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US 9,868,245 B2Granted
Screw elements for extruding plastic compositions
AssigneeCovestro Deutschland AG
InventorsMichael Bierdel, Thomas König, Ulrich Liesenfelder
Life of this patent
Estimating the term…
Abstract
The invention relates to novel screw elements for multi-screw extruders with screw profiles 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.
Claims21
Screw elements for multi-screw extruders with screws co-rotating in pairs and being fully self-wiping in pairs, the screw elements comprising
- a pair of screw elements having tip angles and tip zones,
- wherein a first screw element of the pair of screw elements comprises a generating screw profile and a second screw element of the pair of screw elements comprises a generated screw profile, and wherein the generating screw profile and the generated screw profile are convex profiles consisting of arcs having non-infinite radiuses,
- wherein the tip zones are equal to an outer screw radius,
- wherein a sum of all the tip angles of the pair of screw elements is greater than 0 and less than 2*π−8*arccos(0.5*a/ra), and further
- wherein a is the centreline distance of the first and second screw elements and ra is the outer screw radius of the first and second screw elements,
- the number of tip zones of the pair of screw elements is greater than 4,
- each screw element of the pair of screw elements comprises exactly two screw profile closing zones, consisting, in each case, of the sequence tip zone, flank zone, tip zone,
- each screw element of the pair of screw elements comprises exactly two screw profile channel zones, consisting, in each case, of flank zones and grooved zones, and, in each case, beginning with a flank zone and ending with a flank zone, and in which the sum of the flank and groove angles of each channel zone is in each case greater than π/2, and
- the grooved zones are equal to a core radius and the flank zones are smaller than the outer screw radius and larger than the core radius.
6 more elements
A method of using screw elements in multi-screw extruders, the method comprising:
- producing a pair of screw elements, having tip angles and tip zones, wherein the tip zones are equal to the outer screw radius, wherein a sum of all the tip angles of the pair of screw elements is greater than 0 and less than 2*π-8*arccos(0.5*a/ra), and a total number of tip zones of the pair of screw elements is greater than 4, wherein each screw element of the pair of screw elements comprises exactly two screw profile closing zones, consisting, in each case, of the sequence tip zone, flank zone, tip zone, wherein each screw element of the pair of screw elements is provided with exactly two screw profile channel zones, consisting, in each case, of flank zones and grooved zones, and, in each case, beginning with a flank zone and ending with a flank zone, and in which a sum of the flank and groove angles of each channel zone is, in each case, greater than π/2, wherein the grooved zones are equal to a core radius and the flank zones are smaller than the outer screw radius and larger than the core radius, and wherein each screw element has a convex screw profile consisting of arcs having non-infinite radiuses;
- and
- providing a multi-screw extruder comprising the pair of screw elements, wherein the pair of screw elements are co-rotatable in pairs and fully self-wiping in pairs.
A process for extruding plastic compositions in multi-screw extruders having screw elements, the process comprising:
- providing a pair of screw elements in a multi-screw extruder, wherein the pair of screw elements are co-rotatable in pairs and fully self-wiping in pairs, wherein the pair of screw elements has a sum of all tip angles greater than 0 and less than 2*π−8*arccos(0.5*a/ra), wherein a number of tip zones of the pair of screw elements is greater than 4, wherein the tip zones are equal to an outer screw radius, wherein each screw element of the pair of screw elements comprises exactly two screw profile closing zones, consisting, in each case, of the sequence tip zone, flank zone, tip zone, wherein each screw element of the pair of screw elements are provided with exactly two screw profile channel zones, consisting, in each case, of flank zones and grooved zones, and, in each case, beginning with a flank zone and ending with a flank zone, and in which a sum of the flank and groove angles of each channel zone is, in each case, greater than π/2, wherein the grooved zones are equal to a core radius and the flank zones are smaller than the outer screw radius and larger than the core radius, and wherein each screw element has a convex screw profile consisting of arcs having non-infinite radiuses;
- and
- extruding one or more plastic compositions in the multi-screw extruder using the pair of screw elements.
Dependencies are inferred from the claim text.