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. 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.
Managing the Powder
Wrestling with huge containers of powder is no fun, and if an operation includes color changes, the headaches are just multiplied. That’s why you see plenty of powder coating facilities attempting to manage one or more powder coating booths that may use multiple recovery and spray-to-waste modules for color change flexibility.
That doesn’t have to be the case nowadays as powder management systems built for color change are designed to minimize the amount of powder used in the coating process and simplify color changeover. For many companies, color changes are a bottleneck and reduce production efficiency.
The advanced color change technology available today allows for cleaning and color changeover to take place in minutes, as it opens up production flexibility that was once not available.
These color management systems have pumps that are mounted as close as possible to the hopper, with some pumps sitting on top of the hopper. This allows for short suction tubes and a better efficiency in transporting the powder to the gun. These systems are no longer a spaghetti diagram of extended tubes and cords.
They also reduce the amount of powder in the process, which improves operation efficiency, reduces powder consumption, and shortens the color change process.
Today’s plastic booth designs, with integrated compressed air cleaning, keeps powder overspray off of the walls and floor. These booths work in concert with the powder management systems to more effectively manage the collection of oversprayed powder and immediately recycle and reuse the powder.
Fresh powder material is also easily introduced and mixed with the recycled powder, maximizing material usage and simplifying cleaning and color changeover.
Much of the cleaning for these advanced systems today is automated. User-friendly controls also guide the powder coating technician through the steps.
Different Type of Powder Coating Setup
So what does all of this mean? Today’s powder coating operation is going to look very different from one set up 10 to 20 years ago.
These modern systems aren’t set up to blast powder; material management, delivery, and application are highly controlled, which means the powder is in good condition prior to application and has a higher transfer efficiency during the application process.
Recovery is improved because of the booth design, and because overspray is reduced, the technician doesn’t have to worry about cleaning up large amounts of it.
Color change is quick and easy. Internal parts of the powder coating system are automatically cleaned. All of this means a much cleaner working environment for those involved in powder coating.
Also, if a metal fabricator or an OEM is looking to apply more than one color, they will find that it is possible to do it with one booth, not multiple lines. This results in a much more compact footprint (see Figure 3) when compared to powder coating lines of the past.
Powder coating remains a smart choice for a final finish. Powder coating technology has gotten smarter to make management of the process easier.