Single-Flighted Screw Elements With a Reduced Tip Angle
The invention relates to screw elements for multi-screw extruders with screws co-rotating in pairs and being fully self-wiping in pairs, to the use of the screw elements in multi-screw extruders and to a process for extruding plastic compositions.
1 - 15 . (canceled)
16 . A screw elements for multi-screw extruders comprising
a plurality of screws co-rotating in pairs and being fully self-wiping in pairs, each pair having a tip angle and one screw flight, with a centreline distance a and outer radius ra,
wherein the sum of the tip angles of the pair of screws is less than
2
π
-
4
arccos
(
a
2
·
ra
)
and in the case of axially symmetrical screw profiles none of the centre points of the flank circles lies on the perpendicular to the axis of symmetry of the profile, which axis of symmetry passes through the point of rotation.
17 . The screw elements according to claim 16 , wherein in each case one cross-sectional profile is composed of at least five circular arcs with a radius greater than or equal to zero and less than or equal to a distance a, the circular arcs merging tangentially into one another at their end points.
18 . The screw elements according to claim 16 , wherein the screw elements are mixing elements or conveying elements.
19 . The screw elements according to claim 16 , wherein the screw elements are kneading elements.
20 . The screw elements according to claim 16 , wherein the screw elements display clearances between screw elements and a barrel and/or between neighbouring screw elements.
21 . Screw elements according to claim 16 , wherein the screw elements each have an outer screw radius normalized to the centreline distance, lies in the range from 0.52 to 0.66.
22 . A method of using screw elements for multi-screw extruders, comprising the steps of
providing a plurality of screws co-rotating in pairs and being fully self-wiping in pairs, each pair having a tip angle and one screw flight, with a centreline distance a and outer radius ra,
wherein the sum of the tip angles of the pair of screws is less than
2
π
-
4
arccos
(
a
2
·
ra
)
and in the case of axially symmetrical screw profiles none of the centre points of the flank circles lies on the perpendicular to the axis of symmetry of the profile, which axis of symmetry passes through the point of rotation.
23 . The method according to claim 22 , wherein the screw elements clean one another in pairs with a constant gap over their entire circumference.
24 . The method according to claim 22 , wherein the screw elements clean one another in pairs with a gap which is not constant over the entire circumference.
25 . The method according to claim 22 , wherein the profiles of the screw elements are displaced in pairs relative to the point of rotation located centrally in the barrel bore.
26 . A process for extruding plastic compositions in a twin-screw or multi-screw extruder using screw elements, comprising the steps of
providing a plurality of screws co-rotating in pairs and being fully self-wiping in pairs, each pair having a tip angle and one screw flight, wherein
the sum of the tip angles of a generating and of a generated screw profile is less than
2
π
-
4
arccos
(
a
2
·
ra
)
and in the case of axially symmetrical screw profiles none of the centre points of the flank circles lies on the perpendicular to the axis of symmetry of the profile, which axis of symmetry passes through the point of rotation.
27 . The process according to claim 26 , wherein the plastic compositions are thermoplastics or elastomers.
28 . The process according to claim 27 , wherein the thermoplastics used are polycarbonate, polyamide or polyester or a blend of at least two thermoplastics.
29 . The process according to claim 27 , wherein the thermoplastics used are polybutylene terephthalate and polyethylene terephthalate, polyether, thermoplastic polyurethane, polyacetal or fluoropolymer or a blend of at least two of the stated thermoplastics
30 . The process according to claim 27 , wherein the thermoplastics used are polyvinylidene fluoride, polyether sulphones, polyolefin or a blend of at least two of the stated thermoplastics.
31 . The process according to claim 27 , wherein the thermoplastics used are polyethylene and polypropylene, polyimide, polyacrylate or a blend of at least two of the stated thermoplastics.
32 . The process according to claim 27 , wherein the thermoplastics used are poly(methyl)methacrylate, polyphenylene oxide, polyphenylene sulphide, polyether ketone, polyarylether ketone, styrene polymers or a blend of at least two of the stated thermoplastics.
33 . The process according to claim 32 , wherein the styrene polymers are polystyrene, styrene copolymers or a blend of at least two of the stated thermoplastics.
34 . The process according to claim 33 , wherein the styrene copolymers are styrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene block copolymers, polyvinyl chloride or a blend of at least two of the stated thermoplastics.
35 . The process according to claim 27 , wherein the elastomers used are styrene-butadiene rubber, natural rubber, butadiene rubber, isoprene rubber, ethylene-propylenediene rubber, ethylene-propylene rubber, butadiene-acrylonitrile rubber, hydrogenated nitrile rubber, butyl rubber, halobutyl rubber, chloroprene rubber, ethylene-vinyl acetate rubber, polyurethane rubber, thermoplastic polyurethane, gutta percha, acrylate rubber, fluororubber, silicone rubber, sulphide rubber, chlorosulphonyl-polyethylene rubber or a combination of at least two of the stated elastomers.
36 . The process according to claim 27 , wherein a filler or reinforcing materials or polymer additives or organic or inorganic pigments or mixtures thereof are added to the plastics compositions.