RE: ATM anodizing problem

["Heapy, Chris G" <Chris.Heapy@astrazeneca.com>]

If not controlled, then the total current is dependent on a number of
factors:-  the surface area of the workpiece, the conductivity of the
electrolyte (large number of variables here - most significant being acid
concentration and temperature).  Your power supply does not need to be
regulated or filtered (I use a large battery charger rated at 20Amp
continuous), nor does it need to be 12V. However, if you increase the
current substantially then you need to actively control the temperature of
the bath - difficult without a good cooling circuit. In addition, high
current causes vigorous gassing from the workpiece, sufficient to cause
etching of corners and removal of the oxidised surface - the very thing you
are trying to produce. It's best to stay in the ballpark of around 12V with
a current of 1Amp per 3sq" surface area, unless you want to experiment of
course but then you risk damaging your machined part. 

Chris

> Thanks to the responses.
> 
> I follow the sugestion and throughly checked all the setup.
> 
> The "12V 5A regulated power supply" I was using (I borrowed it from a
> friend) happened to be defective in several ways. It seems that it was
> incorrectly repaired by somebody, but it had the following problems.
> 
> - Inverted polarity. Terminal marked + was - and viceversa
> - It was not 12 V but 9
> - It´s unregulated
> - it was unfiltered
> - 6V AC at the output.
> 
> 
> I somewath fixed it using a diode at the output and succesffully anodyze
> and
> dye a small pice of aluminium.
> 
> 
> I still have one question, How can I have more current in the anodizing
> setup without increasing voltaje?, is current a function of anode area and
> electrolite concentration?
> 
> Thanks very much
> 
> Adrian
> 
> 
>