Method for extruding plastic masses

A process for extruding plastic compositions comprising the steps of providing a twin- or multi-screw extruder, and conveying or kneading and/or mixing a plastic composition in said twin- or multi-screw extruder, said extruder comprising screw elements with screws co-rotating in pairs and being fully self-wiping in pairs, wherein each screw has one of a generating screw profile and a generated screw profile consisting of arcs with non-infinite radiuses, each of the generating and generated screw profiles being axisymmetrial referring to one axis which passes through the point of rotation of the respective screw profile, and each of the generating and generated screw profiles comprises one sealing zone, one or more transition zones, one channel zone, one or more tip zones, one or more flank zones, and one or more grooved zones, and each screw profile consisting of a sequence of the one sealing zone—one of the transition zones—the one channel zone—another of the transition zones, wherein each sealing zone is a sequence of one of the tip zones—one of the flank zones—another of the tip zones, each channel zone is a sequence of one of the grooved zones—one of the flank zones—another of the grooved zones, and each transition zone is one of the flank zones, wherein

• each sealing zone of the screw elements is distinguished in that
• relative to the point of rotation of the screw profile, the flank zone has an angle δ_fb1 which is greater than or equal to half the aperture angle between the two barrel intermeshes (δ_fb1≧arc cos(0.5*a/ra))(wherein “a” is the centerline distance and “ra” is the outer screw radius”) ,
• relative to the point of rotation of the screw profile, one tip zone has an angle δ_kb1 which is less than or equal to the difference of the tip angle of a single-flighted Erdmenger screw profile minus the aperture angle between the two barrel intermeshes (δ_kb1≦π-4*arc cos(0.5*a/ra)),
• relative to the point of rotation of the screw profile, the other tip zone has an angle δ_kb2 which is less than or equal to the difference of the tip angle of a single-flighted Erdmenger screw profile minus the aperture angle between the two barrel intermeshes (δ_kb2≦π-4*arc cos(0.5*a/ra)),
• and each channel zone is distinguished in that
• relative to the point of rotation of the screw profile, the flank zone has an angle δ_fb2 which is greater than or equal to half the aperture angle between the two barrel intermeshes(δ_fb2≧arc cos(0.5*a/ra)),
• relative to the point of rotation of the screw profile, one grooved zone has an angle δ_nb1 which is less than or equal to the difference of the tip angle of a single-flighted Erdmenger screw profile minus the aperture angle between the two barrel intermeshes (δ_nb1≦π-4*arc cos(0.5*a/ra)),
• relative to the point of rotation of the screw profile, the other grooved zone has an angle δ_nb2 which is less than or equal to the difference of the tip angle of a single-flighted Erdmenger screw profile minus the aperture angle between the two barrel intermeshes (δ_nb2≦π-4*arc cos(0.5*a/ra)).