Magnetic fluids (MF) are the artificial liquid medium possessing a unique combination of properties of flow and ability able to co-operate with magnetic field.
Magnetic fluids are stable colloidal dispersions of solid magnetic particles in the fluid- carrying base. Practically any liquid – water, hydrocarbons, petroleum oil, silicones - can serve as a carrying base. The dispersed phase consists of 3-10 nanometers particles of ferromagnetic materials (magnetite, ferrite, iron, nickel, cobalt). Thermal movement does not allow very small particles to settle by gravity. To prevent the adhesion of particles among themselves in MF, surfactants are added.
The most widely used properties of magnetic fluids are the ability of being maintained in a definite point by magnetic field and magnetic fluid levitation, i.e. pushing out non-magnet bodies from magnetic fluids , being under the influence of a non-uniform magnetic field.
The first property is used for developing seals, clutches and highly effective impulse dampers, shock absorbers, separators.
The greatest part of designs in the world with application of magnetic fluids is associated with magnetic fluid seals. It is called by the fact that the majority of traditional seals, especially gland seals and lip seals have such deficiencies as a low resource and impossibility of reaching full tightness. MFS have a number of essential advantages over conventional designs: practically zero leaks of the sealed medium at the set working conditions, minimal wear due to fluid friction in the gap between movable and stationary elements, low power losses.
MFS represent a ring-shape device. Magnetic fluid seal consists of the ring magnetic conduits (the pole ends) embracing the shaft, the permanent magnets located between the magnetic conduits and the case which integrates all the components in the whole structure.
Magnetic field closes the circuit via the shaft and the gaps between the pole ends and the shaft and maintains magnetic fluid 6 which is pulled into them. This is a peculiar liquid gland; it completely fills the gaps and seals them maintaining pressure drop on the both sides of the magnetic fluid seal. The gap between the pole ends and the shaft (the working gap) is to be uniform along its circumference. The working gap usually constitutes 0.2-0.3mm. Besides, the magnetic fluid pushes out nonmagnetic particles getting to a gap.
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The principle of operation of magnetic fluid shock absorbers (MFSA) is based on the phenomenon of stable levitation (rising to the surface) of non-magnetic bodies in magnetic fluid under the action of magnetic field, magnetic fluid carrying out the functions of both an elastic and a damping element.
MF does not deteriorate during its operation, does not change the properties, prevents mechanical contact between a moving element and the case. The basic advantages of levitation type MFSA are low own frequency, effective damping of low-frequency oscillations and high noise absorbing .
