Screw elements with improved mixing effect and pressure build-up

A pair of four-flight screw elements, suitable for a multishaft screw machine comprising:

• m screw shafts SW1 to SWm rotating in the same direction and at the same speed, the respective neighboring axes of rotation D1 to Dm of which have a center distance a in a cross-section at right angles to the axes of rotation;
• and
• m circular housing bores which penetrate one another, each of which has an identical housing inner radius rg and the bore centers M1 to Mm of which are at a distance which is the same as the center distance a, and the bore centers M1 to Mm of which coincide with the respective associated axes of rotation D1 to Dm of the screw shafts SW1 to SWm,
• wherein each of the two screw elements of the pair of four-flight screw elements has a screw profile comprising:
• (1) a closed convex curve, wherein this closed convex curve is composed merely of curve sections of which the radii of curvature are less than or equal to the center distance a,
• (2) at least 16 curves,
• (3) exactly one or no axis symmetry,
• (4) exactly four grooves,
• (5) exactly four crests-labeled as they revolve as K1, K2, K3 and K4,
• (6) a crest radius r(Ki) respectively associated with a crest Ki is the greatest distance of a crest Ki from the pivot point DPm, wherein the following is true:
• (K1)>r(K2) and r(K1)>r(K3) and r(K1)>r(K4), and
• r(K3)>r(K2) and r(K3)>r(K4),
• wherein r(K1) is the crest radius of the screw crest K1 and r(K2) is the crest radius of the screw crest K2 and r(K3) is the crest radius of the screw crest K3, and r(K4) is the crest radius of the screw crest K4,
• wherein r(K1) is equal to the outer radius ra,
• wherein the outer radius ra is the radius of the circle which encloses the entire screw profile and of which the center point is the pivot point associated with this screw profile, wherein the crest K1 is a segment of this circle,
• wherein m is an integer greater than 1, and
• wherein i may assume the values 1, 2, 3 or 4,
• (7) two screw elements located oppositely in pairs and directly adjacently to one another on two of the screw shafts of the multishaft screw machine, which rotate in the same direction and at the same speed, practically clean one another in pairs,
• (8) a groove is separated from the nearest point of a neighboring crest by a flank,
• (9) it has exactly eight curves, which are flanks.