Small workpieces to be coated with plastic material are preheated and dropped onto a fluidized bed of plastic powder subjected to compound vibratory motion which causes the powder and the workpieces to move along a helical ramp onto a screen overlying the point of entry, with some of the particles fusing onto the workpiece surfaces to form a film. The remainder of the powder, on reaching the screen, drops back onto the bed as the coated workpieces move on to a receptable. Fresh workpieces are deposited on the bed through one or more chutes traversing the screen; to prevent the rise of any particles through the chutes, a downward airflow is created therein.