CHARGING SYSTEM FOR FEEDING PROCESSING MATERIAL TO AN EXTRUDER SCREW, HAVING AXIALLY EXTENDING RECESSES IN A HOPPER WALL

Abstract

It is provided a charging system for feeding processing material, in particular granular processing material to at least one extruder screw, comprising a hopper that is adapted to guide the processing material along a feed direction to the extruder screw and extends along a hopper axis, which in the properly mounted state of the charging system extends parallel to a longitudinal axis of the extruder screw.

In the proposed charging system, the hopper includes a plurality of recesses each extending axially with respect to the hopper axis on a hopper wall extending around the hopper axis.

Claims

1. A charging system for feeding processing material to at least one extruder screw, the charging system comprising: a hopper that is adapted to guide the processing material along a feed direction to the extruder screw and that extends along a hopper axis, which in a properly mounted state of the charging system extends parallel to a longitudinal axis of the extruder screw, wherein on a hopper wall extending around the hopper axis, the hopper includes a plurality of recesses, each recess extending axially with respect to the hopper axis.

2. The charging system according to claim 1, wherein the recesses are arranged in succession along a circumferential line around the hopper axis.

3. The charging system according to claim 1, wherein in cross-section the recesses are radially curved towards the outside, with respect to the hopper axis.

4. The charging system according to claim 1, wherein at least one of the recesses is formed to be radially tapering.

5. The charging system according to claim 4, wherein all recesses are each formed to be radially tapering.

6. The charging system according to claim 1, wherein at least one of the recesses is formed to be axially tapering.

7. The charging system according to claim 6, wherein all recesses are each formed to be axially tapering.

8. The charging system according to claim 1, wherein in cross-section the hopper wall formed with the recesses defines an inner circumferential line and an outer circumferential line, wherein the inner circumferential line touches radially innermost areas of the hopper wall and circumscribes a minimum opening cross-section of a hopper opening of the hopper-provided for the extruder screw, and wherein the outer circumferential line touches the radially outermost areas of the recesses.

9. The charging system according to claim 8, wherein the hopper opening tapers along the hopper axis so that the minimum opening cross-section decreases along the hopper axis.

10. (canceled)

11. The charging system according to claim 1, wherein two recesses adjoin each other along a circumferential line around the hopper axis.

12. The charging system according to claim 11, wherein between two adjoining recesses a longitudinally extending separating edge is formed.

13. The charging system according to claim 11, wherein all recesses adjoin each other in pairs along the circumferential line around the hopper axis.

14. The charging system according to claim 1, wherein a connecting portion is formed between two recesses-along a circumferential line around the hopper axis.

15. The charging system according to claim 14, wherein the connecting portion is curved radially inwards, with respect to the hopper axis, or in cross-section the connecting portion extends along a portion of a circular line around the hopper axis and defines a flat wall surface.

16. (canceled)

17. (canceled)

18. The charging system according to claim 12, wherein the separating edge is adapted and provided such that at the separating edge at least part of granular processing material entering the hopper is comminuted while the extruder screw rotates.

19. The charging system according to claim 1, wherein the hopper with the recesses has a flower-shaped cross-section.

20. The charging system according to claim 1, wherein the hopper comprises a number n.sub.max of recesses distributed over the circumference, for which applies n.sub.max=U.sub.D/(a*1.2), wherein n.sub.max is the maximum number of recesses, U.sub.D is a circumferential length of the hopper, and a is a mean maximum outer dimension of a granule of a granular processing material to be fed via the charging system.

21. The charging system according to claim 1, wherein the hopper comprises 4 to recesses distributed over the circumference.

22. An extruder apparatus, comprising at least one extruder screw and at least one charging system according to claim 1.

23. A 3D printing device comprising at least one charging system according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The attached Figures by way of example illustrate possible design variants of the proposed solution.

[0031] FIG. 1 shows a perspective view of an insert for a charging system comprising a first design variant of a hopper flower-shaped in cross-section with a plurality of recesses distributed on the circumference of a hopper wall.

[0032] FIG. 2 shows an alternatively designed insert with a hopper likewise flower-shaped in cross-section.

[0033] FIG. 3 shows a further design variant of the insert with a differently designed hopper flower-shaped in cross-section.

[0034] FIG. 4A shows a cross-sectional view of a hopper.

[0035] FIG. 4B shows a perspective representation of the hopper of FIG. 4A or of the hopper opening defined therewith and of an outer shell surface.

[0036] FIG. 4C shows a segment of the cross-sectional view of FIG. 4A on an enlarged scale.

[0037] FIGS. 5A-5C sectionally and schematically show longitudinal sections through the hopper opening for illustrating different hopper opening geometries.

[0038] FIGS. 6A-6C show different cross-sections for design variants of a proposed hopper with and without separating edges between two adjacent and in particular adjoining recesses.

[0039] FIG. 7A shows a longitudinal section with an extruder screw arranged in the hopper opening of the hopper.

[0040] FIG. 7B in a view corresponding with FIG. 7A shows a differently designed hopper with a conically tapering extruder screw.

[0041] FIG. 8 in a perspective view by way of example shows a granule of a thermoplastic material to be processed by means of the proposed solution.

[0042] FIG. 9 shows a proposed design variant of a charging system in which an insert as shown in FIGS. 1, 2 and 3 and a hopper as shown in FIGS. 4A to 7B are used.

DETAILED DESCRIPTION

[0043] FIG. 9 shows a design variant of a proposed extruder apparatus in the form of a vertical extruder 1. The vertical extruder 1 comprising an extruder screw 2 is shown only in its upper region. The extruder 1 is connected to a charging system B comprising a material reservoir in the form of a bunker 3. At its end facing the extruder screw 2, the bunker 3 is provided with a feed ramp 4 which serves the trouble-free trickling down of granular processing material. The feed ramp 4 is a compact unit which in its upper region is connected to a bunker wall 301.

[0044] A (filling) hopper 5 directly rests against the extruder screw 2, wherein the granular processing material is conveyed from the feed ramp 4 into the hopper 5 by action of gravity. Between the feed ramp 4 and the hopper 5, an opening 80 is provided in the bunker wall 301, wherein the feed ramp 4 represents an upper boundary for the opening 80. An upper edge 501 of the hopper 5 merges into a horizontally extending feed zone 6 which in its length extends up to the outer bunker wall 301. This horizontally extending feed zone 6 is the lower boundary for the opening 80.

[0045] The opening 80 serves to receive a feeding device 8 and is dimensioned corresponding to the size of the feeding device 8. The feeding device 8 includes a pneumatically, hydraulically, mechanically or electrically driven lifting cylinder 801, a connecting rod 802 and a slide 803. The slide 803 is guided over the horizontally extending feed zone 6 along an adjustment direction V in the direction of a filling zone of the extruder 1. On its side facing the interior of the extruder, the slide 803 has an inclined surface 803a which follows the angle of the feed ramp 4. This surface 803a merges into a ramming surface 803b which is perpendicular and parallel to the bunker wall 301. The ramming surface 803b is at least as large as to correspond to the size of the granulate to be processed.

[0046] In the case of small-size screw extruders, the granulate trickling down can be compacted in connection with the granulate pushed back onto the feed ramp 4 and thus forms a wall W of powder that prevents new granulate from being fed to the extruder screw 2. The feeding device 8 prevents the granulate from being pushed back onto the feed ramp 4 on advancement of the slide 803. The stroke of the lifting cylinder 801 is dimensioned such that in the retracted state granulate can perpendicularly fall out of the bunker 3. Based on the retracted state of the lifting cylinder 801, the stroke length of the cylinder 801 corresponds to the distance between the upper edge 501 of the hopper 5 and the vertical ramming surface 803b of the slide 8. The feeding device 8 pierces blockages located in the way of the wall W, and granulate trickling down is actively conveyed into the hopper 5.

[0047] Thus, in operation of the extruder 1 the feeding device 8 conveys the processing material recirculated at the hopper 5 by action of the extruder screw 2 against a feed direction ZR together with processing material trickling down from the bunker 3 in the direction of the extruder screw 2. At the hopper 5, processing material recirculated by action of the rotating extruder screw 2 is blended with processing material additionally fed from the bunker 3. This requires a lower compaction of the processing material by the extruder screw 2, and the extruder screw 2 can be designed shorter.

[0048] In the charging system B of FIG. 9, the hopper 5 is formed with a plurality of recesses 51.2 on a hopper wall 51. The circumferentially extending hopper wall 51 provided with the recesses 51.2 defines a minimum opening cross-section for a hopper opening through which the extruder screw 2 extends along the hopper axis T from an upper hopper end to a lower hopper end. The hopper 5 here can be formed on a replaceable insert, for which different variants are illustrated in FIGS. 1, 2 and 3 by way of example.

[0049] In the insert E of FIG. 1, the hopper wall 51 includes six uniformly distributed, axially extending recesses 51.2 on its circumference. The axially extending recesses 51.2 each are curved radially outwards and thus are formed as recesses of concave cross-section on the hopper wall 51. Each recess 51.2 has a semi-circular cross-sectional area in such a way that a bulge of a recess 51.2 each forms a contour that follows a semi-circular line and extends symmetrically to a straight line extending radially with respect to the hopper axis T. Each recess 51.2 is formed to be radially tapering towards a hopper end 512 of the hopper 5. In the present case, a radial depth of a recess 51.2 decreases continuously with increasing axial extension along the hopper axis T as seen along the longitudinal extension of the respective recess 51.2. Furthermore, a diameter measured in a circumferential direction and hence a width of each recess 51.2 is greater by only a maximum of 20% as compared to a maximum dimension of a granule of the granular processing material to be guided to the extruder screw 2 by means of the charging system B. At the upper end of the hopper 5 a width or a diameter of a recess 51.2 consequently is dimensioned such that a granule can still fall into the respective recess 51.2 from above. At an upper hopper end, an individual granule thus can get into a cavity defined with a recess 51.2. Furthermore, the hopper 5 with its recesses 51.2 is dimensioned in such a way that a granule no longer can easily (i.e. non-destructively and hence without having been comminuted) get out again from a recess 51.2. Thus, the granules are retained in a plurality of defined conveying chambers adjusted to the (mean) dimensions of the granules and are blocked against a displacement out of these conveying chambers, which are each bordered radially on the outside by a recess 51.2 and radially on the inside by the extruder screw 2. In this way, under rotation of the extruder screw 2, an individual granule is forced to perform a downward axial movement along the hopper 5.

[0050] To avoid sharp separating and shear edges on the hopper wall 51, a transition between adjacent recesses 51.2 is provided in the design variant of FIG. 1 by radially inwardly convexly curved connecting portions 51.2 In the hopper geometry shown in FIG. 1, recesses 51.2 and connecting portions 51.1 thus steadily merge into each other along a curved circumferential line. The connecting portions 51.1 convexly curved radially inwards are dimensioned in such a way that no granule of the processing material to be processed fits into a resulting gap between a connecting portion 51.1 and an extruder screw 2 rotating into the hopper opening of the hopper 5. A gap between a connecting portion 51.1 and the extruder screw 2 thus is dimensioned so small that no granule fits into this gap.

[0051] In the design variant of FIG. 2, the insert E with the hopper 5 is designed differently. Here, the recesses 51.2 each directly adjoin each other and are separated from each other in pairs by a separating edge 511 extending along the hopper axis T. This separating edge 511 acts as a comminution edge within the hopper 5 and can be configured as an axially extended sharp-edged rib on which a granulate is crushed by action of the rotating extruder screw 2 and hence is comminuted. Furthermore, in the insert of FIG. 2 the number of recesses 51.2 uniformly distributed on the circumference is distinctly increased with respect to the design variant of FIG. 1. Here, more than fifteen recesses 51.2 are provided.

[0052] In addition, the surface area of the feed zone 6 is expanded with respect to the variant of FIG. 1. In the design variant of FIG. 2, the feed zone 6 with its feed edge portions 6A, 6B extends over a larger circumferential area at the upper end of the hopper 5. Analogously to the design variant of FIG. 1, the feed zone 6 of FIG. 2 however is also designed here such that the feed zone 6 (in the top view) laterally each ends in the region of a recess 51.2.

[0053] This is also realized in the design variant of FIG. 3. For this purpose, additional inclined ramps R1 and R2 are formed at a lateral edge of the feed zone 6 opening into the hopper 5. The number of recesses 51.2 in the hopper 5 of FIG. 3 is slightly reduced with respect to the design variant of FIG. 2.

[0054] In contrast to the design variant of FIGS. 1 and 2, the longitudinally extended recesses 51.2 of the design variant of FIG. 3 additionally are of axially tapering design. Thus, an end portion of each recess 51.2 is pointed in the direction of the lower hopper end 512. However, the recesses 51.2 of the design variant of FIG. 3 furthermore are also formed to be radially tapering so that a radial depth of each recess 51.2 decreases continuously in the direction of the lower hopper end 512.

[0055] FIGS. 4A, 4B and 4C illustrate geometrical parameters for the design of a hopper 5. FIG. 4A shows a top view of a cross-section through a hopper 5 with recesses 51.2 distributed over the circumference, between each of which convexly curved connecting portions 51.1 extend in the manner of bulges. The recesses 51.2 and connecting portions 51.1 merge into each other on the hopper wall 51 corresponding to a geometrically steady function.

[0056] Corresponding to the perspective representation of FIG. 4B, the hopper 5 conically tapers downwards towards the hopper end 512 with respect to an outer circumferential line 51B that touches the radially outermost regions of the recesses 512. Hence, while a diameter of the outer circumferential line 51B decreases continuously along the hopper axis T towards the lower hopper end 512 (due to the radial taper of the individual recesses 51.2), a diameter of an inner circumferential line 51A, which touches the radially innermost regions of the hopper wall 51, remains unchanged however along the hopper axis T. A minimum opening cross-section for the extruder screw 2 thus always remains the same along the hopper axis T.

[0057] In FIG. 4C, the diameter of the inner circumferential line 51A is designated with D2. This diameter D2 corresponds to the sum of a diameter D3 of the extruder screw 2 and a defined clearance in the form of a radial distance s between the extruder screw 2 and the circumferential, radially inwardly curved connecting portions 51.1 or the radially inwardly pointing convex bulge of the hopper wall 51 defined therewith in cross-section. This radial distance s, as already explained above, is smaller than a minimum dimension of a granule, which in uncomminuted form thereby fits into a gap between the extruder screw 2 and a bulge 51.1. When a granule G for example has a height H and a diameter D4 corresponding to FIG. 8, it applies: s<D4 and s<H.

[0058] In the design variant illustrated with reference to FIG. 4C, the individual recesses 51.2 are designed in cross-section to follow a semi-circular line so that each recess 51.2 defines a semi-circular cross-sectional area. A diameter d1 (varying along the hopper axis T) of the corresponding semi-circle hence defines a radial depth of each recess 51.1. The centers of the individual semi-circles of the recesses 51.1 lie on a circumferential line with the diameter D1 (with D1>D2). The diameter of the outer circumferential line 51B consequently is then given by D1+d1/2. At the upper end of the hopper 5, the diameter d1 is dimensioned such that a granule G corresponding to FIG. 8 can fall into the respective recess 51.2 from above. Here, for example d1?D4 and d1?H, respectively, will apply. A maximum number nmax of the recesses 51.1 formed on the hopper 5 and uniformly distributed over the circumference satisfies the restriction nmax=UD/(a*1.2), wherein UD represents a circumferential length of the hopper 5 along the circumferential line 51A and a represents a mean maximum outer dimension of a granule G of a granular processing material to be fed via the charging system. Then, a for example corresponds to the maximum of the two values D4 and H.

[0059] An outer shell surface of the hopper wall 51 also tapers with the outer circumferential line 51B. The shell surface hence is obtained as a linear areal interpolation from the arrangement of the recesses 51.1 each semi-circular in cross-section and of the recesses formed therewith including the interposed transitions towards the bulges 51.1 to form a circle that results from the outside diameter D3 of a screw blade of the extruder screw 2.

[0060] Corresponding to the longitudinal section of FIG. 5A, the outer circumferential line 51B can conically taper in the direction of the lower hopper end 512 along the hopper axis T and thereby along an extension or conveying direction ?z. An outer diameter of the hopper 5 thus is designed to decrease linearly and hence to decrease following a first-order function. However, this is not absolutely necessary. For example, a course corresponding to a curve of at least second order also is possible corresponding to FIG. 5B.

[0061] A radial taper of the recesses 51.2 was found to be advantageous for example especially with regard to granular processing material made of or comprising comparatively tough thermoplastics. In other processing materials it can also be advantageous, however, when the recesses 51.2 do not taper radially along the hopper axis T. Here, an outer circumferential line 51B then remains unchanged in its diameter in a longitudinal section corresponding to FIG. 5C.

[0062] With reference to the cross-sectional views of FIGS. 6A, 6B and 6C different designs of the hopper wall 51 and in particular of the areas between two adjacent recesses 51.2 are illustrated once again.

[0063] In the design variant of FIG. 6A, an axially extending separating edge 511 each extends between two recesses 51.2. In the cross-sectional view, the separating edges 511 lie on a circular line with the diameter D2 of FIG. 4C. The separating edges 511 act as a comminuting edge and in particular can be formed as ribs protruding radially in the direction of the extruder screw 2, on which granular processing material is comminuted when the extruder screw 2 rotates around the hopper axis T in operation of the extruder apparatus.

[0064] In the design variant of FIG. 6B, connecting portions 51.3 each having a flat wall surface are formed between adjacent recesses 51.2. At the transition from one connecting portion 51.3 to an adjacent recess 51.2 an unsteady transition is provided in the present case, so that a separating edge 511 likewise is each formed between a connecting portion 51.3 and an adjoining recess 51.2.

[0065] The variants of FIGS. 6A and 6B with the separating edges 511 are compared with the design variant of FIG. 6C, in which the recesses 51.2 each merge into convexly curved bulges 51.1 and hence connecting portions 51.1 curved radially inwards, steadily and hence free from a separating edge.

[0066] In the case of radially tapering recesses 51.2, as already explained above, a diameter of the inner circumferential line 51A can remain the same along the hopper axis T. In the longitudinal section corresponding to FIG. 7A, a diameter D3 of the extruder screw 2 thus also always remains unchanged. On the other hand, however, a design variant in which a diameter D3 is reduced continuously along the hopper axis T also is possible. Thus, the hopper opening conically tapers in the z-direction. Correspondingly, in the longitudinal section of FIG. 7B, the extruder screw 2 then also has a conical course.

[0067] In all design variants, the incoming granular material G easily falls into the hopper 5 and is moved on by the extruder screw 2. The hopper (inner) wall 51 in the hopper 5 formed with recesses 51.2 on the one hand prevents that the supplied processing material at the edge of the extruder screw 2 only moves in a circumferential direction, i.e. only with the rotation of the extruder screw 2, and is not conveyed downwards. As soon as grains of the granular processing material present at the edge of the extruder screw 2 impinge on the hopper wall 51, the blocking of the movement in a circumferential direction causes a movement in an axial direction. Due to the simultaneously very small space between the screw shaft and the screw blade of the extruder screw 2, the processing material cannot be moved on as a whole and is possibly additionally comminuted at separating edges 511 on the hopper inner wall 51 and moved downwards axially along the hopper axis T. The hardness of the screw shaft of the extruder screw 2 and the hopper wall 51 typically is greater than the hardness of the processing material to be processed.

[0068] It could be observed that by using the proposed hopper 5 without any thermal influence an improved compaction and homogenization of the processing material to be conveyed is obtained, which is distinctly improved as compared to conventional hopper solutions, in particular when comparatively tough thermoplastic materials are supplied. As compared to conventional hopper solutions, verifiably more uniform extrusion patterns can be realized. The compression zone and a discharge zone succeeding along a longitudinal hopper axis T furthermore can be of distinctly shortened design so that the extruder 1 remains very compact and a length-diameter ratio of 1:10 to 1:3 can be achieved.

LIST OF REFERENCE NUMERALS

[0069] 1 extruder [0070] 2 extruder screw [0071] 3 bunker (material reservoir) [0072] 301 bunker wall [0073] 4 feed ramp [0074] 5 hopper [0075] 501 upper edge of hopper [0076] 51 hopper wall [0077] 51.1 bulge (curved connecting portion) [0078] 51.2 recess [0079] 51.3 planar/flat connecting portion [0080] 511 comminuting/separating edge [0081] 512 hopper end [0082] 51A inner circumferential line [0083] 51B outer circumferential line/shell surface [0084] 6 horizontally extending feed zone [0085] 6A, 6B feed edge portion [0086] 7 opening [0087] 8 feeding device [0088] 80 opening [0089] 801 lifting cylinder [0090] 802 connecting rod [0091] 803 slide [0092] 803a inclined surface [0093] 803b ramming surface [0094] B charging system [0095] D.sub.1-D.sub.4, d.sub.1 diameter [0096] E insert [0097] G granulate (processing material) [0098] H height [0099] R1, R2 lateral ramp [0100] s distance [0101] T hopper axis [0102] V adjustment direction [0103] W wall [0104] ZR feed direction [0105] ?z direction of longitudinal extension/conveying direction