Seiffert G., Gibbs B.

Powders can be dislodged from surfaces by inertial or drag forces. Inertial forces are primarily generated by vibrating the coated surface. In industry, inertial forces are generated by shaking (or rapping) the coated surface, such as a collection plate of an electrostatic precipitator. Drag or viscous forces result from exposure of the powder particles to fluid flow, including sound fields. Commercially available sonic cleaning systems are presently available but are not always as efficient as rapping systems. In a series of laboratory experiments, electrostatic deposited powders were exposed to controlled vibration from which estimates of powder bonding forces were possible. The same powder coatings were exposed to low frequency sound the level and frequency of which could be adjusted until the powders were de-bonded. The relationship between the bonding forces and acoustic de-bonding forces is explored. It is demonstrated that an estimate of the required de-bonding sound pressure level is possible from knowledge of the de-bonding vibration level and a third factor, which depends on the drag characteristics of the powder particles.