POWDER COATING DEFECTS: ORANGE PEEL OFF
Q. I want to know the defects of powder coating:
1) WHAT IS ORANGE PEEL OFF?
2) WHY IT IS SEEN IN THE FINISHED PRODUCT AFTER POST OPERATION?
3) IS THERE ANY METHOD TO AVOID IT PROACTIVELY?
4) WHAT IS THE EFFECT OF IT; WILL IT REDUCE SOME PROPERTIES?
COMMUNICATIONS - BANGALORE, KARNATAKA, INDIA
A. Orange peel is basically a surface texture of "hills and valleys" hence the term "orange peel". It is seen post-application once the powdered product has been subjected to heat and flows to form the resultant film layer. Here are a few items that can be looked at to help reduce this defect:
1. Substrate smoothness
2. Substrate temp. ramp in the oven
3. Substrate max temp.
4. Powder size distribution
5. Film thickness
- Windsor, Ontario, Canada
A. Dear Sreenivasan,
"Orange peel" effect does not mean "peeling off". It means that the powder coated surface has the texture of a 'Santare ka chilta" It's mainly caused by oven problems accurately described by Mr. Shane as above.
Bangalore, Karnataka, India
As described orange peel is in fact a surface defect. One of the most common causes for this is the quality of the powder coating you are applying, mainly the particle size distribution as described by Shane. If you are using a re-claim system you must regulate the Virgin : Reclaim ratio correctly.
The other main cause for this effect, which has not yet been mentioned, is incorrect spraying. If you have the kV on your gun too high you will be generating too much charge, this charge will not be able to dissipate, which will cause the powder particles to "Fight" against each other and cause this effect. Turn the kV down on your gun until the orange peel has gone. Alternatively you could fit a "free ion collector" to your gun which will collect the excess charge.
Hope this helps.Drew Devlin
May 16, 2013
A. I would disagree with the advice given so far.
Reverse Ionisation is a totally different effect to "orange peel".
REVERSE OR BACK IONISATION USUALLY SHOWS UP AS SURFACE CRATERS.
Orange peel is usually an unwanted "texture" effect.
Orange peel is almost certainly the result of too heavy a film build.
Normal film builds would be ~60-80 microns.
Perhaps a little heavier with Yellow/ Orange / Red powders: maybe as much as 120 microns.
Anything over this you are getting into Orange peel area.
Hope this helps.
Trainer - Salamander Bay, Australia
August 3, 2013
A. Your parts might not be getting up to temp fast enough. I had trouble with orange peel until I added another heat element. When I would open the oven to load my parts I would drop temp. My oven was not getting back up to temp fast enough bye the time I was up to temp I was past the flow stage. I added one more element and the oven heats up faster and took care of the problem.Chip Brann
- Norton, Massachusetts, USA
April 27, 2013
Q. Please explain how to fit a "free ion collector" to spray gun to collect the excess charge.Javier Barron
- Apodaca. N.L. Mex.