Color Change Time in a Powder Booth
Color change challenge in a powder coating operation.
Color change was one of the early challenges to a powder coating operation. The needs of cleaning and changing colors for powder are different from a liquid booth because the booth interior and the reclaim system need to be considered. In a liquid paint system the spray source (pressure pot or paint line) the hose and the spray gun are the main focus. In a powder system the walls of the booth have powder on them the reclaim system may need to be cleaned or changed.
Color change time has improved a lot over time and there are many options to consider. The first issue that has to be considered is whether or not to recover the overspray powder for re-use. Using the overspray can be a significant economic advantage by reducing waste and getting the most possible value out of a kilogram of powder. However, the value of the powder that is oversprayed has to be weighed against the time and investment required to recover it for re-use. The best way to settle this question is to compare the value of the overspray to the cost associated with recovery. If the powder that is oversprayed is a small volume and the time needed to recover it is substantial then the value of recovery is diminished.
Another key factor is the type of equipment that is being used and the specific type of reclaim system. There are different features with different benefits have to be considered in the decision on whether or not recover powder for re-use.
Cyclone recovery systems use a cyclone as a separator to route the bulk of the oversprayed powder to a container for reuse or disposal. A small percentage of finer grind particles are classified out of the airstream and routed to filter module for capture and disposal.
The alternative to the cyclone system is a filter module system where the cartridge module is attached to the booth and there is no cyclone separator. It collects 100% of the oversprayed powder for re-use or disposal.
Cyclone Recovery System Diagram
In both cases the booth walls and floor have to be carefully cleaned if the powder will be recovered for re-use. If the powder overspray is not going to be re-used the walls need may not need a careful cleaning. The reclaim system will need some action for recovery also. If it is a cartridge module system the color module will have to be changed by decoupling it from the booth, moving it out of the way and moving a new color module in place.
If it is a cyclone system the receiving container will need to be cleaned or replaced for re-use of the powder. The duct and cyclone may need some cleaning operation also.
The cartridge module system is best suited for systems that run one color, make less frequent color changes, and/or have a limited number of colors. More colors mean more modules if all are to be reclaimed. Changing out modules can be comparatively time consuming. However, the module system does return a higher percent of the overspray.
A cyclone system can recover any number of colors without having dedicated color equipment. It does return a slightly lower percent of the overspray due to the removal of finer particles.
A cyclone system can be fitted for very rapid color change. The key is to understand that the entire installation has to have the right features for the fast color change. The booth itself is constructed of a non-conductive material with a sandwich wall construction. It is typically smaller than most booth cabins and the walls are smooth and sloped to the extraction point. The airflow is a downdraft style and includes blow down nozzles to move powder to the reclaim system and minimize accumulation inside the booth. The guns have several fast-color change features including automated interior purging and blow-off nozzles to clean the gun body. A feed center is used to contain the feed hopper and pumps. It has features to speed up color change and contain powder. The entire color change process is carefully designed and executed for speed and efficiency. With all of the right features and a good staff that is well trained it is possible to change colors effectively in less than 15 minutes form one recovered powder color to ranother recovered powder color. Good training and maintenance are essential to keep the system working as intended.
In a situation that is where recovery for reuse is not justified the booth and guns can be prepared for a new color in one to two minutes. The booth and reclaim system do not need a deep cleaning so the main effort is to clean the delivery path and the feed source. This spray-to-waste (STW) approach can also be facilitated for speed with the right features. Manifolds can be used to rapidly purge and switch a manual gun. Automated purge and gun cleaning can be used for automatic guns.
The decisions on color change start with data on how many color, how many color changes and the length of the run of a given color. Then the value of oversprayed powder is evaluated versus the cost of time and equipment needed for recovery. In some systems it is useful to both recovery and STW based on the value of the powder in the run. Powder equipment suppliers can help with input on the options and the best possible fit for a given production situation.