A dosing system for feeding the processed material to the extrusion screw, the dosing system comprising an axially extending recess in the hopper wall.

Abstract

An input system is provided for supplying process ingredients, particularly particulate process ingredients, to at least one extruder screw. The dosing system B comprises a hopper 5 configured to guide the processed raw material G along the feed direction ZR to the extrusion screw 2, the hopper 5 extending along a hopper axis T that extends parallel to the longitudinal axis of the extrusion screw 2 in a suitable mounting state of the dosing system B. The hopper 5 of the proposed dosing system B has a hopper wall 51 extending around the hopper axis T, with a number of recesses 51.2 each extending in the axial direction with reference to the hopper axis T.

Description

[Technical field]

[0001] The proposed solution specifically relates to an input system for feeding process raw materials to an extrusion screw, in particular an extrusion screw used for additive manufacturing with metal and / or ceramic and / or plastic injection molding granules. [Background technology]

[0002] Screw extruders are used in particular for the continuous production of injection moulded or die cast parts. In most cases, the extrusion screw, the injection nozzle and the mould are arranged in a horizontal line with respect to one another. The filling of the raw material, which is mainly present as granules or powder, generally takes place at the rear of the screw extruder in the so-called feeding zone. The raw material is introduced perpendicularly to the extrusion screw directly in a hopper, which sits on top of the barrel of the extruder. The hopper has a cross section large enough to prevent bridging, so that the raw material falls by gravity onto the screw and is drawn into it. For continuous production, so-called three-zone screw extruders are generally used, which draw in the raw material and convey it to the nozzle. The raw material is then compressed, degassed and homogenised. It is then filled into the mould under increased pressure.

[0003] The feed zone of a screw extruder is often configured as a barrel section of the housing of the screw extruder, which is provided with a hopper allowing the raw material to be fed to the screw. The minimum cross section of the barrel section and the hopper is selected so that bridging of the raw material present in granular form is not possible. This depends largely on the angle of repose and the coefficient of friction of the bulk raw material used.

[0004] DE 10 2014 018 081 A1 describes a 3D printing apparatus for additive manufacturing of metal parts. A screw extruder is also used, which processes the process feedstock present in the form of granules. The thermoplastically deformable process feedstock is extruded in layers by the screw extruder, which is arranged vertically in the traversable model head of the 3D printing apparatus, to produce a three-dimensional part. DE 10 2014 018 081 A1 does not contain any details regarding the conveying of the process feedstock to the extrusion screw.

[0005] Since screw-type extruders for additive manufacturing must be of a traversable design or the entire work station would move, their use is subject to limitations, particularly in terms of weight and overall size, which generally depend heavily on the length of the extrusion screw, but if the entire work station moves, the overall size of the 3D printing equipment would have to be significantly larger.

[0006] Against this background, an apparatus and a method for extruding raw material are already known from DE 10 2017 114 841 A1, which allows for improved compaction of granular raw material and thus allows for the extrusion of dense continuous filaments of raw material. For this purpose, the hopper of the input system is provided with a crushing tool, by means of which the raw material is selectively crushed by the rotation of the extrusion screw. This allows for an increased bulk density, particularly in the region of the extrusion screw.

[0007] The solution proposed in WO 2006 / 023663 already makes it possible to significantly improve the extrusion of processing feedstock for the additive manufacturing of parts. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] DE 102014018081 A1 [Patent Document 2] DE 102017114841 Summary of the Invention [Problem to be solved by the invention]

[0009] However, there is still room for improvement in this field, especially with regard to the specific requirements of additive manufacturing processes. [Means for solving the problem]

[0010] In view of the above background, a dosing system is proposed for feeding at least one extrusion screw with a specially designed hopper, which is adapted to guide said processed raw material along a feed direction to said extrusion screw. For this purpose, said hopper extends along a hopper axis which, in a suitable mounting state of the dosing system, runs parallel to the longitudinal axis of said extrusion screw. The proposed hopper has, in a hopper wall extending around said hopper axis, a number of recesses each extending axially relative to said hopper axis.

[0011] That is, the hopper axis of the proposed dosing system, when the dosing system is attached to an extrusion device for additive manufacturing of parts, extends parallel to the longitudinal axis of the extrusion screw, which typically extends vertically. The hopper wall of the hopper has a number of axially extending depressions, i.e. spaces, which locally expand the hopper mouth of the hopper by rebounding radially outward. It has been found that such a hopper shape provides a significant improvement in the extrusion of processing materials associated with additive manufacturing processes, in particular the extrusion of granular processing materials. For example, the proposed dosing system can be used to obtain a more uniform extrusion pattern for plastic granules, particularly for relatively tough thermoplastic materials.

[0012] In principle, the hopper can be configured as a separately manufactured unitary part that can be used interchangeably in an extrusion device with at least one extrusion screw, in particular, the hopper can be configured as part of a replaceable feeding device that can be installed in an extrusion device as a ready-made item for additive manufacturing.

[0013] In one design example, the recesses in the hopper wall are arranged continuously along a circumferential line around the hopper axis. In particular, the recesses can be arranged uniformly distributed on the hopper wall, in particular uniformly distributed along a circular circumferential line.

[0014] In principle, the cross-sectional geometry of the recess can be varied. In one design, the cross section of the recess (transverse to the hopper axis) is a design that is curved radially outwardly relative to the hopper axis. In particular, this includes designs in which the cross section of the recess in the hopper wall is concave.

[0015] At least one of the recesses may be designed to taper radially in order to facilitate the transport of the processed material in the axial direction along the hopper axis (i.e. along the longitudinal axis of the extrusion screw) and radially towards the extrusion screw. This causes the radial depth of the recess to decrease, in particular continuously decrease, at least at one end, and possibly even over the entire longitudinal extension of each recess, as it proceeds axially along the hopper axis. This means that less space can be occupied by the processed material through each recess along the hopper axis. For example, if each recess is dimensioned such that its width measured along a circumferential line around the hopper axis corresponds to or exceeds the maximum width or maximum particle size of the granules of the granular processed material, the granules can be moved axially downward along the recess by the rotation of the extrusion screw after entering the recess at the (upper) end of the hopper. That is, the width and depth of the depression are adjusted, for example, according to the granules of the granular processed raw material, so that a conveying chamber defined by the depression on the radially outer side and the extrusion screw on the radially inner side is formed in the hopper of the extrusion device, and during operation of the extrusion device, the individual granules are held in the conveying chamber adjusted to the (average) size of the granules and are blocked from escaping outside the conveying chamber. The width of the depression is at most 20% larger than the maximum width or maximum particle size of the granules.

[0016] The recess in the hopper wall may be configured to receive granular raw material with a maximum outer dimension of 15 mm or less, i.e. the outer dimension (width, length, height or grain size) of the granules of raw material is 15 mm or less, and the recess is dimensioned such that its width and radial depth at the upper end of the hopper are comparable to the maximum dimension of the granules to be processed. The design example of the proposed solution has been found to be particularly advantageous for processing granular raw material in which each granule can be surrounded by a nominal spherical volumetric space with a nominal diameter of 15 mm or a nominal cylindrical volumetric space with a nominal height of 15 mm and a nominal diameter of 10 mm, i.e. fits completely within the corresponding nominal volumetric space. For example, the proposed solution is advantageous for processing plastic granules with a nominal grain size of 1.5-6 mm, in particular 3 mm, long-fiber granules with a nominal height of less than 15 mm, in particular 9-12 mm, or ceramic granules with a nominal grain size of 1.5-8 mm, in particular 3 mm or 5 mm, in order to obtain a (more) uniform extrusion pattern. The width and depth of the depressions are thus located in the range of 1.875-18.75 mm, respectively.

[0017] To further promote uniform feeding and uniform extrusion of the processed material, in one design, all of the recesses in the hopper wall are each formed to taper in the radial direction, so that, for example, at one end of the hopper, the hopper wall may be circumferentially smooth, i.e., in the form of a smooth cylinder.

[0018] Alternatively or additionally, at least one of the recesses may be tapered in the axial direction, such that the width of the recess, measured in the circumferential direction, at least at one end and possibly even over the entire longitudinal extension of the recess, decreases, in particular continuously, as it proceeds axially along the hopper axis, i.e. in a suitable mounting state of the dosing system, the recess narrows, for example, towards the end of the hopper. As before, all recesses in the hopper wall may each be tapered in the axial direction.

[0019] If the recess is tapered in both the axial and radial directions, then both the width, as measured circumferentially, and the radial depth of the recess will decrease toward the end of the hopper.

[0020] Geometrically, the cross section of the hopper wall in which the recess is formed may define an inner circumferential line and an outer circumferential line. The inner circumferential line is tangent to the radially innermost part of the hopper wall, thereby defining the smallest opening cross section of the hopper opening for the extrusion screw of the hopper. On the other hand, the outer circumferential line is tangent to the radially outermost part of the recess. That is, the outer circumferential line circumscribes, for example, the maximum outer diameter of an imaginary cylinder or an imaginary truncated cone formed by the hopper wall with the recess extending from a first hopper (upper) end to a second hopper (lower) end.

[0021] In this case, as an example of a design, for example, the hopper mouth is tapered along the hopper axis so that the minimum opening cross section decreases along the hopper axis. For example, the hopper mouth can be tapered conically. As a result, the cross section that can be occupied by the extrusion screw, which is determined by the diameter of the hopper mouth, decreases toward the end of the hopper. A hopper designed in this way can be combined with a conically tapering extrusion screw.

[0022] On the other hand, in another design example where the recess narrows in the radial direction, the diameter of the outer circumferential line can decrease along the hopper axis while maintaining the minimum opening cross-section, i.e. the diameter of the outer circumferential line decreases along the hopper axis in cross-section, while the minimum opening cross-section of the hopper mouth provided for the extrusion screw (and therefore also the diameter of the inner circumferential line) remains constant along the hopper axis. As a result, in this example, the screw diameter of the extrusion screw of the extrusion device equipped with the dosing system is constant.

[0023] In one design example, two recesses are in contact with each other along a circumferential line around the longitudinal axis of the hopper, i.e., the two recesses are directly merged with each other. In particular, all recesses evenly distributed around the hopper axis may be in direct contact with each other in pairs along the circumferential line, i.e., for example, a dividing edge is formed between the adjacent recesses, extending in the longitudinal direction (i.e. along the hopper axis). Such a dividing edge may be formed as a crushing edge, in particular as a rib, along which the granular processed raw material is crushed, in particular pulverized, by the extrusion screw. In other words, the dividing edge formed corresponding to the two recesses allows a concentrated shearing action to be generated by the rotation of the extrusion screw.

[0024] As a variant, a connection may be formed between two recesses along a circumferential line around the hopper axis. That is, such a connection is not designed as a recess. In particular, the shape of the corresponding connection may be different compared to the two adjacent recesses. For example, the connection between two recesses is configured to protrude radially inward with respect to the hopper axis, i.e. in the direction of the hopper opening for the extrusion screw formed by the hopper. In particular, this also includes the case where the connection simply protrudes radially inward beyond the adjacent recess. In particular, the connection may form a flat or curved wall surface.

[0025] In the above case, the connecting portion is curved radially inward with respect to the hopper axis. For example, a convexly curved connecting portion is provided between two concavely curved recesses in the cross section of the hopper. In this case, a smooth transition portion may be provided in the circumferential direction so that no disconnection edge occurs between the connecting portion curved radially inward convexly and the recess curved radially outward concavely.

[0026] Alternatively, a non-curved connection may be formed, which in the cross section of the hopper extends along a part of a circular line around the hopper axis and forms a flat wall. The transition between such a connection and the adjacent recess may be a non-gradual transition or a gradual transition. The "non-gradual transition" also includes the case where a breaking edge is formed in the longitudinal direction. The breaking edge between the connection and the recess may also be formed as a crushing edge, in particular as a rib, and may be specifically configured and provided accordingly to break at least a part of the granular processed material entering the hopper during the rotation of the extrusion screw.

[0027] If the hopper is provided with a plurality of recesses in the hopper wall, in one design the hopper may have a flower-shaped cross section.

[0028] The number of recesses n of the hopper, for example distributed around its circumference, in particular uniformly distributed max teeth, Expression:n max =U D / (a×1.2) (In the formula, n max is the upper limit of the number of dimples, and U D is the circumferential length of the hopper, and a is the average maximum outer dimension of the granules of granular processed raw material supplied by the feeding system. By making the depressions distributed in the hopper conform to the above formula taking into account the raw material to be processed, not only is the maximum number of depressions formed in the circumferential direction, but it is also easy to design the depressions with dimensions that will hold the granular material in the depressions and block it from escaping outside the conveying chamber during operation of the extrusion device.

[0029] In principle, the hopper wall of the proposed dosing system can be provided with more than one recess. In one design example, the hopper wall is provided with more than three recesses. For example, the hopper can have 4 to 9, in particular 5 to 7 recesses distributed around the circumference. By providing more than three recesses or spaces, it is also possible, for example, to give the hopper a flower-shaped cross section.

[0030] The proposed solution further comprises an extrusion device comprising at least one extrusion screw and at least one design example of the proposed dosing system, which may be configured as a 3D modeling device or a 3D printer, i.e., the proposed extrusion device is provided for an additive manufacturing process in which a part is additively manufactured by extruding a processing feedstock by means of said extrusion screw.

[0031] The attached drawings illustrate possible design examples of the proposed solution. [Brief description of the drawings]

[0032] [Figure 1] FIG. 2 is a perspective view of an insert for a dosing system having a first design example hopper with a flower-shaped cross section with multiple recesses distributed around the circumference of the hopper wall. [Diagram 2] FIG. 13 shows an alternative insert design, also with a hopper having a flower-shaped cross section. [Diagram 3] FIG. 13 shows a further example insert design with a different hopper design having a flower-shaped cross section. [Figure 4A] FIG. [Figure 4B] FIG. 4B is a perspective view of the hopper of FIG. 4A, that is, the hopper opening and the outer shell surface formed in the hopper. [Figure 4C] FIG. 4B is a partially enlarged view of the cross-sectional view of FIG. 4A. [Figure 5A] FIG. 2 is a schematic, partial longitudinal cross-sectional view of a hopper mouth illustrating the geometry of the hopper mouth. [Figure 5B]4A-4C are schematic, partial longitudinal cross-sectional views of the hopper mouth illustrating other geometries of the hopper mouth. [Figure 5C] 11 is a schematic partial longitudinal cross-sectional view of a hopper mouth illustrating yet another alternative geometry of the hopper mouth; FIG. [Figure 6A] FIG. 13 is a cross-sectional view of a design example of the proposed hopper in which there is a disconnect edge between two adjacent recesses, specifically between two adjacent recesses. [Figure 6B] FIG. 13 is a cross-sectional view of another design of the proposed hopper with a breaking edge between two adjacent recesses. [Figure 6C] FIG. 13 is a cross-sectional view of yet another design example of the proposed hopper, in which there is no dividing edge between two adjacent recesses. [Figure 7A] FIG. 2 is a longitudinal cross-sectional view including an extrusion screw disposed at a hopper mouth of the hopper. [Figure 7B] FIG. 7B is a view similar to FIG. 7A showing an alternative hopper design with a conically tapering extrusion screw. [Figure 8] FIG. 1 is a perspective view of an example of a granule of thermoplastic raw material to be processed with the proposed solution. [Figure 9] 7A to 7C are diagrams showing a proposed design example of a feeding system using the insert shown in FIGS. 1 to 3 and the hopper shown in FIGS. 4A to 7B. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Figure 9 shows a design example of the proposed extrusion device in the form of a vertical extruder 1. Only the upper region of the vertical extruder 1 with the extrusion screw 2 is depicted in the figure. The extruder 1 is connected to a dosing system B with a raw material storage tank in the form of a bunker 3. At the end facing the extrusion screw 2, the bunker 3 is provided with a feed ramp 4, which serves to drop the granular processed raw material little by little without difficulty. The feed ramp 4 is a small element connected in its upper region to the bunker wall 301.

[0034] The extrusion screw 2 is in direct contact with a hopper 5 into which the granular processed raw material is conveyed (charged) by gravity from a feed ramp 4. Between the feed ramp 4 and the hopper 5, an opening 80 is provided in the bunker wall 301. The feed ramp 4 defines the upper boundary of the opening 80. The upper edge 501 of the hopper 5 is connected to a horizontally extending feed zone 6 whose length reaches the bunker outer wall 301. This horizontally extending feed zone 6 defines the lower boundary of the opening 80.

[0035] The opening 80 serves to receive the feed device 8 and is dimensioned according to the dimensions of the feed device 8. The feed device 8 consists of a pneumatically, hydraulically, mechanically or electrically driven lifting cylinder 801, a connecting rod 802 and a slide 803. The slide 803 is guided along an adjustment direction V over the horizontally extending feed zone 6 in the direction of the filling zone of the extruder 1. On its side facing the inside of the extruder, the slide 803 has an inclined surface 803a that follows the angle of the feed slope 4. This surface 803a merges with an abutment surface 803b that is perpendicular and parallel to the bunker wall 301. The abutment surface 803b is at least as large as the grain size of the granular material to be processed.

[0036] In the case of a small screw-type extruder, the granules falling little by little can be compressed together with the granules pushed back to the inlet slope 4, forming a powder wall W. The wall W prevents the next granules from being fed to the extrusion screw 2. The feeder 8 advances the slide 803 to prevent the granules from being pushed back onto the inlet slope 4. The stroke of the lifting cylinder 801 is set so that the granules can fall vertically from the bunker 3 in the retreated state. Taking the retreated state of the lifting cylinder 801 as a reference, the stroke length of the cylinder 801 corresponds to the distance between the upper edge 501 of the hopper 5 and the vertical abutment surface 803b of the slide 8. The feeder 8 breaks through the obstructing obstacle located at the wall W. The granules falling little by little are now actively transported to the hopper 5.

[0037] In this way, during operation of the extruder 1, the feed device 8 conveys the processed raw material returned by the extrusion screw 2 to the hopper 5 in the direction opposite to the feed direction ZR, together with the processed raw material dropping little by little from the bunker 3, toward the extrusion screw 2. In the hopper 5, the processed raw material returned by the rotation of the extrusion screw 2 is mixed with the processed raw material additionally supplied from the bunker 3. To achieve this, it is necessary to only lightly suppress the compression of the processed raw material by the extrusion screw 2, and the extrusion screw 2 can be designed to be short.

[0038] The hopper 5 in the feeding system B of Fig. 9 has a plurality of recesses 51.2 formed in a hopper wall 51. The hopper wall 51 extending in the circumferential direction and provided with the recesses 51.2 determines the minimum opening cross section of the hopper mouth through which the extrusion screw 2 extends along the hopper axis T from the upper end of the hopper to the lower end of the hopper. Here, the hopper 5 may be formed in a replaceable insert. Various examples of the insert are illustrated in Figs. 1 to 3.

[0039] In the insert E of FIG. 1, the hopper wall 51 has six axially extending recesses 51.2 uniformly distributed around its circumference. Each of the axially extending recesses 51.2 is curved radially outwardly, so that it is formed in the hopper wall 51 as a recess of concave cross section. Each recess 51.2 has a semicircular cross section, and the contour formed by the bulging portion of each recess 51.2 follows a semicircular line and extends symmetrically with respect to a straight line extending radially from the hopper axis T. Each recess 51.2 is formed so as to narrow in the radial direction toward the hopper end 512 of the hopper 5, i.e., to taper along the radial direction. In this example, the radial depth of the recess 51.2 decreases continuously over the longitudinal extension of each recess 51.2 as it proceeds axially along the hopper axis T. Moreover, the diameter, i.e. the width, of each recess 51.2 measured in the circumferential direction is at most 20% larger than the maximum dimension of the granules of the granular raw material to be guided by the dosing system B to the extrusion screw 2. That is, the width or diameter of the recesses 51.2 at the upper end of the hopper 5 is dimensioned in such a way that the granules can fall from above into each recess 51.2. At the upper end of the hopper, the individual granules can therefore enter the space formed by the recesses 51.2. The recesses 51.2 of the hopper 5 are also dimensioned in such a way that the granules cannot easily (i.e. without being destroyed, i.e. without being crushed) escape from the recesses 51.2 again. The granules are thus held in a number of predetermined transport chambers adjusted to the (average) dimensions of the granules and blocked from escaping from the transport chambers. The transport chambers are each bounded radially outwards by the recesses 51.2 and radially inwards by the extrusion screw 2. In this way, as the extrusion screw 2 rotates, the individual granules are forced to move axially downwards along the hopper 5 .

[0040] In the design example of FIG. 1, the transition between adjacent recesses 51.2 is provided by a connecting portion 51.2 that is convexly curved inwardly in the radial direction so that the cutting and shearing edges of the hopper wall 51 are not sharp. Thus, in the hopper geometry shown in FIG. 1, the recesses 51.2 and the connecting portion 51.1 merge smoothly into each other along a curved circumferential line. The connecting portion 51.1 that is convexly curved inwardly in the radial direction is dimensioned so that the granular material to be processed does not get stuck in the gap that occurs between the extrusion screw 2 that turns around and enters the hopper mouth of the hopper 5 and the connecting portion 51.1. In other words, the gap between the connecting portion 51.1 and the extrusion screw 2 is set small so that the granular material does not get stuck in this gap.

[0041] In the design example of FIG. 2, the insert E with the hopper 5 has a different design. Here, the depressions 51.2 are in direct contact with each other and are separated from each other in pairs by a dividing edge 511 extending along the hopper axis T. This dividing edge 511 can be configured as an axially extending rib with a sharp edge, which serves as a crushing edge in the hopper 5 and along which the granules are crushed, i.e. crushed, by the rotation of the extrusion screw 2. Furthermore, in the insert of FIG. 2, the number of depressions 51.2, which are uniformly distributed in the circumferential direction, is significantly increased compared to the design example of FIG. 1. Here, more than 16 depressions 51.2 are provided.

[0042] Furthermore, the surface area of ​​the feeding zone 6 is also enlarged compared to the example of Fig. 1. In the design example of Fig. 2, the circumferential area covered by the feeding edges 6A, 6B of the feeding zone 6 at the upper end of the hopper 5 is enlarged. However, here, like the design example of Fig. 1, the feeding zone 6 of Fig. 2 is also configured such that each side of the feeding zone 6 ends (in plan view) in the area of ​​the recess 51.2.

[0043] This is also realized in the design example of FIG. 3. For this purpose, additional inclined slopes R1, R2 are formed on the side edges 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 compared to the design example of FIG. 2.

[0044] In contrast to the designs of Figures 1 and 2, the longitudinally extending recesses 51.2 in the design of Figure 3 are furthermore designed to taper in the axial direction, i.e. one end of each recess 51.2 points towards the hopper bottom end 512. However, the recesses 51.2 in the design of Figure 3 are also designed to taper in the radial direction, so that the radial depth of each recess 51.2 continuously decreases in the direction towards the hopper bottom end 512.

[0045] Figures 4A, 4B and 4C show the geometric parameters used in the design of the hopper 5. Figure 4A shows a plan view in section of a hopper 5 with recesses 51.2 distributed over the circumference, between which convexly curved connecting sections 51.1 extend in the manner of bulges. In the hopper wall 51, the recesses 51.2 and the connecting sections 51.1 merge with each other and correspond to a geometrically smooth function.

[0046] 4B, the hopper 5 tapers conically from an outer circumferential line 51B tangent to the radially outermost region of the recesses 512 downwards towards the hopper end 512. That is, the diameter of the outer circumferential line 51B decreases continuously (due to the radial narrowing of the individual recesses 51.2) along the hopper axis T towards the hopper lower end 512, whereas the diameter of the inner circumferential line 51A tangent to the radially innermost region of the hopper wall 51 remains constant along the hopper axis T. Thus, the minimum opening cross section for the extrusion screw 2 remains the same all along the hopper axis T.

[0047] In FIG. 4C, the diameter of the inner circumferential line 51A is defined as D2. This diameter D2 corresponds to the sum of the diameter D3 of the extrusion screw 2 plus a predetermined gap in the form of a radial distance s in a cross-sectional view between the circumferential connecting portion 51.1 curved radially inward (i.e., the convex bulging portion of the hopper wall 51 facing radially inward, formed by the connecting portion 51.1) and the extrusion screw 2. As described above, this radial distance s is shorter than the minimum dimension of the granular material, so that the granular material in the form before crushing does not get stuck in the gap between the extrusion screw 2 and the bulging portion 51.1. For example, if the height of the granular material G is H and the diameter (particle size) is D4 in accordance with FIG. 8, then s <D4およびs<Hとなる。

[0048] In the design example described with reference to FIG. 4C, the cross section of each of the depressions 51.2 is designed to follow a semicircular line, so that each depression 51.2 forms a semicircular cross-sectional area. The diameter d1 (which varies along the hopper axis T) of the corresponding semicircle thus defines the radial depth of each depression 51.1. The center of each semicircle of the depressions 51.1 is located on a circumferential line of diameter D1 (D1>D2). The diameter of the outer circumferential line 51B is therefore given by D1+d1 / 2. At the upper end of the hopper 5, the diameter d1 is set so that the granular material G corresponding to FIG. 8 can fall from above into each depression 51.2. In this case, for example, d1≧D4 and d1≧H, respectively, apply. The upper limit n of the number of depressions 51.1 formed in the hopper 5 and distributed uniformly in the circumferential direction is max teeth, Expression:n max =U D / (a×1.2) (In the formula, U D represents the circumferential length of the hopper 5 along the circumferential line 51A, and a represents the average maximum outer dimension of the granules G of the granular processing raw material supplied by the feeding system. In other words, a corresponds to the maximum value of the two numerical values ​​D4 and H, for example.

[0049] The outer shell surface of the hopper wall 51 also tapers along the outer circumferential line 51B. In other words, the shell surface is obtained by linearly interpolating the areas of the recesses 51.1 each having a semicircular cross section and the springs including transition portions interposed on the bulge portion 51.1 side so as to form a circle derived from the outer diameter D3 of the screw blade of the extrusion screw 2 together with the recesses 51.1.

[0050] Corresponding to the longitudinal section of Fig. 5A, the outer circumferential line 51B may taper conically along the hopper axis T, i.e. along the extension or conveying direction -z, in the direction of the hopper lower end 512. The outer diameter of the hopper 5 is therefore configured to decrease linearly, i.e. according to a linear function. However, this is not essential. For example, corresponding to Fig. 5B, but also corresponding to a curve of at least a second order, is possible.

[0051] For example, the radially tapered configuration of the recess 51.2 has been found to be particularly advantageous for granular processed feedstock consisting of or containing a relatively tough thermoplastic material. However, with other processed feedstock, it may be advantageous if the recess 51.2 does not taper radially along the hopper axis T. This corresponds to Figure 5C, but the diameter of the outer circumferential line 51B remains unchanged in longitudinal section.

[0052] With reference to the cross-sectional views of Figures 6A to 6C, various designs of the hopper wall 51, in particular the portion between two adjacent recesses 51.2, will again be explained.

[0053] In the design example of Fig. 6A, an axially extending cutting edge 511 extends between each of the two recesses 51.2. In cross-section, the cutting edges 511 are located on a circular line of diameter D2 in Fig. 4C. The cutting edges 511 serve as crushing edges along which the granular processed raw material is crushed when the extrusion screw 2 rotates around the hopper axis T during operation of the extrusion device, and can in particular be formed as ribs projecting radially in the direction of the extrusion screw 2.

[0054] In the design example of Fig. 6B, adjacent recesses 51.2 are provided with connecting portions 51.3 each having a flat wall, such that the transition from one connecting portion 51.3 to the adjacent recess 51.2 is not smooth, so that a breaking edge 511 is also provided between the connecting portion 51.3 and each adjacent recess 51.2.

[0055] In the design example of Fig. 6C, in comparison with the examples of Fig. 6A and Fig. 6B, which have a breaking edge 511, each depression 51.2 merges smoothly with a convexly curved bulge 51.1, i.e., a radially inwardly curved connecting portion 51.1, so that there is no breaking edge.

[0056] As already mentioned, in the case of the radially tapered recess 51.2, the diameter of the inner circumferential line 51A can remain the same along the hopper axis T. Thus, in the longitudinal section corresponding to FIG. 7A, the diameter D3 of the extrusion screw 2 also remains constant. However, on the contrary, designs are also possible in which the diameter D3 decreases continuously along the hopper axis T, i.e. the hopper mouth tapers conically in the z-direction. In the corresponding longitudinal section of FIG. 7B, the trajectory of the extrusion screw 2 also follows a conical trajectory.

[0057] In either design example, the incoming granular raw material G easily falls into the hopper 5 and is carried forward by the extrusion screw 2. The recess 51.2 formed in the hopper (inner) wall 51 of the hopper 5 ensures that the processed raw material fed to the edge of the extrusion screw 2 moves only in the circumferential direction, i.e., does not rotate with the extrusion screw 2 and is not carried downward. When the grains of the granular processed raw material present at the edge of the extrusion screw 2 hit the hopper wall 51, they move in the axial direction because their circumferential movement is prevented. At the same time, the space between the screw shaft of the extrusion screw 2 and the screw blade is also very small, so that the processed raw material cannot move forward intact, and in some cases, it is additionally crushed at the dividing edge 511 of the hopper inner wall 51 and moves axially downward along the hopper axis T. In general, the hardness of the screw shaft of the extrusion screw 2 and the hopper wall 51 is higher than the hardness of the processed raw material to be processed.

[0058] With the proposed hopper 5, it is possible to observe an improved compression and homogenization of the processed material being conveyed without any thermal influence, especially when feeding relatively tough thermoplastic material, compared to conventional hopper solutions. A more uniform extrusion pattern can be achieved and observed compared to conventional hopper solutions. It also allows a significantly shorter design of the subsequent compression and discharge zones along the longitudinal axis T of the hopper, keeping the extruder 1 very compact, with a length-diameter ratio of 1:10 to 1:3. [Explanation of symbols]

[0059] 1. Extruder 2 Extrusion screw 3 Bunker (raw material storage tank) 301 Bunker Wall 4 Supply slope 5. Hopper 501 Hopper upper edge 51 Hopper Wall 51.1 Bulge (curved joint) 51.2 Depression 51.3 Flat / flat joints 511 Crushing / Cutting Edge 512 Hopper end 51A Inner circumferential line 51B Outer Circumferential Line / Outer Shell Surface 6 Horizontal supply zone 6A, 6B Supply edge 7 Openings 8 Feeding device 80 aperture 801 Lifting cylinder 802 Connecting rod 803 Slides 803a Slope 803b Immediately B Input System D1~D4,d1 diameter E Insert G Granules (processed raw materials) H Height R1, R2 Side slope s distance T Hopper axis V Adjustment direction W Wall ZR supply direction -z Longitudinal direction / transport direction

Claims

1. A dosing system for feeding process raw material (G) to at least one extrusion screw (2), comprising: A dosing system comprising a hopper (5) adapted to guide the processed raw material (G) along a feed direction (ZR) to the extrusion screw (2) and extending along a hopper axis (T) parallel to the longitudinal axis of the extrusion screw (2) in a suitable mounting state of the dosing system (B), The dosing system according to claim 1, wherein the hopper (5) has a hopper wall (51) extending around the hopper axis (T) and a plurality of recesses (51.2) each extending in an axial direction with respect to the hopper axis (T).

2. 2. The dosing system according to claim 1, characterized in that the recesses (51.2) are provided continuously along a circumferential line (51A) around the hopper axis (T).

3. 2. The dosing system according to claim 1, characterized in that the cross section of the recess (51.2) is curved radially outwardly with respect to the hopper axis (T).

4. 2. The dosing system according to claim 1, characterized in that at least one of the recesses (51.2) is tapered in the radial direction.

5. 5. The dosing system according to claim 4, characterized in that all the recesses (51.2) are formed so as to be tapered in the radial direction.

6. 2. The dosing system according to claim 1, characterized in that at least one of the recesses (51.2) is tapered in the axial direction.

7. 7. The dosing system according to claim 6, characterized in that all the recesses (51.2) are respectively tapered in the axial direction.

8. 2. The dosing system according to claim 1, characterized in that the cross section of the hopper wall (51) in which the recess (51.2) is formed defines an inner circumferential line (51A) and an outer circumferential line (51B), the inner circumferential line (51A) being tangent to the radially innermost part of the hopper wall (51) and defining the minimum opening cross section of a hopper mouth provided for the extrusion screw (2) of the hopper (5), and the outer circumferential line (51B) being tangent to the radially outermost part of the recess (51.2).

9. 9. The dosing system according to claim 8, characterized in that the hopper mouth is tapered along the hopper axis (T) such that the minimum opening cross-section decreases along the hopper axis (T).

10. 6. The dosing system according to claim 5, wherein the radially tapered recess (51.2) is adapted to reduce the diameter (D) of the outer circumferential line (51B). １ +d １ / 2) decreases along the hopper axis (T) while maintaining the minimum opening cross section along the hopper axis.

11. 2. The dosing system according to claim 1, characterized in that two recesses (51.2) abut each other along a circumferential line (51A) around the hopper axis (T).

12. 12. The dosing system according to claim 11, characterized in that between two adjacent recesses (51.2) a breaking edge (511) is formed extending in the longitudinal direction.

13. 12. The dosing system according to claim 11, characterized in that all the recesses (51.2) are in contact with each other in pairs along the circumferential line (51A) around the hopper axis (T).

14. 2. The dosing system according to claim 1, characterized in that a connection (51.1, 51.3) is formed between two recesses (51.2) along a circumferential line (51A) around the hopper axis (T).

15. The dosing system according to claim 14, characterized in that the connecting portion (51.2) is curved radially inwards with respect to the hopper axis (T).

16. 15. The dosing system according to claim 14, characterized in that the cross section of the connecting part (51.3) extends along a part of a circular line around the hopper axis (T) to form a flat wall.

17. 17. The dosing system according to claim 16, characterized in that the transition between the connection part (51.3) and the adjacent recess (51.2) is formed with a longitudinally extending breaking edge (511).

18. The dosing system according to claim 12, characterized in that the cutting edge (511) is configured and arranged so that at least a part of the granular processed raw material (G) entering the hopper (5) is crushed by the cutting edge (511) while the extrusion screw (2) rotates.

19. 2. The dosing system according to claim 1, characterized in that the cross section of the hopper (5) with the recess (51.2) is a flower-shaped cross section.

20. 2. The dosing system according to claim 1, wherein the number n of recesses (51.2) distributed around the circumference of the hopper (5) is ｍａｘ but, Formula: n ｍａｘ = U Ｄ / (a × 1.2) (In the formula, n ｍａｘ is the upper limit of the number of depressions (51.2), and U Ｄ is the circumferential length of the hopper (5), and a is the average maximum outer dimension (D) of the granules (G) of the granular raw material to be processed that is fed by the feeding system (B). ４ , H) An injection system, characterized in that:

21. 2. The dosing system according to claim 1, characterized in that the hopper (5) has between 4 and 9 recesses (51.2) distributed around the circumference.

22. The feeding system as described in claim 1, characterized in that the hopper (5) has 5 to 7 recesses (51.2) distributed circumferentially.

23. At least one extrusion screw (2); At least one dosing system (B) according to claim 1, An extrusion device comprising:

24. 3D printing apparatus comprising at least one input system (B) according to claim 1.

Images