US 2025/0242533 A1Published application

Screw elements with improved mixing and degassing effect with reduced energy input

AssigneeCovestro Deutschland AG

InventorsThomas Koenig, Michael Bierdel

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Abstract

The present disclosure relates to a pair of screw elements suitable for a multishaft 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 interpenetrating circular housing bores which each have an identical housing bore inner diameter D and of which the bore centers M1 to Mm have a distance equal to the center distance A, and of which the bore centers M1 to Mm coincide with the respective associated axes of rotation X1 to Xm of the screw shafts SW1 to SWm and coincide with the centers of rotation P1 to Pm of the screw elements.

A multishaft screw machine having a pair of screw elements, comprising:

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
m interpenetrating circular housing bores which each have an identical housing bore inner diameter D and of which the bore centers M1 to Mm have a distance equal to the center distance A, and of which the bore centers M1 to Mm coincide with the respective associated axes of rotation X1 to Xm of the screw shafts SW1 to SWm and coincide with the centers of rotation P1 to Pm of the screw elements,
wherein the two screw elements of the pair of screw elements lie opposite each other on directly neighboring screw shafts,
the two screw elements of the pair of screw elements scraping each other with a screw element-to-screw element clearance s,
wherein both screw elements have an asymmetrical screw profile,
wherein both screw elements each have exactly two crests,
wherein for each of the two screw elements, the two crests have different distances to the respective center of rotation P of the screw profile,
wherein in each case one crest has a distance D/2 reduced by a screw element-to-housing wall clearance δ and further reduced by an additional gap SP to the respective center of rotation P and the other crest has a distance D/2 reduced by a screw element-to-housing wall clearance δ, but not reduced by an additional gap SP, to the respective center of rotation P,
wherein the screw element-to-housing wall clearance δ is the same for both screw elements and the additional gap SP is the same for both screw elements,
wherein the sum of the crest angles BKW of the crests of both screw elements in radians is greater than 0, and
for the factor f with
f
=
BKW
/
BKGW
(
44
)
it is true that the factor f is greater than 0 and less than or equal to 0.95,
wherein BKW is the sum of the crest angles in radians of both screw elements and BKGW is determined by:
BKGW
=
2
⁢
(
π
-
1
2
⁢
(
arccos
⁢
(
A
2
-
2
⁢
RE
2
2
⁢
RE
2
)
+
arccos
⁢
(
A
2
-
2
⁢
RE
2
+
2
⁢
RE
⁢
SP
-
SP
2
2
⁢
RE
⁢
(
RE
-
SP
)
)
+
arccos
⁢
(
A
2
-
2
⁢
(
RE
-
SP
)
2
2
⁢
(
RE
-
SP
)
2
)
+
arccos
⁢
(
A
2
-
2
⁢
RE
2
+
2
⁢
RE
⁢
SP
-
SP
2
2
⁢
RE
(
RE
-
SP
)
)
)
-
s
T
⁢
(
2
⁢
6
.
2
⁢
2
⁢
1
⁢
1
⁢
3
-
1
⁢
6
.
0
⁢
3623
⁢
A
D
-
3
⁢
0
.
9
⁢
465
⁢
δ
D
+
1
⁢
4
.
5
⁢
763
⁢
s
D
-
0.20071
T
D
-
0
.
0
⁢
0475
⁢
SP
GT
+
4
.
8
⁢
9626
⁢
erf
⁢
(
-
0
.
8
⁢
55
⁢
T
D
)
)
)
,
(
45
)

219 more elements

Facts

Application

18/855,221Filed 5 Apr 2023

Priority

EP 22167637.211 Apr 2022

Published

31 Jul 2025

Term ends

Not estimatedThe source records don’t support an estimate.

Classification6 codes

B29C 48/402
Using two or more parallel screws or at least two parallel non-intermeshing screws, e.g. twin screw extruders: the screws having intermeshing parts
B29C 48/54
Screws: with additional forward-feeding elements
B29C 48/40
Using screws surrounded by a cooperating barrel, e.g. single screw extruders: using two or more parallel screws or at least two parallel…
B29C 48/405
Using two or more parallel screws or at least two parallel non-intermeshing screws, e.g. twin screw extruders: intermeshing co-rotating screws

Abstract

Claims16