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What is ferromagnetic fluid?
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How ferromagnetic fluid seals a shaft?
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Why ferromagnetic seals last longer than rubber O-rings?
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Can ferromagnetic seals operate under high temperature
environment?
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The fluid is composed of magnetic particles,
surfactant, and base fluid. The magnetic particles are nanometer-size coated with dispersing agent/surfactant
and suspended in base fluid. Using vacuum oil as base fluid, the ferrofluid is ultra-stable under magnetic field
and becomes a frictionless and durable sealant for rotary motion feedthroughs and other imaginative applications.
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Sealing technology of ferromagnetic fluid makes
use of ferromagnetic fluid response to the magnetic field. Ferromagnetic fluid is placed into a gap between the
rotating shaft and stationary pole pieces forming a ring-shape seal in the presence of magnetic field.
Magnetic field is generated by a permanent magnet. Pole pieces and the rotating shaft are
magnetically permeable materials that form a magnetic circuit and trap ferrofluid within circular gaps. Fine
structure of various designs at either surfaces of the gap concentrates local magnetic flux enhancing sustainable
pressure difference.
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Unlike the traditional rubber O-ring seal,
ferromagnetic seal is frictionless to the rotating shaft. Ferromagnetic fluid forming a circular sealing
layer around the rotating shaft as a "liquid O-ring" prevents external atmosphere to enter the vacuum chamber.
There is no possibility of particle pollution, un-wearable, high rotating speed, and low resistance. When
operating in conditions avoiding heavy loading, excess heat generation, and corrosive atmosphere, ferromagnetic seals
are virtually maintenance-free.
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Ferromagnetic fluid and permanent magnet in a
ferromagnetic seal cannot withstand temperature higher than their characteristic temperature. Permanent magnet
lost its magnetism above 120°C
while ferromagnetic fluid fails above 150°C.
Therefore, a ferromagnetic seal should never operate above those temperatures unless a proper cooling scheme is
provided. When higher temperature operations are required, please consider using our AW series water-cooled
ferromagnetic seals.
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