and 6 this mesh helps to break up aggregations of fiber and prohibits oversized pieces from passing through the walls of the drum drum 18 rides on four grooved caster wheels which hold two chine rings 37 welded to the outer surface of drum 18 an enlarged portion of drum 18 is shown in fig4 in cross section it can be seen that drum 18 has a perforated shell 38 to which a layer of expanded metal 39 is welded or otherwise affixed while an expanded metal mesh is believed to be the preferable material other types of mesh or screen could be used as long as the openings are in the general range of one fourth to one half inch across a plurality of baffles or worm bars are shown in phantom lines and indicated by reference character 19 these are welded or otherwise affixed to the interior surface of the drum and tend to work the oversized waste material toward the exit end 20 of drum 18 these spiral worm bars 19 are preferably about three to four inches in height and about 1 2 inch in thickness the exit of drum 18 preferably has a spout 21 to assist in preventing desirable pulp from passing out of.