Pulse anodizing

• Topic 0208 "Interference coloring of aluminum by pulse anodizing"

A. Hello, Lim. Pulse plating is of value in some instances. So I can easily picture that pulse anodizing can be of value, through micro-agitation of the boundary layer if by no other means -- although I have no personal experience with it, and some concern about what it can mess up :-)

Pulsing adds another variable to a process which can already be difficult to manage because of many variables. If your shop has substantial anodizing experience, and your process is under good control, by all means go for it!
But if you have limited anodizing experience, or you presently suffer consistency problems, I say avoid adding another tricky variable that many highly experienced shops have been able to do without.

A. Dear Lim Chaus

Are you still interested in hearing about pulse anodising? Are you intending to pulse anodise MIL-A-8625 / MIL-PRF-8625 [on DLA] type II or type III?
I did my Ph.D thesis on Pulse Anodizing.

Hi, Dilip. Welcome to finishing.com!
Here's a link to Dr. Juhl's terrific paper, "Theoretical Introduction to Pulse Anodizing." This forum introduces finishers to concepts like what is pulse anodizing about, pointing out papers about it, showing you who are the experts in this field, what manufacturers offer pulsed power supplies, what is new in this field of study, etc. And it's also good for quick answers to specific questions, and as an aid for troubleshooting shop problems.

But consultants and suppliers earn their living guiding people through the implementation of such technologies. I doubt that anyone will guide you through such fine detail as you are requesting as a freebie, but your inquiry remains here if I'm wrong :-)

Good luck and Regards,

A. Hi, Abhijit, Sandip, Sudershan.

The most complete book on anodizing is Surface Finishing and Treatment of Aluminum and its Alloys, by Wernick, Pinner & Sheasby. It has a few references to pulse anodizing.

Regards,

A. Hi

I have made a Ph.D thesis about Pulse Anodizing.

Sunny regards,

A. I am currently anodizing type II and type III. Pulse rectifiers are excellent for precision work because I need a tolerance of ± 3 microns in nominal thickness of 75 microns, also consume only 20% energy than conventional rectifiers.
They are also cheaper.
The disadvantages are the lifetime and repairs.
I highly recommend them.
Q. How I can contact Anne Deacon Juhl?
Thanks.

Hi Victor. Thanks for the great input. But I have a hard time believing, in view of Faraday's Law, that conventional anodizing rectifiers are only 20% as efficient as pulse plating rectifiers, although I'd be interested in hearing more about that and an explanation.

Anne was a supporting advertiser of finishing.com with direct live links to all her contact info for a while; but she dropped out so we no longer have current info about how to contact her; if google doesn't work you might see if IHAA can help you find her.

Regards,

A. Hi Danny. You may already realize this, but other readers may not, and so that the discussion doesn't confuse them it should be noted that "switch-mode" and "pulse anodizing" are neither mutually inclusive or exclusive -- and in fact they have little to do with each other :-)

A rectifier always involves a transformer to convert the 115 V or 230 V or 460 Volt line voltage down to the lower voltages needed for plating or anodizing. In the old days, those transformers naturally operated at the 60 Hz frequency of the incoming alternating current. But then at the dawn of the personal computer age, designers realized that the size of transformers could be greatly reduced if they could operate at a much higher frequency. So they designed "chopper" circuits to rapidly turn the power off and back on, simulating a frequency much higher than 60 Hz, and allowing much smaller transformers. Although this development took a number of years to work itself up to the much larger 3-phase power supplies used for plating and anodizing, it eventually did. In this industry those much smaller rectifiers are often called "switch-mode" or "switching" rectifiers. So, as far as the 'switch-mode' aspect is concerned, you can probably just read the nameplates on your old rectifiers and tell the supplier that you want switch-mode rectifiers with the same DC Amperage and DC Voltage output as your old rectifiers.

But the other aspect you inquire about is "pulse anodizing". Not everybody uses it, but what it means is that the rectifier does not put out pure DC current for anodizing, but instead delivers some sort of on-off cycling of the power in the belief that the anodizing will proceed better. If the power supply manufacturer does not have suggestions on that, you would need to inquire of other users or of a consultant regarding what cycles are most useful for anodizing.

Whether you use switch-mode rectifiers or not, another thing that newbies need to know is that bare aluminum is highly conductive and anodized aluminum is not, with the result that anodizing always starts at low voltage to avoid burning the aluminum, and as the resistive anodized films build up, the rectifier must slowly ramp up to higher voltage to keep the process going. So anodizing rectifiers must be capable of "ramp control".

Regards,