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Longevity ofpolished Aluminum vs. Brite dip

June 23, 2008

My name is Michael Patterson. I recently purchased an aluminum anodizing plant in Kansas City, Missouri. The company has been finishing metals for 70+ years.

I have a customer who has moved their anodizing to an out of town metal finisher several years ago due to our inability to provide brite dip finish. I have researched electropolishing aluminum as an alternative and have provided samples to this customer and they have tentatively approved this process. The concern is the longevity of the electropolished aluminum vs. the brite dip. Can electropolished aluminum be considered an equal replacement to brite dip? What concerns should I or my customer have? Customer's greatest worry is consistency.

Thank you,

Michael Patterson
Owner of Metal Finishing Company - Kansas City, Missouri, USA

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Hi, Mike. Brite dipping is a miserable process and if you can accomplish the goal with electropolishing instead, that sounds good. I have never heard of any longevity issue about electropolished parts myself -- and I assume the parts will be anodized whether electropolished or brite dipped -- but we'll see if anyone else has anything to say.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
June 24, 2008

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July 5, 2008

Hi Mike,
Longevity of chemical v electropolishing is not an issue. Both give good, clean passive surfaces. Anodizing, of course, greatly increases longevity.

There are a few things to consider before deciding on the electropolishing route:

1) The current density used is of the order of 100 amps/sq.ft. with voltage around 16 volts. This makes for a expensive rectifier.

2) If the bath is heavily used, you may need cooling the remove the heat due to the electrical input.

3) Racks which are adequate for anodizing at 15 asf may severely overheat at 100 asf: remember that the heating is proportional to the square current.

4) Titanium racks in particular may cause "burning" at the contact points.

5) Although the "throwing power" of electropolishing solutions is better than electroplating, spacing between components needs to be greater than for anodizing. This means smaller throughput per load.

Sorry if this is a rather depressing list.

Finally, may I ask if you propose to use a chromic acid containing electrolyte?

Harry Parkes
- Birmingham, UK