Patent ID: 7461591

Claim:
A screw press ( 1 ) suitable for pressing fibrous material, in particular sugar beet pulp, comprising: a pair of adjacent counter-rotating first and second shafts ( 20 , 30 ) having their axes (X-X, X′-X′), disposed parallel to each other, said shafts ( 20 , 30 ) each being provided externally with a box-like helical structure ( 21 , 31 ), each of said helical structures ( 21 , 31 ) winding in an opposite direction with respect to the helical structure of the other shaft; a perforated walled filtering cage ( 4 ) enclosing said helical structures ( 21 , 31 ) as an exact fit; a loading hopper ( 10 ) for feeding the fibrous material to the press ( 1 ); a discharge aperture ( 11 ) for the exit of the pressed material; a collection sump ( 12 ) positioned externally to said filtering cage ( 4 ) to collect the liquid component of the pressed fibrous material, wherein each of said box-like helical structures ( 21 , 31 ) comprises a helix ( 22 , 32 ), each of said helixes having a pitch (P) and a helical element ( 23 , 33 ), said helical element ( 23 , 33 ) forming a collection interspace ( 27 , 37 ) in cooperation with the outer surface of the shaft ( 20 , 30 ) and comprising at least one perforated surface ( 24 , 34 ), said perforated surface ( 24 , 34 ) having a length (L) along the axis (X-X, X′-X′) of the shaft ( 20 , 30 ) which at every point is less than the pitch (P) of the helix ( 22 , 32 ) creating an open channel abutting the helix ( 22 , 32 ) of the first shaft, wherein the helix ( 32 , 22 ) of the adjacent second shaft ( 30 , 20 ) is received in the open channel.