Letter 115

Improved process to finish aluminum for vacuum application

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I am looking for methods to finish Aluminum so they may be used as sealing surfaces in Ultra High and Medium Vacuum systems. Because they are used in vacuum systems, they must be cleaned to remove any machining oils prior to use. Presently the parts are finished with sandpaper and 0000 steel wool [link is to product info at Rockler]. The desired final finish is in the 8 range (after cleaning). It appears the parts are being etched, during cleaning, just enough to degrade the finish. The only way to get the desired finish back is to polish the surface with 0000 steelwool. It should be noted that some of the surfaces are at the bottom of dovetail o-ring grooves which can have an entry width of 1/8 inch.

Either a different method of finishing or plating is desired. The present method is too time consuming to be practical. Thanks in advance for your help!

Marty Kangiser -

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I don't know whether it has real applicability to your particular need, but aluminum can be bright dipped in nitric-phosphoric solution to mirror brightness (and commonly is, for reflector use) or it can be electropolished.

Plating is certainly possible, but it sounds like it may be adding a complication factor without addressing the basic issue.


Ted Mooney, P.E. 
finishing.com
Brick, New Jersey

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