Magnetorheological fluid

As a magnetorheological fluid (MRF ) refers to a suspension of magnetically polarizable particles ( carbonyl iron ), which are finely dispersed in a carrier liquid.

The particles of magnetorheological fluids are approximately one to three orders of magnitude greater than that of ferrofluids, so that a MRF - unlike a ferrofluid - solidified when applying a magnetic field. Mechanism: the particles become polarized and form chains along the field lines. Through the alignment of the particles, the suspension with increasing field strength becomes more viscous. Thus, an MRF can be changed drastically, rapidly and reversibly in a magnetic field.

Magnetorheological fluids have been known since the 1940s. Only in recent years, negative characteristics such as abrasion, sedimentation and aging with special additives and polymers surface coating of the particles could be avoided, so that the use of serial products is now possible.

Composition

In magnetorheological fluids spherical particles (prepared by synthesis, > 99% pure iron ) with a diameter of 1 to 10 microns and a high purity is used. The particles themselves are therefore non-toxic and are used because of their high purity, for example, as a dietary supplement in iron pills. When used in magnetorheological fluids, the excellent electromagnetic and mechanical properties are crucial. Carrier liquids petroleum and synthetic oils, ethylene glycol and water are used. As adjuvants additives such as stabilizers and viscosity buried. These prevent, inter alia, sedimentation and agglomeration. The proportion of the iron powder is from 70-90 % by weight and 20-40 % by volume. The liquid has a dark gray color, its density is between approximately 2.2MB and 4 g · cm -3.

Mechanical and magnetic properties

The viscosity of the fluid is 0.07 Pa · s to 14 Pa · s. At a shear rate of 10 s-1 Temperature affects the viscosity of the MRF depends on the base fluid; the operating temperature is between -40 ° C and 150 ° C. When applied magnetic field outweighs the magnetorheological effect; Changes in viscosity are then made less than one millisecond, since only the particles need to be aligned. Thus, changes in force are dependent on the design feasible within a few milliseconds, see measurement ( 3000 N / ms). The shear stress behaves in the magnetic field free space as in a Newtonian fluid and the magnetic field as a Bingham fluid.

Shear stress over a typical magnetorheological fluid B-field

Measurement response MRF damper

All values ​​are dependent on the mixing ratio and the carrier liquid.

Possibilities of magnetic field generation

Depending on the application and application it makes sense to generate the magnetic field in different ways:

When used correctly, efficiently and EMC-compliant design of a system with magnetorheological fluid, this causes no interference from other systems.

Areas of application

Variable attenuator to adjust to changing load / stress, ie dynamic control of the viscosity by using sensors and electromagnets

  • Automotive: suspension shock absorber ( for example, Audi TT, R8, Acura MDX, Chevrolet Corvette, Ferrari 599 GTB), dampers in seats, engine bearings (eg Porsche ) and all-wheel drive couplings
  • Building: dampers in bridges and skyscrapers
  • Medical: Prostheses
  • Appliances: Washing machine with MRF damper ( for example Zaboon by Toshiba) to reduce the wash time for more cleaning power, less vibration, less noise and a compact, simple design.
  • Technical Optics: Processing of surfaces using magnetorheological polishing
Stabilizer (chemistry) Bingham plastic Running gear Audi R8
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