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Cataphoresis coat

Cataphoresis coat

Cataphoresis coat

(OP)
Good evening everyone, I'm restoring a vintage car that has some corrosion points (rust) inside the overlapping joints of the sheet metal, nothing serious but it is present. On the inside of the body I tried to lift the metal near some spot welds and I noticed that practically every spot weld has a slight ring of corrosion around the weld itself despite the fact that the cataphoresis went deep inside. Is this corrosion caused by humidity and therefore crevice corrosion or by a bad cataphoresis process? If I had to proceed with paint strip, acid bath of the entire body and subsequent cataphoresis, is there a risk that the acid remains trapped in the overlapping joints which have a very limited gap or will the final rinse reach every crevice? I'd like to do a definitive job but I'm stuck at this point
Thanks

RE: Cataphoresis coat

This patent for a cataphoresis process lays out many of the problems associated with acid phosphating of car bodies.

https://patents.google.com/patent/US4210506A/en

The acid processes must be carefully controlled to prevent contaminated. Some acid processes can't form coatings in weld seams. Some cataphoretic coatings allow the acid step to be skipped altogether.

There is no crevice corrosion for carbon steel alloys. Body seams are simply a very challenging feature to protect. Modern cares utilize seam sealers in addition to EC.

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