When used as the moving support for the present invention, e.g., as mounted on the drum 2', by means of radial support members 24 fastened to the rim 3', the grid or lattice supporting surface can be formed by rods or tubing 25 and 26 composed of wood, rubber or other suitable material, including non-adherent plastic or ceramic elements, arranged on a drum 2' as shown in FIG. 7a, or as a screen be