Powder coatings can be applied in an efficient manner that minimizes wasted material. They provide a robust protective covering, even when exposed to harsh environments. They also are looked upon as being environmentally friendly because they contain no volatile organic compounds and powder overspray can be recycled for reapplication.
Powder coatings have proven their worth over the past three decades. In many instances, fabricators are either applying the powder to metal parts and assemblies themselves or relying on nearby custom coaters to do the job.
Regardless of whether powder coating is a core competency, it is challenging to keep up with the latest developments in powder coating application and recovery technology.
For those interested in new technology, it is no surprise to learn that advancements in application control and color changeover now result in less powder usage, minimized downtime, reduced labor costs, and better quality (see Figure 1) when compared to older, more traditional powder coating technology.
Applying the Powder
The act of sending electrostatically charged powder particles toward a grounded metal part hasn’t changed much over the years. The powder material still passes through an energy field emitted by the spray gun and receives an
electrostatic charge all while being projected toward the grounded object, typically hung on a rack. Using the electrostatic charge, the powder clings to the metal part until it is cured at the required temperature in an oven where it is transformed into the desired tough and durable coating.
Good transfer efficiency still relies heavily on factors outside of the gun. Parts need to be hung in a stable and repeatable way so that the powder coating technician can apply the material in a consistent manner. The racks have to be cleaned of previously cured powder coating overspray to ensure a solid ground. The powder coating technician also has to maintain appropriate gun-to-part distances based on the parts to be sprayed.
What has changed over the years is charge control technology that helps to provide better material coverage, even with challenging powder chemistries (see Figure 2). More specifically, these are the metallic and special-effect powders that are harder to apply and control with older spray application technology.
New technology that allows the technician to fine-tune current settings below 10 microamperes better directs the highly chargeable powders, such as the metallics; makes them easier to apply; and eliminates rejects caused by application errors. These precise adjustments avoid overcharging of the powder, which often reveals itself as “orange peel,” an unwanted textured and inconsistent film thickness on the part.