Anodizing time

[buckeyevs]

Is it good or bad to just anodize until no more amperage shows on the meter. If a zero amperage reading is a good or even decent way to tell when it is done then that will make a future project so much easier than calculating surface area. If zero amperage is a bad thing then let me know that also, and why. If it is bad then that might be what's wrong with my practice piece from my other message.

[Fibergeek]

The only way you can have zero current flowing in an anodizing setup is if you have an open circuit. If you are seeing this your electrical connection has failed. It's probably the anode to the work connection. If you are just tightly twisting an Al wire around the work you will find that it fails more often than not. In your previous post the connection had partially failed (had high resistance). This resulted in your growing an anodic layer too thin to dye properly. The other possibility is that you aren't properly cleaning the work, or you aren't removing the natural aluminum oxide layer (which forms over time) before anodizing. This would be a lot easier and faster if you provided enough detail about what you are doing in your process.

What I do is make use a threaded hole in the work to make the connection. If there isn't one I add one. Only coarse thread Al hardware is available, I use 10-24 or 1/4-20 thread aluminum machine screws and aluminum hex nuts. The Al wire is literally crushed between the screw head and a hex nut. And the screw is tightened into the work so tight you worry about breaking off the screw. Deliberately deforming a few threads on the screw is a good idea, you won't have to crank it down quite so tight. I've been using this method for 8-9 years now, and it has yet to fail.
Only aluminum, lead, or titanium hardware and wire may be used in the electrolyte of course.

Although you won't see a zero current condition in anodizing, there is a practical way to detect, in real time, when the anodize has stopped growing in your setup. Unfortunately it contradicts several Caswell anodizing mantras, which makes me reluctant to post it here. The Caswell Moderator should have access to my email address if he would like to see this method before giving me permission to post it.

[buckeyevs]

Well...

Since no one from caswell has replied to either of my questions I don't think they would even care(or notice). Anyway, there were 3 contact points and it seemed to be a tight connection.
Procedure:
I hight speed wire brushed the entire surface well.
Then cleaned it in detergent and hot water and rinsed it with distilled water.
I then connected it to the wire using rubber gloves to keep oils off of it.
I put it in the acid as quickly as I could, connected the wires and let it go. The acid temperature was about 70*F the entire time.
Being it was my very second attempt I left it go for longer than the calculated time for surface area.
After anodizing I rinsed it with distilled water and put it in the dye for about an hour(waiting for more distilled water to arrive so I could boil it).
I then boiled it and everything seemed fine, aside from a very small amount of black rubbing of on my finger. The surface was very hard. Wouldn't scratch with a metal edged ruler. Then I tried bleaching it and my disappointment began.

I'm going to try again this weekend and I have some de-oxidizer and LT sealer that I will through into the process and see if it works. Any suggestions would be much appreciated.

[Fibergeek]

I was contacted by the Caswell Moderator and he did ask to see my method. I will type it up and email it to him. That will happen this weekend, but not tonight.

But back to your issues.
Electrical connections; you need a better way, my method may appear extreme but it's really not, considering that this connection is under constant attack by the anodizing process. As little as 1/2 an Ohm of contact resistance occuring here can completely hose your anodizing job.

Lose the bleach. I haven't had time to look this up yet (and it's been over 25 years since undergrad inorganic chemistry) But I think chlorine will attack aluminum and/or the anodic layer. Once the work has been sealed, what little dye remains on the surface can be rubbed off with a paper towel. After that none will come out. I think your test for sealing is actually distructive.

What are you using for a power source? This is one crucial piece you haven't mentioned. I'll assume it's a 12 V battery charger. If you just hook it up and let it rip the real high currents generated at startup are quite capable of damaging your connections right then and there (and several other bad things). Without a provision for current limiting at startup, the higher the rated current of the charger, the more likely connection damage. At least start on the 6V range if it has one, switch to 12V when the current has dropped to 5 A or less (less is better). A power resistor in series with the work is better, say 3 to 5 Ohms rated at 10 watts or higher will help a lot for a 6 -10 amp charger. If the charger is higher current, scale both the resistance and wattage accordingly. If the charger has a 6V range, use that too.

I'll have more information for you later.

[buckeyevs]

The power source is a manual 12v 2or6 amp selectable battery charger.

On a positive note, I took an old spyder asa that I'm assuming was professionally hard coat anodized and put it in bleach. Some of the black came off of it also, leaving a grey color. I'm thinking my test piece was just anodized thin and maybe not very well sealed. Let me know if the charger is a problem, and I will try to come up with a different way of connecting the wire. I really don't have any spot on the piece that I can tap to thread the wire in. Any where I do will either be visible or will weaken the mounting point, neither of which I want to have happen.

[Fibergeek]

I have no clue what a spyder asa is, but if you can't use a tapped hole I'll guess it something made of sheet Al. Can you fashion an all aluminum clamp? Something reminicent of a small C clamp, but made entirely of aluminum, the screw too. The only flaw will be the small area where the tip of the screw contacted the aluminum and didn't anodize.

[buckeyevs]

FYI The spyder asa is a part of a spyder paintball gun. The part the air tank screws into to be exact.

What I'm attempting is to make a gun stock for a paintball gun out of aluminum 3/8" rod.

I will try using an alumium screw and nut to smash the wire against the threaded part of it.