Galvanize on top of Phosphate

[swall]

My company makes large springs and the customer wants some galvanized, which they will source. They wanted a light rp on the parts and referenced a certain manufacture's product. However, they wanted us to cut the rp with xylene, which we refused to do, as we don't want the hazmat and OSHA issues. We have proposed a phos coat on the parts, which we can do in house and our thoughts were that the phosphate would be removed by the acid pickling used prior to galvanize. Anyone got thoughts on this?

 

[israelkk]

Phosphate produces hydrogen and acid removal produces hydrogen too. Therefore, you cause more risk for hydrogen embrittlement in the springs.

 

[swall]

I am not concerned about H2 embrittlement, as it is generally accepted that phosphate coated parts are self relieving after 24 hours as long as they are not loaded. Additionally, the customer has a satisfactory history of usage of hot dipped galvanized springs. In our own plant, millions of springs have gone through our phospate and powder coat process with no H2 embrittlement issues. I am mainly concerned about providing a substrate that will be conducive to galvanizing.

 

[TVP]

Acid pickling will remove phosphate coating. Acid will also remove light RP, which begs the question why can't RP be used?

 

[TomDOT]

I am puzzled here - why phosphate at all if you're going to strip it back off and galvanize?

 

[swall]

The customer wanted something for rust protection in storage and transit.The xylene diluted rp spec'd by the customer was not acceptable to us, and since we have a phospating line in house, that seemed like an easy choice.

 

[ck1999]

why not use a water based RP? This can be easily cleaned off and will provide better corrosion protection that an iron phosphate line. The chances are that the RP he wants to cut with xylene will be a lot harder to clean than a synthetic RP

Or use safety solvent (142 flash solvent) and cut the RP.

ck1999

 

[swall]

Unfortunately, sometimes your customers tie your hands insofar as what RP can be used. BTW, we did the trial with having the phosphated parts galvanized and things worked out just fine. So, we will leave it at that.