Spray Booth Material Differences

My company is considering a new system designed for quick color change. We obtained quotes from several vendors and noticed that the spray booths are made from different materials. How important is the booth material, and which is better?

To reduce color change time in modern powder coating systems, vendors evaluate multiple booth-canopy materials. Recommending one material over another is not appropriate here. A better approach is to help you understand the impact of material selection on your system's performance and to provide you with questions you can ask your vendors.

Powder attraction to the booth walls. Whether the booth is made of double-wall materials, solid plastic or composite dielectric material, the electric field will penetrate it. There is no difference in the way double-wall ("sandwich" construction) material works in the presence of the electric field compared to a solid or composite material. However, if there is a metal support structure near the outside booth wall, the electric field will concentrate on it, resulting in more intense powder deposition on the inside of the booth in that area. Make sure there are no metal hardware or support structures touching or near the booth walls.

The ease of powder release from booth walls. No matter the material, some powder will deposit on the booth walls. The color change time then will depend on how easy it is to blow that powder off. The ease with which powder is released from the booth walls is the principal difference between available booth materials. Ask your equipment vendors to conduct a demonstration in their test facilities and judge for yourself which material cleans better.

Sustainable performance. With time, any booth material will accumulate water vapor, residual charge, oils (from being touched by hands) and other contaminants on its walls and will require cleaning/conditioning to restore its original performance. Some materials require chemicals to restore their original performance; others, water or a mild soap solution. Talk to your equipment vendors about cleaning materials, and don't forget to visit systems that have been operating for some time.

Ease of damage/repair. Available booth materials vary in strength, impact and scratch resistance, and ease of repair. Ask your vendors about repair procedures if the booth material is scratched or broken. How long does it take to replace or repair panels inside the booth? What is the delivery time on replacement panels? What's the impact resistance?

Presence of seams inside the booth. Even well sealed seams, with time, can entrap powder. Thus, having fewer seams on booth surfaces is better. The number of seams will depend on the booth size and the manufacturing process used to construct booth panels.

-Sergey Guskov, Nordson Corp.

Maintain Consistent Level in Powder Hopper

Can you explain the purpose of the powder coating fluidizing hopper and how it can change the film thickness on my parts?

Fluidization in the gun hopper is the process of preparing the powder to become "fluid-like" for easy transport through the suction tube and to the gun. Powder also can be prepared by vibration, agitation (stirring the powder) or combinations of these methods.

Fluidization is the most frequently used method. To fluidize the powder, compressed air is brought into the hopper through a plenum chamber and membrane. As the air moves up through the powder, it lifts, or "fluffs," the powder.

Most users cannot take the time to adjust the hopper fluidization air setting each time the powder level changes. As the level raises and lowers, the density of the powder/air mixture in the hopper changes. As a result, the density also changes in the suction tube assembly.

This means that as the powder becomes more or less dense as the level changes, the delivery air remains constant. The result is that the powder pump is actually delivering more or less powder to the gun. Users will notice that the gun outputs vary throughout the day as the powder level in the hopper changes.

The best approach is to maintain a constant level of powder in the hopper. This minimizes the adjustments to the fluidization air and delivery air, keeping a consistent delivery of the powder to the gun and assisting the gun in applying the powder uniformly on the substrate.

-Jeff Hale, ITW Gema