FAQ

What is magnetorheological fluid?

Magnetorheological fluid is an intelligent fluid material that can control rheological properties (such as kinematic viscosity, shear stress between liquids, yield strength of solid-liquid transition, plastic modulus of liquids and so on) by adjust the magnitude of the magnetic field. It is a solid-liquid two-phase suspension composed of base fluid and magnetizable particles. Under the action of an external magnetic field, it can instantly change from a fluid with good fluidity to a viscoelastic solid, the yield stress can reach 50-100kPa, and the apparent viscosity can be increased by 100,000-1,000,000 times. When the magnetic field is removed, the magnetorheological fluid can be transformed from its original viscoelastic solid to a fluid state again. Therefore, the viscosity (fluidity) of the fluid can be regulated by the magnitude of the surrounding magnetic field. Magnetorheological fluids have the advantages of low conversion energy consumption, easy control, and fast response time (millisecond response), which have broad application prospects in many fields such as aviation, precision polishing, automotive and civil engineering.

What is the application of magnetorheological fluid?

As a new type of controllable fluid, magnetorheological fluid has very outstanding performance, mainly for fast solid-liquid performance conversion, simple magnetic field layout, low energy consumption and so on. Thus, it has a broad application prospect, such as automotive, military, construction, bridge, medical, precision polishing and intelligent robotics. The mature products include automotive electromagnetic dampers, building seismic dampers, bridge anti-swing dampers, prosthetic limbs, magnetorheological polishing equipment and so on, and the application of magnetorheological fluid is still expanding.

What are the components of magneto-rheological fluids?

Magnetorheological fluids are mainly composed of magnetic particles, carrier fluid, and various additives. Soft magnetic materials are often chosen as magnetic particle, because they have high magnetic saturation strength and low magnetic coercivity, magnetic particles provide the mechanical properties of magnetorheological fluid under magnetic field, and generate high magnetic moment between particles under the action of magnetic field, which makes magnetorheological fluid produce high shear yield strength, after the magnetic field disappears magnetic particles basically do not exist remanent magnetism, so it can be quickly dispersed in the carrier fluid; carrier fluid provides fluid properties for magnetorheological fluid, and as the medium for suspension of magnetic particles. In addition to the magnetic particles and carrier fluid, various additives are needed to improve the stability, redispersibility, initial viscosity and lifetime of the magnetorheological fluid, such as dispersants, thixotropic agents, anti-settling agents and antioxidants.

What are the base fluids of magneto-rheological fluids? What are the common magnetic powders?

The carrier fluid mainly provides the fluid properties of magnetorheological fluid and also as the medium for the suspension of soft magnetic particles, generally there are synthetic oil, mineral oil, silicon oil, water, ethylene glycol and so on. Soft magnetic materials are often chosen as magnetic particle, which mainly provide the mechanical properties of magnetorheological fluid under magnetic field, generally there are carbonyl iron powder, cobalt powder, iron-cobalt alloy and iron-nickel alloy, triiron tetroxide, compound soft magnetic particles, etc.

How to prepare magnetorheological fluid?

The key difficulty in the preparation of magnetorheological fluids is the high content of magnetic particles, how to disperse the high content of magnetic particles in the carrier fluid is a difficult problem to be solved. When preparing magnetorheological fluid, the magnetic particles can be added to the carrier fluid one by one according to the principle of multiple times and small amounts with the help of high-speed stirring or ball mill stirring equipment, while adding exclusive surface active additives to the carrier fluid to improve the stability of the magnetic particles in the carrier fluid by using the physical and chemical interactions between the surfactant and the magnetic particles,  finally obtaining a stable magnetorheological fluid.

What is the working environment and temperature range of magnetorheological fluids?

The working temperature range of magnetorheological fluids is mainly determined by the actual temperature range of the carrier fluid, the working temperature of the oil-based magnetorheological fluids prepared by Bohai company is -40~140 in general. The working environment and temperature range of magnetorheological instruments in actual use are mainly determined by the design of the instrument, whether it is a vacuum environment, or 10,000 meters deep, whether it is low frequency vibration damping, or high frequency vibration, as long as the design of the structure of instrument is reasonable, theoretically the magnetorheological fluid can be used.

What is the magnetorheological effect?

The magnetorheological effect of magnetorheological fluids refers to the presence of soft magnetic particles with high magnetic saturation strength and high permeability in the liquid, when stimulated by the surrounding magnetic field, the rheological properties of magnetorheological fluids change abruptly and rapidly transform into viscoelastic solids and lose fluidity, while the process is reversible, when the surrounding magnetic field is removed, the magnetorheological fluid can quickly regain its original fluidity and exhibit fluid properties.

What happens to magnetorheological fluids under magnetic fields?

Under the stimulation of magnetic field, the magnetorheological fluid exhibits magnetorheological properties, the liquid changes from a fluid state to a viscoelastic solid-state, and when the surrounding magnetic field is removed, the magnetorheological fluid can return to its previous fluid state, This conversion process includes significant changes in material fluidity (including elasticity, plasticity, viscosity), magnetic properties, electrical conductivity, heat transfer, mechanical properties, physicochemical properties and so on. It should be clear that the conversion process between liquid and solid-state is a completely reversible and controllable process.

How does magneto-rheological fluid work?

Under the stimulation of magnetic field, the magnetic particles in magnetorheological fluid can quickly form chain structure along the direction of magnetic force lines of magnetic field, and the magnetic force lines can form closure along the chain structure of magnetic powder particles, at this time, the chain structure is extremely difficult to be destroyed and can provide extremely strong yield stress for magnetorheological fluid, and the fluid properties of magnetorheological fluid are changed after the stimulation of magnetic field. When the magnetic field strength increases, the magnetic flux around the magnetic particles further increases, more chain structures of magnetic powder are formed along the added magnetic force lines, and the fluid properties of the magnetorheological fluid further mutate and gradually transform to the solid state, the yield strength of the magnetorheological fluid further increases. When the magnetic field is removed, the chain structure of magnetic particles repel each other due to the interaction of surfactants, the magnetic particles quickly separate and evenly disperse into the carrier fluid, the magnetorheological fluid quickly returns to fluid performance, the above process always remains reversible and controllable state. We can control the solid-liquid state of magnetorheological fluid by controlling the strength and state of magnetic field (with or without magnetic field). The state transition process of magnetorheological fluid has the advantages of low energy consumption, easy control and fast response time (millisecond response), which is one of the best choices for new intelligent controllable materials.

What are the different types of magnetorheological fluids? How to distinguish and how to choose?

When choosing magnetorheological fluids, you can choose magnetorheological fluids with different carrier fluids according to your actual needs. There are two series of mature products: oil-based magnetorheological fluids and water-based magnetorheological fluids, oil-based magnetorheological fluids are commonly used in the field of vibration damping, and some oil-based magnetorheological fluids are used in the field of polishing, water-based magnetorheological fluids are commonly used in the field of coarse and precision polishing. The physical properties (such as service temperature, flash point and so on) of magnetorheological fluids prepared by different carrier fluids can vary greatly. Each series of magnetorheological fluids is further divided by the weight percent of magnetic particles, where a higher content of magnetic powder particles means a higher yield stress under magnetic field, but as the magnetic powder content increases, the zero-field viscosity of the magnetorheological fluid will inevitably become higher. When the fluid has a high zero-field viscosity in the damper, it will result in a higher zero-field damping force output by the apparatus. Therefore, different models of magnetorheological fluids correspond to different mechanical ranges, and you can choose different types of magnetorheological fluids according to your application requirements. At present, we mainly provide three types of oil-based magnetorheological fluids, such as A172, A181 and A186, which correspond to 72%, 81% and 86% of the weight ratio of magnetic powder respectively. Water-based magnetorheological fluids are mainly available in model B285.

What is magnetic fluid? What are the differences between it and magneto-rheological fluid?

Magnetorheological fluids are composed of micron-sized magnetic particles and carrier fluid, in which the content of magnetic particles is extremely high, and the magnetic particles are mostly metal-based soft magnetic materials, which have high saturation magnetization strength. From the microscopic analysis, the magnetic particles can form a chain structure quickly under the action of magnetic field, and the magnetic force linecan form a closure through the chain structure of magnetic particles. From the macroscopic analysis, the magnetic particles in magnetorheological fluid form a stable chain structure under the action of magnetic field, and this structure has good stability, which can provide high yield stress for magnetorheological fluid. Under the magnetic field of 0.8mT, a minimum yield stress of 20kPa or more should be provided.

The magnetic fluid is composed of nanoscale magnetic particles and carrier fluid, in which the content of magnetic particles is low, and the magnetic particles are mostly metal oxide type soft magnetic materials with low saturation magnetization strength. Affected by the nanoscale effect, the nanoparticles in the magnetic field environment can exhibit a near superparamagnetic state. The major difference between magnetic fluids and magnetorheological fluids is that the magnetic particles in magnetic fluids are not chained under the magnetic field, and the magnetic force line cannot be closed along the direction of magnetic particles, which cannot provide large yield stress. In the magnetic field environment, magnetic fluid is mostly used in fields such as rapid shape change and low energy consumption, and there is no requirement for the magnitude of shear stress. Common application scenarios are sealing, audio transmission, toy demonstration and so on. Since the magnetic particles used in magnetic fluids are nanoparticles, while the content of magnetic powder in carrier fluid is relatively low, so it has good anti-settling properties, and the magnetic particles can be stably suspended in the carrier fluid with the help of surfactants, while the magnetic particles used in magnetorheological fluids are mostly micron-sized powder, which has a high density, the density difference between magnetic powder and carrier fluid is large, so the settling phenomenon will also inevitably occur.

What is a non-Newtonian fluid? What is rheology (rheological fluid)? Is a magnetorheological fluid a non-Newtonian fluid?

Non-Newtonian fluid is a fluid that does not satisfy the experimental law of Newtonian viscosity, the shear stress and shear rate are not linearly related to each other. The rheological property of a fluid is the deformation and flow properties under the action of external forces, mainly referring to the relationship between stress, deformation, deformation rate and viscosity under the action of process. The viscosity of the fluid is different, the quantitative relationship between the shear stress and shear rate (shear deformation rate) is also different. The magnetorheological fluid basically shows Newtonian fluid properties under zero magnetic field, the shear stress is linearly related to the shear rate, under the effect of constant magnetic field, the magnetic powder particles in the magnetorheological fluid form a chain structure,  showing non-Newtonian fluid properties, the chain structure can be destroyed under the high speed shear rate, and the fluid exhibits Newtonian fluid properties again, under the effect of controlled variation of magnetic field, the magnetorheological fluid shows non-Newtonian fluid properties. Influenced by the surrounding magnetic field, the shear stress of magnetic particles is programmable and controllable with the change of magnetic field, and not linearly related to the shear rate.

What is magneto-rheological fluid and current-rheological fluid? What is the difference between them?

Magnetorheological fluid and galvanic fluid are both new intelligent controllable fluid materials. The rheological properties of magnetorheological fluid materials are controlled by the change of magnetic field, and the rheological properties of galvanic fluid materials are controlled by the change of electric field (voltage change). Both of them can achieve reversible and controllable fluid performance and short response time, the difference between them mainly lies in the composition and energy consumption. The composition of magnetorheological fluid usually consists of magnetic particles with high saturation magnetization strength and synthetic hydrocarbon, while the composition of galvanic fluid usually consists of solid particles with high dielectric constant and insulating oil with low dielectric constant. Meanwhile, magnetorheological fluids only need to consume low energy (current) to realize the transformation from liquid to viscoelastic solid, while galvanic fluids need to reach the critical value of electric field strength to realize the transformation from liquid to viscoelastic solid, which requires sufficient voltage to realize the process, and too high working voltage will also have certain hidden dangers and need to pay attention to insulation protection. In addition, the yield stress of traditional current-variable fluids is generally lower than 15 kPa due to the limitation of voltage change, while the yield stress of magnetorheological fluids can reach at least 20~30 kPa under the action of strong magnetic field, so the application environment of magnetorheological fluids will be more extensive.

What is magnetorheological material?

Magnetorheological materials are the materials that can produce magnetorheological effects under the action of a magnetic field. The fluidity  (including elasticity, plasticity, viscosity), magnetic properties, electrical conductivity, heat transfer, mechanical properties, physicochemical properties, can be changed and controlled by controlling the change of magnetic field.  Magnetorheological materials mainly include magnetorheological fluids, magnetorheological elastomers, magnetorheological greases, magnetorheological foams and so on.

What can magnetorheological fluids do in the field of vibration damping?

Magnetorheological dampers filled by magnetorheological fluid can play a good role in vibration damping in construction, automotive engineering and marine engineering. By applying a corresponding current to the coil of the magnetorheological dampers, a magnetic field is generated to stiffen the magnetorheological fluid, thus changing the damping force and achieving the purpose of vibration damping

What is the role of magnetorheological fluid in the military industry?

Magnetorheological fluid plays an important role in ultra-precision polishing, damping of helicopter propellers, human exoskeleton joints, damping of artillery systems, cushioning of aerospace landing gear, damping of precision equipment in ships, damping and silencing of submarine engines and so on.

What is the role of magnetorheological fluids in the field of robotics?

Magnetorheological fluid can be applied to robot flexible gripper, magnetorheological flexible gripper makes robot can grasp the irregular shape of objects, magnetorheological rotary damper can be applied to robot flexible joint, compared with the traditional robot reducer joint, the structure of magnetorheological rotary damper is simpler, also easier to maintain subsequently, and other advantages such as low energy consumption and step-less variable speed.

What are the role of magnetorheological fluids in the field of precision processing?

At present, magnetorheological polishing fluids have important applications in polishing fields such as ultra-high precision polishing, non-ball grinding shaped polishing and so on. The main products include flat magnetorheological polishing equipment, wheel type magnetorheological polishing equipment and magnetorheological jet polishing equipment. In addition, magnetorheological dampers also play an important role in damping and vibration damping in precision processing equipment, the main products are long-bar damping boring tools, damping drill bits, vibration isolation platform for precision equipment, etc.

What is the role of magnetorheological fluids in the automotive field?

Magnetorheological fluids have a wide range of applications in the automotive field, such as: electromagnetic suspension systems, engine damping, electromagnetic clutches and so on.

How can magnetorheological fluid dampers make the car run smoothly?

Magnetorheological dampers are filled with sufficient magnetorheological fluid, which can generate magnetism through the control coil, so that the magnetic particles in the magnetorheological fluid are immediately arranged perpendicular to the direction of pressure, thus changing the damping coefficient to adjust the damping effect, finally making the vehicle drive steadily and smoothly.

What is magnetorheological suspension system?

The magnetorheological suspension system includes a sensor, controller, spring, guide mechanism, magnetorheological shock absorber, and so on. The magnetorheological shock absorber is filled with magnetorheological fluid, which can adjust the damping effect by controlling the coil to generate magnetism, so that the magnetic particles in the magnetorheological fluid are immediately arranged perpendicular to the pressure direction, thus changing the damping coefficient.

How does the magnetorheological suspension system work?

The magnetorheological suspension system includes: sensors, controllers, springs, guide mechanisms, magnetorheological shock absorbers and so on. The vehicle senses the current vehicle attitude and road surface information through the sensor, and feeds it back to the controller. The controller adjusts the damping force of each magnetorheological shock absorber through a comprehensive judgment and pre-judgment algorithm to achieve the purpose of stable and smooth driving of the vehicle.

How does the magnetorheological damper work?

The magnetorheological damper mainly includes: outer cylinder, piston, coil, piston rod, end cap and other major components. By supplying current to the coil, a magnetic field is generated around it and the magnetorheological fluid in the damper forms a magnetic chain, and the damper then generates a damping force.Changing the magnitude of the current can cause the magnetic field strength to change and eventually change its damping force.

What are the uses of magnetorheological dampers?

Due to the advantages of simple structure, small size, rapid response (millisecond response) and low energy consumption, magnetorheological dampers are widely used in many scenarios of intelligent active damping, such as automotive electromagnetic suspension, cushioning and anti-vibration of precision instruments, aerospace landing gear and so on.

Who invented magnetorheological fluid?

Rabinow (an American) discovered magnetorheological fluid in 1948.

What is the principle of water-based magneto-rheological polishing?

The focus of the Magnetorheological fluid (MRF) polishing system is the MRF delivery system, which creates a stable, continuous, circular flow of magnetorheological fluid. During operation, a dose of magnetorheological fluid is delivered to the surface of the polishing wheel, where the magnetic particles are closely packed in a magnetic field, squeezing out the water and abrasives within the fluid and forcing them to form a film on the upper layer of the polishing wheel. In the gap between work pieces, a shear fluid layer is formed. Under the pressure gradient and high speed shear, grinding removal based on shear stress is created.

The workpiece is placed above the moving spherical polishing wheel and forms a fixed gap with it. An electromagnet or permanent magnet is located below the surface of the wheel, and a magnetic field is present on the surface of the wheel and in the gap between it and the workpiece. When the magnetorheological fluid is transferred to the polishing wheel, it is captured by the magnetic field and fixed on the surface of the polishing wheel. Subsurface polishing occurs when the workpiece is inserted into the magnetorheological fluid flow layer. A complex, precision polishing process is completed when the workpiece passes through the polishing zone in a spiral (spinning on itself) or a path developed by a computer program. The MRF polishing can process many types of workpieces such as spherical, aspheric, special surfaces and so on.

Computer numerical control, precision machine workstations and sophisticated programming algorithms ensure the automation as well as the reliability of the MRF polishing system.

What is the application direction of magnetorheological rotary damper?

Magnetorheological rotary dampers can be applied to robot joints, and line body speed control, the future development direction is: electromagnetic brake, electromagnetic clutch and so on.

Why the magnetorheological fluid settle so fast?

Magnetorheological fluid is widely used as a new intelligent controllable material, its advantages mainly  include simple control, low energy consumption, large adjustment ratio and fast response time and so on. One of the biggest problems is the fast settling speed of magnetorheological fluid. The main components of magnetorheological fluid consist of base fluid and magnetic particles, where the base fluid mainly includes synthetic oil, mineral oil, water and glycol and other liquids, whose density is generally low, while the magnetic powder particles are generally carbonyl iron powder, cobalt powder, iron-cobalt alloy, iron-nickel alloy, triiron tetroxide and other soft magnetic particles, whose density is generally high. The main components of magnetorheological fluid consist of base fluid and magnetic particles, where the base fluid mainly includes synthetic oil, mineral oil, water and glycol and other liquids, whose density is generally low, while the magnetic powder particles are generally carbonyl iron powder, cobalt powder, iron-cobalt alloy, iron-nickel alloy, triiron tetroxide and other soft magnetic particles, whose density is generally high. The density deviation of the two components is relatively large, and it is difficult to form a stable mixture. Under the molecular Brownian motion, the two components are very easy to separate and cause sedimentation.

What is the biggest problem with magnetorheological fluid applications?

Magnetorheological fluid is widely used as a new intelligent controllable material, its advantages mainly  include simple control, low energy consumption, large adjustment ratio and fast response time and so on. One of the biggest problems is the fast settling speed of magnetorheological fluid. The main components of magnetorheological fluid consist of base fluid and magnetic particles, where the base fluid mainly includes synthetic oil, mineral oil, water and glycol and other liquids, whose density is generally low, while the magnetic powder particles are generally carbonyl iron powder, cobalt powder, iron-cobalt alloy, iron-nickel alloy, triiron tetroxide and other soft magnetic particles, whose density is generally high. The main components of magnetorheological fluid consist of base fluid and magnetic particles, where the base fluid mainly includes synthetic oil, mineral oil, water and glycol and other liquids, whose density is generally low, while the magnetic powder particles are generally carbonyl iron powder, cobalt powder, iron-cobalt alloy, iron-nickel alloy, triiron tetroxide and other soft magnetic particles, whose density is generally high. The density deviation of the two components is relatively large, and it is difficult to form a stable mixture. Under the molecular Brownian motion, the two components are very easy to separate and cause sedimentation. After the magnetic particles settle, it is easy to plate and difficult to disperse again, resulting in the gradual separation of the base liquid and the magnetic powder particles, the magnetorheological effect gradually disappears.

What is the difference between response time of magnetorheological fluid and response time of magnetorheological damper?

The response time of magnetorheological fluid refers to the time when the magnetic powder particles are aligned along the magnetic line of force under the action of the magnetic field, this time is related to the magnetic line of force distribution time and the movement time of the magnetic powder particles in the base fluid, the field speed corresponding to the magnetic field distribution is consistent with the speed of light, the magnetic powder particles are also instantly aligned linearly in the base fluid, the response speed is extremely fast, the overall magnetorheological fluid response time is millisecond response. The magnetorheological damper’s response time is when the power supply accepts the instruction from the controller and starts to respond, the current reaches the coil from small to large to stable, and the magnetic field produces a magnetorheological fluid response. When the magnetorheological damper damping force reaches 66% of the theoretical value, it can be considered that the magnetorheological damper responds. This time includes the control, power supply, coil, other response time, and magnetorheological material response time. The general response time of small devices is 100 ms or less, and the response time of very large devices may be greater than 100 ms.

What are the advantages of magnetorheological dampers?

Magnetorheological dampers have the advantages of fast response, simple structure, small size, low energy consumption and continuous change of damping force compared to traditional dampers.

What are the disadvantages of magnetorheological dampers?

Compared to conventional dampers, it needs to be equipped with corresponding sensors and controllers. Magnetorheological dampers are not effective in dealing with ultra-high frequency vibration.

what is the difference between magnetorheological dampers and traditional dampers in terms of sealing?

There is no special requirement on sealing between the traditional damper and magnetorheological damper, because the magnetic particles are mostly micron level but not to nano level size, the skeleton oil seal of the traditional damper can still play a sealing role in magnetorheological damper. After 3 million times of repeated experiments on magnetorheological dampers, the magnetorheological liquid will not leak, and the skeleton oil seal of traditional dampers can perform the sealing requirements of magnetorheological dampers. The magnetic particles will be worn and stripped to a certain extent after 3 million times, and some nanoparticles will appear. At this time, a small amount of nano magnetic powder may be brought out with the movement of the damper piston, and a certain leakage will occur, but the use of a magnetorheological damper will not be affected

What is the difference between a magnetorheological suspension and an air suspension? What are the advantages of each of these two dampers?

Magnetorheological suspension uses magnetorheological dampers to control vibration, air suspension uses air dampers to control vibration, air suspension can actively lift the height of the suspension system, magnetorheological suspension cannot.  The advantages of magnetorheological suspension are faster response, longer life, lower energy consumption, simpler structure and smaller size.

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