Suggested ASF for hardcoat anodizing

A. One reference you may find useful information is ASM Handbook Vol. 5 Surface Engineering. The Anodizing chapter contains various references to alloys and processing parameters.

Best of Luck.

A. Generally for MIL-A-8625 / MIL-PRF-8625 [on DLA] type III 30-35 ASF with a ramp time of 1.5 to 3 min for all alloys except for 2000 & 7000 which should run 20-24 ASF with a longer ramp time of 8-12 min

A. Hi David. I am not familiar with such technology. Surprisingly, it looks like that topic has never come up in this forum in all these years . . . so thanks.

But please don't cast it in the abstract like that. Tell us what you have achieved and how, and then people may be able to point to what the next limiting factor will be, and whether they think it is addressable or a hard limit. My bet is that there is a need for extreme agitation to remove the heat and provide fresh solution. 24 ASF is conventional, 30-36 ASF is sometimes achievable, but I wouldn't build a line that counts on 45 ASF for conventionally racked parts without pre-proving it.

A question I'd like to add to the thread is how much time this will save? Although it's easy to see that plating at 45 ASF instead of 30 ASF will reduce plating time by a third, do we think that this will hold for anodizing?

Regards,

A. In 2010, the International Hard Anodizing Association (IHAA) conducted a series benchmarking studies of it's worldwide membership of leading hardcoat anodizers. The results of these surveys were presented at the IHAA 13th Technical Symposium in Las Vegas. One of the benchmarking studies was on the current density most used for hardcoating in their facilities. The average current density for all members was 33A/ft2 (3.3A/dm2) with a high of 40A/ft2 and a low of 20A/ft2.

Note: I am now a Past-President of the IHAA and a Board Member and Treasurer.

A. In theory, you would cut your process time by 33% if you raise your CD from 30 ASF to 45 ASF. If you are processing the same part all the time, you could likely make 45 ASF work.

If you raise your CD from 30 to 45, your heat input will increase more than 50%, all other parameters constant. As Ted mentioned, keeping the part surface refreshed with electrolyte would be the biggest challenge, followed by removing the heat from the bath itself; you're likely going to need a bigger chiller. Unless you're running your tank partially loaded and use the balance of the solution as a heat sink.

Might be cheaper to put in a bigger tank, or an additional tank to increase throughput, if that's what you're after.

A. Thanks for the insight, Willie -- I think you nailed it.

Transistors beat vacuum tubes every time; so were there a new enabling technology to allow hardcoat anodizing to be done faster and in a smaller space, then we should go for it. But when people just want to increase their production rate without that new type of technology, then simply adding an extra anodizing cell will probably be simpler, less expensive, and much more reliable than trying to tweak the current density beyond established standards.

A. Hi Casey. Although you want/need to hold the current constant on your actual load, I am not seeing what would allow the current on the actual load to remain constant at 28 ASF while it is dropping on the parallel/dummy load. Are you sure your 1 square foot parallel/dummy load is the same alloy and condition as the actual load?

Regarding pulse anodizing, I offer the same caution as for pulse plating: it is no doubt useful, but it represents yet another variable to tame. Don't fool with it until you solve mysteries like why current is dropping on the dummy load when you are continuously increasing voltage to maintain the ASF on the actual load. For more on pulse anodizing, start with letter 52350, "Hardcoat Anodizing Voltage" which includes entries by Dr. Anne Deacon Juhl, who earned her PhD in pulse anodizing. Good luck.

Regards,

A. The thing that jumps out at me here is "I have multiple various parts on the bar".

Are all of these parts from the same lot of material? It sounds to me as if you have some current robbing going on here to where the other parts, if not from the same lot, or are not of the same alloy, are robbing current from your test panel.

Even if they are all of the same alloy (6061), different heat lots, or material from different manufacturers can rob current from other parts.

A. Chad

All day long.

Your amp-hour calculation is off a bit; I get 1005.