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Going without a rinse between cleaner and etch

We are starting a chromic acid anodizing process. The steps involved are aqueous alkaline cleaning, alkaline etching, rinsing, deoxidizing, rinsing, anodizing, rinsing, sealing. My inquiry is how would it affect our process if rinsing after aqueous cleaning is omitted and instead go directly to alkaline etching. What would be the expected problem if we continue doing so? Will there be a contamination?

Thank you,

Nila O. Par
- Winnipeg, Manitoba, Canada
2003

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Nila, we probably all already know that the answer is "Yes it can be done but it's a bad idea" :-)

So we're down to seeing who expresses the answer in words flowery enough to sway us one way or the other. In fact, some shops use a single tank for both cleaning and etching; so, separate tanks with no rinse is certainly no worse than that. But whatever is in the first tank, that distinguishes a non-etch cleaner from an etch tank, will quickly get into the etch tank. So I think you're better off biting the bullet and choosing to use either one tank or three tanks rather than two tanks.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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Most (or all) aluminum soak cleaners contain corrosion inhibitors which retard the attack of the otherwise highly caustic conditions on the aluminum. Without rinsing your caustic etch will become inhibited and you'll loose the ability to etch predictably. Since it's chromic anodize, I'm guessing you're installing this line for the aerospace industry. Besides the aforementioned problem, any aero firm would frown on such a practice!

My suggestion: DON'T DO IT!

Milt Stevenson, Jr.
Syracuse, New York
2003

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2003

Ted, Thank you very much for your input, it's just our consultant designed the flow process the way I described to you. Now we are to rinse it before going to etching but we will use the tank for rinsing parts after etching. So the process will be tank 1 to tank 3 to tank 2 then to tank 3. tank 1 cleaning, tank 2 etching, tank 3 rinsing. Will the drips from the racks affect so much the solution in tank 2?

Thanks again,

Nila Par
- Winnipeg, Manitoba, Canada

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Using a common rinse is a fairly typical compromise which I would not be able to argue against based on the limited amount of information available in a forum like this. But I think the drippage of cleaning solution into the etch tank is a bad idea. Any chance of rearranging the order of the tanks so that, physically, the etch tank is first, then the rinse, then the cleaner? If this could be done, dry work would proceed to the cleaning tank, then it would be rinsed, then it would go to the etch tank, then it would be rinsed, then it would pass over the cleaning tank.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

To get a uniform etch it is not only best to rinse the part of cleaner but also to deoxidize it before etching. If you go straight from the cleaner to etch you can get an uneven etch. This may be due to inhibitors in the cleaner. On the other hand if you can get satisfactory results going from the cleaner to the etch go for it. Less handling is more money.

Todd Osmolski
- Charlotte, North Carolina, USA
2003