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topic 60999

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?

Lalit Malvi
Shop employee - India
  ^- Privately contact this inquirer -^


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
Rachel Mackintosh
Plating Solutions Control Specialist / Industrial Metals Waste Treatment - Brattleboro, Vermont


September 2019

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,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


simultaneous September 10, 2019

Q. Thanks Rachel Sir and Ted sir for your kind reply.
Actually sir I have samples that in this sample dye color was not remove during bending. I have no current photos. But I will post you photos in this week.
First time sir I was doing anodizing at 24 °C to 29 °C bath temperature. Anodizing was OK but more colour was removed during sheet bending. So that for checking we doing anodizing at 18 °C to 20 °C bath temperature. That time color was a little bit removed during sheet bending. But I was doing anodize like original sample.

Lalit Malvi [returning]
- Gujarat, India


September 11, 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 probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina


September 11, 2019

thumbs up sign  OK thanks. Robert Sir. I will try and give reply.

Lalit Malvi [returning]
- Gujarat India


September 16, 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...

alaattin tuna
- TURKEY,sakarya


September 17, 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

Lalit Malvi
- Gujarat India

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