What is the Best Airflow for Painting Aircraft?
There is no disputing that the most critical element of a professional finishing program is the painters themselves. Their skill, touch and precision are often the difference between an ordinary paint job and an extraordinary paint job.
Even among the world’s best painters, there is still debate: Is crossdraft or downdraft the ideal airflow pattern in a aircraft paint booth?
It is not easy designing a paint booth for an airplane — something that Global Finishing Solutions (GFS) does for military, commercial and business aircraft of all sizes. The natural shape and function of a plane causes disruptions in airflow. When trucks and buses are painted in paint booths, they possess enough volume that they significantly affect the remaining volume of the booth. However, that is not the case with airplanes.
GFS has pioneered the use of conformal aircraft paint booths. In this design, air is introduced at a higher velocity in the spraying zone than in the non-spraying areas of the paint booth. This provides excellent painting performance, while minimizing the amount of air and energy required for the process. In some cases, these designs can result in a savings of 15 to 30 percent in capital and operating costs, compared to a traditional booth design.
Let’s explore the differences between crossdraft and downdraft airflow styles for aircraft paint booths:
Crossdraft Paint Booths
Accounting for about 75 percent of GFS’ aircraft paint booths, crossdraft spray booths contain intake filtration on one end, drawing air through the booth. The exhaust filter bank on the other side of the booth has three stages of filtration, in accordance with National Emission Standards for Hazardous Air Pollutants (NESHAP) standards. All three stages may be placed in a single filter rack, while the exhaust fan is positioned on the clean air side of the filter chamber. GFS’ three-stage filtration system is highly effective at capturing high volumes of paint or dust, with up to 99.9 percent filter efficiency at five microns.
The air into the spray booth may be forced draft or natural. In natural-draft style, the supply air is drawn through filtered product doors, and replacement air is discharged into the hangar from an air make-up unit. In forced-draft style, air is supplied to the spray booth’s interior via a duct, typically from an air make-up unit. This requires a plenum — usually a door — in the front of the booth to receive the forced-draft air; the plenum is often filtered, allowing for clean supply air to the booth.
Downdraft Paint Booths
A downdraft spray booth allows air to enter the booth from the ceiling through intake filters and then flow downward over the plane and into exhaust pits in the floor. The primary exhaust pit is laid out in the same shape of the plane’s shadow. The first layer of the three-stage filtration is located just under the pit grating, and the other two stages of filtration are located in the filter house.
The pits allow the exhaust system to draw air from the floor level to a nearby filter house. From there, the air expands and moves through the other two stages of filters. Exhaust fans are located on the clean air side of the filter house, discharging the filtered air above the roof line of the facility.