wherein the amorphous iron alloy has a faster response speed and magnetic induction intensity under low magnetic field, which can ensure that the magnetorheological fluid responds faster and the vehicle body shakes less; the soft magnetic particles have no residual magnetism and low magnetic loss, ensuring use.

[0009] Furthermore, the alkane carrier fluid is one of mineral oil, synthetic oil, and PAO, preferably a low pour point and high viscosity index alkane carrier fluid to ensure low-temperature fluidity and stability in use.

[0010] Furthermore, the lubricant is one or more of the following: triphenyl thiophosphate tripolyphosphate, ashless liquid butyl triphenyl thiophosphate, ashless liquid dithiophosphate ammonium salt derivative aluminum molybdenum, dialkyl dithiophosphate molybdenum, and dialkyl dithiocarbamate molybdenum.

[0011] Furthermore, the lipophilic surfactant is specifically a long-chain fatty acid or polyol ester surfactant, which can fully occupy the active sites on the surface of the magnetic flux particles, preventing the magnetic particles from contacting each other and causing sedimentation and caking.

[0012] Furthermore, the dispersant is specifically a block polyether or polyester with a molecular weight of 3000-8000, preferably a block polyether or polyester with high branching degree and low polarity. The higher molecular weight can ensure that the magnetic particles are effectively separated after binding with the surfactant, thereby improving stability, while the higher branching degree and lower polarity can ensure flowability at low temperatures.

[0013] Furthermore, the organic bentonite is specifically an oleophilic organic bentonite, and the thickener is specifically a mixture of oleophilic organic bentonite and silica in a weight ratio of 9:1. On the one hand, the better oleophilicity can effectively improve the dispersibility of the thickener in the oily carrier liquid and reduce the viscosity of the system; on the other hand, the addition of silica can weaken the structural failure of the oleophilic bentonite under long-term high temperatures, thereby reducing the probability of caking failure of the magnetorheological fluid at high temperatures. A method for preparing any of the magnetorheological fluids described above, exhibiting excellent high and low temperature fluidity and sedimentation stability, comprises the following steps: S1. Mix the thickener with the alkane carrier liquid and use a high-speed mixer to mix for 10-30 minutes to disperse and activate the thickener, thus obtaining premix A; S2. Add the magnetic particles, lubricant, surfactant, and dispersant to premix A, and mix evenly using a dispersing pan at high speed for 10-30 minutes to obtain premix B. S3. Grind and mix the premixed liquid B to obtain a magnetorheological fluid product with excellent high and low temperature fluidity and sedimentation stability.

[0014] Furthermore, the grinding and mixing process specifically involves: pouring the premixed liquid B into a ball mill for grinding and mixing. The specific processing technology of the ball mill is as follows: the diameter of the grinding balls is 1-10mm, preferably 5-10mm, to avoid excessive deformation of the magnetic particles; the mass ratio of grinding balls to materials is 2:1-1.5:1; the rotation speed is 200-500rpm; and the grinding time is 60-300min.

[0015] Furthermore, the grinding and mixing process specifically involves: pouring the premixed liquid B into a sand mill for grinding and mixing. The specific processing technology of the sand mill is as follows: the diameter of the grinding balls is 1-3mm; the grinding ball filling amount is 40-70% of the cavity volume, preferably 50-60%, to avoid excessive deformation of the magnetic particles; the rotation speed is 500-2000rpm, preferably 500-1500rpm; the sand milling time is 5-30min, which needs to be determined according to the processing efficiency of the sand mill.

[0016] Beneficial effects: This invention achieves long-term stable dispersion of magnetic particles under high and low temperature conditions through the synergistic design of thickeners, surfactants and dispersants. This simultaneously improves the low-temperature fluidity, high-temperature anti-settling and anti-caking ability and reliability of magnetorheological fluids. The zero-field low-speed damping value is significantly lower, which can provide a smaller passive damping value and effectively improve the problem of poor comfort of magnetorheological vibration dampers. Attached Figure Description

[0017] Figure 1 This is an appearance diagram of an embodiment; Figure 2 The SEM image is magnified 5000 times for the example. Figure 3 This is a 10,000x magnified SEM image for comparison. Figure 4 This example compares the sedimentation rate at room temperature over 6 months with that of the comparative example. Figure 5 This example compares the force values ​​under different magnetic fields (currents) at low piston speeds with those of the comparative examples. Figure 6 This example compares the force values ​​under different magnetic fields (currents) at high piston speeds with those of the comparative examples. Figure 7 A comparison of the delamination and hardening of the two embodiments and the comparative examples after 168 hours at 120°C. Detailed Implementation

[0018] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example: A magnetorheological fluid with excellent high and low temperature fluidity and sedimentation stability comprises the following components by weight percentage: 72% magnetic particles, 23.7% alkane carrier fluid, 0.3% lubricant, 1% surfactant, 1.5% dispersant, and 1.5% thickener; the magnetic particles are 90% carbonyl iron powder with a D50 of 6.5 μm and 10% water vapor co-atomized Fe–Co-based amorphous powder with a D50 of 10.8 μm; the alkane carrier fluid is PAO4; the lubricant is molybdenum dialkyl dithiophosphate; the surfactant is oleic acid; the dispersant is random block polyether (EO / PO copolymer) with HLB=6 and molecular weight 7000; the thickener is lipophilic organobentonite and hydrophobic nano-silica, wherein the lipophilic organobentonite accounts for 90% by weight. The preparation process of the above magnetorheological fluid is as follows: The thickener was mixed with an alkane carrier liquid and the mixture was stirred for 30 minutes using a high-speed mixer to disperse and activate the thickener, resulting in premixed liquid A. Magnetic particles, lubricant, surfactant, and dispersant are added to premix A in proportion and mixed evenly using a dispersion disc at high speed for 20 minutes to obtain premix B. The sample can be obtained by adding premixed liquid B into the hopper of the sand mill. The sand mill filling volume is 60% of the chamber volume, the grinding ball size is 1.2um, the peristaltic pump speed is 400rpm, the sand mill speed is 1000rpm, and the sand milling time is 15min.

[0020] The comparative example is a commercially available sample from China, and the test results are as follows: The time required for the flow to recover to 5 ml after freezing at 40℃ was determined according to standard ISO 2431 "Paints and varnishes - Determination of flow time using flow cups"; The test data and SEM analysis show that, compared to the comparative example: like Figure 2 In the SEM images of the embodiment, the edges are clearer, there is less adhesion, and the magnetic particles are better dispersed; such as Figure 3 The magnetic particles in the comparative example showed significant adhesion and generally poor dispersibility; for example... Figure 4 In the figure, a is the comparative example and b is the specific example. The specific example shows a significantly better sedimentation rate at room temperature after 6 months, indicating better anti-settling stability; it also exhibits lower rotational viscosity at -5℃ and faster recovery of flow at -40℃, demonstrating better low-temperature fluidity. Figure 7 In the figure, c is the comparative example and d is the example. The example has less stratification after 168 hours at 120℃, the lower layer is fluid and no caking occurs. In the power indicator characteristic test, the zero field low speed damping value is significantly lower, which can provide a smaller passive damping value and effectively improve the problem of poor comfort of the magnetorheological vibration damper.

[0021] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any indirect modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A magnetorheological fluid having excellent high and low temperature fluidity and sedimentation stability, characterized by comprising: The following components are included by mass percentage: magnetic particles 70-90%, alkane carrier liquid 7-25.2%, lubricant 0.2-0.8%, surfactant 0.3-1%, dispersant 0.5-1.5%, thickening agent 0.5-1.5%; The surfactant is an oleophilic surfactant, HLB < 6; The dispersant is one or more of a fatty acid modified polyester, a phosphoric acid modified acrylate, a block polyether, and a polymethacrylate; The thickening agent is one or more of organic bentonite, magnesium aluminum silicate, and silicon dioxide.

2. The magnetorheological fluid having excellent high-low temperature fluidity and sedimentation stability according to claim 1, characterized by, The magnetic particles are one or more of carbonyl iron powder, iron oxide particles, and iron alloy particles, with a particle size of 3-20 um.

3. The magnetorheological fluid having excellent high-low temperature fluidity and sedimentation stability according to claim 1, characterized by, The alkane carrier liquid is one of mineral oil, synthetic oil, and PAO.

4. The magnetorheological fluid having excellent high-low temperature fluidity and sedimentation stability according to claim 1, characterized by, The lubricant is one or more of triphenylphosphine sulfide phosphate, ashless liquid butyl triphenyl sulfide phosphate, ashless liquid dithiophosphoric acid amine salt derivative aluminum molybdenum, molybdenum dialkyldithiophosphate, and molybdenum dialkyldithio carbamate.

5. The magnetorheological fluid having excellent high-low temperature fluidity and sedimentation stability according to claim 1, characterized by, The oleophilic surfactant is specifically a long-chain fatty acid or polyol ester surfactant.

6. The magnetorheological fluid having excellent high-low temperature fluidity and sedimentation stability according to claim 1, characterized by, The dispersant is specifically a block polyether or polyester with a molecular weight of 3000-8000.

7. The magnetorheological fluid having excellent high-low temperature fluidity and sedimentation stability according to claim 1, characterized by, The organic bentonite is specifically an oleophilic organic bentonite, and the thickening agent is specifically a mixture of oleophilic organic bentonite and silicon dioxide in a weight ratio of 9:

1.

8. A method of producing a magnetorheological fluid having excellent high and low temperature fluidity and sedimentation stability according to any one of claims 1 to 7, characterized by, The steps are as follows: S1, mix the thickening agent with the alkane carrier liquid, use a high-speed mixer to mix for 10-30 min to disperse and activate the thickening agent, and obtain premix A; S2, add the magnetic particles, lubricant, surfactant, and dispersant to premix A, use a high-speed stirring disc to mix for 10-30 min to obtain premix B; S3, grind and mix premix B to obtain a magnetorheological fluid product with excellent high and low temperature fluidity and sedimentation stability.

9. The method of claim 8, wherein the magnetorheological fluid having excellent high and low temperature fluidity and sedimentation stability is prepared by adding the dispersant to the magnetic particles and the base fluid, and then adding the thickener. The grinding and mixing is specifically: pouring premix B into a ball mill for grinding and mixing processing; The ball mill processing process is specifically: grinding ball diameter 1-10 mm, grinding ball to material mass ratio 2:1-1.5:1, self-rotation speed 200-500 rpm, grinding time 60-300 min.

10. The method of claim 8, wherein the magnetorheological fluid having excellent high and low temperature fluidity and sedimentation stability is prepared by adding the dispersant to the base fluid, and then adding the magnetic particles to the base fluid having the dispersant added thereto. The grinding and mixing is specifically: pouring premix B into a sand mill for grinding and mixing processing; The sand mill processing process is specifically: grinding ball diameter 1-3 mm, grinding ball filling volume 40-70% of the cavity volume, rotation speed 500-2000 rpm, sand grinding time 5-30 min.

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