Twin screw extruder and method for processing a rubber material

Abstract

Between the inlet opening (9) and the outlet opening (not shown) of the counter-rotating twin screw extruder the screws (1a, 1b) are arranged such that they mesh tightly, i.e. each crest portion (2a, 2b) reaches up to the surface of the screw shaft (3b, 3a) of the respective other screw (1b, 1a) while ensuring the usual tolerance range. In the region of the axial extent of the inlet opening (9), the crest portions (2a, 2b) are partially reduced relative to the main diameter of the screws (1a, 1b) so that in this region the screws do not mesh tightly.

Description

[0001] Description

[0002] TWIN-SCREW EXTRUDER AND METHOD FOR PROCESSING A RUBBER MATERIAL

[0003] Technical area

[0004] The present invention generally relates to screw extruders, in particular to twin-screw extruders. Furthermore, the present invention relates to a method for processing a rubber material.

[0005] State of the art

[0006] Those skilled in the art are familiar with a variety of different screw extruder designs, which are differentiated by the number of screw(s) used, the relative arrangement of the screws, and the screw geometry. Common screw extruder designs can be divided into single-screw, twin-screw, and multi-screw extruders. Twin-screw extruders can be divided into co-rotating and counter-rotating twin-screw extruders, both non-intermeshing and intermeshing, particularly close-intermeshing.

[0007] In non-intermeshing or tangent twin-screw extruders, which play only a minor role in plastics extrusion, the screw flights do not engage with the screw flights of the other screw. In an intermeshing arrangement, the screw flights of the two screws are in engagement with each other, i.e. the screw flight or flights of one screw extend into the screw flight or flights of the other screw. Intermeshing twin-screw extruders are generally designed to mesh closely. In a closely intermeshing arrangement, the screw base of one screw is scraped off by the flank of the screw flight of the other screw, i.e. the flight height of the screw flight approximately corresponds to the distance between the screw base of one screw formed by the surface of the respective screw shaft and the screw base of the other screw.The screw base is the location of the surface of the screw shaft in the screw flight between two revolutions of the screw flight (base flight) in single-flight screws or between two adjacent screw flights (base flights) in multi-flight screws.

[0008] Depending on the application, different screw extruder designs predominate. While co-rotating, closely intermeshing twin-screw extruders are highly important in many areas of plastics preparation and processing, counter-rotating, closely intermeshing twin-screw extruders are particularly prevalent in rigid PVC extrusion.

[0009] In counter-rotating twin-screw extruders, the tight meshing creates a closed chamber volume, thus conveying material volumetrically (similar to a gear pump). In contrast to friction conveying, this results in good pumping efficiency, temperature-friendly conveying, and minimal axial mixing. These properties would make counter-rotating twin-screw extruders attractive for processing rubber materials. On the other hand, the tight meshing prevents the ingress of rubber feed strips, and pre-plasticization is also conventionally impossible. Therefore, single-screw extruders are generally used in rubber processing.Here, the energy pump efficiencies are still higher than in co-rotating twin-screw extruders. However, as a friction feeder, in addition to undesirably high heat dissipation, problems with pressure build-up can arise. Therefore, single-screw extruders often have to be connected to a gear pump to achieve sufficient pressure build-up, especially to overcome high extrusion resistance. Description of the invention.

[0010] Against this background, it is the object of the invention to create an apparatus alternative to the prior art, particularly for the processing of rubber materials, but possibly also for the processing of other plastic masses, which at least reduces problems occurring in connection with conventional screw extruder designs.

[0011] According to one aspect of the present invention, this object is achieved by a twin-screw extruder according to claim 1.

[0012] According to one aspect, the invention thus relates to a twin-screw extruder having two counter-rotating screws and a housing in which the screws are arranged, wherein each of the screws has a screw shaft and at least one base web wound around the screw shaft, the screw housing has an inlet opening and an outlet opening arranged downstream of the inlet opening in the conveying direction of the screws, and the screws are arranged so as to mesh tightly at least in sections between the inlet and the outlet opening.Within the axial extent of the inlet opening, relative to the screw shafts, at least between a base web of one of the screws and the screw shaft (and thus the screw base) of the respective other screw, a minimum gap width of, for example, at least 5%, preferably at least 10%, particularly preferably at least 25% of the distance between the surfaces of the screw shafts from one another (i.e., the distance between one screw base and the other screw base) is maintained in said section, at least in one section, so that meshing rather than tight meshing preferably occurs in this section. Thus, a meshing arrangement, particularly of the screws, preferably exists in this section, i.e., no non-mesh and (yet or equally) no tight meshing, or no tightly meshing and no non-mesh arrangement.Compared to a conventionally designed counter-rotating twin-screw extruder, according to the invention at least one base flight in the feed area is at least partially removed or designed with a reduced flight height (= radial distance between the outer radius of the base flight and the screw base).

[0013] The non-tightly intermeshing design in at least part of the feed area along the axial direction enables fully continuous conveyance of the fed product stream into the inner process chamber of the extruder, so that even conventional rubber feed strips can be reliably fed in, whereas with a continuously tightly intermeshing design, there are one or more points in time at each screw revolution, depending on the runout, at which the product flow at the feed is interrupted. Even when no feed strips are fed in, the present invention enables more uniform product feeding in many cases. In addition, by suitably designing the web geometry in the feed area, the shear conditions there can be adapted to the rheological properties of the products used or to the desired process properties. This means that compared to a continuously tightly intermeshing design, locally increased shear forces can be introduced into the product stream.

[0014] The further material transport to the extruder's injection mold can be achieved with very low temperature due to the volumetric conveying provided by the dense mesh, and this at higher throughputs than conventional single-screw extruders. An improvement in the achievable throughputs is particularly evident when conveying against high extrusion resistance; in applications that would otherwise require the use of a gear pump with a single-screw extruder, the latter can also be omitted according to the invention.

[0015] The housing can essentially be designed like extruder housings known from the prior art. In cross-section, the housing interior thus has a substantially figure-eight shape, with the respective base web scraping along the housing wall in the respective axial region where the seal is formed, correspondingly tightly within the usual tolerances.

[0016] While the following description primarily describes designs with a parallel screw arrangement and a correspondingly partially cylindrical basic shape of the two concave parts of the housing interior, the invention can advantageously also be designed with conical twin screws and thus screw axes that are at an angle to one another. The basic shape of the two concave parts of the housing interior is then also conical. With a parallel screw arrangement, the basic shape of the screw is cylindrical; the diameter of the cylindrical envelope surface is referred to as the main diameter. Particularly advantageous for the implementation of the present invention is a pitch (thread height) of the at least one base flight in the range from 0.5 times to 3 times, preferably 1.2 times to 1.5 times, in particular 1.33 times the main diameter.

[0017] When selecting the materials for the production of the screws and the barrel, the skilled person can rely on materials known per se from the state of the art in extruder construction. The screw bearings and the screw drive can also be designed according to the invention as per se from the state of the art. The skilled person is not forced to develop complex new designs in this case.

[0018] Advantageous embodiments of the invention can be implemented in particular according to one of the subclaims.

[0019] In an advantageous embodiment, an interrupted screw flight is arranged in the said section on the outer circumference of at least one of the base flights. This increases the number of degrees of freedom for the implementation of even more complex screw geometries in order to align the conveying and shear behavior of the extruder in the feed area with the desired process conditions. This means that a different screw geometry can be implemented in the area radially outside the base flight than in the radial area of ​​the base flight. The respective outer screw flight is interrupted, particularly where it overlaps with a screw flight of the base flight geometry.

[0020] In particular, it is advantageously possible to arrange a plurality of interrupted screw flights on the outer circumference of at least one of the base flights in the said section, so that in the radial region of these screw flights, i.e. radially outside the base flight, a different number of flights results than in the radial region of the at least one base flight. Preferably, the ratio of the number of screw flights formed by the at least one base flight to the number of screw flights formed by the interrupted screw flights arranged on its or their outer circumference is in a range from 1:2 to 1:8, particularly preferably this ratio is 1:3, i.e. for example, a six-flight screw geometry of the interrupted outer screw flights is implemented radially outside a two-flight base flight geometry.

[0021] Preferably, the pitch of the interrupted screw flight(s) differs from the pitch of the at least one base flight on which the interrupted screw flight(s) are arranged. The ratio of the pitch of the at least one base flight to the pitch of the interrupted screw flight(s) is preferably in a range from 1:1.5 to 1:5, particularly preferably in a range from 1:2 to 1:3, in particular 1:2.5.

[0022] While the interrupted screw flight(s) can advantageously extend to the screw base of the other screw (in the case of parallel screws, the outer diameter of the interrupted screw flight(s) can thus correspond to the main diameter), a minimum gap width can also advantageously be maintained between the interrupted screw flight(s) of one screw and the screw shaft of the other screw. In particular, in the case of parallel screws, the outer diameter of the interrupted screw flight(s) can be slightly reduced compared to the main diameter.

[0023] According to a particularly preferred embodiment, the screws each have two or more base webs wound around the screw shaft, so that the screws each have two, three or more flights, particularly preferably two flights.

[0024] According to a further particularly preferred embodiment, the minimum gap width is maintained at least in one section within the axial extent of the inlet opening, relative to the screw shafts, at least between a base land of each of the screws and the screw shaft of the respective other screw. This means that in both screws the base land is at least partially removed or the outer radius is reduced compared to a completely tightly meshing arrangement. In particular, both screws can advantageously have a screw geometry that only has an opposite direction of rotation but is otherwise exactly identical to one another at least over one axial region, in particular the region in which the tight meshing is eliminated, and can therefore be designed to be mirror-symmetrical in longitudinal section at least in sections.

[0025] According to a further advantageous embodiment, the screws are also not tightly meshed in sections between the inlet and outlet openings. Thus, while the volumetric conveying effect is maintained in sections, the skilled person has the option, depending on the desired process conditions in the individual case, of arranging shearing, mixing, kneading, homogenizing, plasticizing, or other areas with tailored flow mechanical conditions in between. According to an advantageous development of the invention, one of the screws can be longer than the other screw, so that it projects beyond the other screw on the outlet opening side. Such an arrangement essentially corresponds to a single-screw extruder connected downstream of a twin-screw conveyor.In the axially projecting part of the longer screw, the geometric conditions of conventional single-screw extruders can be simulated, with the upstream area of ​​tightly meshing twin screws ensuring pressure build-up with sufficiently high energetic pump efficiency.

[0026] According to a further aspect, the object underlying the present invention is achieved by a method according to claim 13.

[0027] According to the invention, rubber material can be processed by feeding it into a twin-screw extruder as described above. Rubber materials include, in particular, natural rubbers and synthetic rubbers, including silicone rubbers.

[0028] The remaining process steps can be carried out as in conventional processing methods for rubber materials. In particular, the rubber material can advantageously be supplied as rubber feed strips.

[0029] However, the use of a gear pump can be omitted compared to conventional processes using single-screw extruders. Under certain circumstances, cooling of the extruder barrel, which might be required in a conventional process, can also be eliminated or achieved with less coolant, since the present invention ensures more gentle conveying in the extruder.

[0030] The invention is explained in more detail below by way of example with reference to the attached schematic drawings. The drawings are not to scale; in particular, for reasons of clarity, the relationships of the individual dimensions to one another do not necessarily correspond to the dimensional relationships in actual technical implementations.

[0031] Preferred embodiments are described, to which, however, the invention is not limited. In principle, any variant of the invention described or suggested within the scope of this application may be particularly advantageous, depending on the economic and technical conditions in the individual case. Unless otherwise stated, or to the extent technically feasible, individual features of the described embodiments are interchangeable or can be combined with one another or with features known per se from the prior art.

[0032] Short description of the characters

[0033] Fig. 1 shows a section of a twin-screw extruder according to the invention in longitudinal section, whereby the area of ​​the screw bearings and the area of ​​the outlet opening are not shown.

[0034] Fig. 2 shows a section of another twin-screw extruder according to the invention in longitudinal section similar to Fig. 1, wherein the area of ​​the screw bearings and the area of ​​the outlet opening are not shown.

[0035] Fig. 3 shows a section of another twin-screw extruder according to the invention in a longitudinal section similar to Fig. 1, wherein the area of ​​the screw bearings and the area of ​​the outlet opening are not shown.

[0036] Fig. 4 shows in perspective view the arrangement of the screws of another twin-screw extruder according to the invention with a sectioned barrel, the position of the inlet opening being indicated by a bold dashed line.

[0037] Preferred embodiment of the invention

[0038] Corresponding elements are designated by the same reference numerals in the drawing figures.

[0039] Fig. 1 shows an embodiment of a twin-screw extruder according to the invention in longitudinal section, wherein the screws 1a, 1b are shown uncut as usual. Figures 2 and 3 similarly show variants of the embodiment from Fig. 1. As explained below, the variant from Fig. 2 differs from the variant from Fig. 1 in that in Fig. 2 the flight height of the base flights 2a, 12a is reduced in sections only in one of the two screws 1a, 1b. In Fig. 3, the barrel 10 is modified compared to the variant from Fig. 1 in that in the area of ​​the reduced flight height of the base flights 2a, 2b, 12a, 12b it has reduced inner diameters.

[0040] Figures 1-3 each depict only an axial section of the extruder; the area of ​​the outlet or injection mold (further left in the plane of the drawing) and the screw drive (further right in the plane of the drawing) are not shown. Both the injection mold and the drive, which sets the screws 1a, 1b in counter-rotating directions, as well as the bearings of the screws 1a, 1b, are designed in a conventional manner.

[0041] The screws 1a, 1b are arranged in parallel in a common housing 10, the housing interior of which has a figure-eight cross-section, wherein the partially cylindrical regions of the housing inner wall 11 each have a cylinder diameter that essentially corresponds to the main diameter D of both screws 1a, 1b, but with the usual tolerances that prevent the screws 1a, 1b from grinding against the housing inner wall 11. The position of the inlet opening 9, through which rubber material is fed to the screws 1a, 1b, is indicated by a dashed line. The position of the inlet opening 9 is symmetrical with respect to the position of the two screws 1a, 1b.

[0042] The geometry of both screws 1a, 1b is opposite but otherwise identical, at least between the inlet opening 9 and the outlet opening, and in Figures 1 and 3 also in the area of ​​the inlet opening 9. Each of the screws 1a, 1b has two base flights 2a, 12a and 2b, 12b, respectively, and is therefore double-flighted. The pitch (flight height) of each of the base flights 2a, 12a, 2b, 12b is 1.5 times the main diameter D.

[0043] Between the inlet opening 9 and the (not shown) outlet opening, i.e. to the left of the inlet opening 9 in Fig. 1, the arrangement of the screws 1a, 1b is tightly meshing, i.e. the respective base flight 2a, 2b, 12a, 12b extends to the surface of the screw shaft 3b, 3a of the other screw 1b, 1a, while maintaining the usual tolerances in order to prevent the screws 1a, 1b from grinding against one another. The outer diameter of the base flights 2a, 12a, 2b, 12b in this section therefore corresponds to the main diameter D of the screws 1a, 1b. Downstream of the inlet opening 9, the twin-screw extruder thus functions as a volumetric screw conveyor. The screw base 4a or 4b of one screw 1a or 1b is scraped off by the flank of the base web 2b, 12b or 2a, 12a of the other screw 1b or 1a, iethe web height of the base web 2a, 2b, 12a, 12b corresponds approximately to the distance of the screw base 4a or 4b of one screw 1a or 1b formed by the surface of the respective screw shaft 3a or 3b from the screw base 4b or 4a of the other screw 1b or 1a.

[0044] In the area of ​​the axial extension of the inlet opening 9 (relative to the screws 1a, 1b), the base webs 2a, 2b, 12a, 12b are reduced relative to the main diameter D of the screws 1a, 1b, so that the sealing mesh is eliminated in this area. A minimum gap width remains between the respective base web 2a, 12a or 2b, 12b and the screw shaft 3b or 3a (the screw base 4b or 4a) of the other screw 1b or 1a, in the present example, a minimum gap width of approximately 25% of the distance between the surfaces of the screw shafts 3a, 3b.

[0045] Furthermore, with an axially continuous, partially cylindrical design of the housing inner wall 11, in the axial section in which the base webs 2a, 2b, 12a, 12b are removed, a gap also arises between the respective base web 2a, 2b, 12a, 12b and the housing inner wall 11, the gap width of which essentially corresponds to the above minimum gap width. In some applications, such a gap between the housing inner wall 11 and the base web 2a, 2b, 12a, 12b can excessively influence the conveying effect in the intake zone, i.e. reduce it, by creating an axial backflow or a dead space zone in the gap area. In other applications, such axial mixing may be desirable.

[0046] If a gap between the housing inner wall 11 and the base webs 2a, 2b, 12a, 12b is undesirable, the housing inner wall 11 can also, as shown in Fig. 3, have two partially cylindrical areas for each screw 1a, 1b, each with different cylinder diameters, wherein the partially cylindrical areas are each

[0047] While in the embodiment of Figure 1 the base webs 2a, 12a, 2b, 12b are removed over the entire area of ​​the axial extension of the inlet opening 9, designs are also conceivable and, depending on the individual case, advantageous in which the design of the base webs 2a, 12a, 2b, 12b varies over the area of ​​the axial extension of the inlet opening 9.

[0048] While in the embodiment of Figure 1 the base webs 2a, 2b, 12a, 12b of both screws 1a, 1b are removed in the area of ​​the axial extension of the inlet opening 9, designs can also be implemented in which the corresponding base webs 2a, 12a are removed in this area on only one of the two screws 1a, 1b, as is shown in Figure 2 for the upper screw 1a in the figure.

[0049] Figure 4 shows the two screws 1a, 1b of another twin-screw extruder according to the invention in perspective. The opposing rotational direction of the screws 1a, 1b is indicated by arrows. The wall of the housing 10 is sectioned and only partially shown. The arrangement of the inlet opening 9 is again indicated by a dashed line.

[0050] The screws 1a, 1b are arranged in parallel in a common housing 10, the housing interior of which has a figure-eight cross-section, wherein the partially cylindrical regions of the housing inner wall 11 each have a cylinder diameter that essentially corresponds to the main diameter D of both screws 1a, 1b, but with the usual tolerances that prevent the screws 1a, 1b from grinding against the housing inner wall 11. The position of the inlet opening 9 is again symmetrical with respect to the position of the two screws 1a, 1b.

[0051] Between the inlet opening 9 and the outlet opening (not shown), the screws 1a, 1b are arranged in a tightly meshing manner, i.e., the respective base web 2a, 2b extends to the surface of the screw shaft 3b, 3a of the other screw 1b, 1a, while maintaining the usual tolerances to prevent the screws 1a, 1b from grinding against each other. Downstream of the inlet opening 9, the twin-screw extruder thus functions as a volumetric screw conveyor.

[0052] In the area of ​​the axial extension of the inlet opening 9 (relative to the screws 1a, 1b), the base flights 2a, 2b are partially removed relative to the main diameter of the screws 1a, 1b, so that the sealing mesh is eliminated in this area. The removal of the material of the base flights follows a spiral, spiral geometry, resulting in interrupted screw flights 5a, 5b on the outer circumference of the removed base flights 2a, 2b.

[0053] On the screw shafts 3a, 3b, two different screw geometries are formed in the area of ​​the axial extension of the inlet opening, in a radially inner and a radially outer layer. The interruptions in the outer screw flights 5a, 5b arise because the pitch or thread height in the radially outer screw geometry is greater, i.e. steeper, than the pitch or thread height of the radially inner screw geometry formed by the base flights 2a, 2b, in the example shown by approximately a factor of 2. The interruptions arise where the screw flights 5a, 5b of the radially outer screw geometry overlap with the screw flights of the radially inner screw geometry formed between the base flights 2a, 2b. Due to these interruptions in the outer screw flights 5a, 5b, the sealing mesh in these areas is canceled out.

[0054] The possibility of creating a second, superimposed screw geometry with the selective partial removal of the material from the base flights 2a, 2b results in additional degrees of freedom, allowing the twin-screw extruder to be adapted to its specific application. Thus, as shown in Fig. 4, the radially outer screw geometry can differ from the radially inner screw geometry not only in terms of its respective pitch or thread height, but also in terms of its number of threads. In the example shown, the base flights 2a, 2b form a two-flight screw geometry. The radially outer screw geometry in Fig. 4, in contrast, has four threads.

[0055] With regard to the pre-selection of the respective screw geometries in the feed area, the specialist can generally draw on experience from the field of single-screw extruders regarding fundamental aspects of shear behavior. The detailed design of the screw geometries can be optimized through design tests by gradually varying the aforementioned parameters such as pitch / flight height, number of flights, and minimum gap width.

[0056] List of reference symbols a, 1 b Screws a, 2b Base flights a, 3b Screw shafts a, 4b Screw base a, 5b Interrupted screw flights a, 6b Conical transition a, 7b, 8a, 8b Partially cylindrical wall sections Inlet opening 0 Housing 1 Housing inner wall 2a, 12b Base flights

[0057] Main diameter

Claims

Claims 1 . Twin-screw extruder comprising two counter-rotating screws (1a, 1b) and a housing (10) in which the screws (1a, 1b) are arranged, wherein each of the screws (1a, 1b) has a screw shaft (3a, 3b) and at least one base web (2a, 2b, 12a, 12b) converted around the screw shaft (3a, 3b), the screw housing (10) has an inlet opening (9) and an outlet opening arranged downstream of the inlet opening (9) in the conveying direction of the screws (1a, 1b), the screws (1a, 1b) are arranged so as to mesh tightly at least in sections between the inlet opening (9) and the outlet opening, and within the axial extent of the inlet opening (9), relative to the screw shafts (3a, 3b), at least between one base web (2a, 2b, 12a, 12b) one of the screws (1a, 1b) and the screw shaft (3a, 3b) of the respective other screw (1a, 1b) a minimum gap width is maintained at least in one section,so that there is no dense combing in this section.

2. Twin-screw extruder according to claim 1, wherein an interrupted screw flight (5a, 5b) is arranged in said section on the outer circumference of at least one of the base flights (2a, 2b, 12a, 12b).

3. Twin-screw extruder according to claim 2, wherein in said section a plurality of interrupted screw flights (5a, 5b) are arranged on the outer circumference of at least one of the base flights (2a, 2b, 12a, 12b), so that in the radial region of the screw flights (5a, 5b) a different number of flights results than in the radial region of the at least one base flight (2a, 2b, 12a, 12b).

4. Twin-screw extruder according to claim 3, wherein the ratio of the number of screw flights formed by the at least one base flight (2a, 2b, 12a, 12b) to the number of screw flights formed by the interrupted screw flights (5a, 5b) arranged on its or their outer circumference is in a range from 1:2 to 1:8, in particular 1:

3.

5. Twin-screw extruder according to one of claims 2-4, wherein the pitch of the interrupted screw flight (5a, 5b) or the interrupted screw flights (5a, 5b) is different from the pitch of the at least one base flight (2a, 2b, 12a, 12b) on which the interrupted screw flight (5a, 5b) or the interrupted screw flights (5a, 5b) are arranged.

6. Twin-screw extruder according to claim 5, wherein the ratio of the pitch of the at least one base flight (2a, 2b, 12a, 12b) to the pitch of the interrupted screw flight (5a, 5b) or the interrupted screw flights (5a, 5b) is in a range from 1:1.5 to 1:5, in particular in a range from 1:2 to 1:

3.

7. Twin-screw extruder according to one of claims 2-6, wherein in said section between the interrupted screw flight (5a, 5b) or the interrupted screw flights (5a, 5b) of one of the screws (1a, 1b) and the screw shaft (3a, 3b) of the respective other screw (1a, 1b) a minimum gap width is also maintained.

8. Twin-screw extruder according to one of the preceding claims, wherein the screws (1a, 1b) each have two or more base flights (2a, 2b, 12a, 12b) wound around the screw shaft (3a, 3b), so that they each have two, three or more flights.

9. Twin-screw extruder according to one of the preceding claims, wherein within the axial extent of the inlet opening (9), relative to the screw shafts (3a, 3b), the minimum gap width is maintained at least in one section at least between a base web (2a, 2b, 12a, 12b) of each of the screws (1a, 1b) and the screw shaft (3a, 3b) of the respective other screw (1a, 1b).

10. Twin-screw extruder according to one of the preceding claims, wherein the minimum gap width is at least 5%, preferably at least 10%, in particular at least 25% of the distance between the surfaces of the screw shafts (3a, 3b) in said section.

11. Twin-screw extruder according to one of the preceding claims, wherein the screws (1a, 1b) are not tightly meshing in sections between the inlet and outlet openings.

12. Twin-screw extruder according to one of the preceding claims, wherein one of the screws (1a, 1b) is longer than the other screw (1a, 1b) so that it projects beyond the other screw (1a, 1b) on the outlet opening side.

13. A method for processing a rubber material, wherein the rubber material is fed to a twin-screw extruder according to any one of claims 1-12.

14. The method according to claim 13, wherein the rubber material is supplied as a rubber feed strip.

15. A method according to any one of claims 13 or 14, wherein the use of a gear pump is omitted.

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