by the delivery rolls 5 from the feed chute 4 and deposited on the feed tray 5a to uniformly densify and to maintain constant the fiber quantities the blower 8 generates a compressing air stream b which is directed downwardly into the feed chute 4 the blower 8 draws air from a suction channel 9 whose lower end communicates the air outlet openings 6 provided in the feed chute 4 and drives compressed air down through the duct 7 through the fiber column in the feed chute 4 and out of the air outlet openings 6 as indicated by the arrows c the opening roll 3 is surrounded by a housing 10 formed of two arcuate wall portions 10a and 10b while the feed roll 2 is surrounded by a wall 11 as shown in fig2 the wall 11 as well as the wall portions 10a 10b conform to the curvature of the feed roll 2a and the opening roll 3 respectively the housing portions 10a and 10b are separated from one another by a clearance 12b which forms the upper intake end of the feed chute 4 and through which thus the fiber material is advanced into the feed chute 4 by the opening roll 3 the densifying air.