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Chromating aluminum - must do wet tape adhesion test although we don't paint?

Q. Hello community. I am Amos, Quality Manager for a Metal Finishing/ Chemical Processing provider. I have long appreciated the forum and knowledge sharing within.

Would anyone help technically explain the mechanism(s) at play during the Wet Tape Adhesion Test per MIL-DTL-5541? To my understanding, this is a requirement for those processing to the specification, regardless of whether or not priming/ painting is a part of the organization's scope. That being said, if a continuous primer layer is separating the conversion coating from the water, preventing direct interaction between the two; how is the 24-hour soak testing the integrity/ effectiveness of the conversion coating itself?

Thank you,

Amos Webb
- Tucson, Phoenix Arizona
April 3, 2024

⇩ Related postings, oldest first ⇩

Chromating aluminum - must do wet tape adhesion test although we don't paint?

Q. My shop does aluminum finishing i.e., anodize, hardcoat & chromate.

Regarding the chromate - we do our salt testing monthly, but just recently one of our major customers is asking why we do not do the wet tape adhesion testing. I explained to them that we do not do painting here nor do we job out any painting work & this is a paint test. My testing lab tells me the painter would do this test - not us. The testing lab also informed me that any failure of this test is usually attributable to the painter, not the chromate.

My customer's response to this explanation was :

"The wet tape test is a classified as a process control test and must be performed monthly in accordance with MIL-DTL-5541 [on DLA] paragraph 4.2.1 and table 1. It should also be noted that the results of a wet adhesion test used as part of a lot inspection may be used satisfy this requirements provided that it is performed at or near the time a normally scheduled test is to be performed.

However, the supplier may omit the wet tape adhesion test if there are verifiable assurances (as specified in MIL-DTL-5541 paragraph 6.3) that the end product will not be painted. Because my shop does not perform the wet tape test as part of the monthly process control test, we must have a provision within its procedures, normally the Contract Review sections of the Quality Manual, notifying the customer that the monthly wet tape adhesion test is not performed and request relief from this requirement.
Additionally, we must maintain a file of these approved wavers as objective evidence of compliance."

For those of you who do chromate, but not paint - do you do tape test?

Any help would be appreciated?

David A. Kraft
- Long Island City, New York
May 1, 2008

simultaneous replies

A. David

We have the wet tape adhesion test performed monthly. We process captive as well as outside work. None of the captive work is painted, and to our knowledge, none of the outside work gets painted either. But why limit the application of your process to work that is not painted? The wet tape adhesion test is one of the least costly to perform.

Willie Alexander
- Colorado Springs, Colorado

A. Yes, If your customers' parts are intended for paint then the test must be performed.

Bill Grayson
- San Jose, California

A. Regardless of the end use, the wet tape test is a required monthly test for 5541 the same as salt spray.

Chris Jurey, Past-President IHAA
Luke Engineering & Mfg. Co. Inc.
supporting advertiser
Wadsworth, Ohio
luke banner

Q. So, we do not do ANY painting here, so we now have to job out painting on our sample panels before submitting for wet tape test?

David A Kraft
- Long Island City, New York

simultaneous replies

A. David

The wet tape adhesion test is a test of the chemical film and not paint. It is a P/F test of how well your CF 'sticks' to the underlying aluminum. If it does not 'stick' it is an indication that any subsequent paint that is applied will not have proper adhesion.

Willie Alexander
- Colorado Springs, Colorado

A. Check out para 3.6.2 of MIL-DTL-5541 [on DLA]. See if you can get an exemption based on that paragraph. It seems rather daft to me to require paint adhesion testing on a company that doesn't paint.

Brian Terry
Aerospace - Yeovil, Somerset, UK

A. It seems to me from my reading of the method description that this test is also a measure of the integrity of the painted coating. Weaknesses there that allow penetration of the water through to the chromate coated substrate will permit rehydration of the chromate film. I imagine this would have a substantial effect on the adhesion of the paint.

The only time I witnessed adhesion failure that was attributable to the Alodine was in a customer of mine's shop, where effluent from the waste treatment system was used to make up the post chromate rinse.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

A. Dear David

The information that you have received regarding doing the wet tape test is correct. If your customer or his end user requires Nadcap approval than the wet tape test must be done. In addition to meet the Mil spec you are obligated to do the test, but unless you are Nadcap approved no one is available to enforce this requirement except your customer. If you certify to the mil spec then you should perform the required tests otherwise you should put a disclaimer on the certification that it was not done. It will get harder to skip these test as requirements filter down. One other thing about the issue: You are not only certifying that the chem film sticks to the parts but you are also certifying that paint will stick to the chem film and to prove that the test is required.

drew nosti
Drew Nosti, CEF
Anodize USA
supporting advertiser
Ladson, South Carolina
May 29, 2008

Q. Is there any requirement to perform a tape test on chem film?

Tammy Peck
plating buyer - San Diego, California
March 12, 2009

A. Hi Tammy,
'Chem film' is slang widely used in the USA for chromate conversion coating (chromating, Alodining (a popular trademark) and Iriditing (another popular trademark). So, what you re reading on this page is applicable and, assuming that the chem film is being done to some specification, the wet tape testing is probably required.
Luck & Regards,

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

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