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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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Alocrom 1200 bend test failures
Q. Hi Greg,
Did you come to a solution on this issue?
We are experiencing similar issues during customer specific qualification.
We are using Alodine 1200 and priming with CA7233 (MIL-PRF-7233 Type 1 Class C2) and/or 44GN098 (MIL-PRF-85582 Type I Class N). Specification demands priming after 24 hrs of conversion coating and ambient curing. Testing 7 days after curing.
Customer spec requires test coupons to be bent around a mandrel no larger than 4x the panel thickness prior to corrosion testing.
This test is a new requirement for us and we have no experience with how to improve the conversion coating bond.
The paint is peeling at the bend and removing the conversion coating with it. Corrosion test fails.
I am toying with the idea that the deox time of 4 minutes is too long and the desmut of 2 minutes is too short. The conversion coating time should be scaled back too. Currently at 90 seconds immersion, achieving a heavy coating weight of 0.9 - 1.0g/m2.
Any further information or advise is welcome.
Production Engineer - Wingfield [Australia]
September 9, 2024
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⇩ Related postings, oldest first ⇩
Q. Does anybody have any experience of bend test failures on Alocrom 1200 test pieces primed with PR205.
GREG YATES- Manchester, England
2002
Q. We had some problems with epoxy primer applied on conversion coating (Alocrom 1200). I think that the loss of primer adhesion is caused by the contaminated, powdery Alocrom or by unsuccessful deoxidizing process. The paint surface was damaged by only the bend test. The adhesion test is good. Deoxidized surfaces inadequately rinsed can produce interfering films or previous conversion coating. What is the procedure for inspecting previous conversion coating?
Garbacia Stefanpainting- Bucuresti, Romania
2003
A. Hi Greg, hi Garbacia. You could proceed per a specification like MIL-DTL-5541 [on DLA]. Compliance with the spec would be a good sign that you will not have subsequent epoxy adhesion problems, whereas lack of compliance with the spec will be a sign of coming trouble.
Practically speaking, overheating the chromate film before it has 24 hours to cure seems to be a very common cause of flaking chromate conversion coatings. You should not exceed 140 °F. It's just a theory but, since the curing of epoxy coatings generates significant heat, I think it could spell trouble to epoxy prime sooner than 24 hours after conversion coating. Good luck.
Let us know if you learn anything. Thanks.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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