Letter 15030

Hard anodize with big thickness [Israel] 

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We are working with hard anodize of aluminium with standard sulphuric acid solution and cannot reach a thickness more that 75-80 micron. Please let me know if there is a possibility to reach a thickness of 150 micron and more with this process or do we need something else.

Thanks in advance.

Lisakov Ian
- Israel

Yes..it is possible (but unusual) to get 150 microns (.006")depending on the alloy, your use of proper racking techniques, and processing parameters.

Marc Green anodizer - Boise, ID, USA

I think in inches so 0.000 040 X 80 = 0.0032 inches thick. If that is right, then YES, let us now know the alloy and we will come back to you with more data.

Robert H Probert Robert H Probert Technical Services Garner, NC, USA Editor's note:        Mr. Probert is the    author of Aluminum How-To

Am I incorrect? I believe approx 25.4 microns = 1 mil (.001")?

Marc Green anodizer - Boise, ID, USA

You're both right. 25.4 microns to the mil, so divide the microns by 25.4 to get mils, or multiply the microns by .000 040 to get inches.

Ted Mooney, P.E.  finishing.com Brick, NJ

But Ted,

By my calculations..he is wanting almost a 6 mil coating, yet by Roberts figures...the coating is 3.2 mil...unless Robert was looking at coating growth on top of the substrate?

Marc Green anodizer - Boise, ID, USA

Exactly. The coating he is getting is 75-80 microns, equals 3.2 mil. The coating he'd like to get is 150 microns, equals 6 mil.

Ted Mooney, P.E. 
finishing.com
Brick, NJ

We anodize at 0°C in a 10% H2SO4 electrolyte and can achieve that kind of thickness, temperature is critical because if the part gets too hot due to a high curent density you will burn the part.

Guillermo Luna Compañia Estañadora Nacional, S.A. de C.V. Mexico City, Mexico

Max thickness of hardcoat is limited primarily by the alloy. Since the coating is an electrical insulator, the better the structure (tigher, denser, etc.) the better it insulates and the lower the maximum thickness obtainable will be. On 6xxx alloys, getting anything over 75 microns (roughly 3 mils) is nearly impossible. On 7xxx alloys on the other hand, getting 150 microns is possible. Ramping is critical ( how fast the maximum current density is acheived ). Others may argue that modified power, either superimposed AC over DC or pulse rectification will have a benefit. That would be up to the suppliers of the specific process you employ.

Good luck and let me know how you make out.

For your information, there is an International Hard Anodizing Association (www.ihanodizing.com)that has technical symposiums every 2 years. Attending something like this might establish the network you need to tackle hardcoat concerns.

Milt Stevenson, Jr. Anoplate Corp Syracuse, NY, USA

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