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Type II Anodizing blows fuses, diodes, and thyristors

November 2, 2010

First of all I am not an anodizing expert. I am a new Maintenance Manager for a company that does aluminum extrusions and anodizing. They have for many years had problems with the rectifiers blowing fuses and burning diodes and thyristors on a regular basis. My past experience with rectifiers tells me SOMETHING IS WRONG. I have had the OEM out and went through both rectifiers, bussing..etc.....etc...they can't find any issues mechanically or electrically with these units. I have also had both the power company and an independent contractor in to datalog the incoming power for voltage spikes or any anomalies that may be affecting these units.

I am now looking at the process to see if maybe we are doing something wrong.

Below is some data on out process coating 6XXX series parts.

Rectifiers: 30 VDC @ 15,000 Amp

*Tank Sulfuric Acid and DI Water / 176 g/l
*Al: 9-12 g/l
*Solution Temp 80F ± 2F

Talking with the operators of the line they are shooting for .4 mil to .7 mil Thickness coatings on a regular basis.
*Target ASF is 24
*They run appx 30-35 min load times this includes a 1.5 minute ramp. @ 15,000 Amps constant amperage control.
*Load Sizes range but they max at about 1500 sq ft time is adjusted by sq ft. and thickness required.

Looking through the forums my first concern is
*Sulfuric is low should be around 190 g/l
*Tank Temp is too high should be around 70F
*Running to large of loads
*Running rectifier at Maximum rated amps

If anyone has any information that may be helpful or if I can provide any more info on our process that may help me resolve this issue please let me know.

Shawn Gavin
Maintenance manager - Fonda, New York, USA