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Feedthroughs

SuperSeals

Magnetic fluid (ferrofluid) fills a small annular gap between a rotating shaft and a stationary magnetic pole piece. The gap is part of a high-energy magnetic circuit which includes the shaft and pole piece. The very large magnetic flux in the gap exerts a force on the fluid, holding it in place against pressure difference from atmosphere to vacuum, yielding a dynamic rotary seal in which there is no solid friction. Therefore, very long operating lifetimes are achieved.

Because the magnetic fluid has very low vapor pressure, it remains permanently in place for the entire lifetime of the seal, and does not contaminate the system. Some applications have special requirements (high temperature, highly reactive gases) which can be satisfied by selection of the optimum fluid from our family of fluid materials.

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SuperSeals: A breakthrough in feedthrough design

Researchers at Rigaku have found a way to simplify and further improve the design of fluid sealed feedthroughs.

Two opposed-polarity magnets are placed within the rotating shaft and the housing (made of ferromagnetic material) is an integral part of the magnetic circuit. A number of carefully formed grooves on the surface of the shaft determine the location of the fluid sealing rings. Because the shaft diameter is larger than the bearing journals in the region containing the magnets and grooves, there is no loss of strength as a result of using a grooved shaft.

The magnets are embedded in a matrix of ferromagnetic shaft material, which acts as a magnetic shunt. The casual observer may think this would weaken the magnetic field in the fluid seal, leading to a very weak seal. However, the reality is that by proper selection of materials and careful design, it is possible to make SuperSeal feedthroughs with very high pressure capacity.

Features

New patented design
Superior hermetic Magnaseal ferrofluid sealing principle
No internal O-rings
Very low stray magnetic fields
No magnets in the vacuum
Solid 3/8" shaft with 160 in-lbs torque capacity or 1/4" shaft with 50 in-lbs capacity
5,000-7500 rpm no-load operating speed
2.5 atmosphere differential pressure capacity
High tolerance to external fields (> 500 Gauss)

The SuperSeal design is protected by United States and International patents.

Models

In some applications, it is desirable to use a separate pole piece. Here a related design, called SuperSeal II, can be used. The figure at right shows a pole piece machined from a single piece of magnetic stainless steel, with small internal grooves to define the fluid regions. The shaft is smooth. Magnets are mounted in deep internal grooves. This design minimizes the number of parts required to produce a separate pole piece. Because the housing is not part of the magnetic circuit, an O-ring is required for static sealing of the pole piece to housing.

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