RUST how do I retard it?

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Good afternoon. I work for a company in the lighting industry we make light poles out of square tubing. We have see an increase in returns from customers on rust issues and it seems to be metallic powder coating. We do a 1K hour salt spray test and everything seems to be fine. Our process is to shot blast to white metal and then off to powder coat. We do not use primer or a chemical process before powder coating. What is your suggestions to decrease the amount of rejects we are seeing.

Albert Willis
lighting mfgr. - Abingdon, VA

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Residue could be left on the surface after the shot blast or possible contamination from handling while in transport to the paint process. The shot itself could be contaminated with oils or particles. The powder would then stick to the particles or any film on the base and not to the material.

Is your test part randomly pulled from production or is it pulled from a clean first setup? The process sounds straightforward so you should try to "create" the rust issue inside your standard process by tweaking something you might not think to control.

A wash operation to remove such films may be necessary or controlling the handling or shot operation.

Mike McMillan
Plant Operations Engineer - Sanford, North Carolina