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topic 1438

Central electrode in anodizing bath


We anodize aluminium extrusions in a sulphuric acid bath. We are planning to add a central cathode to our bath so that we can anodize 2 loads simultaneously. Is this a good idea? Will this work for our electrocolouring tank too?


Sanjay A. Bulchandani
- Bombay, India


Should work OK with a central cathode. Be sure your rectifier can handle the load. You probably should anodize the loads at the same time and be sure the surface area of the two racks are about the same or you could get coating thickness differences. Remember it's an electrical circuit and the electricity will take the easiest path.

Lee Branch
Richmond, Virginia


As Lee has pointed out, this should be OK. However you will be halfing the current density and this may cause a very different anodic film to be deposited. This may or may not be acceptable, but for sure the parameters for colour anodising after will alter. I think you need to experiment.

Personally, I added centre cathodes not to increase the load, but to give a more even film to improve colouring afterwards.

Good Luck!

Ian Peart
- building systems


Yes, you can use central electrode in both anodizing and electrocoloring tanks. Take care in racking of extrusions, if any loose contacts, you get uneven film thickness and difference in color shades.

Timur Ulucak
aluminum extrusions & finishing - Istanbul, Turkey

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