tomcannon
Mechanical
- Oct 15, 2010
- 26
Hi, I have had some aluminium parts water jet cut for a job, and needed them anodised. I decided to try myself as there will be a slow but steady trickle of these parts to do and it is not economical to have them done professionally with minimum orders.
I set up a small rig along with tanks for the pre-cleaning operations etc, the main anodising tank is approximately 14" square and holds in the region of 2.5 gallons of sulphuric/water mix, approximately 13% acid.
In trials it was going quite well but the aluminium hangers I used (12g aluminium wire) would dissolve over 20mins when used with a decent current of say 10amps at 24v. To get over this I made a titanium T shape hanger to hang 2 pieces on which did not dissolve of course- but I could not get a good connection between the titanium hanger and the test pieces, as soon as the power was connected and the first lot of bubbles had risen the connection would disappear, I put it down to the poor conductivity of the material as touching the hanger would make small sparks appear between it and the aluminium pieces, current would rise then disappear again.
I then made up a much thicker aluminium hanger (8mm diameter bar welded to 25x6mm flat bar in a T shape), the pieces to be annodised have 8mm holes though 3mm plate, all countersunk (so not much area in contact with hanger) but were a tight fit and pushed onto my new hanger. When powered up though I could not get more than 2-3amps to draw through the set up which dropped to nothing and did very little. When I took it out and popped a piece of 12g wire back in and connected it the current shot back up to 15amps.
I'm obviously overlooking something simple, but I have tired myself over the subject and can't think what. If anyone has any advise it would be greatly appreciated. The power supply by the way has 12/24v, 20/80a, but I can use resistive wire to lower the current which I did succesfully in testing. The surface area of each workpiece is approx 14"sq.
I set up a small rig along with tanks for the pre-cleaning operations etc, the main anodising tank is approximately 14" square and holds in the region of 2.5 gallons of sulphuric/water mix, approximately 13% acid.
In trials it was going quite well but the aluminium hangers I used (12g aluminium wire) would dissolve over 20mins when used with a decent current of say 10amps at 24v. To get over this I made a titanium T shape hanger to hang 2 pieces on which did not dissolve of course- but I could not get a good connection between the titanium hanger and the test pieces, as soon as the power was connected and the first lot of bubbles had risen the connection would disappear, I put it down to the poor conductivity of the material as touching the hanger would make small sparks appear between it and the aluminium pieces, current would rise then disappear again.
I then made up a much thicker aluminium hanger (8mm diameter bar welded to 25x6mm flat bar in a T shape), the pieces to be annodised have 8mm holes though 3mm plate, all countersunk (so not much area in contact with hanger) but were a tight fit and pushed onto my new hanger. When powered up though I could not get more than 2-3amps to draw through the set up which dropped to nothing and did very little. When I took it out and popped a piece of 12g wire back in and connected it the current shot back up to 15amps.
I'm obviously overlooking something simple, but I have tired myself over the subject and can't think what. If anyone has any advise it would be greatly appreciated. The power supply by the way has 12/24v, 20/80a, but I can use resistive wire to lower the current which I did succesfully in testing. The surface area of each workpiece is approx 14"sq.