SKIMMER MOUNTING
Can you provide advice on skimmer mounting?
Skimmers
are usually mounted by clamping the brim to a mounting plate or vacuum bulkhead.
Mounts should be designed bearing in mind the maximum pressure
differential that will appear during vacuum pumpdown or venting. (See also Pressure,
Heat and Corrosion Resistance) The Model 1 and Model 2 skimmers are strong
enough to withstand a 1-atm differential. If
a shallow (e.g. 0.2 mm deep) recess is machined into the mounting plate to just
fit the outside diameter of the brim, then the skimmer can be removed and
replaced without losing alignment.
The
skimmer orifice is always precisely centered on the same axis as the edge of the
brim.
Skimmers
can also be soldered, brazed or glued in place. When soldering or brazing with a torch, the flame should
never be allowed to come into direct contact with the very thin skimmer wall.
Arc welding of nickel skimmers to stainless steel is possible, but this
delicate operation requires a highly skilled technician.
The nickel or copper metal in the skimmers as supplied is hard-tempered
and will spring back into shape if bent slightly.
Skimmers which have been heated above about 400°C will anneal and become
ductile, and should be handled more carefully to avoid bending the brim or
skimmer wall.
We would like to prepare our skimmer mounting in
advance of receiving our order. How accurate are the outside diameter at base
measurements?
+0.00 / –0.05mm.
We
were thinking of using a CONFLAT flange to mount a skimmer. Is this feasible?
Yes.
Skimmers can be mounted on any flange or bulkhead which provides stable support
for the skimmer brim. See above for
the preferred ways of mounting the skimmer.
In systems which are to be baked at high temperatures, the skimmer flange
may simply be clamped between two metal plates, or it could be clamped against a
soft metal gasket, such as annealed copper or gold.
Does
Beam supply flanges for mounting?
Sorry,
but we do not. There are a number of commercially available flanges and the
manufacturer or distributor should be able to supply dimensions.
We
are planning our skimmer mounting and need to know the typical brim thickness.
The
thickness of the brim is 0.05mm to 0.08mm. The brim widths are listed on the
skimmer specifications pages (dimension C) of this web site.
We
are concerned with leakage around the skimmer mounting. Do you have any
recommendations?
The
seal on the mounting needs only to have a leak rate that is small compared with
the gas conductance through the skimmer orifice. Clamping is often sufficient
and the use of a gasket or O-ring under the brim of the skimmer would completely
eliminate this leakage. If the system does not get hot or need to be super
clean, sealing with epoxy would also be effective.
We
plan to mount our skimmer using holes drilled through the brim. Would Beam
provide skimmers with the appropriate holes?
We
prefer not to do any additional machining operations after the completion of the
skimmer.