Screw elements with improved mixing effect and improved heat transfer, and the use of same

A pair of three-flight screw elements,

• wherein the pair of screw elements consists of the screw element SE and the screw element SE′,
• and
• wherein the pair of screw elements SE and screw element SE′ is suitable for a multi-shaft screw machine
• with m screw shafts SW1 to SWm rotating in the same direction and at the same speed, the respective neighboring axes of rotation X1 to Xm of which have a center distance A in a cross section at right angles to the axes of rotation and
• with m circular housing bores which penetrate one another, each of which has an identical housing inner radius R 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 X1 to Xm of the screw shafts SW1 to SWm,
• wherein the screw element SE has a screw profile SP and the screw element SE′ has a screw profile SP′, wherein it is true that
• (1) each of the two screw profiles SP and SP′ is 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) either none of the two screw profiles SP and SP′ has mirror symmetry, or the screw profiles SP and SP′ are not congruent with each other,
• (3) each of the two screw profiles SP and SP′ has precisely three grooves,
• (4) each of the two screw profiles SP and SP′ has exactly three crests-peripherally labeled K1, K2, K3 for the screw profile SP and K1′, K2′, K3′ for the screw profile SP′,
• (6) two screw elements of the pair of 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,
• (7) a groove is separated from the nearest point of a neighboring crest by a flank,
• (8) it has exactly six curves, which are flanks,
• wherein
• (9) r(Ki) is the crest radius of the crest Ki and r(Ki′) is the crest radius of the crest Ki′, wherein the following is true:
• r(K1)>r(K2) and r(K1)>r(K3) and r(K1′)>r(K2′) and r(K1′)>r(K3′) and r (K2)>r(K3) and r(K2′)>r(K3′) and at least one of the conditions a) or b), wherein
• a) r(K2)>(K3) and r(K2′)>r(K3′)
• b) r(K2) is unequal to r(K2′) and r(K3) is unequal to r(K3′)
• 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(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′,
• (10) the screw crest K1 has the crest angle KW1, the screw crest K2 has the crest angle KW2, the screw crest K3 has the crest angle KW3 and the screw crest K1′ has the crest angle KW1′, the screw crest K2 has the crest angle KW2′ and the screw crest K3 has the crest angle KW3′, wherein
• (10.1) (10.1.a) when KW1>0, then KW1<KW2 and KW1<KW3,
• and
• (10.1.b) when KW1′>0, then KW1′<KW2 and KW1<KW3,
• or
• (10.2) (10.2.a) when KW1>0, then KW1<KW2 and KW1<KW3,
• and
• (10.2.c) when KW1′=0;
• then KW2>=0 and KW3>=0,
• or
• (10.3) (10.3.b) when KW1′>0, then KW1′<KW2 and KW1<KW3,
• and
• (10.3.d) when KW1=0, then KW2>=0 and KW3>=0,
• or
• (10.4) (10.4.d) when KW1=0, then KW2>=0 and KW3>=0,
• and
• (10.4.c) when KW1′=0;
• then KW2>=0 and KW3>=0,
• wherein r(K1) equals r(K1′) equals the outer radius RA or RA′ of the screw elements
• and m is an integer greater than 1,
• and i may assume the values 1, 2 or 3,
• and the outer radius RA is the radius of the circle which encloses the entire screw profile and of which the center point is the center of rotation associated with this screw profile, wherein the crest K1 is a segment of this circle.