anodizing a container with small opening

[blackcote]

The container happens to be a 2 gallon gas tank, The customer has requested to anodize both inside and out. We're unsure of the quality of anodizing on the inside due to the relatively small hole for bubbles from anodizing to escape through. plus the fact that there would be no agitiation inside the tank. Should there be concern for this or nothing to worry about?

[acidrain]

Unless you insert a cathode, very little anodizing would take place inside the tank. If it were me, I'd devise a way to insert a combination cathode/propeller driven by an external motor. At least a hose leading to the inside with acid pumped contuously. A lot of effort for one project.
I have to think that the welds will be a different alloy than the shell. Do you think they may show a different color after dyeing?
An interesting project to say the least!

[blackcote]

Thanks for the tips. clear anodize so dye variation at welds is not of much concern. Although they did want bright dip in clear, but I haven't figured out what that means yet. We get that request fairly often.

[luminous]

I agree with Acid... you'll need to get a cathode inside that tank if you want any action. Unfortunately, the cathode area will probably be quite small compared to the internal area to be anodized.
And you'll need to circulate acid through the tank to get rid of the heat that's generated inside it and to get rid of bubbles that form. Maybe a piece of aluminum tubing that's got holes in it that you can shove into the opening.. Pump acid through it so it shoots out the holes and gives good circulation and turbulence inside the tank?

Have you done a square footage calculation on it yet?
A 2 gallon (462cu in) tank that's a perfect sphere would have a diameter of roughly 9.6" and an internal area of about 190sq in. (2sq ft).
A perfect cube would be about 7.75" square and have an internal area of about 360 sq in. (2.5 sq ft)
Odd shapes get tougher to calculate.

I hope you get the job... I'm curious how it goes and what solutions you come up with to make it work. Sounds interesting.

steve

[blackcote]

Interesting to say the least. I like your perforated tubing Idea. I do happen to have some flexible tubing that I could try this. as far as calcs go, I haven't seen the part yet so no idea on that. Sounds like this will be a bit time consuming to set up. and might be cost prohibitive to the customer. Ya never know though. Definately would be interesting though.

Hey just thought of an idea to get the surface area needed inside. How about bending the tubing in a sort of 3D spiral shape and threading it into the tank ...but it that might be limited too due to the shape of the tank. Now of course rigging it all up so its steady and not short circuited is another story. Hope there's some place I can sput weld a few support wires to.

[destroyer125]

The bright dip finish your customer is requesting is a mixture of nitric, phosphuric, sulfuric, in low concentrations, and water. Nasty stuff, the fumes themselves will eat everything in sight. This provides a flawless polished look.

[acidrain]

Originally Posted by blackcote

Hey just thought of an idea to get the surface area needed inside. How about bending the tubing in a sort of 3D spiral shape and threading it into the tank ...but it that might be limited too due to the shape of the tank. Now of course rigging it all up so its steady and not short circuited is another story. Hope there's some place I can sput weld a few support wires to.

A spiral tube is a great idea... add a bit of rubber tubing or electrical tape to it where it passes through the opening would ensure that it doesn't touch and short-circuit.

Originally Posted by blackcote

Although they did want bright dip in clear, but I haven't figured out what that means yet. We get that request fairly often.

Bright dip is a chemical brightener... only big commercial companies use it. It's REALLY toxic. You can achieve the same results by buffing. Bright dip doesn't remove scratches, etc, and is usually only used on new parts.

[blackcote]

Well I'm trying to upload a pic and it won't let me. But in a few words, I don't know how anyone would anodize the inside of these gas tanks. Is it really like plating where you need a cathode on the inside? blind holes anodize fine with out sticking something in them when there facing up in our tank. To describe the tank in a few words... it's about 8-10"L x 8-10"W x 6-8"H with a triaglular cross section along the LxH. This tank has about 4 holes that are about 3/4" - 1" diameter and there is a baffle about 1" from the end of each hole on the inside. impossible to get anything in there of any substantial size. The owner claims that others can anodize the insides.... so what's the trick or has the owner been fed misinformation. The reason for the ano on the inside is claimed that the alcohol race fuel eats aluminum. Anyone have any experience with that?

[luminous]

Originally Posted by blackcote

The reason for the ano on the inside is claimed that the alcohol race fuel eats aluminum. Anyone have any experience with that?

I don't have any direct experience, but I've heard before that fuels containing high percentages of alcohol can eat up aluminum.
It's not uncommon for guys to rinse out the fuel systems with gasoline to remove the alcohol from aluminum parts after a race session.

Long ago in a galaxy far away I used to hang out at the old (and now extinct) Baylands raceway in Fremont CA...

I'm not sure how you would even verify that you got a good ano coating on a tank like you describe. Can you see inside most of it with a mirror on a stick and a flashlight?

[blackcote]

Originally Posted by luminous

Can you see inside most of it with a mirror on a stick and a flashlight?

Not even close.