Extruder screw, extruder, and method for producing an extruder screw

Abstract

An extruder screw includes an extruder shaft and at least one extruder segment. The extruder shaft has a prismatic mandrel having external teeth and a longitudinal mandrel axis. The extruder segment has internal teeth and a longitudinal internal-teeth axis and can be slid onto the mandrel, such that the extruder segment can be connected to the mandrel for rotation therewith. The internal teeth have a profile having a meshing profile and, in an inner area between the first and second end faces of the extruder segment, include a prismatic main profile that has a main cross-section. Furthermore, the internal teeth of the extruder segment have an edge profile adjacent to at least one end face of the extruder segment, which edge profile has a smaller edge cross-section than the main profile at least in the area of the meshing profile.

Claims

1. An extruder screw, comprising: an extruder shaft having a prismatic mandrel provided with external teeth and defined by a mandrel longitudinal axis; and at least one extruder segment comprising an external screw, the at least one extruder segment configured for placement onto the mandrel, said extruder segment defined by a longitudinal internal-teeth axis in coaxial relationship to the mandrel longitudinal axis and having internal teeth in mesh with the external teeth of the mandrel so that the extruder segment is connected in fixed rotative engagement with the mandrel, said internal teeth having a profile which has a meshing profile and a prismatic main profile with a main cross-section in an inner area between a first end face and a second end face of the extruder segment, said internal teeth have an edge profile adjacent to at least one of the first and second end faces, said edge profile having an edge cross-section which is smaller than the main profile at least in an area of the meshing profile, wherein the internal teeth have a profile correction which describes a deviation of the edge cross-section from the main cross-section as a function of an edge distance from a nearest one of the first and second end faces, said profile correction extending up to the edge distance from the nearest one of the first and second end faces of at least 2 millimeters, wherein the profile correction has a profile correction height which is smaller than a tooth height of the internal teeth minus a base rounding radius.

2. The extruder screw of claim 1, wherein the profile intersects in a meshing profile longitudinal course an imaginary cylinder surface having a longitudinal axis extending in coaxial relationship to the longitudinal internal-teeth axis of the internal teeth at half a tooth height, said meshing profile longitudinal course being smooth.

3. The extruder screw of claim 1, wherein the profile correction extends over a profile correction length which amounts to at most one third of a width of the extruder segment.

4. The extruder screw of claim 1, wherein the internal teeth are involute teeth.

5. The extruder screw of claim 1, wherein the second end face lies opposite the first end face, said profile being mirror-symmetrical with respect to a plane of symmetry which runs perpendicularly to the longitudinal internal-teeth axis and centrally between the first end face and the second end face.

6. An extruder, comprising a barrel and at least one extruder screw within the barrel which extruder screw includes an extruder shaft having a prismatic mandrel provided with external teeth and defined by a mandrel longitudinal axis, and at least one extruder segment comprising an external screw, the at least one extruder segment configured for placement onto the mandrel, said extruder segment defined by a longitudinal internal-teeth axis in coaxial relationship to the mandrel longitudinal axis and having internal teeth in mesh with the external teeth of the mandrel so that the extruder segment is connected in fixed rotative engagement with the mandrel, said internal teeth having a profile which has a meshing profile and a prismatic main profile with a main cross-section in an inner area between a first end face and a second end face of the extruder segment, said internal teeth have an edge profile adjacent to at least one of the first and second end faces, said edge profile having an edge cross-section which is smaller than the main profile at least in an area of the meshing profile, wherein the internal teeth have a profile correction, which describes a deviation of the edge cross-section from the main cross-section as a function of an edge distance from a nearest one of the first and second end faces, said profile correction extending up to the edge distance from the nearest one of the first and second end faces of at least 2 millimeters, wherein the profile correction has a profile correction height which is smaller than a tooth height of the internal teeth minus a base rounding radius.

7. The extruder of claim 6, constructed in the form of a double screw extruder.

8. The extruder of claim 6, wherein the profile correction extends over a profile correction length which amounts to at most one third of a width of the extruder segment.

9. The extruder of claim 6, wherein the internal teeth are involute teeth.

10. The extruder of claim 6, wherein the second end face lies opposite the first end face, said profile being mirror-symmetrical with respect to a plane of symmetry which runs perpendicularly to the longitudinal internal-teeth axis and centrally between the first end face and the second end face.

11. A method, comprising: producing a prismatic mandrel with external teeth by hammering with a hammer tool; producing a pre-extruder segment with prismatic internal teeth; producing an eroding tool with the hammer tool; producing a profile correction of the internal teeth by sink erosion with the eroding tool, and connecting the pre-extruder segment with the prismatic mandrel for rotation with the prismatic mandrel.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention is explained in further detail below with the aid of the enclosed drawings. There are shown

(2) FIG. 1a a perspective view, true to scale, of an extruder segment according to the invention,

(3) FIG. 1b an enlarged detail according to FIG. 1a,

(4) FIG. 1c a front view of a tooth of the internal teeth at the height of the end face,

(5) FIG. 1d a top view onto the tooth according to FIG. 1c,

(6) FIG. 1e a perspective view of an extruder in the form of a double screw extruder,

(7) FIG. 2a a cross-section through a mandrel of an extruder shaft of an extruder according to the invention and

(8) FIG. 2b a portion side view of the mandrel according to FIG. 2a.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(9) FIG. 1 shows an extruder segment 10 according to the invention, which has internal teeth 12, by means of which it is able to be slid onto complementary external teeth of a mandrel of an extruder shaft for rotation therewith. The internal teeth 12 have a meshing profile P, which is shown in FIG. 1c. FIG. 1a shows that the extruder segment 10 comprises an external screw 14. Alternatively, the extruder segment 10 can have for example a conveying, kneading or mixing structure.

(10) The extruder segment 10 has a first end face 16 and a second end face 18 lying opposite the first end face 16, which second end face runs parallel to the first end face 16. The internal teeth 12 have a longitudinal teeth axis L.sub.12, along which the extruder segment 10 has a segment width B.sub.10.

(11) FIG. 1b shows the detail A according to FIG. 1a. It can be seen that the internal teeth 12 have a plurality of teeth 20.1, 20.2, . . . , which respectively have the same contour. The internal teeth 12 have an inner area 22 to which an end-face area 24 adjoins. The boundary between inner area 22 and end-face area 24 is marked by a dot-and-dash line.

(12) In the inner area 22, the internal teeth 12 have a prismatic main profile P.sub.G, the main cross-section of which is shown in FIG. 1c. FIG. 1b shows in addition that the internal teeth 12 have in the end-face area 24 an edge profile P.sub.R, the edge cross-section of which is also shown in FIG. 1c. The profile P is understood to mean the two-dimensional surface of the internal teeth in the respective area. The main profile is the part of the profile P in the inner area 22, the edge profile P.sub.R is the part of the profile P in the end-face area 24, which could also be named the edge area.

(13) The respective cross-section, i.e. the main cross-section or respectively the edge cross-section, is understood to mean the cross-section through the internal teeth 12 perpendicularly to the longitudinal internal-teeth axis L.sub.12 (cf. FIG. 1a) of the internal teeth 12 in the area of the respective profile.

(14) Adjacent to the end face 16, the internal teeth 12 have the edge profile P.sub.R with the edge cross-section, which is smaller than the main cross-section. In FIG. 1b this is to be seen in that the internal teeth 12 adjacent to the end face 16 taper towards the end face. When the extruder segment 10 is placed onto the prismatic mandrel of the extruder shaft, a small gap occurs adjacent to the end face 16, in which gap the internal teeth 12 do not lie with their full surface against the external teeth of the mandrel.

(15) FIG. 1c shows a front view of a tooth, for example tooth 20.1, at the height of the end face 16. This corresponds to a projection of the profile along the mandrel longitudinal axis onto a plane, namely the plane of the drawing, which runs perpendicularly to the mandrel longitudinal axis. The main profile P.sub.G and the edge profile P.sub.R can be seen in the form of the main cross-section and of the edge cross-section. The edge cross-section is smaller than the main cross-section.

(16) FIG. 1b shows in addition an imaginary cylinder surface 26, which is drawn as a dot-and-dash line in FIG. 1c and runs at half the tooth height Z. This imaginary cylinder surface 26 intersects the profile P in a meshing profile longitudinal course k(x), which is drawn in FIG. 1d. FIG. 1d is a top view onto the tooth according to FIG. 1c,

(17) FIG. 1d shows the view from above onto the profile, which is applied against x as longitudinal coordinate along the longitudinal internal-teeth axis L.sub.12. x=0 applies for the point in which the longitudinal internal-teeth axis L.sub.12 intersects the plane in which the end face 16 lies. It can be seen that the meshing profile longitudinal course k(x) is a straight line in the inner area 22, and runs in a curved manner in an edge area 28. The meshing profile longitudinal course k(x) is smooth, i.e. constantly differentiable. This applies in particular at the boundary between edge area 28 and inner area 22.

(18) The edge profile P.sub.R is dependent on the distance x from the end face 16. FIG. 1c shows the situation for x=0, i.e. directly at the first end face 16. The profile correction D can be seen, which designates the area between the main cross-section and the edge cross-section. The description of the profile correction D as the area between the projection of the main profile onto a plane perpendicular to the longitudinal internal-teeth axis L.sub.12 in the edge distance x and the intersection of the edge profile with this plane is equivalent.

(19) The profile correction D is therefore dependent on the edge distance x. The profile correction D extends from the end face 16 up to an edge distance x, which is designated as profile correction length L.sub.D. The profile correction length L.sub.D is drawn in FIG. 1d. It amounts to at the most one third of the extruder segment width B.sub.10, which is drawn in FIG. 1a.

(20) The profile correction D has in addition a profile correction height H.sub.D, which designates the extent along the radial axis r, at the height of which the profile correction D is present. The profile correction height H.sub.D is preferably smaller than the tooth height Z minus a base rounding radius R, with which the meshing profile P.sub.E of the main profile P.sub.G continues into a base area P.sub.F.

(21) FIG. 1e shows a perspective view of an extruder in the form of a double screw extruder.

(22) FIG. 2a shows a cross-section through a mandrel 30 of an extruder shaft of an extruder according to the invention. The mandrel 30 comprises external teeth 32, which are constructed in a complementary manner to the internal teeth 12. The mandrel 30 has a mandrel longitudinal axis L.sub.30, which coincides with the longitudinal internal-teeth axis L.sub.12 (cf. FIG. 1a).

(23) FIG. 2b shows the mandrel 30 in a portion in a longitudinal view, in which the external teeth 32 can be seen.

(24) An extruder segment 10 according to the invention is produced in particular in that firstly a pre-extruder segment is produced with prismatic internal teeth. Subsequently, the profile correction D is produced by sink erosion. For the erosion treatment preferably an eroding tool is used, which was also used for the production of the external teeth 32 of the mandrel 30.