flex tendency than a continuous sheet of screen and are easier to replace when the screen does wear for a given rate of the production the collection drum is rotated faster for the collection of fine diameter fibers than for the collection of coarse fibers since finer fibers tend to block the screen holes more rapidly in an actual working embodiment of the present invention the speed of the rotation of the collection drum is set so as to maintain a collection screen loading of 2 63 grams of fibers per square foot however slower rotational speeds can be used e g 3 31 gms sq ft loading but slower rotational speed results in a high pressure drop across the fibers and collection screen which forces the fibers into and through the interstices of the screen resulting in fiber emission through the exhaust duct 33 the spiders 27 at the end of the drum 17 adjacent the exhaust duct 33 provide openings so that the interior of the collection drum 17 communicates as indicated by arrow e in fig7 via the exhaust duct 33 with a suitable large capacity exhaust or suction blower not shown the exhaust duct 33 may also be equipped with conventional dampers to control the amount of air drawn through the collection drum as shown in fig3 an approximately 80 u00b0 segment of the.