Magnet-fluid seal

The magnetic-fluid seal (ferrofluidic technology) is one of the rotary, contactless seals . A ferrofluid is used as the barrier medium , which is held in the gap between the rotating shaft and the seal housing with a suitably shaped magnetic field .

Magnet-fluid seals are used almost exclusively as gas seals and are cascaded for higher pressures , since a single stage can only withstand approx. 200 hPa (0.2 bar).

Applications

In semiconductor manufacturing , it is particularly important that no particles get into the process. Conventional contact seals cannot be used for this purpose, but the liquid barrier medium of a magnetic-fluid seal does not generate any particles in the process space. In addition, certain processes require a high vacuum . Since there is no convection in a vacuum , components such as electric motors are usually not adequately cooled. Therefore, they are often operated outside the process chamber. Only a magnetic-fluid seal can ensure sealing of the drive shaft .

Another aspect is the lack of the stick-slip effect that occurs with all touching seals. In positioning with control loops , this effect becomes noticeable as a very disruptive hysteresis that cannot be controlled with conventional PID control technology. High-precision optical systems therefore use ferrofluidic sealing technology.

Ferrofluidic sealing technology is widely used in process systems in which components must be as wear-free as possible in order to guarantee a long service life. The maintenance intervals for ferrofluidic seals are much longer than for conventional contact sealing technologies.

This sealing technique was also used in computer technology. Magnetic fluid seals are used for hard disks (of the 8-inch generation) in which the drive motor is positioned outside of the disk enclosure. Normal seals would release particles into the disk housing, which would lead to problems with the small distances between the magnetic head and disk.