Short Paper Proc. of Int. Conf. on Recent Trends in Mechanical, Instrumentation and Thermal Engineering 2011
Cost Effective Magnetorheological Fluid Future of Automatic Vibration Damper Mr. Arupratan Ghosh School of Mechanical Engineering SRM University, Kattankulathur Tamilnadu-603203, India e-mail: arupbankura@gmail.com Contact: +918144806562 Abstract—Magneto-rheological Fluids are type of smart material comes under the category of smart fluids. The properties of magneto-rheological fluid depend on its compositions and their proportion. In normal condition MRfluid behaves like a liquid but when a magnetic field is applied through it, MR-fluid behaves like a solid (semi-solid in practical cases). Normally oil of higher density like vegetable oil can be used as matrix material and very fine magnetic particles like iron particles can be used as suspended particles on the matrix. For the stabilization and longer life of the MRfluid some additives materials are mixed proportionately with the composition. For its unique property, MR-Fluids can be used in industries to protect a machine while it is vibrating above its permissible vibration range. Even it can be used as earthquake damper in earthquake prone areas. The manufacturing cost of M R-fluid increases due to the application of very expensive additives. In this paper the main properties of Magneto-rheological Fluid, the mechanism behind them and its scope as a vibration damper. And also manufacturing process of an additive-less and cost effective MR-fluid is highlighted.
II. MECHANISM BEHIND MR-FLUID MR fluids use magnetiseable particles suspended in a non-magnetiseable carrier liquid. In both cases of ER-Fluid and MR-Fluid the flow mechanism is the same: excitation of the fluid by the appropriate field (electric or magnetic, respectively) causes polarization and subsequent alignment of the particles suspended within the liquid. The resulting chain structure is held in place by the applied field, and hence resists fluid flow. The resulting behavior is analogous to the class of fluids known as Bingham plastics – non-Newtonian fluids capable of developing a yield stress. For MR-Fluids, this yield stress is a function of the applied magnetic field. However, once this yield stress is exceeded, the behavior of the smart fluid deviates from that of a Bingham plastic. This is attributable to a breakdown of the chains of particles under the forces of the fluid flow, and results in a shear-stress / shear-rate characteristic that is highly non-linear. When used in a damping device, the result is a damper whose force / velocity characteristic is non-linear, but can be changed by way of the applied electric or magnetic field. As mentioned earlier this fluid is a suspension of magnetisable micron sized particles over a matrix of non-magnetisable liquid (generally hydrocarbon oil or silicon oil). In normal condition the particles move haphazardly in its matrix and so has no effect on the fluid property of the liquid. But when an external magnetic field is applied, each of the moving magnetisable particles acts as magnets and thus forms magnetic dipoles with each other and arranged in a liner manner with a strong dipole strength and high dipole moment. So the movement of each layer of the fluid is resisted by the dipole moment of the suspended particles. As the particles are strongly bound to each other they will show this characteristic and hence the viscosity of the fluid enhances instantly to a very high value resulting in sudden increment of the yield stress value and thus the liquid turns to solid with much higher viscosity and yield stress instantly within a fraction of a second.
Keywords-component; Smart Materials, Smart Fluid, Magnetorheological Fluid, Vibration damper, Zero Additive MR Fluid.
I. INTRODUCTION MR- Fluid is a fluid whose properties (like viscosity, yield stress) can be changed by applying external magnetic field. Without an effect of external magnetic or electric field, MRfluid behaves like a liquid but when an external magnetic field is applied it becomes solid(or semisolid) in a fraction of a second. These fluids are indeed non-homogeneous suspensions of polarizable micron-sized particles that form chain like structures upon the application of the external field. The particle chains are parallel to the field direction and restrict the fluid flow, requiring a minimum field dependent shear stress (called yield stress) for the flow to be initiated. It is also important to avoid confusion between magnetorheological fluids and colloidal ferrofluids composed of nano-sized particles. Ferrofluids are also attracted by a magnetic field but do not exhibit any rheological change (and in particular, no yield stress) MR-fluids exhibit a broader operating temperature range (“40æ%C to +150æ%C, limited by the properties of the carrier fluid) and are insensitive to impurities. The researches conducted on MR-fluids since the beginning of the 1990s led to some major developments and commercial successes, especially in the car industry. © 2011 AMAE DOI: 02.MIT.2011.01.1
Figure:1 schematic visualization
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Short Paper Proc. of Int. Conf. on Recent Trends in Mechanical, Instrumentation and Thermal Engineering 2011 C. Additives Many types of additives, often proprietary, are used in MR-fluid formulations. They have many purposes such as: inhibit particle settling and agglomeration, reduce friction, and prevent particle oxidation and wear. Tween- 80, Polysorbate-40 are few commercially available additives. IV. MR-FLUID VIBRATION DAMPER Figure. 2 On state and off state flow properties
Engineers in Japan were the first to install MRF damping technology to help stabilize buildings against earthquakes and the diagonal cables of China’s Dong Ting Lake bridge are kept steady in high winds by the technology. Although MRF damping systems are costly to implement, Scientists believes the investment would prove worthwhile for critical structures such as hospitals and major data centers.
With more number of suspended particles the dipole moment will increase and so the yield stress under effect of magnetic field will increase. But there is a drawback of this. As the suspended particles are heavier than the fluid after a certain time period they may sediment and so the magnetorheological effect will vanish. So it is clear that all MR-Fluid has a certain and short life period. To enhance the life period different additives are used. The additives prevent the particle from sedimentation up to a certain extent. The density of the oil used as matrix should be higher for the same reason and also the finer size of the particles increases the life of MR-Fluid. Additives may be proposed which makes a coat surrounding the suspended particles so that the buoyancy increases. This also can increase the life span of the MR-Fluid. III. MR-FLUID COMPOSITIONS MR-fluid formulation consists of three main components: magnetizable particles (with a volume fraction typically between 20% and 45%), a carrier fluid and an association of various additives. The proper selection and combination of these components is of prime importance since it will define all the macroscopic characteristics of the fluid such as its offstate viscosity, its maximum yield stress, its resistance to settling, its operating temperature range.
Figure. 3 MRF operated vibration damper
MR-Fluid can be used in machines to protect them when they vibrate violently exceeding their permissible vibration range. For example, as shown in the diagram, a piston is moving in a cavity the cavity is full of MR-Fluid. There are flow control gaps in the piston through which MR-fluid flows with the movement of piston. Electromagnets are placed adjacent to the flow control gaps with which a sensor is connected with remote computer, is attached. When the movement or frequency of the piston exceeds the permissible range the flow velocity of MR-Fluids through the flow control gap exceeds and as programmed in the computer the circuits of the electromagnets are connected and hence they produce steady magnetic field through MR-fluid. As a result the viscosity of the MR-fluid raises very highly and it acts like a semi-solid and opposes the motion of the piston. But when the frequency of the piston comes to its permissible range the computer withdraws the electric flow in the circuit connecting electromagnets and hence the magnetic field disappears. so the MR-fluid again starts behaving like a liquid and the piston can move freely. The entire process need less than a second or two to complete.
A. Suspended particles The most widely used material for MR-fluid particles is carbonyl iron, thanks to its high saturation magnetization. Carbonyl iron powder is obtained by the thermal decomposition of iron pentacarbonyl (Fe(CO)5), leading to highly spherical particles in the 1-10Âľm range. The spherical shape is of particular interest since it makes the particles less abrasive, more robust and durable. These particles are further characterized by an onion skin structure and an iron content up to 97.8%. highly irregular particles lead to higher fluid viscosity compared to spherical particles at the same volume fraction. B. Carrier Fluid Carrier fluids are selected based on their intrinsic viscosity, their temperature stability and their compatibility with other materials of the device. The most common carrier fluids are hydrocarbon oils, which can either be mineral oils or synthetic oils (or a combination of both), thanks to their good lubrication, durability and the availability of a large range of additives.
Figure. 4 road grip vs current
Š 2011 AMAE DOI: 02.MIT.2011.01.1
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Short Paper Proc. of Int. Conf. on Recent Trends in Mechanical, Instrumentation and Thermal Engineering 2011 The off state viscosity of MR-fluid will raise to an intermediate working viscosity which will be slightly higher than the off state viscosity but much lower than on-state viscosity of MR-fluid. This is a cutting edge technique but can effectively slash down the cost of MR-Fluid by getting rid of the expensive additives.
This shows that the road grip of the car increases with increasing input current. As current is directly proportional to the induced magnetic flux in the electromagnet, it is proved in other way that yield stress resistivity of MR-Fluid increases with increasing magnetic flux. V. ZERO ADDITIVE MR-FLUID The main difficulty in the preparation of MR-Fluid is with its very poor stability. As discussed earlier to increase its stability and life span very expensive additives are used. In deed these additives increases the cost of manufacturing MR-Fluid. As mentioned earlier the other manufacturing needs of MR-fluid are not expensive at all. Just an amount of vegetable oil and proportional quantity of iron particles can easily form MR-Fluid. But only the additives used are making this useful material very expensive in world market as only LORD’s corporation has the right to commercially manufacture the MR-Fluid additives. In this paper the idea of Zero additive mechanical MR-Fluid and an intermediate state viscosity are proposed. Without using any additive, use of a controlled magnetic field is proposed. As the on state yield stress of MR-Fluid is directly proportional to the magnetic flux, introduction of a controlled and low magnetic flux will generate a negligible amount of yield stress but can fix the problem of instability due to sedimentation. As sedimentation occurs due to the downward gravitational force, the constant magnetic flux will oppose the effect of gravity by creating a opposite directional force. This magnetic flux will be controlled by the same sensor and can be increased when a higher yield stress is needed.
Š 2011 AMAE DOI: 02.MIT.2011.01.1
Figure. 5 zero additive Mr fluid
ACKNOWLEDGMENT Mrs. A. Vijaya, (Asst. professor) School of mechanical engineering. SRM University. REFERENCES [1] Smart- material mechnisms as actuation alternatives for aerospace, robotics and automotion by Michael Kapps. [2] MR-Fluid brake design and its application to a portable mascular rehabilitation device by more thomas avraam, universite libre de Bruxelles.
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