Starting the HARD way.

[Rapt]

Hi all,

I've been following this forum for awhile and reading as much as possible. The reason is that my small business makes parts that need to be Type III anodized, preferably to about .003"-.005" thickness. I'm trying to set-up to run them myself.

I purchased the essential chemicals (de-smut, stripper, anti-mist) from Caswell and have made my first sample runs.

Now I'm looking for some guidance on interpreting my results.

Solution is Napa sourced acid, 2 parts distilled water, 1 part H2S04.

Temperatures are fairly steady and below 40F even when I try to get readings as close as possible to the part I don't see any temperature rise. In fact over the course of the two runs the bulk tank temperature dropped from 40F to 36F.

Cathode area is 32 sq.in.

Agitation is by aeration, and is quite strong, I based my airflow setting on photos of the amount of churn visible in commercial anodizing tanks. I'm not getting any apparent misting, or residue on the covers though.

The hanger wire I'm using is 5000 series, tig 3/32 welding filler rod. It comes out really nice and nearly black, with a hint of brown/green. Thickness gain is easily measurable. I'll include the dimensions with each set of run data.

All parts were treated the same, with degrease, rinse, stripping, rinse, desmut straight to anodizing bath (no rinse). Anodize, then neutralize in a room temperature baking soda solution followed by thorough room temp or colder rinsing.

The parts are between 5 and 8 sq.in.

Run 1 -->approx. 9 ASF
Volts Time
19v 0 min
21v 15 min
23v 60min
24v 120 min
27v 180min
32v 240min
Part is 8 sq in and made of 7075. It has been anodized and stripper prior to this run. The colour wet was a medium brown/green with metallic look shining through. Dry its a medium gray, about the same as an 18% photographic reference card (battleship gray or slightly darker, it looks lighter in the photo than it looks in person). Hanger wire went from .092" diameter to .098" diameter. Part is matte sheen, but feels slightly "sticky" and the sheen is easily burnished to a higher shine (with say a fingernail), showing handling marks.


Run 2 --> 14.4 ASF
Volts Time
21v 0
22.5v 15 min
24v 30 min
26v 45 min
27.1v 60min
26.5v 70 min
Part is 5 sq in and made of 6061, colour wet was a dark grey with metallic sheen. Dry its a dark grey, but still clearly not black.
This hanger wire went from .0925" to .096" diameter. Part is matte sheen, doesn't have the same slightly "sticky" feel and doesn't burnish with a fingernail.

My questions to the more experienced:
Is the colour difference due to a lower current density or just the material?
Why the difference in feel between the two parts, did I mess something up?
What would you change/adjust to get the best Type III anodizing, in the darkest colour possible?

Thanks!

[acidrain]

I have no experience in type III, but I can offer this:
7xxx alloy will anodize much quicker than 6xxx. I think you have gone past desolution with the 7xxx alloy. I typically run 2xxx and 7xxx for only 3/4 of the time need for the same color depth of 5xxx and 6xxx.

Isn't type III usually performed at much higher densities? 4hrs is a long time to be in the bath. I would have thought something like 24A/sq. ft. for 1 hr. It sounds like your cooling system will certainly handle it.
Obviously, with higher CD's, you will have more gasses to deal with, so good ventilation will be needed.
You're probably going to have to do quite a bit of experimentation before settling on a formula that works good with your apparatus.
BTW, what was the measurable build?

[Rapt]

Thanks for the info... I thought I might have gone to far with the 7XXX Al, but wasn't sure.

Forgot to measure the parts prior to anodizing so I missed being able to collect that data, unfortunately.

Its been tough getting real insight into the Type III stuff as most sites etc just say, low temperatures and give very broad ranges for volts or current density. Mainly it seems to be limited to commercial operations.

Most commercial operations run Type II at 24-40 ASF (typical range I've seen). But I thought I might be able to run it slower/lower sort of an LCD Type III, just like the Caswell system does for Type II.

I guess I'll just have to do some more testing and see what happens.

(FWIW if people are looking for an easy way to strip parts, TSP (trisodium phosphate) reacts to form NaOH and strips Aluminum anodizing if people are looking for "home brew" stripper or can't get Sodium hydroxide itself. TSP is readily available at most hardware/DIY stores in the paint department.)

[Rapt]

It occurred to me that the measured build on the 5xxx wire was around .002"-.003".

Just don't know about the actual part build. It was one of those d'oh! moments when I realized I'd started without measuring the parts.

Probably going to try some more runs this week and record more data.

Always welcome any additional insights.