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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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Dye color removed when bending anodized sheet
September 8, 2019
Q. I am using 20% sulfuric acid bath for anodizing.
My process is
1. Bright dip
2. Rinse
3. 10% nitric cleaning
4. Rinse
5. Anodizing
6. Rinse
7. 10% nitric cleaning
8. Rinse
9. Dip in Dye bath 50 °C to 60 °C
10. Cold sealing.
Our final product is anodized sheet.
Anodizing is fine. But after anodizing, we need to bend the sheet. But during sheet bending time dye color was removed where stress came on sheet.
Our problem is that dye color was removed at where stress is come on sheet during bending time.
Kindly help.
Where is the fault?
Shop employee - India
Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)
September 10, 2019
A. Anodic coatings are rather more brittle than one might expect.
Can you perform the anodize/dye AFTER bending instead, so there is no stress placed on the finished coating?
Rachel Mackintosh
lab rat - Greenfield, Vermont
A. Hi Lalit. Please send pictures if you can. Tight bending changes the color even of clear anodizing to a whitish look; as you 'thin' the anodizing (although this isn't quite the right term because you're actually chopping it into mesas rather than thinning it), the dyed color becomes far less saturated and at best becomes lighter.
If you must bend after finishing, powder coating is probably a better bet than anodizing.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 2019
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Q. Thanks Rachel Sir and Ted sir for your kind reply. - Gujarat, India September 10, 2019 20% by weight or volume would produce a very large pore. 16%/wt (180 g/L) would produce a much smaller pore and would show less damage after bending.  Robert H Probert Robert H Probert Technical Services  Garner, North Carolina  September 11, 2019 |
OK thanks. Robert Sir. I will try and give reply.
- Gujarat India
September 11, 2019
A. I advise you to try less coating thickness such as 7-8 micron or decrease anodizing bath's temperature to 17-18 °C. But in both conditions coloring time (I think you make yellow color-ammonium ferric oxalate) should be more then current coloring time. Also at the same time you can try to increase coloring bath temperature to 60-65 °C.
Good luck...
- TURKEY,sakarya
September 16, 2019
Q. Thank you alaattin tuna sir for reply.
I'm already anodizing in bath temperature 17 to 18 °C and dye temperature 50 to 60 °C. But still problem persists.
Sir I listen that in chromic acid bath maybe it's possible. What is your suggestion about chromic acid bath?
Sir I am facing this problem from last 6 months. So that somewhat success in this problem. Before 6 month I used anodizing bath temperature 25 to 28 °C. So that time more color removed. After long experiment I decrease temperature up-to 18 to 20 °. And after that little bit colour remove compare to before. But I need 0% color removed as a sample.
Kindly give your suggestion.
Thank you
- Gujarat India
September 17, 2019
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