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Chromic Anodizing blade burn

I am presently working in an aviation repair facility here in the kingdom of Saudi Arabia as an Electroplater..Recently we encountered CHROMIC ANODIZING PROBLEM that we can't find any answer. I am having a BURN area on the thinnest part of the item that I am anodizing..The part is an aluminum C-130 aircraft propeller blade and I'm using a jig which is a combination of Titanium and Aluminum...The Butt face of the blade is where we bolted/attach the jig.The horizontal fixture is 10 in. X 4 X 3 in. solid titanium and the vertical attachment is a 50.8 millimeters diameter threaded aluminum. I am experiencing a KICK of high amperes even at 4 Volts to 12 volts as I evenly increase the current to 40 volts. I am using 150 ampere rectifier and operates at 32 °C. I am not sure if the problem is the TITANIUM fixture coz' I think the rectifier is forcing the titanium to oxidize as well with the aluminum blade. Will titanium Jigs pull up much current that's causing this problem in chromic acid anodize?...Any help and advise will be very much appreciated here...

Sam Barrameda
plating shop employee - Saudi Arabia
May 24, 2011

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Check your sulphate level. It does not take much to mess up an anodize tank.
150 amps seems like a small power supply. There is a lot of surface area in one blade.

James Watts
- Navarre, Florida
May 26, 2011

Could anyone please help me to understand if it will indeed pull up the rectifiers current if I'm using titanium rather than aluminum?? Tanks solution is well balanced and all parameters in chromic anodizing were met.I would appreciate it if you guys can enlighten me more on this and what's the recommended rectifier capacity for this big blade and what ASF is best prescribed per your expertise....

Sam Barrameda
aviation - Jeddah Saudi Arabia
June 1, 2011

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June 29, 2011

Our experience is that Titanium jigs do not form the passive film in Chromic anodising that they do in sulfuric anodising, consequently keep pulling amps, certainly evident if you use the Bengough-Stuart cycle (as we do) - I've no experience with the constant voltage process.

I would try changing to aluminium jigging.

Regards

Richard Guise
- Lowestoft Suffolk United Kingdom

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Hi,
The past 2 weeks we again had two burned C130 Prop. Blades issue and we can't figure it out why and how to stop it from appearing. The use of a 150 amp rectifier was ruled out since we've been using the same rectifier for 15 years now. Can anyone of your experts give more concrete and "DETAILED" possible SOLUTION for this...The oxidation of the process is also producing a very thin oxide and it's opaque in color....

Sam Barrameda
- Jeddah Saudi Arabia
July 25, 2011

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Hi, cousin Sam. Although I can certainly understand your frustration, I think it is unlikely that anyone can offer a detailed solution to this problem sight unseen. All they can do is suggest paths for investigation. A path that I would investigate is loss of contact because the thin sections sound like they would be the highest current density areas and most prone to burning if contact was bad early in the cycle and became established later when the voltage was higher. I would also suggest looking at letter 48908.

But realistically, if you need a concrete and detailed solution, you probably need to hire an anodizing consultant to make a visit. Best of luck.

P.S.: Despite your understandable frustration, please say "thanks" to the previous responders before jumping to a demand for a better and more complete answer, or all you will do is scare potential responders away :-)

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 26, 2011

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Thanks cousin Ted for that help and reminder...Really I appreciate and thank Mr. Watts and Mr. Guise for responding in my queries...Salute Salute.......When we say BELOW 0.2 g/l of chloride as NaCl and BELOW 0.5 g/l of sulphate as H2SO4, how much "LOW" is the minimum/maximum for each? BIG THANKS again guys for the inputs.

Sam Barrameda
- Jeddah, Saudi Arabia
July 27, 2011