ALUMINUM ALLOY VACUUM CHAMBER WITH CONFLAT.
TYPE SEAL TO AN ALUMINUM ALLOY FLANGE FOR ULTRAHIGH VACUUM
Hajime Ishimaru·National Laboratory for High Energy Physics
Abstract:
A bakeable (continuous a 150°C) aluminum alloy vacuum chamber (6063~T6)
which is structurally the same as traditional'co nflat types flange ('2219-T87) anda pure aluminum gasket (1050) have been constructed. A CrN treatment(S~m) on theknife edge and other surfaces of the 'flange is performed for hardening (100 gr, Hv"-1800).
A bakeable aluminum alloy vacuum chamber (6063-T6) and bellows (5052) withan aluminum alloy flange ~2219-T87) and metal seal (Helicoflex aluminum 0-ring)were developed by author~- 2 This system can withstand many 150 °C bakeout.s without
leaking. To demonstrate an all aluminum ultrahigh vacuum system to the conservative
vacuum engineer a suitable aluminum conflat flange/gasket combination as shown· inFig. 1 had to be designd and fabricated.
The composition of the aluminum flange and metal
seal pose a problem since the surface hardness and the226
mechanical strength at bakeout temperatures are insufficient in ordinary aluminum alloys. However, a 'special
aluminum alloy 2219-T87 has been found to be have thenesessary mechanical properties. The mechanical properties of 2219-T87 hold up to 200°C. In practice thebakeout temperature is limited to approximately 170°C.
7
by the aluminum alloy extruded pipe (6063-T6). A CrN
coating by the ion-plating method was carried out on
the aluminum alloy surface of _the conflat flange. The..
thickness of the CrN layer was about 5 ~m. The surface hardness of .the CrN was very high and its microVicker's (100 gr) was about 1800. The CrN treatment on
2
the flange gave nearly perfect protection against bonding
between the knife edge of the aluminum alloy flange and4
the pure aluminum gasket, and other surface scratching.
The CrN treatment has no problem for surface outgassing
Fig.l ICF structure
in ultrahigh vacuum. A CrN coated conflat flange looks
conflat type aluminum
like a stainless steel conflat flange. The aluminumalloy vacuum flange-with·alloy vacuum chamber and the flange were welded by alter~ metal seal. !.aluminumnating current (SO Hz) TIG process using an aluminumalloy pipe (6063-T6), 2.
alloy filler wire (4043). The necessary lathe processing aluminum alloy flange
of.:the CrN coated aluminum flange was performed before(2219:-T87), .· 3;AC-TIG weld,welding. Distortion after welding was neg],igible and4.pure alinninum gasket
remachining was not necessary. Separation between CrN(1050), 5.CrN treatment,
film and the aluminum alloy flange and decrease of the
6.anodized aluminum alloy
surface hardness of the knife edge could not detected
tiolt (2024-T4), nu~
after welding. The pure aluminum gasket '(1050) is used
(6063-T6) and washer
for sealing. The dimensions of the aluminum gasket are(5052).
.same as -ordinary oxygen free 'copper' gaskets. The sealingchar~cter:istLs of this system are th~ same as for theordinary cortflat system. A torque wrench (<vlSO kg-em)
is required for .,tightening the flanges.

~.;:$9~~-143.'15

Vacuum testing was carried out for ICF-70,ICF-114 , ICF-152 and ICF-203 asshown in Fig. 2. The following cleaning procedure was adopted: degreasing in-201-Leak testing wastoluen and an ethylalc ohol rinse both at room tempera ture.
to 150°C. The leak
carried out during repeate d cycling from room tempera turewith helium leakrate of the flange and metal seal combina tion was measure d
11 atm cm 3 sec- 1 •Mass spectrum are shown
detecto r and found to be less than 10in Fig. 3.
d opening andSuch a system can withsta nd many 150°C bakeout s and repeate
aluminum alloy
theofedge
knife
theoftion
closing without leaking . The deforma
and 150°C 24 hourscycles
closingandopening
10
after
small
bly
negligiwasflangelex 0-ring for thisbakeout s. An aluminum gasket can replace the aluminum Helicof
alloy and theconflat system. An aluminum alloy conflat system or the aluminum
ss steelstainleyordinar
thereplacecansystem
mixed
stainle ss steel conflat
vacuumhultrahig
forsystem
vacuumconflat system. Thus a complet e aluminum
operatio n and is resiste nt to hard radiatio n.
ions.
The author wishes to thank Prof. G. Horikos hi for useful discuss
ies Ltd. for their
Acknowl edgemen t is made to Ishikaw ajima-H arima Heavy Industr
work-on the welding and assembl y constru ction.
Referen ces
1853.
1. H.Ishim aru, J. Vac. Sci. Techno !., 15(6), Nov./De c., 1978,
4000.
1979,
No.3,
NS-26,~ci.,
Nucl.
Trans.
IEEE
al,
2. H.Ishim aru at

Fig. 3.a Mass spectra at the pressur e of2 x 10- 9 Torr without baking.

Fig. 2 Test vacuum ch~mber, 150£/sec turbomo lecular pump and~j+ -~-~ ::_+f>f:t- l-£ --= 1-4--i")(---11-G-r-------1--+='1~- r- .eL
1---'---"-u: ~-- ---t-- -__:r--__:::1---+- "--+"'-' -"- '-'-±(_:::_:::=:j::= :::1_::: ~_:::_t:_::= ---~=----==r=:

ing _.,..
quadrup fole m
7a2 shs filte~.h Outbgaks~
a 1ng
ours w1t out
rate a ter
10Torr£/s ec
is approxi mately 2 x 10-~--t~==~~-= _+___~--~::_I_::!~==+~~}~_::: ~j:-~-=~-1~1::::::-~
t=='=-=--i-- =-:r:: r:--f--t -- --__ --- _____,__ -- t:::::iJ l--f-----1---'-' ---1-~----1-1=-- - t - --1---+-1---r--~-'-~A--+
Fig. 3.b Mass spectra at the pressur e of
4 x 10- 10 Torr after 150°C, 24 hours baking.

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