Equipment/High Vacuum Station

Summary

The HVS is an in-progress equipment project to provide LondonHackspace members with access to a multi-purpose high vacuum system.

Proposed Uses

Resin degassing (backing pump ONLY - separate degassing chamber) Creating x-ray sources, CRTs & other electron-beam experiments Vacuum glasswork (EG; thermionic valve making/repair) Surface coatings (optical coatings, photocathodes, metalic finishes, titanium oxide coatings) Electron microscopy

Design concept

To enable all the uses people are interested in, the system needs to have vacuum access at a number of stages in the pumping system.

Backing/roughing pump

The backing pump is a rotary pump that should be capable of reaching near 0mbar. On a double valve setup one pump should be able to act as backing pump to the diffusion pump or to directly pump a separate degassing chamber. This should allow the degassing to be used without the worry of contaminating the ultraclean conditions of the High-Vacuum chamber or diffusion pump.

User:Andrewgodwin:Adrian has offered the use of his rotary pump for this componant. It should be fine for the degassing section, but unless we find detailed specifications for the diffusion pump we'll just have to wait and see if it's powerful enough to back the diff-pump. If not, cost of a 2nd hand one should be about £130.

Degassing chamber

The initial chamber is a home-made one made by Sci from an old fire extinguisher and water fittings.

Degassing resins allows small air bubbles to expand under low pressure and burst, removing the gas from the liquid. In plain resins this leads to stronger smoother castings, and with filler powders it creates a stronger bond between filler and resin.

As resins can bubble quite a lot in degassing, the vacuum line on the chamber should have a catch-pot fitted for safety. This is an empty vacuum-sealed container with two connections at the top. Any spilt resin or spray that makes its way down the initial vacuum line will be caught in this "dog-leg" and prevented from contaminating or damaging the rotary pump.

If you want to watch marshmallows expand, this is the portion of the system you'll be using.

Diffusion pump

The diffusion pump, as well as the majority of the vacuum manifolds and high-vacuum parts are from James Collings. A diffusion pump operates from approximately 10-30mbar down to as low as 10^-10mbar, though we are unlikely to be able to reach that extreme. 10^-6mbar (0.000001mbar) seems likely though.

The diff pump operates by boiling a special silicone oil to vapour and forcing it out through special baffles onto a cooled jacket. There the oil re-condenses and trickles down along with any air molecules it grabbed on the way. It sets up a pressure differential across the pump, where at its exist it should be at a high enough pressure the backing pump will be able to pump it away.

Currently the recommended pump oil for the Edwards E04 is Santovac 5. This is currently priced at £220 per 100ml.