Vinyl covered 304 SS sheets and Clear powder coat issues

[DWilliamA]

304 SS sheets, vinyl covered, #4 brushed, vinyl is stripped parts wiped with MEK type cleaners, run through typical powder coat wash cycle. They come of the wash cycle with streaks and drip marks (scum, light whitish) that bake on if allowed to run through heat dry cycle. Next we want a clear powder coat

Thinking the seal coat stage of the wash cycle is doing this... and wouldn't normally matter except we want clear. Or maybe we have an issue with a glue residue left over from the vinyl that gets smeared around with MEK, or its the MEK residue ?....... If this were simply the seal coat residue - why wouldn't several powder coat companies and representatives from Cardinal not know this?

Thinking of skipping the wash cycle altogether if adhesion test works....

another interesting factoid... we stripped some parts that had been poweder coated and the scum still shows, but it is not streaked it is nice and evenly sheened.. but not perfect, not good enough.

any thoughts?

 

[btrueblood]

Ick. Sure looks like the rinse is contaminated in your cleaning process...but I have no real idea what that stuff is. Can you get it analysed by a lab?

The protective sheets on sheet metal aren't pvc...I thought. But whatever the plastic is, likely there is a mold release (could be silicone, or a stearate soap?) applied to ensure it peels away "cleanly". You'll want a solvent rinse and strong alkaline cleaner, and clean water rinse to get rid of it. Possibly with a water-break test, or uv inspection to make sure it's really gone before further processing.

 

[tnatale]

Looking at the picture, it is clearly an issue with your pretreatment. You can clearly see the drip pattern on the surface of the part.

A "typical" powder coat process means may things to many people. Are you using an alkaline cleaner or neutral?, Iron phospahte? Sealer?

Talk to your pretreat supplier, he should be able to tell you what you have to do to correct the problem.

 

[ornerynorsk]

Your vinyl covering that you speak of, is this the blue protective masking found on new polished sheetstock? Have you, in fact, verified that there is a residue that must be removed with MEK? I'd be curious to try if you could forego the entire "prep" phase altogether and go from stripping the mask directly to shooting the clearcoat.


It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[DWilliamA]

Resolved...

The consensus is that SS parts in the polished or smooth grained conditioned (shiny and bright vinyl covered #2 for example) that get covered by clear powder have no business at all running through any powder coat pre wash process.... period. If they did they would have to be wiped clean between the wash and the bake, hard to do on a conveyor line. The consensus is to skip the pre wash and wipe the parts with a cleaner by hand... i.e., MEK or a citrus based solvent, or Ditzler DX 330, and then bake. We ran samples and tested for adhesion and all was good, now the problem is dust/debri control. Our new powder coater (read between the lines) has problems controlling the debri.... it never ends.