Second coating on Hard Anodized Aluminum - sealing helium
Second coating on Hard Anodized Aluminum - sealing helium
(OP)
We have a helium/LOX valve that is leaking even with heavy spring PTFE seals. The valve finish is hard anodized aluminum and even with a 4 Ra finish, leakage is higher than desirable.
Can we apply some type of second coating to reduce this leakage? Something to fill up the deep pores in the anodized aluminum?
Many thanks,
Can we apply some type of second coating to reduce this leakage? Something to fill up the deep pores in the anodized aluminum?
Many thanks,





RE: Second coating on Hard Anodized Aluminum - sealing helium
RE: Second coating on Hard Anodized Aluminum - sealing helium
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RE: Second coating on Hard Anodized Aluminum - sealing helium
IRstuff, I don't know. The only think we could do now is to measure the surface finish and they are around 4 Ra, 30 Rz, and 10 Rp which is very good.
RE: Second coating on Hard Anodized Aluminum - sealing helium
TTFN

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RE: Second coating on Hard Anodized Aluminum - sealing helium
According to MIL-A-8625 hard anodize is type III and it is normally NOT sealed.
Here is a quote from MIL-A-8625F
3.8.2 Type III. Type III coatings shall not be sealed where the main
function of application is to obtain the maximum degree of abrasion or wear
resistance. Where Type III coatings are used for exterior non-maintained
applications requiring corrosion resistance but permitting reduced abrasion
resistance, the contract or purchase order shall specify that sealing is
required. Sealing for such Type III coatings shall be accomplished by
Immersion tn a medium, such as boiling deionized water, In a hot aqueous 5
percent sodium dichromate solution, in a hot aqueous solution containing
nickel or cobalt acetate or other suitable chemical solutions (see 6.2). When
Type III coatings are provided unsealed, parts shall be thoroughly rinsed in
cold, clean water and dried after anodizing.
This post appears in other forms too. Please do not double or triple post!
Only Type II (sulfuric anodize) and type I (chromic anodize) require sealing to produce hard surface. What type of aluminum alloy are you using.