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topic 6930

Aluminum etch additives?


Q. Happy Holidays Fellow Finishers! My company does both rack and barrel sulfuric acid anodizing. Many parts need to be etched prior to finishing. We currently use sodium hydroxide with no additives and have to deal with the difficult aluminum hydroxide sludge that develops over time. We would like to start using an additive (sodium gluconate?) that will keep more aluminum in solution (and possibly make tank clean-up easier). Does anyone have any info on the concentration of sodium gluconate needed or if there is a better choice of additive?

Victor Waldman
- Naugatuck, Connecticut


A. You might be just as well off buying a pre-mixed caustic etch. That's what I use. Liquid based, it has all the agents pre-mixed into the make-up. Takes the guesswork out of the whole situation really. There are tons of suppliers of these types of products, listing them would be somewhat pointless as anyone that deals with anodizing and anodizing chemical additives will have access to such a product.

Matthew Stiltner
J & J Plating Company - Toledo, Ohio


A. Hello fellow anodizer! just browsing and saw this. We use an additive called ax-1888 from Houghton chemical. It is a good chelator; it keeps the solids in suspension therefore gets drug out into the rinse tanks. We have no-dump etch tanks. The aluminum stays between 140 g/l to 160 g/l. I will say that it gives the material a matte finish, not shiny. If that's a problem there are other additives. Well I've probably gabbed enough. It's just a thought.

Brian Vandivier
- franklin, Indiana

How much sodium gluconate should be in an aluminum etch


Q. I have a question regarding the amount of sodium gluconate I need to add to my caustic bath that I use in my aluminium anodizing plant.The literature I have suggests a "few" grams/liter. Could any one tell me what "few" is? Thanks, Sanjay

Sanjay A. Bulchandani
- Bombay, India


A. I was looking for information about sodium gluconate in solutions of sodium aluminate. I have found something that may helps you: I think you should add 1% to 5% of gluconate to your bath. I found that in Vulcan Chemicals-Technical and environmental services: "Caustic Etching of Aluminum"

Prouvez Charlotte
- France


A. My friend I am also involved in the anodizing process. You can use 10 grams/liter of Sodium gluconate.

Syed Iqbal Hussain
- Pakistan

Non-proprietary aluminum etch alternatives?

December 5, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hello all, I own a small metal finishing business and have to save money where I can when I can at this point. Previously I worked for a larger metal finishing company that acquired all of their treatment chemicals from Macdermid. I am currently working on getting an aluminum chromate conversion line (immersion) set up and will be getting most of the chemicals for this process from Macdermid. However I have been doing reading and have seen that caustic NaOH bath can be used for etching in this process. Currently the proprietary etch chemical from Macdermid, is about $xxxx [Ed. note: Sorry, we can't post prices here] per barrel and isn't sold in smaller quantities than a 350 lb drum whereas I can buy a 50 lb bag of soda beads for $yyy ....

Can someone elaborate on whether this is a viable option or not and how using NaOH as a caustic etch instead of a proprietary might effect salt spray testing?

As a side question as well, is it possible to use the soap as an etch instead since the Data sheet from Macdermid indicates that it can etch aluminum fairly easily at the right concentration.

Also, since someone will probably ask, here is my current process setup:

Soap (Isoprep 740)
Deox (Isoprep 184)
Iridite 14-2

Paul Hurley
owner, metal finishing business - Oregon, USA

December 2014

A. Hi Paul. Yes, it's possible to use a single tank both as a soak clean and an etch, and some small labs do so. But it's not good practice for a production shop to couple the two processes together this way because it opens the door wide for unintended consequences -- as soon as you have a cleaning problem, you'll find yourself over-etching; plus you may have some carry over of oils this way; finally, you will probably be dumping sooner than you should because this tank will fill with both soils and aluminum, and you'll have to dump as soon as either becomes an operational problem.

As for proprietaries vs. home brew, I think you should find out from experience how much the proprietary really costs you in practice vs. how much you really spend in practice if you try to do without. You may find that the additives prolong the solution life more than you anticipated, and a pound by pound comparison isn't all that useful.

Please consider this as simply the spouting of an aphorism, rather than as me "lecturing" people who know a lot more about their business than I do: If you can't afford the customary costs of the chemistry, you may be doing the wrong kind of work for the wrong customers :-)

Luck and Regards,

Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

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