molten lead quench residue?

[vipereyes]

We recently received some Oil Tempered Chrome Silicon spring wire that appeared to have some surface contamination. Our vendor stated that all wire goes through a molten lead quench and that it must be lead that was not burnt off in the subsequent burn off operation.
We had an outside lab analyze the coating/contamination on that wire and others that appeared clean (using a wipe test method) and was amazed at the amount of lead on the surface of all the wires we tested, but especially the wire with visible contamination. For instance, we wiped an area clean that was approximately 12” by 20” (240 sq inches) and the analysis showed it contained 2.6 grams of lead. Doesn’t that seem like a lot of lead for such a small area? Even the “clean” wires contained an average of .75 grams of lead.
We are following up with more testing to make sure that we are RoHS/ELV compliant but I am curious if anyone else has come across this situation.

Thanks,

Kim

 

[TVP]

We use OT Cr-Si wire for a number of different springs, and I have never seen any Pb residue/contamination. High quality OT wire has a thin, but well-developed black oxide layer that acts as a pseudo-lubricant during the cold coiling process. The oxide layer is brittle and spalls off during coiling. Almost always, springs using this type of wire are subsequently stress relieved, which discolors the spring. Our springs get shot peened and heat treated again (low temperature strain aging process, sometimes called stress relieving or tempering), which turns them a gold, bronze, or copperish color.

 

[swall]

I've seen lead from time to time on rectangular oil tempered wire. When it is at such a level as to be readily spotted with visual examination only, the wire gets rejected. Even if the lead does not affect fit,form or function of the finished parts, our customers have requirements concerning lead on the surface.