You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
Pfeiffer <strong>Vacuum</strong><br />
Page 136<br />
<strong>Vacuum</strong> <strong>Technology</strong><br />
What are used most frequently are radial shaft seal rings or cap seals, even though they<br />
require lubrication. Hydrocarbons in the form of vapors or crack products can penetrate into<br />
the vacuum system through the lubricant.<br />
A magnetic coupling consists of a bell-shaped permanent magnet arrangement on the outside<br />
that rotates the rotor, which is rotatably mounted in the vacuum and is also equipped with<br />
magnets. The two components are separated by a can that forms a hermetic seal. In the case<br />
of slow rotation, dry-running ceramic ball bearings can be used in the vacuum. Fast-running<br />
shafts in vacuum can be magnetically levitated.<br />
So-called cat’s-tail or wobble-tail feedthroughs also afford hermetic separation between<br />
vacuum and atmosphere.<br />
4<br />
5<br />
6<br />
1) Drive shaft<br />
2) Spring bellows<br />
3) Crank pin<br />
Figure 6.14: UHV cat’s-tail feedthrough<br />
3<br />
<strong>Vacuum</strong> Atmosphere<br />
5<br />
4) Driven shaft<br />
5) Ball bearings<br />
6) CF flange<br />
Figure 6.14 shows the design of such a feedthrough. The angled drive shaft (1), whose end<br />
is supported in a crank pin (3), rotates the driven shaft (4) in the vacuum. The hermetic seal<br />
consists of a non-rotating bellows seal (2) that performs a wobbling movement. UHV-suitable<br />
dry-lubrication ball bearings are used for mounting the drive shaft in the vacuum.<br />
Electric feedthroughs<br />
A major factor in engineering an electric feedthrough is the type of current and voltage for<br />
which it will be used and the requirements it will have to satisfy with respect to vacuumtightness<br />
and temperature resistance. The manufacturing processes for feedthroughs are<br />
discussed in Section 6.4. Feedthroughs with organic insulating materials can only be used<br />
for lower voltages. Simple cast-resin feedthroughs are frequently used for moderate current<br />
loads, e.g. for measurement currents. Epoxy resin is very well suited as an insulator and<br />
as a vacuum seal for moderate temperatures.<br />
Multi-pole glass-molded feedthroughs to which the leads can be soldered on both sides are installed<br />
in small flanges. There are also versions with tubes through which leads can be inserted<br />
and soldered in place.<br />
2<br />
5<br />
1<br />
www.pfeiffer-vacuum.net
Change language