Pin holes in powder coated wire mesh... 1

[Ratheesh_n]

We are doing powder coating in wire mesh.The mesh is welded using resistance.Now after powder coating there is pinholes near in weld areas and some areas in bottom side of wire . Coating in the sheets found ok . What will be possible reasons for pinholes only in wire mesh ...?

 

[Compositepro]

One common cause of pinholes are are voids or pockets in the substrate. Air or other fluids trapped in these pockets expand during heating and will pop a hole through the coating.

 

[Ratheesh_n]

Thank you..Compositepro ,

As you said, After welding voids are created .. image attached. i think we cant do much change in our process of welding . So what precautions we should take to avoid pinholes in these welded areas

 

[IRstuff]

I don't think welds are supposed to look like that

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[Ratheesh_n]

@IRstuff . This ios pressurer resistance / spot welding .

 

[dik]

To reiterate IR:
I don't think welds are supposed to look like that. and, likely a significant cause of your poor coating. Surface profile for successful powder coating is critical.

Dik

 

[SwinnyGG]

The welds on your WWF should not have any visible extruded flash. This is a resistance welding problem, not a powdercoat problem. Have you recently changed wire sizes or pitch without studying the weld settings required?

This could be caused by any number of problems with the setup of your WWF system- too much weld current or pressure causing the extrusion, an imbalance of conductivity causing one side of the weld to soften more than the other, etc.

See below for what a properly set up WWF joint looks like.

 

[Ratheesh_n]

@jgKRI

Yss . Its looking good .

We are using 4.5 mm dia wire only .

Due to the cavities created in the weld area , it results in pinholes after powder coating.

 

[dik]

4.5mm wires don't make any difference. You have to fix your welding process before your coating system works.

Dik

 

[IRstuff]

The cavities created in the weld area is a welding problem, not a powder coating problem.

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[berkshire]

Ratheesh_n,
The splatter at your weld sites is caused by either not enough contact pressure or too much current, either one can leave small holes under the weld.
B.E.

You are judged not by what you know, but by what you can do.

 

[btrueblood]

Spatter could also be due to contaminated/rusty material.

Ratheesh, you say there are pinholes in the wire away from the welds also? Could be a defect (cold shut or lap) in the wire, poorly drawn/descaled material?