The needs of the application — what is to be painted in the booth — determines everything about the booth system. Objects from small to gigantic are painted in spray booths. Coatings are applied by humans and robots alike. Perhaps the application is refinishing and the object is a car or other vehicle. Or maybe a complicated coating is applied, under the most stringent temperature, humidity and airflow requirements, to super-secret jet fighters. Or perhaps parts travel on a conveyor system and pass through the booth system to be sprayed.
Regardless of the application, careful matching of the system and equipment to the needs of the coating operation is critical to the successful performance of the finishers and the spray finishing equipment.
Selecting the booth and sizing it for an application takes review of several areas. Knowledge about the facility and production process is important in choosing the right equipment. It is important to take time to understand the application and any future plans that may influence the choice of spray booth design. The following are some general guidelines for selection and sizing.
All booths require regular maintenance for optimum performance. As a first step, evaluate the capability of the maintenance department or maintenance contractor. This will influence the sophistication level of the equipment required.
Balancing the application requirements and available funds will help identify the most effective exhaust chamber, air flow and booth options for the job.
3. Selecting the Booth Design
The first step in selecting an appropriate booth design for an application begins with an investigation of the production requirements, which helps determine the direction of air flow through the booth, as well as the appropriate filtration method, either dry filter or water wash.
The spray booth is an investment that pays many dividends by providing a cleaner painting environment for a better quality finish, a means of increasing productivity, and a superior working environment for the finisher.
Production Requirements & Configuration
The size and style of vehicle/part, the carrier that conveys it into/through the booth, and the relationship of the spray gun to the vehicle/part, all play a role in determining the direction of airflow as well as the velocity or speed of air through the booth. Airflow and velocity are needed to transport paint and coatings overspray into the filter assembly.
There are three types of airflow through a booth: crossdraft, semi-downdraft and downdraft
Production Rate and Transfer Efficiency
Production rate is a measure of the number of vehicles/parts that can be finished within a certain time frame, usually per hour, per shift or per day. Production rate includes the entire production process, including any time the vehicle/part spends drying or curing.
Transfer efficiency is the percentage of material being sprayed that adheres to the part; the remainder is overspray. The type of application equipment — conventional, electrostatic or HVLP (high volume low pressure) — largely determines how efficiently paint is transferred from the gun to the part. The recent development of a laser-guided sight for spray guns and the resulting precision spraying has increased transfer efficiency an additional 25-30% in some instances, proving that the technique of the spray operator also impacts transfer efficiency.
Together, production rate and transfer efficiency influence the choice of air flow.
Material Being Sprayed
The type of material being sprayed affects the choice of filtration or exhaust method to remove overspray from the booth, and determines whether or not heat or other curing means is also required to bring the finish to a final state.
A dry-filter or paint-arrestor booth traps airborne paint particles (overspray) in disposable filters. A dry filter can be used where the material usage does not exceed 2 gallons per hour with minimal overspray. This represents the majority of applications. Depending on the material being sprayed, removal efficiency ranges from 95% to 99%.
If more than one type of material is being sprayed, it’s important to ensure the compatibility of the materials. Combinations of incompatible materials in the dry filter can be a cause of spontaneous combustion.
In a water wash booth, air washing action traps the paint solids from overspray. Removal efficiency for a water-wash booth can be as high as 98-99%, depending on the type of material being sprayed.
If the coating material requires a period of heat or air movement to finish it, then heaters and other curing mechanisms will be part of the final configuration as well.
The quality of the finish on the completed part has become more critical as customers’ expectation levels have increased. The total process must now be considered in order to achieve first-time-through quality levels.
The spray booth design is a key element. Airflow, direction, filtration, air velocity and balance are critical to accomplishing the various desired quality levels. Unpressurized crossflow designs are at the low end and pressurized downdrafts are at the high end of quality potential.
But it’s important to also realize that the spray booth is only one part of the process. Many other elements of the process must be designed and controlled to achieve the desired quality level. These elements include the preparation and cleanliness of the object going into the booth, the maintenance of the booth and surrounding processes, the quality of compressed air to the tools (including spray gun), the quality of clothing and equipment the painter uses, and the quality of the paint or coating preparation activities. The finish quality can only be as good as the design and control of the process.