Where the
world gathers for metal finishing
Q&As since 1989


-----

Powder coating is thick at sharp corners

2003

Dear Sir,

We apply electrostatic powder coating with corona charging. My main problem is that the powder becomes very thick at the sharp edges. For example the thickness of metal is 0,5 mm but after powder applied the thickness becomes about 1 mm. When I look to the edges I see a very thick layer at the edges. What can I do with this problem ?

Kenan Koyun
white goods - Eskiþehir, Turkey

---

Sharp edges here means the edge of the metal sheet (the cutting line if you like) and not the edge of a bended sheet. The phenomena you describe is a result of the concentration of electrostatic field-lines on sharp edges. It is also well known in powdercoatworld. But how to avoid it?

a: Try to apply the powder with less HV
b: Normally this is just a visual problem and not a functional. If you really must avoid it then you have to change to tribocharging

Good luck,

John Bradshaw
Saunderstown, Rhode Island
2003

---

2003

The phenomena you are describing is referred to as "picture framing." It is caused by multiple variables that can be controlled in the formulation, particle size distribution and application of the powder coat. I will try to provide some understanding at each level of the process. These are some quick recommendations, but you should demand support from your powder coat supplier to overcome this problem.

Formulation:

Smooth, High Gloss formulations (particularly Urethanes) are prone to this problem due to their long gel times and glass plate flow.

Ask for a shorter gel time and GPF in the formulation of your product.

Consult your powder manufacturer about these issues, but be willing to allow some orange peel to eliminate the edge build up.

Particle size distribution:

I would consider the following recommendation a sin in the powder coat business, but it is a fact. Ask your supplier for a "flat" or "dead" particle size distribution. A poor particle size distribution will effectively reduce the effect of superior grounding and transfer efficiency on the edge of the coated part.

Application:

Reduce your KV. Similar to what Mr. Bosklopper said in the previous response, the edges of the coated part have dynamic electrostatic fields due to ground transfer. The edges attract better, so you need to "govern" or reduce the overall application efficiency of your powder coating.

Andy Peal
Automotive Components - Grand Rapids, Michigan, USA

---

2004

Dear Sir,

With ref to the message of Mr. Koyun, What seems to be problem of Mr. Koyun, might be a solution to mine.

We would like to coat the sharp edges of our material that we cut with application of less, if possible, with no edge grinding at all. However, we would like to avoid heat curing. Would a liquid based electrostatic coating be helpful or would you be able to suggest some other application.

Thank you in advance.

Murat Mengenecioglu
shipbuilding - Istanbul, Turkey