Screw elements with improved dispersing action and low energy input

Patent metadata

Field	Value
Publication number	US-9688002-B2
Application number	US-99794009-A
Country	US
Kind code	B2
Filing date	Jun 6, 2009
Priority date	Jun 20, 2008
Publication date	Jun 27, 2017
Grant date	Jun 27, 2017

Abstract

The present invention relates to new screw elements for multi-screw extruders with pairs of co-rotating and fully wiping screws.

First claim

The invention claimed is:

1. Screw elements for multiscrew extruders with screws co-rotating in pairs and being fully self-wiping in pairs, wherein the screws comprise screw profiles and sections, and having two or more flights, wherein the screw profiles have continuously differentiable profile contours over the entire cross-sections and comprise at least a generating screw profile and a generated screw profile, wherein each screw profile of the screw profiles is composed of four or more arcs over the entire cross-section that merge tangentially into each other at starting and end points of each arc, and wherein the centre distance between the generating screw profile and the generated screw profile is a
the number of arcs of the generating screw profile is n,
the outer radius ra of the generating screw profile is greater than 0 (ra>0) and smaller than the centre distance (ra<a),
the inner radius ri of the generating screw profile is greater than 0 (ri>0) and smaller than or equal to ra (ri≦ra),
all of the arcs of the generating screw profile merge tangentially into each other,
the arcs form a closed screw profile, i.e. the sum of the angles α j of all of the arcs j is 2π, wherein π is pi (π≈3.14159),
the arcs form a convex screw profile,
all of the arcs of the generating screw profile are located between and/or on the boundary rings of an annulus which has an outer radius ra and an inner radius ri and whose centre point is located at the point of rotation of the generating screw profile,
at least one of the arcs of the generating screw profile touches the outer radius ra of the generating screw profile at point P A ,
at least one of the arcs of the generating screw profile touches the inner radius ri of the generating screw profile at point P I ,
the number of arcs n′ of the generated screw profile is the same as the number of arcs n of the generating screw profile,
the outer radius ra′ of the generated screw profile equals the difference between the centre distance and the inner radius ri of the generating screw profile (ra′=a−ri),
the inner radius ri′ of the generated screw profile equals the difference between the centre distance and the outer radius ra of the generating screw profile (ri′=a−ra),
the angle α j ′ of the j′th arc of the generated screw profile is the same as the angle α j of the jth arc of the generating screw profile, wherein j is an index which represents all integers in the range from 1 to the number of arcs n and j′ is an index which represents all integers in the range from 1 to the number of arcs n′,
the sum of the radius r j ′ of the j′th arc of the generated screw profile and the radius r j of the jth arc of the generating screw profile is the same as the centre distance a, wherein j is an index which represents all integers in the range from 1 to the number of arcs n and j′ is an index which represents all integers in the range from 1 to the number of arcs n′,
the distance between the centre point of the j′th arc of the generated screw profile and the centre point of the jth arc of the generating screw profile is the same as the centre distance a and the distance between the centre point of the j′th arc of the generated screw profile and the point of rotation of the generated screw profile is the same as the distance between the centre point of the jth arc of the generating screw profile and the point of rotation of the generating screw profile, and the connecting line between the centre point of the j′th arc of the generated screw profile and the centre point of the jth arc of the generating screw profile is a line parallel to the connecting line between the point of rotation of the generated screw profile and the point of rotation of the generating screw profile, wherein j is an index which represents all integers in the range from 1 to the number of arcs n and j′ is an index which represents all integers in the range from 1 to the number of arcs n′,
the starting point of the j′th arc of the generated screw profile lies in an opposite direction, in relation to the centre point of the j′th arc of the generated screw profile, to that of the starting point of the jth arc of the generating screw profile in relation to the centre point of the jth arc of the generating screw profile, wherein j is an index which represents all integers in the range from 1 to the number of arcs n and j′ is an index which represents all integers in the range from 1 to the number of arcs n′, and
wherein at least one screw profile, selected from the generating screw profile and the generated screw profile, comprises a first arc and a second arc, wherein
a center point of the first arc is located on a line segment that extends from a center point of the second arc to a rightmost end point of the second arc,
both the first arc and the second arc share a common line segment that extends from the center point of the first arc to the rightmost end point of the second arc and a leftmost end point of the first arc,
a leftmost end point of the second arc is located at a point that corresponds to an inner radius of the screw profile, and
a rightmost end point of the first arc is located at a point that corresponds to an outer radius of the screw profile,
wherein both the center point of the first arc and the center point of the second arc are located within a circle having a radius equal to the outer radius of the screw profile and having a center point corresponding to the point of rotation D, and
wherein the center point of the first arc is located on a line segment, which starts at the point of rotation D and ends at the point that corresponds to the outer radius of the screw profile, and wherein the center point of the second arc is located on a line segment, which starts at the point of rotation D and ends at the point that corresponds to the inner radius of the screw profile.

2. The screw elements according to claim 1 , wherein the screw elements are dot-symmetrical and the profile contour in a segment of 360°/(2·Z) is composed of at least two arcs, wherein Z is the number of flights of the screw elements.

3. The screw elements according to claim 1 , wherein the screw elements are axially symmetrical and the profile contour in a segment of 360°/(2·Z) is composed of at least two arcs, wherein Z is the number of flights of the screw elements.

4. The screw elements according to claim 3 , wherein the profile contour in a section is composed of two arcs which merge into each other in a continuously differentiable manner at point P FP , wherein point P FP is located on a straight line FP and the perpendicular to FP at point P FP passes through the centre points of the two arcs.

5. The screw elements according to claim 4 , wherein the screw elements have a point of rotation D, a point P A which is located on a circle around the point of rotation having the outer radius ra of the screw element, a point P I which is located on a circle around the point of rotation having the inner radius r I of the screw element, a straight line DP A which passes through points P A and D and a straight line DP I which passes through points P I and D, and which, using a Cartesian coordinate system with point D at its origin and point P A on its x-axis, are characterized in that a vertical line intersects straight line DP A at the centre point of one of the arcs and the straight line passing through points D and PI intersects the centre point of the other arc, and in that the straight line FP is located at a distance from the point of rotation which corresponds to half the centre distance a and has a gradient, in terms of radian measurement, of −1/tan(π/(2·Z)).

6. The screw elements according to claim 1 , wherein the screw elements are designed in the form of mixing elements or conveying elements.

Assignees

• Bierdel Michael
• König Thomas
• Liesenfelder Ulrich
• Covestro Deutschland Ag

Inventors

• Bierdel Michael
• König Thomas
• Liesenfelder Ulrich

Classifications

• B29B7/481 Primary

  provided with paddles, gears or discs (B29B7/482 takes precedence) · CPC title

• B29B7/489 Primary

  Screws (B29B7/482 takes precedence) · CPC title

• B29C48/395

  using screws surrounded by a cooperating barrel, e.g. single screw extruders · CPC title

• B29C48/57

  provided with kneading disc-like elements, e.g. with oval-shaped elements · CPC title

• B29C48/65

  neighbouring threads or channels having different configurations, e.g. one thread being lower than its neighbouring thread · CPC title