ULTRA HIGH VACUUM (U.H.V.) FLANGES
To ensure total reliability under all conditions it is essential that
the material employed, the flange design and manufacture are of the
highest quality. For the demanding requirements of U.H.V. operation
we normally use austenitic stainless steel specification EN 1.4307 (304S11).
This low carbon material is very suitable for welding with minimum risk
of intergranular corrosion. It will withstand repeated high temperature
bakeouts with very low outgassing levels and is easily cleaned to the
high level of chemical cleanliness required for U.H.V. applications.
In addition to good corrosion and oxidation resistance EN 1.4307 has
a low magnetic permeability (less than 1.1).
For applications where it is necessary to have the lowest level of
magnetic permeability and where greater corrosion resistance is required
stainless steel specification EN 1.4406 (316LN) can be provided. This
material will usually have to be produced specially and may incur a
significant extra cost.
METALLIZATION
Development of the metallization process dates back to approximately
1935 in Germany where firms such as AEG and Telefunken started to independently
investigate this technique for valve construction to replace glass
to metal seals. The process was employed extensively in Germany during
the early 1940's and then 'exported' to the USA sponsored by their
government.
Some 10 years later Ferranti International plc developed their own
process, initially using Steatites, to replace the glass to metal seals
in microwave valves. After replacing Steatite with stronger high alumina
ceramics, the technique was employed in many other applications outside
the Company requirements. In 1990 the ceramic-to-metal seal division
of Ferranti became an independent Company, Ceramic Seals Limited, thus
retaining the knowledge and expertise built up over 30 years primarily
in the Defence industry. Metallization is continued on the next
page.
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