Metal finishing Q&As since 1989
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How to avoid sealing blooms in anodizing of aluminum?
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Q. Can anybody help me on how to avoid sealing blooms which occur after hot acetate sealing. We do small parts which are Anodised followed by black electrocolouring and then sealed. We want solutions to avoid sealing blooms as then it is very time consuming to to buff them to remove them.
Any help is appreciated.
Best Regards
ACPL - UK
2002
A. Hey, Calcium Acetate is a white powder, and so are 12 other compounds that may form in your line, either in the seal or due to what happened up stream. I will send you or any other reader a copy of my two page list of causes of white spots or white smears. First look up stream for calcium and/or zinc both of which form white colored compounds with oxalates, citrates, acetates, fluorides, glyconates, metasilicates, carbonates, sulphates, et al.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
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A. There are commercially available additives that prevent "bloom" or "smut". In addition, filtering your sealing bath with a 5 micron filter will also help.
Guy Lester- Ontario, California
Q. Hi,
I am currently experiencing some challenges with black anodising. I have looked all over the net for an answer but I can never seem to get a definite reason to my issue. I'm hoping you could help!
After the process of anodising I am getting a "smut/bloom" finish over the work. Now I'm pretty certain this is caused from the vat too high in temperature or over-anodising. Is there a solution to prevent this from occurring, or do I have to start the whole process again? The job goes grey and smutty after etching but de-smuts after nitric bath, so this tells me it's Durrell aluminium. Could this be a reason why? I don't want to buff the work after as you can't get the same quality finish!
Thank you for your time,
Martin
Electroplating and anodising - Bedfordshire United Kingdom
August 2, 2016
? You didn't mention the most important thing, and that would be your sealing medium and operating parameters.
Marc Green
anodizer - Boise, Idaho
August 6, 2016
A. Hi Martin
Firstly, I'm pretty sure when you say "Durrel aluminium" that it should read "Dural aluminium". Dural is an old trade name for high copper containing aluminium. It falls into the 2000 series of alloys.
My immediate reaction was can 2000 series be black anodized? But, I don't have enough experience with them to be sure. Can someone comment please?
Marc is quite right, we need to know much more about your operating conditions. You really need to take a more structured approach to this problem. For example, do you know whether the smut is forming in the anodizing stage, as you suggest, or dyeing or sealing?
Lastly, are you prepared to answer questions as well as ask them so we can try to help?
Best wishes
Harry
Harry Parkes
- Birmingham, UK
August 10, 2016
A. Martin
It would be a good practice for you to know what alloy of aluminum you are working with rather than relying on the presence of the etch smut. Ask your customer.
If you are fairly certain your bath temperature is too high, lower it. Or alter your immersion time. Depending on the part geometry and operating parameters, lack of agitation could be a factor.
As Harry suggested, determine where in your process the problem is occurring so you can eliminate subsequent steps as a cause.
- Green Mountain Falls, Colorado
August 12, 2016
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