Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Discoloration of MIL-5541 Alodine
June 10, 2022
Q. Hi, everyone
I am Morgan form Taiwan, and currently we are running a surface treatment shop.
We are now having the discoloration issue for the Alodine process.
We use the crane to do the dipping process for our product.
The advantage of the crane is that we can do more parts at once. But it pulls up the part at a very slow speed. When we pull up the part, the chemical flows over the part and causes the discoloration. Even if we keep spraying water on the part, it doesn't help.
Can anyone give us some suggestion?
Thank you in advance for the help.
- Tainan Taiwan
A. Hi Morgan. Apparently you've figured out that the problem is a lift speed that is too slow, but send photos to mooney@finishing.com for posting if you wish.
It's not clear to me why you have to lift very slowly. Why not simply speed it up?
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
June 2022
A. I suspect the film is forming too fast due to low pH, high temp or high concentration. In a beaker, try raising the pH in increments of 0.1. This will slow the film formation, get it to about 90 seconds, then see if that helped the problem until you can do the recommended Mooney thing and speed up the hoist.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
June 13, 2022
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