Causes of Back Ionisation
Back Ionisation occurs when the substrate has reached the saturation point at which no additional powder can be deposited. During the spraying process, negatively charged powder particles build up on the workpiece until the work has reached saturation. After this point, the coating layer will repel further particles. Additionally, election streams will discharge from the surface, disrupting the coating film and creating voids and craters.
Indications that the saturation point has been reached include:
- sprayed powder not being deposited and falling off the work;
- swirl patterns
- powder being attracted to other objects rather than the work.