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"Powder Not Electrostatically Sticking to Substrate"

December 16, 2017

Q. Hi all,
I have a Gema OptiFlex machine that has done little work, we now have a problem where the powder does not seem to have any electrically static charge. When spraying, the powder won't stick to the substrate & falls straight off.
We did a run of same parts 1 day ago and all was okay as every other time. We did have heavy rain the next day and then lost mains power for a few hours; besides that no change in PT chemicals, substrate, hanging system, powder etc. -- all same as previous runs.
I have checked grounding (even made direct grounding wire to substrate) & direct earth to eliminate possible grounding issues.
The Gema machine has error coding system and no errors are showing at all. The machine & gun seem to be working fine.
I'm at a loss what the issue could be. I'm the only half-serious powder coater in the country and will have to fly a technician in if I can't find the problem; and of course need to get these parts finished.
Any suggestions in fault finding would be greatly appreciated.


Trevor Huf
- Phnom Penh, Cambodia

simultaneous December 18, 2017

Update: Just an update on OptiFlex gun issues, I have now found that the gun is not allowing any current (Kv is ok) & therefore not charging the powder; if I hold the gun really close to the parts 2" (50 mm) the current or amps start to increase and the powder starts to charge. I then need to drop the powder and air output to stop the air blowing the powder off the parts.
Not the solution, but makes it almost usable and it helps to identify the cause. Might help anyone else having this problem in the future and curious to know if others have ever experienced this problem & what was the cause?

Trevor Huf [returning]
- Phnom Penh, Cambodia

December 18, 2017

A. If you are satisfied that your earthing is OK then you are left with only two possibilities:
Gun fault
Powder fault
You mention heavy rain, is it possible that your powder was left uncovered and exposed to very high humidity?
Noting that powder is hygroscopic,
Try another box and at least you can eliminate that possibility which would leave either a solution or narrowing it down to gun fault.
Hope this helps.

William Doherty
trainer. - salamander bay, nsw, australia

December 2017

thumbs up sign Glad to hear that you are at least making progress, cousin Trevor :-)
Thanks Bill.


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

December 18, 2017

! Hi Bill,

I think you nailed it with the moisture in the powder. I spent a good part of the weekend playing around with it with little progress but never changed the powder. Today (Mon) we changed the powder as advised and it's almost back to normal on factory pre-settings. Scenario went like this...

Thursday -- Start painting no problems, midday heavy rain & finished the day trouble free. (Thurs. powder stayed in pot.)
Friday -- Problems started with remaining powder from Thurs.
Sat. & Sun. -- Slight improvement still using Thurs. powder.
Monday -- New powder, and almost back to normal; it starts off drawing 1-2 Amps and within a few min. returns to normal.

I will have my 1st good sleep tonight :)

I would be interested in the theory behind this for better understanding. As water or moisture is conductive do you have any reason as to why it drops the current/Amps & charging the powder?

Ted - Your forum is a great idea, thanks for allowing me to be a part of it. I think its obvious now my experience is not enough to start giving advise to others yet I hope others can learn from this. Maybe the subject heading should be changed to better describe the problem & cause? Thanks again. Trevor

Trevor Huf
- Phnom Penh, Cambodia

December 2017

thumbs up sign Hi again. Happy to hear of your success! Thanks for the kinds words, and yes I've changed the title.


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

December 19, 2017

A. Hi Trevor,
Glad to hear of your success.
I do not have a thorough scientific explanation.
My advice was based on experience.
I theorize that the moisture creates a ground thus dissipating charge of the powder. I stress my theory only.
I hope that you have also addressed other opportunities for moisture to adversely affect the electrostatic process. For example your air supply line to both fluidising hopper and gun (propellant air) must, of course, be fed through a well maintained refrigerant dryer system to avoid problems.
Best Regards,

William Doherty
trainer - salamander bay

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