Problems & Solutions in Powder Coating of Steel Tubing

A. The only time I have experienced this on my line was when the maintenance crew cranked up the Lube Con and oil overflowed out of my inverse monorail conveyor. Otherwise, if it happens exclusively at the weld there is most definitely a breach of cutting/milling oils penetrating the weld and pooling inside of the "tubular" cavities of the finished part. It may not be visible with incoming inspection, but dry off and cure oven temperatures may reduce the viscosity of these oils allowing them to flow all over the painted surface and staining the cured film. I would recommend investigating inside the cavity where it looks like the "runs" originated and see if there is a glob of oil or a defined outline of a pool of oil near the source of the defect. If this is the problem, hire a new welder.

A. It's not a pinhole, it's a fisheye. Fisheyes are caused by a contaminate on the substrate. Usually a drop of oil from somewhere in the system. The cause is very hard to find for someone that is searching for it in the facility let alone a third party that is just guessing. Good luck with it.

A. Something strange here.
Powdercoating isn't likely to develop a crack like that on its own.
I winder if this is the seam weld opening (perhaps not fully welded). You did say cold drawn tube, so presumably ERWelded tubing. Sometimes can have seam weld faults?

There appears to be another issue too. In the images there seem to be streaks of lighter colour. That doesn't look right either.
Thin coats sometimes have defects showing through, where thinness causes lack of opacity, but not typically in long narrow lines like that.

Sorry that hasn't been very helpful!

Hi Geoff. I had bigger and higher resolution photos, and I think the streaks of lighter color are just reflections. I believe Eduardo's complaint is those long splits in the paint. You may be right about the tubing; thanks.

Regards,

A. Eduardo

Thanks for clarification about the reflections. I could see that some lines were that, but some I wondered about.

One way to tell if this is the weld seam is to look at the inside of the tube. (if you can).At the seam you will see a raised line, perhaps as much as the wall thickness of the tube. If that runs along the same line as the "crack", then for sure this is faulty seam weld.
If the crack is not truly parallel to the tube (if it spirals at all), then maybe not seam weld.

There's a distant possibility of a slag inclusion in the sheet the pipe was made from. Slag inclusions get rolled into elongated faults, which sometimes are not so visible until some other treatment, then they're obvious.

Thanks Geoff, I probably will take it to the painters this week and they will make some investigation on it.

Unfortunately it is in the top tube of a bicycle frame so it is impossible to explore inside (ends closed).

Will let you guys know how it develops...

Regards!

A. I totally agree with Geoff on this fault.
I doubt whether the Coater will add to the solution.
Faulty tube is back to the Tubemaker.
Is it imported Tube?
Does it comply with First World Standards?
These are questions for the Tube Supplier.
Bill

Hello Guys, today I took the frame to the painter's and after removing some paint we found the "crack" on the tube.
Pictures:



We will probably have to build a new frame or replace the faulty tube.

Thanks for all the help and let me know in the case I can help anybody with the experience.

-Eduardo

A. Does your powdercoater do any tests on the coating (or on sample panels) after each coating? If not how do they know they have done it properly.

It seems likely that the concrete before coating makes the material react differently to heat for curing the powder. It will take longer to cure the powder with this "heat sink" inside the tube.

You mention pretreatment. 7 tank process sounds good, but it depends what's in those tanks? On such steel is this iron phosphate?
For the powder to "peel off" either it's not cured, or not adhered. Curing is a temperature issue. Adhesion is a pretreatment issue.
Have you tried one without concrete to see if that's different?

A. Totally agree with Geoff on this one.
How can you possibly expect such a heat sink to achieve a cure?
I can imagine it would take hours to reach an acceptable cure and unless the temperature was moderated possibly even an overbake surface temperature would be achieved.
This is definitely an amateur attempt to achieve an impossible objective.
Regards,
Bill

? Hi Shriram. People would like to help, but how can anyone know where to begin? Please start with a careful description of what "woos out" means, some photos of defective parts, and a brief summary of your process. Thanks.

Luck & Regards,

A. Shriram,
Agree with Ted's response.

On this site there's people who would like to help, and who quite possibly can help, but we're engineers, coaters, and manufacturers. We're not mind readers, or prophets!

All we know about your situation is what you tell us, and nothing more.

If you ask a question that doesn't help us to answer; doesn't give the background, then all we can answer is that "You're doing it wrong".