Showing papers on "Magnetorheological fluid published in 1993"

Magnetorheological fluid devices

Abstract: Magnetorheological (MR) fluid dampers (16) are optimized. Dimensional relationships involved in the flow of magnetic flux are related to an operational parametric ratio of magnetic flux density in the fluid to the flux density in the steel. A magnetic valve (30) is utilized to change the flow parameters of the MR fluid and, hence, the operational characteristics of the damper (16). Several embodiments depicting improved piston designs, including spool as well as toroidal configurations, are disclosed. In addition, both single (16) and twin-tube (16) housing designs are presented, along with several sealless designs. Baffle plates (50) and toroidal magnetic segments (40) interspersed with flow slots (56) are utilized to increase contact between the fluid and the magnetic coil (40).

Magnetorheological materials based on alloy particles.

Abstract: A magnetorheological material containing a carrier fluid and an iron alloy particle component. The particle component can be either an iron-cobalt alloy or an iron-nickel alloy. The iron-cobalt alloy has an iron:cobalt ratio ranging from about 30:70 to 95:5 while the iron-nickel alloy has an iron:nickel ratio ranging from about 90:10 to 99:1. The iron alloy particle components are capable of imparting high yield stress capability to magnetorheological materials.

Thixotropic magnetorheological materials

Abstract: A magnetorheological material containing a carrier fluid, a particle component and a thixotropic additive to provide stability against particle settling. The thixotropic additive can be a hydrogen-bonding thixotropic agent, a polymer-modified metal oxide, or a mixture thereof. The utilization of a thixotropic additive creates a thixotropic network which is unusually effective at minimizing particle settling in a magnetorheological material.

Elements and devices based on magnetorheological effect

Abstract: The magnetorheological suspension (MRS), due to its controllability, can be used as the basis for new devices and technologies. The most important element of any MR device is a magnetorheological transducer (MRT), a controllable hydraulic resistance. Its mathematical model is obtained using quasi-stationary approximation and taking into account the transient processes in the magnetic field inductor. The designs of damping and anti-shock devices using the MR element base are ideologically most simple. A description of such a device is obtained by supplementing the system of equations that describe MRT dynamics with the relations, including hydromechanical pro cesses, in a hydraulic cylinder. MRT can be used to design flexible bridge-like distributors to control hydraulic actuators. The experimental study has shown the possibility of using MRS as a working medium in seals.

Magnetorheological materials utilizing surface-modified particles

Abstract: A magnetorheological material containing a carrier fluid and a magnetically active particle. The particle has been modified so that the surface of the particle is substantially free of contamination products. The contamination products are removed from the surface of the particle by abrader processing, chemical treatment or a combination thereof. Magnetorheological materials prepared using the particles from which contamination products have been removed exhibit significantly enhanced magnetorheological effects.

Magnetorheological valve and devices incorporating magnetorheological elements

Abstract: A valve used to control the flow of fluid of a mangetorheological fluid, in which the mechanical properties of the magnetorheological fluid are varied by applying a magnet (1, 2, 3), is described The valve can comprise a magnetoconducting body (1) with a magnetic core that houses an induction coil winding (2), and a hydraulic channel located outside of the core (3) and the inside of the body connected to a fluid inlet port (6) and an outlet port (7), in which magnetorheological fluid flows from the inlet port (6) through the hydraulic line (5) to the outlet port (7) Devices employing magnetorheological valves are also described

Magnetorheological fluids and methods of making thereof.

Abstract: A magnetorheological fluid composition comprising magnetosolid particles, magnetosoft particles, a stabilizer, and a carrying fluid comprising an aromatic alcohol, a vinyl ether, and an organic solvent or diluent carrier such as kerosene, in proportions sufficient to provide substantially no agglomeration or sedimentation of magnetic particles over temperatures of from about -50 to 120 °C. The composition can be made by preparing a carrying fluid comprising a vinyl ether, an aromatic alcohol and kerosene; preparing a first carrying fluid composition comprising magnetosoft particles, a stabilizer and a first sample of the carrying fluid; preparing a second carrying fluid composition comprising magnetosolid particles and a second sample of the carrying fluid; and admixing the first carrying fluid composition and the second carrying fluid composition.

Low viscosity magnetorheological materials

Abstract: A magnetorheological material containing a particle component and a carrier fluid having a change in viscosity per degree temperature (Δθ/ΔT ratio) less than or equal to about 9.0 centipoise/°C over the temperature range of 25 °C to -40 °C. The magnetorheological material exhibits a substantial magnetorheological effect with a minimal variation in mechanical properties with respect to changes in temperature. The magnetorheological material is advantageous in that it provides for the design of devices that are smaller, more efficient and consume less power.

Magnetic dimer motion effects in a rotating magnetic field (A qualitative model of magnetoviscosity and permittivity in magnetorheological suspensions)

Abstract: The motion of a pair of uniform interacting spherical mesoscopic particles situated in a viscous fluid under the influence of a rotating magnetic field was studied. The coupling interactions between the particles were chosen as a superposition of steric and dipolar pair potentials (for the dipoles parallel to the external field). The model dynamics consisting of particular rotation and vibration modes is the result of the interplay of viscous and interaction forces. The transition from the synchronous to the asynchronous regime of dimer rotation has been found. The results were discussed from a synergetic point of view. A qualitative picture of behaviour of the effective magnetoviscosity and permittivity for dimerized magnetorheological suspension has been given.

Magnetoriheological fluid device

Abstract: Magnetorheological (MR) fluid dampers are optimized. Dimensional relationships involved in the flow of magnetic flux are related to an operational parametric ratio of magnetic flux density in the fluid to the flux density in the steel. A magnetic valve is utilized to change the flow parameters of the MR fluid and, hence, the operational characteristics of the damper. Several embodiments depicting improved piston designs, including spool as well as toroidal configurations, are disclosed. In addition, both single and twin-tube housing designs are presented, along with several sealless designs. Baffle plates and toroidal magnetic segments interspersed with flow slots are utilized to increase contact between the fluid and the magnetic coil.

Colloidal stability influence on rheology of magnetic fluids

Abstract: Rheology of suspensions [1] is a complex hydrodynamic question. If the very dilute regime is now well understood from a theoretical point of view, the concentrated regime still raises many questions. In his pioneering works Einstein [2] proposed a powerful model, derived from the flow field of pure strain perturbed by the presence of a sphere, which correctly accounts for viscosity of suspensions in file limit of low concentrations of suspended particles, taking in account hydrodynamic interactions, Batchelor [3] then calculated the second order in concentration contribution to viscosity. Many other laws, semiphenomenological [4], are proposed to describe the whole viscosity dependence on concentration. Viscosity of colloids [5] is an even more difficult problem, because thermodynamical interactions between particles such as van der Waals or electrostatic interactions, have to be encountered together with Brownian motion and hydrodynamic interactions. In magnetic colloids [6,7,8], in addition to dipolar-magnetic interactions, an external parameter enriches the system. If a magnetic field is applied to the flowing system, it introduces an anisotropy inside the fluid, which is different of the anisotropy of the shear flow, leading then to specific effects [9]. Rheological properties of magnetic fluids (also called ferrofluids) are fundamental in regards to their technical applications[7]. To use such a fluid in a seal, a damper, a clutch, a car-springing or an accelerometer sensor, a well defined rheological behaviour is oftenly required from the magnetic fluid, at least during the life-time and in the working conditions of the mechanical device. The viscosity of magnetic fluids is discussed as a function of different parameters such as temperature or volume fraction of particles, in absence or in presence of an applied magnetic field,. We are here concerned with colloidal solutions containing magnetic particles of typical mean diameter 10 nm. Rheological behaviour, as most of physical properties of ferrofluids is related to a major problem : the colloidal stability of the magnetic fluid. Lowering the temperature or applying a large magnetic field, a phase separation [10] may be induced in the ferrofluid which may become diphasic. Macroscopic structurations [ 11] then appear inside the fluid leading to large apparent viscosities, usually going with nonNewtonian behaviours [ 12,13,14]. To some extents, rheology of such diphasic solutions may be compared to that of "magnetorheological fluids" which are non-colloidal suspensions of a few pm-sized magnetic grains [15]. First section deals with colloidal stability of ferrofluids. In the second section, viscosity of monophasic ferrofluids is described as a function of various experimental parameters. The third section shows how these rhcological properties are modified with ferrofluids undergoing a phase separation.