Powder coating can deliver many advantages including more-efficient operations, waste reduction, and the absence of solvents and the associated volatile organic compounds (VOCs). This makes it an environmentally sound and financially attractive alternative to traditional liquid finishing, and many manufacturers are therefore considering powder coating for a wide range of applications. However, in order to optimize coating operations and enhance product quality, it is critical to understand how a powder will behave in transit, during storage and ultimately in the final process. Powders are complex assemblies of solids, liquids and gases, and the way they can behave certainly provides their industrial value, but it also makes it challenging to characterize them and predict how they will perform. There are many traditional methods for testing powders, but the limitations to these methods are quickly becoming recognized as applications become more demanding and the need to test powders under process-relevant conditions is acknowledged as being crucial.
In spray coating, a fine powder is drawn from a storage chamber before being fluidized and ejected through a charged nozzle onto a substrate. It is essential that the powder is effectively and consistently fluidized without the formation of agglomerates that may block the nozzle and affect the charging of individual particles. This ultimately leads to poor adhesion or the formation of agglomerates on the surface of the substrate. Uniform flow from the storage chamber is also important, as any evidence of erratic flow will affect the fluidization process and result in a poorly distributed product.