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Pitting of hot dipped Galvannealed parts during e-coating

Am experiencing a pitting problem on the underside of a spring seat on a shock absorber. Am running a PPG black cathodic e-coat. Paint Temp. is >92 degrees F, conductivity is 1150 us. pH 5.68. Parts are four to a hanger (vertical) Am only getting the pitting on the top part. The other three parts are unblemished. Top part enters the bath last and exits first, least amount of dwell time on this part. Why is this affecting only this part and not the others. The actual damper tube is CRS, and this is not being affected. Only the galvanneal component part is pitted.

Chuck Colwell
Sr. E-Coat Tech. - Sunbury, Oh, USA
February 5, 2010

Dear Mr Colwell,

It may be correct to assume that the top part is not getting enough time in your permeate rinses. You should increase the time in the permeate rinses and see if the pitting reduces; It may be worthwhile to get a solvent analysis for the E Coat bath as well.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

March 10, 2010

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