Rust and Paint adhesion with new Weld Nut Supplier

[vardar3]

Our coater just informed me that they are seeing Rust and Paint adhesion with new weld nut supplier. Everything seems similar to the old supplier, and Im wondering if you could provide any insight as to why an M8 weld nut would rust and not have good paint adhesion after a 3 projection welding operation:

• 1010-Ak material. I'm not sure what the "AK" stands for???
• Weld nut gets washed and applied rust inhibitor after cold forming.
• I don't see detail if the rust inhibitor get rinsed off of the weld nut, should it???

 

[Jen Kirley]

Good day vardar3,

AK stands for the "Aluminum Kill" process that uses aluminum to deoxidize steel when forming.

I want to better understand your question. Are you using rust inhibitor and then sending the unit for paint?

Is the issue that paint does not adhere or that it does adhere?

Are the newly supplied weld nuts coated with a rust inhibitor when you receive them? If so, I would think the coating needs to be removed in order for a finish to adhere.

Are you Mig welding these fasteners? WeldingTipsandTricks.com says "MIG welding does not like dirt, rust, oil, and grease. Here is where the 3 C's come in. Clean , clean, clean."

 

[vardar3]

Thanks for you help:

Are you using rust inhibitor and then sending the unit for paint?

Our Cold Header is using 2-5% Rust inhibitor and water after their cleaning process. After that they get shipped to our shop, where they get welded in a projection welded (resistance welding) process.

Is the issue that paint does not adhere or that it does adhere?

The issue is that weld nuts are rusting after welding, before they get plated (not that long maybe a wk or 2). Also at plating, paint is not adhering to the weld nuts, paint is adhering the rest of the part. After welding, we ship to A-coating, where it goes through 5 stages of cleaning (Spray cleaning, immersion cleaning) until it gets coated, followed by tap water immersion, seal rinse and oven bake.

Are the newly supplied weld nuts coated with a rust inhibitor when you receive them?

The new parts are lightly oiled, and I'm told that they should have shelf life of about 30 days. I believe all of our uncoated rivets get lightly coated with rust preventative oil.


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[Jen Kirley]

Thanks for the clarification.

Is the base metal 1010-Ak, or the weld nut, or both? The weld nuts I know about are WN material - carbon steel, or WNS (stainless steel).

Why did you switch suppliers?

I wonder also, is your new supplier from overseas?

I also wonder what that new fastener's coating is. Have you tried experimenting with alternative methods for cleaning them, then sending through the finish process?

 

[vardar3]

Weld nut is 1010AK and the base it gets welded to is ASTM 1011 HSLA Grade 65. No we haven't experimented with different rust inhibitors, I was just wondering if anyone had experience with coating issues on welded part, and what was some of the root causes. Thanks for the help.

 

[Jen Kirley]

When I look for root causes on things like this I ask myself "What is different?"

You know you have a new supplier, so I wonder if they really sent you weld nuts made of 1010-Ak because some overseas suppliers or their suppliers substitute materials. I was also wondering if they are using something to coat those nuts that your previous supplier didn't use - a coating that isn't effectively dealt with using your current cleaning process.

Why did you switch suppliers? If it was due to price, with all of this chasing down issues I wonder if it was worth it.