Since the particles in the powder coating basically have the same granularity, they all receive the same amount of lift force and can thus all be suspended in the air.

There are large differences in grain size, so the air can only suspend the finer fractions of the powder coating. It cannot suspend the coarser and thus significantly heavier fractions, which collect at the bottom of the powder container as soon as fluidized air is introduced. The coarser fractions end up being pulled into the intake tube first. Within a short time, only the finer fraction remains in the container, making it impossible to achieve the desired surface finish.

Vibration does not physically disrupt the powder coating much, so that the individual coating components separate very little. As a result, the surface finish remains consistent throughout the entire coating process. The vibration is only needed to continue feeding the powder into the intake tube.