Posted by Kevin McArdle (86.40.211.70) on March 25, 2009 at 12:20:18:
I am currently working on a project to set up my own anodizing line. I am anodizing cylindrical aluminium tubes, 80mm in length and 10 mm outer diameter. I have a problem when I anodize the parts. The anodizing process is removing material from the aluminum tubes instead of building up an oxide layer. I was wondering what the solution would be to this problem.
The electrolyte I use is 20% sulphuric acid and I use a current of 4.5 amps and 15 volts. Before anodizing I etch the parts in 20% sodium hydroxide and then desmut in phosphoric acid. I have aluminium cathodes and I hang the parts on aluminium welding wire. Also the anodizing tank I use is 100mm x 200mm x 100mm (LxWxH) and i space the cathode/anode as far away as possible.
All the chemicals I use came from a chemistry lab in my college so they should not contain any impurities.
Also my parts dont seem to take the dye I am using. After i seal, and the part has dried the dye has just stuck to the outer surface of the part and falls off when rubbed. If anyone can help it would be much appreciated, thanks, Kevin.