18.104.22.168 Sealed elastomer rotation and translation
For vacuum-suitable seals subjected to dynamic stress, special elastomer seals are used, which are often made of the FKM (fluoroelastomer) material. The adjustment of the limiting size between housing, seal and actuator shaft must be done carefully, the same goes for the design and implementation of surface finishes.
For frequent movements and for the increase of the sealing effect, elastomer seals must be lubricated on the moving contact points, which reduces friction, prevents premature wear and evens out small irregularities on the surfaces. When selecting a suitable vacuum grease or oil for maximum operating and bakeout temperature, their properties must be considered, particularly the vapor pressure.
Elastomer-sealed feedthroughs are only partially bakeable. In addition, it must be examined whether components of the grease or low amounts of hydrocarbons are compatible with the application. In consideration of these limitations, elastomer-sealed mechanical feedthroughs represent an economical alternative to more expensive devices with functional principles, if highest demands on vacuum quality are not priority.
An advantage of the continuous actuator shaft is the direct connection of the vacuum-side application with the drive on the atmosphere side. There is no play or load-dependent positioning error. Depending on the dimensioning and mounting of the actuator shaft, large loads can be moved as well.
With elastomer-sealed feedthroughs, rotational and linear motion and simultaneous rotation/linear motion can be implemented.
- Grooved ball bearing
- Radial shaft seal ring
- Vacuum grease reservoir
Figure 3.27: Elastomer-sealed rotary feedthrough