Ferrofluidic seals utilize a non-wearing “liquid O-ring” of magnetic fluid as a positive hermetic barrier. These seals have become established art and are now widely used in vacuum and nuclear systems for rotary shaft penetrations and in gas pressure systems. Leakage rate is immeasurably low (less than 10-11 std. cc/sec of helium) as measured on a mass spectrometer. The liquid seal is generally forgiving of surface finish, mechanical run-out and eccentricity. Fluids of many different physico-chemical families have been developed for operating under widely differing conditions - diesters for vacuum and wide temperature range; fluorocarbons for highly reactive environments such as chlorine, ozone, sulphur dioxide and acidic vapors; and polyphenylethers for ultra-hard vacuum and maximum radiation resistance.
They have also found wide application as exclusion seals preventing liquid, vapor, metallic and non-metallic contaminants from reaching machinery parts in applications such as digital disc drives, grinding spindles and textile wind-up heads.
New engineering developments now make these seals applicable on oil systems for gear boxes, transmissions, drives and other sealed lubrication systems where they totally contain the oil while excluding external contaminants.
This paper reviews the rapidly advancing state-of-the-art of ferrofluidic seals including sealing vacuum, gases, liquids, ultra-high speed seals, exclusion seals and sealed ferrolubricant systems (SFS).