The Client
A multinational automotive company.
The Challenge
To be able to coat large truck bodies that required a very large booth. The problem the team faced was how to manage the enormous air volume needed for safety and containment air, how to handle this large volume of air loaded with recovered powder, and how to be able to separate the powder from the large air volume so that it could be reused.
The Solution
We often hear the phrase “mind over matter,” but even though it happens every day, it is rare to read stories about minds innovatively manipulating matter with known technology to achieve a specific goal. What follows is an old story of accomplishment that is little known even in the powder coatings industry.
Two of the largest powder systems in the world were designed and installed in the United States. One booth, for primer coat application, measures approximately 164 FT (50 Meters) and the other was built for future use of top coating or top clear coat. This second booth measures 186 FT (56.7 Meters). The true innovation involves managing volume of air, powder collection, powder recovery, and in the automatic return, recovery of powder for re-use in the primer booth.
In the mid 1970s the design team was assigned this task. The problem the team faced was how to manage the enormous air volume that loaded with recovered powder. After several late night sessions, the team came up with a very simple solution. They decided to combine two technologies to collect and recover powder: the twin air belt system and the cartridge filter recovery system. The team then created the system to coat trucks.
The booth was two levels high. The upper level coated the trucks with both automatic and manual powder electrostatic guns; the lower floor constituted the combined recovery system. For those who may not be familiar with the Twin-Air System, better known initially as the “Flying Carpet,” it was unique in the fact that it used two separate air systems. One air system represented the high-volume, low-pressure air, referred to as safety and/or containment air, which is the air that keeps the powder concentration in the booth at a safe level and maintains air flow at all openings at a minimum of 125 FPM. The second air system was the low-volume high static pressure air that is used to recover the powder and bring it back for re-use.
The separation of the two air systems gave the twin-air belt system a tremendous advantage. The high volume safety air went through the filter belt at low velocity and low static pressure where powder was removed from the air by the filter belt. The very low static pressure allowed the powder to just rest on top of the belt while the belt was constantly moving. The belt carried the collected powder out of the booth to a point where it could be collected by the recovery air at high vacuum. This was accomplished by placing a pick-up head mounted on the belt at a location outside the proximity of the booth and the high volume airflow. That vacuum pick up head required only 140 CFM at a high static pressure to remove the powder from the belt. The vacuum head was connected to what was known as a “Mini-Cyclone”, in case of multi-color systems, or “Cycart” for minimal color change.
The Cycart again combined two known technologies to accomplish the job. The Cycart was a combination of a cyclone with a cartridge filter imbedded in the center of the cyclone so that the Cycart was nearly 100 % efficient. Since the vacuum head required only 140 CFM, it needed only a small filter to accomplish the recovery. The majority of the powder was removed from the recovery air by the cyclonic action. Any powder remaining in the air was collected by the cartridge filter. The Cycart was connected to an after (Hepa) filter, which allowed air to return to the room.
Since the booth was so large, the initial problem the design team encountered was the amount of safety and/or containment air needed. Such a significant volume of air would have required a prohibitive number of belts in the lower part of the booth. Another advantage of the Twin-Air system was the slow moving air that flowed through the belt. The air was evenly balanced over the surface of the belt and was restricted to about 40 FPM at a low static pressure. It was extremely important that the powder not be forced through the belt, but rather just rest on top of the belt and be carried out to be recovered by the vacuum head.
This requirement initiated the idea of combining the two filtering systems. Cartridge filters were installed in the side walls of the lower section. The large volume safety air was then divided by being directed to the side wall cartridge filters and the moving belt. The side wall filters were designed so that the suction was done in the base of the mini module. In so doing, the design team was able to slow down the air velocity of the air proceeding to the belt filter. Due to gravity and airflow direction into the side cartridge modules, the remaining air carried the majority of the powder to be deposited on the moving belt.
Benefit to Client
The most significant benefit was the new design’s ability to reduce the number of twin air belts in each booth. As a result of the combined systems design, the primer booth required only 21 twin air belt systems and the top coating booth utilized only 24. Many other features were designed into the system as well, including for example a quick change of the filter belt if needed and a constant pulsation of the cartridge filters in order to keep them clean. The pulsed powder automatically fell on the recovery belt below so that it could be recovered.
Conclusion
All of this was accomplished by a very small team of dedicated engineers who were driven to create a “better mouse trap.” The management of the team responsible for the design and installation of the systems now manages Modean Industries, Inc., a company which is still innovating and installing powder systems worldwide.
