EXTRUDER COMPRISING A DEFLECTION ELEMENT FOR TARGETED FLOW AGAINST PERFORATED PLATE REGIONS

Abstract

The invention relates to an extruder comprising a housing having a flow channel (1) for a melt and a perforated plate (2) delimiting the flow channel (1) on the outlet side, wherein an inlet flow element (3) having passage areas (4) and covering surfaces (5) is arranged so as to be movable ahead of the perforated plate (2) in the direction of flow of the melt in such a way that, when the inlet flow element (3) is moved, a first subset of holes in the perforated plate (2) is exposed and a second subset of holes in the perforated plate (2) is closed, wherein the covering surfaces (5) extend radially from the center of the inlet flow element (3) to the rim thereof.

Claims

1. An extruder, comprising: a housing having a flow channel for a melt and a perforated plate delimiting the flow channel on an outlet side, wherein an inlet flow element having passage areas and covering surfaces is arranged so as to be movable ahead of the perforated plate in a direction of flow of the melt in such a way that, when the inlet flow element is moved, a first subset of holes in the perforated plate is exposed and a second subset of holes in the perforated plate is closed, and wherein the inlet flow element has an inlet flow cone, a base of which faces in a direction of the perforated plate and which tapers conically counter to the direction of flow of the melt.

2. (canceled)

3. The extruder as claimed in claim 1, wherein the inlet flow element has a circular cross-sectional area, and the movement is accomplished by rotation about a center of the cross-sectional area.

4. The extruder as claimed in claim 1, wherein the covering surfaces extend radially from a center of the inlet flow element to a rim thereof.

5. The extruder as claimed in claim 4, wherein the covering surfaces have a profile in a longitudinal section which has its widest extent at a base thereof facing the perforated plate and tapers counter to the direction of flow of the melt.

6. (canceled)

7. The extruder as claimed in claim 4, wherein the inlet flow element has a circular cross-sectional area, and the movement is accomplished by rotation about a center of the cross-sectional area.

8. The extruder as claimed in claim 1, wherein the covering surfaces are in contact with the perforated plate at least with their edges.

9. The extruder as claimed in claim 1, further comprising an actuator for moving the inlet flow element, at least one sensor for detecting a pressure in the flow channel, and a control module, wherein the control module is configured such that the inlet flow element is moved with the aid of the actuator when a predetermined critical value for a pressure or for a pressure difference is reached.

Description

LIST OF REFERENCE SIGNS USED

[0023] 1 . . . flow channel [0024] 2 . . . perforated plate [0025] 3 . . . inlet flow element [0026] 4 . . . passage area(s) [0027] 5 . . . covering surface(s) [0028] 6 . . . inlet flow cone [0029] 7 . . . actuator [0030] 8 . . . through-flow area(s) of the perforated plate [0031] 9 . . . first plate [0032] 10 . . . second plate [0033] 11 . . . seal [0034] 12 . . . granulating tool

[0035] FIG. 1 shows a first preferred embodiment of an inlet flow element 3 for use in an extruder. The illustration at the top left corresponds to the view in the direction of flow of the melt, while the illustration at the bottom right corresponds to the view from the opposite direction, starting from the perforated plate. The inlet flow element 3 has a circular cross-sectional area and, at its rim, has an extension, which is provided for the purpose of moving the inlet flow element 3. In the middle of the cross-sectional area there is an inlet flow cone 6, the base of which faces in the direction of the perforated plate and which tapers counter to the direction of flow of the melt.

[0036] Starting from the inlet flow cone 6, which is in the center of the inlet flow element 3, six covering surfaces 5 extend radially outwards to the rim of the inlet flow element 3. Between the covering surfaces 5 there are open regions, which form the passage areas 4 for the melt.

[0037] In the example shown, the covering surfaces 5 become wider in a radial direction towards the rim as the circumferential distance from the center to the rim increases. The bases of the covering surfaces 5 are dimensioned in such a way that they correspond to the passage areas 4. In longitudinal section (perpendicularly to the cross-sectional area), the covering surfaces 5 have a profile which has its widest extent at the base facing the perforated plate and tapers counter to the direction of flow of the melt. Melt impinging upon the inlet flow element 3 is thus, on the one hand, directed away from the center by the conical shape of the inlet flow cone 6 and, on the other hand, guided away from the covering surfaces 5 to the edges of the covering surfaces 5 by virtue of the shaping of said surfaces and thus guided onto the adjacent passage areas 4.

[0038] FIG. 2 shows another preferred embodiment of an inlet flow element 3 for use in an extruder. This embodiment differs from that shown in FIG. 1 only in the geometrical configuration of the inlet flow cone 6 and of the covering surfaces 5. The inlet flow cone 6 is significantly larger in diameter and in axial extent than the embodiment shown in FIG. 1. Accordingly, the covering surfaces 5 and the passage areas 4 are significantly smaller. An inlet flow element 3 according to this embodiment therefore exposes a significantly smaller area of the perforated plate for the melt to flow through.

[0039] FIG. 3 shows a plan view of an inlet flow element 3 according to the embodiment in FIG. 1 installed in an extruder, viewed in the direction of flow of the melt. The inlet flow element 3 is mounted rotatably in a flange. To move or rotate the inlet flow element 3, said element is connected to an actuator 7. In FIG. 4, the inlet flow element 3 illustrated in FIGS. 1 and 3 is shown partially cut away in the installed state.

[0040] The upper depiction in FIG. 3 shows the inlet flow element 3 in a first position, in which there are holes in the perforated plate behind the passage areas 4, with the result that a first subset of holes in the perforated plate is exposed. A second subset of holes in the perforated plate is situated behind the covering surfaces 5 and is thus closed. In the lower depiction in FIG. 3, the inlet flow element 3 has been rotated anticlockwise by 30 relative to the position in the upper depiction. The previously open holes in the perforated plate are now covered by the covering surfaces 5, while the melt can now flow through the previously covered holes.

[0041] In the example shown, the holes in the perforated plate are embodied differently in the two subsets. In the subset of holes which is open in the upper depiction, a large number of small holes is arranged. In contrast, fewer but larger holes are arranged in the subset of holes which is open in the lower depiction. The apparatus according to the invention makes it possible to switch between the two sizes of hole without stopping the flow of melt in the extruder, i.e. shutting down the extruder. As a result, it is possible to switch over flexibly between modes of operation without losing running time.

[0042] A preferred embodiment of the invention is shown schematically in an exploded view in FIG. 5. Of the extruder, only the extruder outlet is shown. The direction of flow of the melt is from left to right. A first plate 9 and a second plate 10 are flanged to the outlet end of the extruder and connected firmly to the extruder.

[0043] Between the upper and lower end, the second plate 10 has an internal recess, in which a perforated plate 2 is movably mounted. The perforated plate 2 comprises two through-flow areas 8, which both contain a multiplicity of through-flow openings. The outer contour of the through-flow areas 8 (envelope around the through-flow openings) is in each case circular and corresponds in cross section to the internal cross section of the flow channel 1 at this point. To move the perforated plate 2, an actuator is provided, which can move the perforated plate substantially perpendicularly to the flow channel 1 by means of a linear motion.

[0044] Arranged between the extruder outlet and the first plate 9 is an inlet flow element 3, which can be rotated through a predetermined angle with the aid of an actuator 7. In this example, the inlet flow element 3 corresponds to that shown in FIG. 2. To avoid the melt escaping at an unwanted location, sealing elements 11 are provided between the extruder outlet, the inlet flow element 3, the perforated plate 2 and the second plate 10. A granulating tool 12 is provided at the outlet end of the apparatus, resting on the perforated plate 2 and cutting the melt strands emerging through the through-flow openings into small granules by means of a rotary motion.