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Oxalic Acid Spot Test as per AMS 2485-J (Coating Black Oxide)

Q. Hello,
I am in charge of the qualification of special processes applied on our company products (bearings for Aerospace applications).We use a subcontractor to perform a Black Oxide coating on our carburized parts.

During an audit for the qualification of this process, we performed the Oxalic Acid Spot Test required by AMS2485 Issue J paragraph 3.3.3 and the result after black oxide process is non conforming (areas under the drop exhibit a grey center), but after de-embrittlement treatment (8 hours at 135 °C) the results of this test is conforming.
All parameters during the process and during the test are under control and are in accordance with AMS2485 standard. We have obtained the same results with a new Black Oxide bath.
Did you have some explanations about this problem and many thanks for your reply.

Jacky G [last name deleted for privacy by Editor]
user - Valenciennes - France
2006

A. Hi, Jacky. I can't answer this, so I am disappointed that no one else has yet :-(

Barring hearing from someone who really knows, I would say if the spec requires this baking procedure, and it does not say to do the test before baking, then you are in compliance; but if you are meeting the test by extending the baking time, or doing anything else that the spec does not explicitly call for, then you are out of compliance.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 10, 2008

Pics of passed and failed oxalic acid test of black oxide?

Q. I am providing a presentation to Nadcap Auditors on Black Oxide in a couple of weeks and have been asked to provide pictures of the Oxalic Acid testing, both pass and fail results. Do you have any examples or know of a web page where I can download them?

Michael Coleman
- Lewes, Delaware
October 1, 2014

A. Michael

You can find images in MIL-DTL-13924 [on DLA] D and in ISO 11408 (1999).

Willie Alexander
- Colorado Springs, Colorado
October 2, 2014

Q. Hello everyone, hope you all are in good health. I am facing a problem in qualification of black oxidation via oxalic acid spot test. The black oxide finishing is quite fine but it fails oxalic acid spot test. Any reason?

Osama Farooq
- Rawalpindi, Punjab, Pakistan
August 1, 2018

A. Hi Osama,

I find that the usual reason for failing the oxalic acid test is that the dilute chromate seal has aged and is no longer effective. How often do you change your seal? I my previous company we changed the seal every three weeks, regardless of the volume of work performed and very rarely had a failure.

Brian Terry
Aerospace - Yeovil, Somerset, UK
August 1, 2018

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