Vacuum Technology and Vacuum Design Handbook for Accelerator ...

• Electric arc with rods is not recommended due to flux trapping. This can cause pits which
have long lasting outgassing periods.
• All welds that form a seal against atmospheric or other positive pressures must be made to
the internal side (vacuum side) of the joint.
• Tack (stitch) welding is recommended on the external side only with less than 50% of the
diameter covered in small intervals. This minimises the chance of trapped voids and
facilitates He leak testing post welding.
• All welds must be free from pitting and scale. Must be cleaned to bare metal. If chemicals
are used to clean welds care must be taken to remove all traces of chemicals.
• Some chambers such as magnet boxes will need to have some joints welded externally due
to access problems on thin chambers. In this case, good penetration must be achieved to
ensure minimal gas trapping points.
3. Surface finishes
• The inside of the chamber and ports must be 1.6 micron or better for mechanical finishes.
• Can be chemically cleaned (polished) but all traces of chemicals must be neutralised and
removed prior to use in vacuum.
• All machining oil to be removed with an alcohol scrub then acetone rinse, minimum. The
use of kerosene, turpentine or other oily solvents is not encouraged however where they are
used the final clean must be with acetone followed by alcohol. Water based cutting fluids
can be used as they are more readily removed therefore having less effect on outgassing.
• Nitrile gloves to be used when assembling cleaned components. Other un-powdered gloves
may be used but only those that do not react with the solvents being used.
• Care must be given to cleaning and handling surfaces that will be exposed to vacuum.
Gloves should be used to minimise the transfer of dirt and oils from the skin to vacuum
surfaces.
• A suitably clean area should be used for the preparation of vacuum systems and all tolls used
should also be cleaned (degreased).
• Stainless steel can be cleaned in nitric acid to remove scale that remains from rolling or wire
cutting. It is may also be used to prepare stainless steel components for use in ultra-high
vacuum systems.
4. Flanges
• Flanges must be standard flanges selected from the group referenced this document for
compatibility reasons. Exceptions may be made but all ‘o’ ring seals must be to Australian
Standard AS 2842-1986. External flange rings not in contact with the vacuum space may be
aluminium alloy. Stainless flanges are not economical or necessary unless the seal requires
forces to crush metal seals such as copper ConFlat, aluminium or indium wire.
• Minimum thicknesses for top and bottom flanges to be calculated using the standard in
Appendix 1 – Structural Calculations for Scientific Vacuum Vessel Design.
• All other flanges to have threads consistent with their design standard.
• ANTARES – Primary flanges will be Dependex unless interface is necessary to
accommodate other standard flanging.
• For Dependex, screws to be imperial sizes consistent with UNC series.
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