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Hard anodizing of piston ring grooves



We have some diesel engine pistons for repair.

We have had a chemical analysis performed and it tells us that we have 4032 cast aluminum.

The repair is to the top ring groove and we have repaired this by welding with a suitable filler rod by the TIG welding method.

The customer wants this area hard anodized can you explain if this is correct in doing also how much penetration we would expect.


Mac Horne

McAllister Horne
- Ontario, Canada

Hi, Mac. Hard anodizing can be varied somewhat in thickness, but is usually in the neighborhood of .001" to .002". Anodizing is a conversion process where aluminum is consumed to make the aluminum oxide film. You consume about .001" of aluminum in building .002" of anodizing. So the net dimensional change is about half of the coating thickness.


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

I would like you direct you to:
US Patent 6425364 - Two-stroke direct fuel injected marine engine having anodized piston ring grooves, which I found in a single search together with your post.

The Gramm Technik deals with partial hard-anodizing of pistons. The hard anodised surface treatment will leave about 50-100 micrometers thick oxide layer. Their leaflet is pretty informative even for those who will not use that particular technology. The "gammat" process creates 15 µm layer in just 60 seconds of anodising and the hardness is 350 HV.

Mario Bee
- Zapadna, Slovakia
July 10, 2008

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