Apparatus for processing plastic material

Abstract

Disclosed is an apparatus for the processing of plastics, with a container with a rotatable mixing, where, in a side wall, an aperture is formed, where a conveyor is provided, with a screw rotating in a housing, wherein the imaginary continuation of the longitudinal axis of the conveyor in a direction opposite to the direction of conveying passes the axis of rotation, and wherein the ratio (V) of the active container volume (SV) to the feed volume (BV) of the container or of the cutter compactor (1), where V=SV/BV, is one where 4?V?30, where the active container volume (SV) is defined by the formula $\mathrm{SV}=D^3\frac{?}{4}$
and D is the internal diameter of the container, and where the feed volume (BV) is defined by the formula $\mathrm{BV}=D^2\frac{?}{4}.Math.H,$
where H is the height of the intake aperture.

Claims

1. An apparatus for treatment of plastic material, the apparatus comprising: a container configured to hold the plastic material for initial treatment, wherein the container comprises a sidewall having an outlet aperture configured to pass initially treated plastic material from the container; a mixing and/or comminution implement comprising first and second blades configured to rotate about an axis of rotation in a first direction of rotation so as to initially treat the plastic material in the container by at least one of mixing, heating, and comminuting the plastic material, each of the first and second blades protruding convexly in the first direction of rotation; and a conveyor, comprising: a housing comprising an intake aperture configured to receive the initially treated plastic material from the outlet aperture of the container, and a screw in the housing, wherein the screw is configured to rotate within the housing in a second direction of rotation to further treat the initially treated plastic material by at least one of plastifying and agglomerating the initially treated plastic material and to convey the initially treated plastic material away from the intake aperture in a first direction, wherein an imaginary continuation of a central longitudinal axis of the screw infinitely extending in a direction opposite the first direction, does not intersect the axis of rotation of the mixing and/or comminution implement, wherein a scalar product of a first direction vector that is parallel with the first direction and a second direction vector that is tangential to a circle described by a radially outermost point of the mixing and/or comminution implement at a point on the circle nearest the outlet aperture is zero or negative, wherein a ratio (V) of an active container volume (SV) to a feed volume (BV) of the container, where V=SV/BV, conforms with 4?V?30, where the active container volume (SV) is defined by the formula $\mathrm{SV}=D^3\frac{?}{4}$ where D is an internal diameter of the container, where the feed volume (BV) is defined by the formula $\mathrm{BV}=D^2\frac{?}{4}.Math.H,$ and where H is a height of the intake aperture with respect to a bottom surface of the container, wherein a ratio (VS) of the feed volume (BV) of the container to a screw volume (SE) at the intake aperture complies with 20?VS?700, wherein the screw volume (SE) is defined by the formula $\mathrm{SE}=F.Math.L\frac{?}{4}\left(2\mathrm{dT}-T^2\right),$ where L is an effective length of the intake aperture extending in the first direction, factor F >0, and T is a flight depth of the screw, wherein the first and second blades are separated by an empty space configured to receive a portion of the plastic material for initial treatment, wherein a line from the first blade to the second blade intersects the empty space, and wherein the axis of rotation of the mixing and/or comminution implement intersects the empty space, wherein a scalar product of the first direction vector and a third direction vector that is tangential to a circle described by a radially innermost point of the mixing and/or comminution implement adjacent the empty space at a point on the circle nearest the outlet aperture is zero or negative, wherein a substantially planar surface of each of the first and second blades of the mixing and/or comminution implement is parallel with the bottom surface of the container, and defines a plane which intersects the outlet aperture, and wherein the sidewall defines a radius, and wherein an outermost portion of the planar surface of the first and second blades of the mixing and/or comminution implement when nearest the outlet aperture is spaced apart from the outlet aperture by about 5% of the radius, wherein when one of the first blade and the second blade is in a position closest to the screw of the conveyor, the one of the first blade and the second blade protrudes convexly in a second direction opposite to the first direction.

2. The apparatus according to claim 1, wherein the height H of the intake aperture complies with the formula H=k.sub.1d, where d is a diameter of the screw and k.sub.1 is a constant, and where 0.3?k.sub.1?1.5.

3. The apparatus according to claim 1, wherein L is defined by the formula L=k.sub.2d and k.sub.2 is a constant, with 0.5?k.sub.2?3.5.

4. The apparatus according to claim 1, wherein T is defined by the formula T=k.sub.3d, where k.sub.3 is a constant, with 0.05?k.sub.3?0.25.

5. The apparatus according to claim 1, wherein 0.85?F?0.95.

6. The apparatus according to claim 1, wherein an angle (?) between the first direction vector and the second direction vector when a plane defined by the axis of rotation and the radially outermost point of the mixing and/or comminution implement first intersects the outlet aperture as the mixing and/or comminution implement passes the outlet aperture is greater than or equal to 90? and is less than or equal to 180?.

7. The apparatus according to claim 1, wherein an angle (?) between the first direction vector and the second direction vector when the radially outermost point of the mixing and/or comminution implement is nearest the outlet aperture is greater than or equal to 170? and less than or equal to 180?.

8. The apparatus according to claim 1, wherein the shortest distance between the axis of rotation and the imaginary continuation is at least one of: greater than or equal to half of a diameter of the screw, and greater than or equal to 7% of a radius of the container.

9. The apparatus according to claim 1, wherein the imaginary continuation passes through the container.

10. The apparatus according to claim 1, wherein at least one of: the conveyor is attached tangentially to the container; the central longitudinal axis of the conveyor runs tangentially with respect to an inner side of the sidewall of the container; the screw runs tangentially with respect to the inner side of the sidewall of the container; the housing runs tangentially with respect to the inner side of the sidewall of the container; and an envelope of the screw runs tangentially with respect to the inner side of the sidewall of the container, wherein the apparatus further comprises a drive connected to the screw, wherein the screw is configured to convey further treated material to an extruder head at an end of the housing.

11. The apparatus according to claim 1, wherein there is a direct connection between the outlet aperture and the intake aperture, such that there is substantially no separation between the outlet aperture and the intake aperture.

12. The apparatus according to claim 1, wherein the first and second blades on or a rotatable implement carrier parallel to the bottom surface of the container.

13. The apparatus according to claim 12, wherein the implement carrier is spaced apart from the bottom surface by 10 mm to 400 mm.

14. The apparatus according to claim 1, wherein a leading edge of the first and second blades different from a trailing edge of the first and second blades.

15. The apparatus according to claim 1, wherein the container has a circular cross section, and wherein the bottom surface is substantially perpendicular to the sidewall.

16. The apparatus according to claim 1, wherein the conveyor comprises a single-screw extruder with a single compression screw, or comprises a multiscrew extruder comprising a plurality of screws, where the diameters of the individual screws of the multiscrew extruder are all substantially identical.

17. The apparatus according to claim 1, wherein 5?V?25.

18. The apparatus according to claim 1, wherein the height H of the intake aperture complies with the formula H=k.sub.1d, where d is a diameter of the screw and k.sub.1 is a constant, where 0.5?k.sub.1?1.15.

19. The apparatus according to claim 1, wherein a ratio (VS) of the feed volume (BV) of the container to a screw volume (SE) at the intake aperture complies with 50?VS?450.

20. The apparatus according to claim 1, wherein L is defined by the formula L=k.sub.2d and k.sub.2 is a constant, with 1?k.sub.2?2.8.

21. The apparatus according to claim 1, wherein T is defined by the formula T=k.sub.3d, where k.sub.3 is a constant, with 0.1?k.sub.3?0.25.

22. The apparatus according to claim 1, wherein T is defined by the formula T=k.sub.3d, where k.sub.3 is a constant, with 0.1?k.sub.3?0.2.

23. The apparatus according to claim 1, wherein F=0.9.

24. The apparatus according to claim 1, wherein an angle (?) between the first direction vector and the second direction vector when a plane defined by the axis of rotation and the radially outermost point of the mixing and/or comminution implement last intersects the outlet aperture as the mixing and/or comminution implement passes the outlet aperture is greater than or equal to 90? and is less than or equal to 180?.

25. The apparatus according to claim 1, wherein the shortest distance between the axis of rotation and the imaginary continuation is at least one of: greater than or equal to half of a diameter of the screw, and greater than or equal to 20%, of a radius of the container.

Description

(1) Further features and advantages of the invention are apparent from the description of the inventive examples below of the subject matter of the invention, which are not to be interpreted as restricting, and which the drawings depict diagrammatically and not to scale:

(2) FIG. 1 shows a vertical section through an apparatus according to the invention with extruder attached approximately tangentially.

(3) FIG. 2 shows a horizontal section through the embodiment of FIG. 1.

(4) FIG. 3 shows another embodiment with minimal offset.

(5) FIG. 4 shows another embodiment with relatively large offset.

(6) Neither the containers, nor the screws nor the mixing implements are to scale, either themselves or in relation to one another, in the drawings. By way of example, therefore, the containers are in reality mostly larger, or the screws longer, than depicted here.

(7) The advantageous cutter-compactor/extruder combination depicted in FIG. 1 and FIG. 2 for the treatment or recycling of plastics material has a cylindrical container or cutter compactor or shredder 1 with circular cross section, with a level, horizontal basal surface 2 and with a vertical side wall 9 oriented normally thereto with the shape of a cylinder jacket.

(8) Arranged at a small distance from the basal surface 2, at most at about 10 to 20%, or optionally less, of the height of the side wall 9measured from the basal surface 2 to the uppermost edge of the side wall 9is an implement carrier 13 or a level carrier disc orientated parallel to the basal surface 2, which carrier or disc can be rotated, in the direction 12 of rotation or of movement indicated by an arrow 12, around a central axis 10 of rotation, which is simultaneously the central axis of the container 1. A motor 21, located below the container 1, drives the carrier disc 13. On the upper side of the carrier disc 13, blades or implements, e.g. cutter blades, 14 have been arranged, and together with the carrier disc 13 form the mixing and/or comminution implement 3.

(9) As indicated in the diagram, the blades 14 are not arranged symmetrically on the carrier disc 13, but instead have a particular manner of formation, set-up or arrangement on their frontal edges 22 facing in the direction 12 of rotation or of movement, so that they can have a specific mechanical effect on the plastics material. The radially outermost edges of the mixing and comminution implements 3 reach a point which is relatively close to, about 5% of the radius 11 of the container 1 from, the inner surface of the side wall 9.

(10) The container 1 has, near the top, a charging aperture through which the product to be processed, e.g. portions of plastics foils, is charged by way of example by means of a conveying device in the direction of the arrow. The container 1 can, as an alternative, be a closed container and capable of evacuation at least as far as an industrial vacuum, the material being introduced by way of a system of valves. The said product is received by the circulating mixing and/or comminution implements 3 and is raised to form a mixing vortex 30, where the product rises along the vertical side wall 9 and, approximately in the region of the effective container height H, falls back again inward and downward into the region of the centre of the container, under gravity. The effective height H of the container 1 is approximately the same as its internal diameter D. In the container 1, a mixing vortex 30 is thus formed, in which the material is circulated in a vortex both from top to bottom and also in the direction 12 of rotation. By virtue of this particular arrangement of the mixing and comminution elements 3 or the blades 14, this type of apparatus can therefore be operated only with the prescribed direction 12 of rotation or movement, and the direction 12 of rotation cannot be reversed readily or without additional changes.

(11) The circulating mixing and comminution implements 3 comminute and mix the plastics material introduced, and thereby heat and soften it by way of the mechanical frictional energy introduced, but do not melt it. After a certain residence time in the container 1, the homogenized, softened, doughy but not molten material is, as described in detail below, removed from the container 1 through an aperture 8, passed into the intake region of an extruder 5, and received by a screw 6 there and subsequently melted.

(12) At the level of the, in the present case single, comminution and mixing implement 3, the said aperture 8 is formed in the side wall 9 of the container 1, and the pretreated plastics material can be removed from the interior of the container 1 through this aperture. The material is passed to a single-screw extruder 5 arranged tangentially on the container 1, where the housing 16 of the extruder 5 has, situated in its jacket wall, an intake aperture 80 for the material to be received by the screw 6. This type of embodiment has the advantage that the screw 6 can be driven from the lower end in the drawing by a drive, depicted only diagrammatically, in such a way that the upper end of the screw 6 in the drawing can be kept free from the drive. The discharge aperture for the plastified or agglomerated plastics material conveyed by the screw 6 can therefore be arranged at this upper end, e.g. in the form of an extruder head not depicted. The plastics material can therefore be conveyed without deflection by the screw 6 through the discharge aperture; this is not readily possible in the embodiments according to FIGS. 3 and 4.

(13) There is connection for conveying of material or for transfer of material between the intake aperture 80 and the aperture 8, and in the present case this connection to the aperture 8 is direct and immediate and involves no prolonged intervening section and no separation. All that is provided is a very short transfer region.

(14) In the housing 16, there is a screw 6 with compressing effect, mounted rotatably around its longitudinal axis 15. The longitudinal axis 15 of the screw 6 and that of the extruder 5 coincide. The extruder 5 conveys the material in the direction of the arrow 17. The extruder 5 is a conventional extruder known per se in which the softened plastics material is compressed and thus melted, and the melt is then discharged at the opposite end, at the extruder head.

(15) The mixing and/or comminution implements 3 or the blades 14 are at approximately the same level as the central longitudinal axis 15 of the extruder 5. The outermost ends of the blades 14 have adequate separation from the flights of the screw 6.

(16) In the embodiment according to FIGS. 1 and 2, the extruder 5 is, as mentioned, attached tangentially to the container 1, or runs tangentially in relation to its cross section. In the drawing, the imaginary continuation of the central longitudinal axis 15 of the extruder 5 or of the screw 6 in a direction opposite to the direction 17 of conveying of the extruder 5 towards the rear passes the axis 10 of rotation and does not intersect the same. On the outflow side, there is an offset distance 18 between the longitudinal axis 15 of the extruder 5 or of the screw 6 and the radius 11 of the container 1 that is parallel to the longitudinal axis 15 and that proceeds outwards from the axis 10 of rotation of the mixing and/or comminution implement 3 in the direction 17 of conveyance of the conveyor 5. In the present case, the imaginary continuation of the longitudinal axis 15 of the extruder 5 towards the rear does not pass through the space within the container 1, but instead passes the same at a short distance therefrom.

(17) The distance 18 is somewhat greater than the radius of the container 1. There is therefore a slight outward offset of the extruder 5, or the intake region is somewhat deeper.

(18) The expressions opposite, counter- and in an opposite sense here mean any orientation of the vectors with respect to one another which is not acute-angled, as explained in detail below.

(19) In other words, the scalar product of a direction vector 19 which is associated with the direction 12 of rotation and the orientation of which is tangential to the circle described by the outermost point of the mixing and/or comminution implement 3 or tangential to the plastics material passing the aperture 8, and which points in the direction 12 of rotation or movement of the mixing and/or comminution implements 3, and of a direction vector 17 which is associated with the direction of conveying of the extruder 5 and which proceeds in the direction of conveying parallel to the central longitudinal axis 15 is everywhere zero or negative, at each individual point of the aperture 8 or in the region radially immediately prior to the aperture 8, and is nowhere positive.

(20) In the case of the intake aperture in FIGS. 1 and 2, the scalar product of the direction vector 19 for the direction 12 of rotation and of the direction vector 17 for the direction of conveying is negative at every point of the aperture 8.

(21) The angle ? between the direction vector 17 for the direction of conveying and the direction vector for the direction 19 of rotation, measured at the point 20 that is associated with the aperture 8 and situated furthest upstream in relation to the direction 12 of rotation, or at the edge associated with the aperture 8 and situated furthest upstream, is approximately maximally about 170?.

(22) As one continues to proceed downwards along the aperture 8 in FIG. 2, i.e. in the direction 12 of rotation, the oblique angle between the two direction vectors continues to increase. In the centre of the aperture 8, the angle between the direction vectors is about 180? and the scalar product is maximally negative, and further downwards from there the angle indeed becomes >180? and the scalar product in turn decreases, but still remains negative. However, these angles are no longer termed angles ?, since they are not measured at point 20.

(23) An angle ?, not included in the drawing in FIG. 2, measured in the centre of the aperture 8, between the direction vector for the direction 19 of rotation and the direction vector for the direction 17 of conveying is about 178? to 180?.

(24) The apparatus according to FIG. 2 represents the first limiting case or extreme value. This type of arrangement can provide a very non-aggressive stuffing effect or a particularly advantageous feed, and this type of apparatus is particularly advantageous for sensitive materials which are treated in the vicinity of the melting range, or for product in the form of long strips.

(25) FIG. 3 shows an alternative embodiment in which the extruder 5 is not attached tangentially to the container 1 but instead is attached by its end 7. The screw 6 and the housing 16 of the extruder 5 have been adapted in the region of the aperture 8 to the shape of the inner wall of the container 1, and have been offset backwards so as to be flush. No part of the extruder 5 protrudes through the aperture 8 into the space within the container 1.

(26) The distance 18 here corresponds to about 5 to 10% of the radius 11 of the container 1 and to about half of the internal diameter d of the housing 16. This embodiment therefore represents the second limiting case or extreme value with the smallest possible offset or distance 18, where the direction 12 of rotation or of movement of the mixing and/or comminution implements 3 is at least slightly opposite to the direction 17 of conveying of the extruder 5, and specifically across the entire area of the aperture 8.

(27) The scalar product in FIG. 3 at that threshold point 20 situated furthest upstream is precisely zero, where this is the point located at the edge 20 that is associated with the aperture 8 and situated furthest upstream. The angle ? between the direction vector 17 for the direction of conveying and the direction vector for the direction 19 of rotation, measured at point 20 in FIG. 3, is precisely 90?. If one proceeds further downwards along the aperture 8, i.e. in the direction 12 of rotation, the angle between the direction vectors becomes ever greater and becomes an oblique angle >90?, and at the same time the scalar product becomes negative. However, at no point, or in no region of the aperture 8 is the scalar product positive, or the angle smaller than 90?. No local overfeed can therefore occur even in a subregion of the aperture 8, and no detrimental excessive stuffing effect can occur in a region of the aperture 8.

(28) This also represents a decisive difference in relation to a purely radial arrangement, since there would be an angle ?<90? at point 20 or at the edge 20 in a fully radial arrangement of the extruder 5, and those regions of the aperture 8 situated, in the drawing, above the radial 11 or upstream thereof or on the inflow side thereof would have a positive scalar product. It would thus be possible for locally melted plastics product to accumulate in these regions.

(29) FIG. 4 depicts another alternative embodiment in which the extruder 5 is somewhat further offset than in FIG. 3 on the outflow side, but still not tangentially as in FIGS. 1 and 2. In the present case, as also in FIG. 3, the rearward imaginary continuation of the longitudinal axis 15 of the extruder 5 passes through the space within the container 1 in the manner of a secant. As a consequence of this, the aperture 8 ismeasured in the circumferential direction of the container 1wider than in the embodiment according to FIG. 3. The distance 18 is also correspondingly greater than in FIG. 3, but somewhat smaller than the radius 11. The angle ? measured at point 20 is about 150?, and the stuffing effect is therefore reduced in comparison with the apparatus of FIG. 3; this is more advantageous for certain sensitive polymers. The inner wall of the housing 16 or the right-hand-side inner edge, as seen from the container 1, is tangential to the container 1, and therefore, unlike in FIG. 3, there is no oblique transitional edge.

(30) FIGS. 1 to 4 show the diameter D of the container or of the cutter compactor 1, the diameter d of the screw 6 and the effective length L of the intake aperture 80. It should be noted that these parameters D, d and L have been depicted in a manner that is merely illustrative and not true to scale and that does not correspond to actual conditions.

(31) Series of experiments have shown that the ratio V of the active container volume SV, i.e. the active volume of the container 1, to the feed volume BV of the container 1, in particular the volume located in front of the intake aperture (80), where V=SV/BV, is to be one where 4?V?30, preferably 5?V?25, where the active container volume SV is defined by the formula

(32) $\mathrm{SV}=D^3\frac{?}{4}$
and D is the internal ammeter of the container 1, and where the feed volume BV is defined by the formula

(33) $\mathrm{BV}=D^2\frac{?}{4}.Math.H,$
where H is the height of the intake aperture 80. The parameter H is selected in such a way that H complies with the formula H=k.sub.1d, where d is the diameter of the screw 6 and k.sub.1 is a constant, with 0.3?k.sub.1?1.5, preferably 0.5?k.sub.1?1.15.

(34) A further provision is that the ratio VS of the feed volume BV of the container 1 to the screw volume SE in the region of the intake aperture 80, where VS=BV/SE, is one where 20?VS?700, preferably 50?VS?450, where the screw volume SE is defined by the formula

(35) $\mathrm{SE}=L\frac{?}{4}\left(2\mathrm{dT}-T^2\right).$
L is the effective length of the intake aperture 80 extending in the direction 17 of conveying, and can be defined by the formula L=k.sub.2d, where k.sub.2 is a constant, with 0.5?k.sub.2?3.5, preferably 1?k.sub.2?2.8, and T is the flight depth of the screw 6, and is defined by the formula T=k.sub.3d, where k.sub.3 is a constant, with 0.05?k.sub.3?0.25, preferably 0.1?k.sub.3?0.2.

(36) Finally, it is advantageous if the effective length L has been provided with a factor F, and

(37) $\mathrm{SE}=F.Math.L\frac{?}{4}\left(2\mathrm{dT}-T^2\right),$
where 0.85?F?0.95, preferably F=0.9.

(38) The stated constants permit adaptation of the apparatus to different materials or feed compositions with different materials, in order to avoid blockages and in order to increase throughput.

(39) The container 1 is preferably a cutter compactor to which an extruder has been attached as conveyor.

(40) In the case of a container 1 which has a non-circular cross section, the diameter D is determined by a calculation which relates the cross-sectional area of the container to the area of a circle, and the diameter of this circle is taken as the container diameter. D is therefore the internal diameter in mm of a container 1 with cylindrical cross section or the internal diameter in mm of an imaginary container with cylindrical cross section with identical height, calculated to have identical capacity.