Anodizing question

[hk940]

I want to set up an anodizing system and have a few questions.

As the process uses 12V dc some people use a battery charger, the problem the newer ones have a safety circuit built in that shuts down when used as an anodizing power source (the unit sees it an overload).

I also want to anodize Titanium that starts to anodize at a much higher voltage (up to 110V DC).

I could build a variable power supply with a variac and bridge rectifier (I have both).

I have read that an isolation transformer should be used for safety purposes. It was not clear where it should be used.

Does it go on the AC or DC side?

I have not seen a smoothing capacitor used for AL but have seen them on TI are they necessary?

 

[torchroadster]

You'll probably find better answers to your questions here: https://forum.caswellplating.com/forum/anodizing-questions

The isolation transformer is on the AC side. Transformers do not function on DC.

 

[LoneGoose]

Wow, torchroadster, good information. Just another example of why THR rocks!

 

[FROGO207]

The reason for the isolation transformer is to keep you from becoming a path for the high voltage from your electrical outlet to reach ground/the earth through your body. The reason you use a capacitor on the higher voltage DC is to smooth out the AC ripple component to an averaged constant DC voltage. Some electroplating processes require a basically pure DC voltage, some are not as fussy.

 

[MachIVshooter]

I want to set up an anodizing system and have a few questions.

As the process uses 12V dc some people use a battery charger, the problem the newer ones have a safety circuit built in that shuts down when used as an anodizing power source (the unit sees it an overload).

I also want to anodize Titanium that starts to anodize at a much higher voltage (up to 110V DC).

I could build a variable power supply with a variac and bridge rectifier (I have both).

I have read that an isolation transformer should be used for safety purposes. It was not clear where it should be used.

Does it go on the AC or DC side?

I have not seen a smoothing capacitor used for AL but have seen them on TI are they necessary?

First, you need more than 12 volts to get a decently thick anodic layer. I try to hold around 20-22V with a 50 amp 24 V power supply.

Yes, for most colors, Ti needs much more voltage. Remember, though, that Ti anodizing is really just cosmetic.

Isolation transformers won't be necessary at 24V, it's just not enough to conduct through our bodies under normal circumstances. You can grab the terminals of big truck batteries in series for 24V at over 1,000 amps and be just fine. At higher Ti anodizing voltages a risk presents (around 40 VDC is where DC power can conduct through our skin, especially if moist), but common sense can mitigate any risk; just turn the power supply off before touching any bare conductors.

There's a lot to anodizing, and I'm by no means an expert, but have learned a fair amount. Metal prep, bath solution, bath temperature, cathode material and cathode/anode ratio are every bit as important as getting voltage and amperage right. Everything can be dialed in and produce great results the first batch, and then the second one comes out like crap because the bath was 15° warmer. Too much cathode, it's really easy to burn parts. Solution too strong, you get erosion. Too weak, you have a thin & fragile layer. The list goes on and on. And, of course, different alloys behave very differently; I ran a 2219 part and a 7075 part together through the same surface prep, desmut, anodizing bath, dye bath and sealing, got very different results.

Just do as much reading as your brain can handle and then start learning the hands on way with scrap material.

 

[JohnKSa]

Isolation transformers won't be necessary at 24V, it's just not enough to conduct through our bodies under normal circumstances. You can grab the terminals of big truck batteries in series for 24V at over 1,000 amps and be just fine. At higher Ti anodizing voltages a risk presents (around 40 VDC is where DC power can conduct through our skin, especially if moist), but common sense can mitigate any risk; just turn the power supply off before touching any bare conductors.

I would add one caution. Do NOT wear any kind of metal on your hands/arms while working with this kind of setup. It isn't enough to shock you, but it is definitely enough to instantly turn a ring into a red-hot finger cooker. It's an especially unfun way to lose a finger, and the heat damage makes reattachment unlikely.

 

[FROGO207]

I agree if the power supply has an internal transformer then an additional one for separate isolation is not needed. SOME setups use a variable auto transformer to vary the voltage (usually older ones). THOSE have one side directly connected to the input power and thus NO isolation from the power mains . So know what you have and work safely. FWIW I did not start to feel a "tingle" until the voltage was about 34 volts. Your body chemistry may be different though and results will vary. The warning about rings and such is good. A co worker got his metal band watch across 12 VDC (alternator output) and severely burned one wrist/palm as well as several fingers on the corresponding hand trying to pull it off!