Powder coating is a great way to create a durable finish on many projects, but it is considerably different than traditional painting. Because electric charge is applied to the powdered paint, one unique challenge is a phenomenon called the Faraday effect. Sometimes also known as the Faraday Cage effect, this occurs when the electrostatic charge on the powder particles causes them to be attracted to and adhere more strongly to certain areas of a metal part than others, which may receive less coverage or even repel the powder particles altogether.
Overcoming the Faraday effect, however, is not impossible. There are several strategies to counteract it, and with some experience you can even predict where you might encounter challenges. And of course, the beauty of powder is you can always blow it off and start over if you don’t like the way it sprays out. But we’d rather prepare you for preventing mistakes in the first place.
Faraday Effect Explained
When a metal part being is placed in an electric field (in this case, created by the electrostatic charge of the powder particles), the charges within the metal redistribute themselves. This creates an opposing electric field within the metal, effectively canceling out the external electric field within the metal part. The electrostatic forces that would normally attract the charged powder particles to the surface are weakened in certain areas. This is the Faraday effect, often experienced in deeply recessed regions, corners, edges, or intricate geometries of the metal part.
Areas shielded by the Faraday field may receive less powder or no powder at all. This results in incomplete coverage and leaving the metal exposed. In extreme cases, the repulsion caused by the Faraday cage effect may even cause the powder particles to “bounce off” the metal surface, leaving behind bare patches.
Remediating the Effect
There are numerous ways to reduce or eliminate the Faraday effect, depending on the part. Most of this requires subtle adjustments to the application process. Identifying trouble spots at the beginning and starting your application there can avoid many headaches and wasted materials.
Fine-tuning the settings of the powder coating equipment, for instance, is usually the first step. Adjust the electrostatic charge, powder flow rate, and air pressure to help optimize powder deposition. Lowering the electrostatic charge or increasing the powder flow can enhance penetration into recessed areas.
You can also apply the powder from different angles and make multiple passes over the part can help ensure better coverage. This is particularly helpful in hard-to-reach areas shielded by the Faraday effect. Varying the direction of spraying can also help overcome obstacles posed by intricate geometries.
Preheating the metal part to at least 90º F before spraying it with powder can reduce the Faraday effect. By reducing the contrast in temperature between the metal and the powder particles, you can improve powder flow and adhesion, resulting in better coverage in recessed areas.
Masking and shielding can be used in some case. Using tape, plugs, or special shields can selectively block powder from being deposited in certain areas, redirecting powder flow to areas affected by the Faraday effect.
Finally, in some cases specialized powder coating equipment is required to overcome the Faraday effect, especially in professional applications. These include corona charging systems or automated oscillating guns. These help improve uniformity of the coating on complex geometries by delivering powder more effectively into recessed areas.
Conclusion
By implementing these strategies, even a DIY powder coater can effectively mitigate the Faraday effect. You can eventually anticipate problems before they begin, to achieve more uniform, consistent powder coating finishes on your projects. Even on the most challenging geometries or intricate surfaces.
