Considering Conversion Coating

[Martensyte]

Hello Group,

My company builds a line of weatherproof enclosures made from pickled & oiled hot-rolled mild steel sheet which we currently coat by solvent wash, 3 mil industrial epoxy, and 3 mil urethane top coat after final assembly.

The enclosures are assembled from pre-manufactured parts which are welded together; primarily by plug welds and a few fillet welds (all by MIG).

I'd like to look into the feasibility of phosphating the parts prior to assembly. What I would hope to accomplish by
this is to reduce finishing costs by eliminating the solvent wash process (which is completely manual), and switching from the high-build epoxy/urethane coatings to perhaps a single coating.

What I'm curious about is:

(1) assuming an iron phosphate system, how would a conversion coating affect the welding process?

(2) What would be the effect of welding on the coating? My concern would be areas on the outside of the enclosure where welding is done on the other side (inside) of the sheet. The inside is not as important.

Thanks,

David G.

 

[unclesyd]

I have not seen Phosphate Coatings interfere with welding.

The problem is that the weld area will not have the phosphate coating and will cause adherence problems with some coatings.