Patent ID: 7476096

Claim:
A screw extruder comprising an extruder body ( 4 ) with a bore ( 4 H), and a screw ( 5 ) rotatably disposed in the bore ( 4 H), the screw ( 5 ) comprising a screw shaft ( 7 ), and two screw flights ( 8 and 9 ) disposed in the form of a double helix, wherein one of said two screw flights ( 9 ) forms a main passage (G) between the helical portions of the one screw flight ( 9 ), the main passage (G) extending helically around the screw shaft ( 7 ), the other of said two screw flights ( 8 ) is provided with large interruptions ( 11 ), whereby the other screw flight ( 8 ) is divided by the interruptions ( 11 ) and screw flight pieces ( 12 ) are formed between the interruptions ( 11 ), when the helical main passage (G) is unrolled into a straight form, the one screw flight ( 9 ) extends in a straight line, and the screw flight pieces ( 12 ) of the other screw flight ( 8 ) are arranged in a straight line, within each of the interruptions ( 11 ), two additional flight pieces ( 13 A and 13 B) which are substantially parallel with each other are disposed, and each of the two additional flight pieces ( 13 A and 13 B) is spaced apart from each of the two adjacent screw flight pieces ( 12 ) by a positive distance (WJ 1 , WJ 2 , WJ 3 , WJ 4 ) in the longitudinal direction of the main passage (G), wherein the distance (WJ 1 ) between one additional flight piece ( 13 A) and one of the two adjacent flight pieces ( 12 ) is smaller than the distance (WJ 2 ) between the other additional flight piece ( 13 B) and the same flight piece ( 12 ); and the distance (WJ 3 ) between the additional one flight piece ( 13 A) and the other of the two adjacent flight pieces ( 12 ) is larger than the distance (WJ 4 ) between the other additional flight piece ( 13 B) and the same flight piece ( 12 ), and said extruder body ( 4 ) is provided with mixing/kneading pins ( 15 ) protruding into the bore ( 4 H), wherein paths ( 17 ) for the mixing/kneading pins ( 15 ) are provided between the additional flight pieces ( 13 A and 13 B) and the screw flight pieces ( 12 ) so that each of the interruptions ( 11 ) forms two of the paths ( 17 ) on the upstream side and downstream side of the additional flight pieces ( 13 A and 13 B); and the one screw flight ( 9 )is provided with clearances ( 16 ) to form the paths ( 17 ) for the mixing/kneading pins ( 15 ), wherein the clearances ( 16 ) have a shape slightly larger than that of the respective pins ( 15 ) enabling the passing of the mixing/kneading pins ( 15 ) so that each of the clearances ( 16 ) forms one of the paths ( 17 ), and the one screw flight ( 9 ) has no interruption except for the clearances ( 16 ).