Screw feed elements for extrusion of viscoelastic masses
View Patent ↗The invention relates to novel screw feed elements for multi-shaft screw feed machines having screw feed profiles rotating in the same direction in pairs and precisely abrading in pairs, to the use of the screw elements in multi-shaft screw feeding machines and to a method for extrusion of viscoelastic masses.
1. Screw elements for a multi-shaft screw machine with a paired co-directionally rotating screw shafts, wherein:
adjacent screw elements have an unlike, unsymmetrical profile,
said screw elements having a single flight land region,
a sum of all flight land angles of an adjacent pair of screw feed elements is greater than 0 and less than
2
π
-
4
·
arc
cos
(
A
DE
)
,
wherein A is the centreline distance between two screw elements, DE is the outside diameter of the screw elements, and π is the constant of a circle,
free cross-sectional areas F 1 frei and F 2 frei of profiles of adjacent screw elements differ from each other in size.
2. The screw elements according to claim 1 , wherein the sum of the flight land angles of a generated screw profile and a generating screw profile is less than
0.8
·
(
2
π
-
4
·
arc
cos
(
A
DE
)
)
.
3. The screw elements according to claim 1 , wherein a ratio of a larger free cross-sectional area to a smaller free cross-sectional area of adjacent profiles is at least 1.2.
4. The screw elements according to claim 1 , wherein a profile of one element of a pair of elements has a tapering region which extends over an angle, with respect to a point of rotation of the profile, which is greater than 90°, the tapering region comprising one or more circular arcs, and all points that lie on the arcs of the tapering region have a distance from a point of rotation of a profile that lies from (RA+RI)/2 to RA, RA being an outer screw radius and RI an inner screw radius.
5. Screw elements for a multi-shaft screw machine with paired co-directionally rotating screw shafts, wherein:
adjacent screw elements have an identical, unsymmetrical profile,
the profile comprises a single flight land region with a flight land angle less than
π
-
2
arc
cos
(
A
2
·
RA
)
,
and
in the profile, the flight land region is adjoined on one side by a tapering region, which comprises one or more circular arcs, all points that lie on the arcs of the tapering region have a distance from a point of rotation of the profile that lies from (RA+RI)/2 to RA, A being a centreline distance, RA an outer screw radius, RI an inner screw radius and π the mathematical constant of a circle.
6. The screw elements according to claim 5 , wherein the land flight angle is less than
0.8
·
(
π
-
2
arc
cos
(
A
2
·
RA
)
)
.
7. The screw elements according to claim 5 , wherein the tapering region extends over an angle, with respect to the point of rotation of the profile, which is greater than 30°.
8. Screw elements for a multi-shaft screw machine with paired co-directionally rotating screw shafts, wherein:
adjacent screw elements have an unlike profile,
in the case of an adjacent pair of screw elements, one profile has just one flight land region and an adjacent profile has just two flight land regions,
free cross-sectional areas F 1 frei and F 2 frei of adjacent profiles differ from each other in size.
9. The screw elements according to claim 8 , wherein a ratio of a larger free cross-sectional area to a smaller free cross-sectional area of adjacent profiles is at least 1.2.
10. The screw elements according to claim 8 , wherein the profiles are in each case mirror-symmetrical.
11. The screw elements according to claim 1 , wherein a ratio of an outer screw radius RA to the centreline distance A lies in a range from 0.51 to 0.7.
12. The screw elements according to claim 1 , which are derived from fully wiping profiles by having clearances between screw elements and a barrel and/or between adjacent screw feed elements.
13. The screw elements according to claim 1 , capable of being used in a multi-shaft screw machine.
14. A process for extrusion of viscoelastic masses in a twin-screw or multi-shaft extruder using the screw elements according to claim 1 .
15. The screw elements according to claim 1 , wherein the sum of the flight land angles of a generated screw profile and a generating screw profile is less than
0.6
·
(
2
π
-
4
·
arc
cos
(
A
DE
)
)
.
16. The screw elements according to claim 1 , wherein a ratio of a larger free cross-sectional area to a smaller free cross-sectional area of adjacent profiles is at least 1.5.
17. The screw elements according to claim 5 , wherein the land flight angle is less than
0.6
·
(
π
-
2
arc
cos
(
A
2
·
RA
)
)
.
18. The screw elements according to claim 8 , wherein a ratio of a larger free cross-sectional area to a smaller free cross-sectional area of adjacent profiles is at least 1.4.
19. The screw elements according to claim 1 , wherein a ratio of an outer screw radius RA to the centreline distance A lies in a range from 0.52 to 0.66.