Views: 81 Author: Site Editor Publish Time: 2025-08-28 Origin: Site
Back ionization is a common phenomenon during powder spraying that causes coating film defects, like orange peel, pitting, craters, and honeycomb-like depressions.
Brietly, it occurs when the powder layer (already coated) on the object surface accumulates excessive negative charge, causing it to ionize itself, generating positive ions that "rebound" toward the spray gun, thus disrupting the coated film's uniformity and smoothness.
1) The powder particules are overcharged or two much powders are sprayed towards the object surface.
2) The charge accumulates, generating a very strong negative electric field at the surface of the powder layer.
3) When the electric field is strong enough to penetrate the air (approximately > 30 kV/cm), it produces microscopic lightning (corona discharge), ionizing the air to produce positive ions.
4) These newly generated positive ions will be strongly attracted by the negative high voltage of the spray gun, neutralizing the newly ejected negatively charged powder, as well, they repel the positive ions and bombard the already deposited powder film, creating small craters.
| Causes | Remedies |
| The output voltage is too high | Lower the kilovolt (kV) value of the spray gun (10-20kv). This is the most direct and effective method. Try to use the lowest voltage that can normally apply powder. |
| The coating layer is too thick. | Control the powder film thickness through finding a precise powder output value to avoid too thick powder layer, as well as reduce the spraying times. |
| Poor grounding | Check and ensure the workpiece is properly grounded. Clean the hanger, remove any old coatings, and ensure the chain and hanger are properly conductive. Poor grounding is the primary culprit for various coating problems. |
| The spray gun is too close to the objects | Keep a proper distance between the spray gun and the object (usually 15-20 cm is recommended), too close distance will result in excessive electric field strength. |
| Powder dielectric constant | Choose a powder type that flows better and dissipates charge more easily. |
Back ionization is a phenomenon caused by an imbalance in charge management (input > output) during electrostatic powder coating. It manifests as defects such as orange peel and pitting.
This problem can be effectively avoided by reducing voltage, ensuring good grounding, and controlling film thickness. COLO's professional powder coating gun has ability to solve this problem to a great extent and delivers consistent, smooth coating film.
Thanks to the world's latest digital valve controlled technology, COLO-191S allows the powder output is precisely controlled and intuitively displayed on the LCD screen, which help you easily find the appropriate powder output parameters for an optimal film thickness, prevents excessive spraying causing back-ionization or lacking powders causing revealing
The COLO-191S is also flexible to adjust the voltage and current by digital. All your parameters can be saved into a specific program and recalled next time. This is an excellent tool to improve the powder coating quality and efficiency, and let you to be an outstanding powder coater.
