Ferrofluid Rotary Seal Vacuum Feedthroughs
Hermetic High Vacuum Seal
A Ferrofluid seal provides a hermetic atmospheric to high vacuum rotary vacuum seal under both static and dynamic conditions against gas, vapor and other contaminants. Leakage rate specification of each ferrofluid seal is 1 x 10‐9 std. cc/sec. All ferrofluid vacuum seals are leak checked with a helium leak detector. Rotary seals with con-flat (CF) flanges are designed as a UHV rotary feedthrough.
In the ferrofluid feedthrough, the seal is formed with the ferrofluid, transmitting minimal to no friction. There are also no wear parts that can break off and contaminate the vacuum system. The ferrofluid, itself, is inert, stable and with low vapor pressure. The lifetime of the seal is dependent on the application, but a 10+ year time maintenance timeframe is not unexpected.
The Ferrofluid seal contains a simple permanent magnetic circuit and low volatility ferrofluid. The only wear parts are self-contained ball bearings. These ball bearings are designed for a robust, high speed transmission and long lifetime.
Unlike o-ring vacuum seals, there is a lack of mechanical friction in the seal. No particles are produced which could contaminate the vacuum system. Low vapor pressure ferrofluids maintain seal integrity even in high vacuums better than 10-9 mbar (ultra-high vacuum systems).
High Speed Capability
Ferrofluid seals provide hermetic vacuum sealing at high rotational speeds (>10,000 rpm) with smooth motion.
Ferrofluid seals provide leak-free performance, even in intermittent and static rotating conditions. Elastomeric (or o-ring type seals) seals can be susceptible to plasticizing and relaxation effects during idle periods.
Principles of Operation
A ferrofluid style rotary seal vacuum feedthrough uses the response of a magnetic fluid with an applied magnetic field. Rotary seal components include a ferrofluid, permanent magnet, two pole pieces and a magnetically permeable shaft. The magnetic circuit, employs a stationary pole pieces and the rotating shaft, concentrates magnetic flux in the radial gap under each pole piece. When the ferrofluid is applied to this radial gap, it takes the shape of a liquid O-ring and produces a hermetic vacuum seal. Ferrofluidic vacuum rotary feedthroughs use fabricated multiple rings or grooves with ferrofluid locating in stages formed by grooves machined into either the shaft or pole pieces. Typically each single stage or grove can sustain a pressure differential of 0.2 atmospheres (200 mbar). The total vacuum pressure achieved is the sum of all the differential pressures provided by the grooves.