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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
my brain has been pondering how to rotate a shaft and still keep the atmosphere from bursting through the shaft seal and poof....!!! vacuum gone? How is this done !?
I include these pics captured from evil Russian technicians....
the plates inside do not rotate. Do you see that "corrigated" cilinder - this allows the plate to move up and down keeping the vacuum. It has someting like bolt and nut configuration inside - when you turn to adjust the nut moves on the bolt and moves the plate inside in or out of the other plate.
P.S. Those puppies are qute popular around here - always wanted to add one to my collection of tubes or made a VTTC with it ....
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
that copper acordians shorter and longer, whoa! thats cleaver, whats the cycle lifetime for such a device before it comes apart like a paper clip bent too and fro?
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
A simple o-ring groove with the proper gland design will hold a vacuum fine. For ultra high vacuums, a Teflon seal would work great. The only issue is getting it machined. It has to be seated against a well polished surface and the rod has to be slightly larger than the seal inside diameter. Teflon is used to seal vacuum ball valves.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
They use bellows for the movement.
While what Turkey has written is used for low to medium vacuums for rotational movement, ferrofluidic seals are used for medium-high vacuums for rotational movement.
Registered Member #191
Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720
Sorry for digging up this old thread, but I was looking at the cool tube thread and noticed Anders' cool tube collection. So the next obvious question is, what about rotating anode xray tubes? Quick google search points to ferrofluid seals, is that the only way?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Electroholic wrote ...
what about rotating anode xray tubes? Quick google search points to ferrofluid seals, is that the only way?
This generally takes the form of a synchronous motor, with the stator winding outside the evacuated envelope. A typical two-phase stator has two windings, one of which is fed by a capacitor such that a phase shift of 120° between the two windings produces a rotating magnetic field.
The rotor inside the envelope takes the form of a heavy copper cylinder mechanically coupled to the anode. The ball bearings must withstand 500° C, and use lead or silver powder as a lubricant. Tube life is largely dependent on bearing wear, with life expectancy typically being 1000 hrs. Valuable tubes are often rebuilt.
Typical rotation speeds are ~2800 rpm - i.e. 3000 rpm (in 50Hz countries) with losses - but a new generation of high speed tubes reach ~8500 rpm - 9000 rpm with losses - using 150Hz stator supply.
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How do Vacuum caps rotate, yet keep there vacuum?
or made a VTTC with it ....
