Extruder with multi-screw zone

Abstract

Extruder for processing a material with a main screw 202 and at least one multi-screw zone 123 in which several auxiliary screws 203 are located in auxiliary bores 205, the auxiliary bores 205 partially penetrate the base of the main screw 202. characterized by the fact that in at least 30% of the length of the multi-screw zone 123 at all axial positions the minimum number of threads of the main screw 202 in at least one intermediate part 206 is at least 3 greater than the maximum number of threads of at least one auxiliary screw 203.

Description

[0001] The invention relates to an extruder with exactly one main screw which has at least one multi-screw zone with several auxiliary screws and in particular to the design and arrangement of the main screw and / or the auxiliary screws.

[0002] Extruders are known and proven in a wide variety of designs. In plastics processing, for example, they serve to plasticize a processing material, usually in granular or powder form, typically raw plastic material, as well as to convey the resulting melt and build up pressure for a subsequent tool, such as an extrusion die. A similar design is found in the processing of meltable foods.

[0003] A wide variety of differently designed extruders can be found in the state of the art.

[0004] DE 101 50 627 A1 describes an extruder for removing low molecular weight components and achieving higher molecular sizes with an extruder screw that has a section on which several screw spindles roll.

[0005] DE 10 2013 008 201 A1 describes a method and a device for producing a foam body using multiple extruders, wherein at least one extruder is equipped with an extruder screw assembly and several screw spindles distributed around the circumference of the extruder screw assembly. The aim is to reduce temperature differences between different radial positions in the cross-section of the polymer melt.

[0006] DE 10 2013 008 202 A1 also describes a method and a device for producing a foam body using multiple extruders, wherein at least one extruder can be equipped with an extruder screw assembly and several screw spindles distributed around the circumference of the extruder screw assembly. Here, too, the aim is to reduce temperature differences between different radial positions in the cross-section of the polymer melt.

[0007] Both DE 101 50 627 A1, as well as DE 10 2013 008 201 A1 and DE 10 2013 008 202 A1, describe and / or illustrate screw spindles arranged exclusively around a main screw, which, as is typical for screw spindles, have continuously circumferential screw webs. As a result, only a small amount of material passes from one screw spindle to the next. While radial mixing is ensured, circumferential mixing of the entire material is made more difficult.

[0008] DE 10 2018 128 884 A1 describes a method and a device for processing a polymer melt using a multi-screw system consisting of a rotor element comprising a main screw web and at least one satellite mixing element. The aim is to generate a large polymer surface area and / or achieve a high level of surface exchange in the polymer melt. To this end, the degree of enclosure of the satellite mixing element is varied along the length of the rotor element. DE 10 2018 128 884 A1 does not aim to achieve an adjustment of the conveying capacity of the main screw web and the satellite mixing element. Rather, the conveying effect of the satellite mixing element is intended to be significantly reduced or even negligible.

[0009] CN 1 01 837 633 B describes a method and apparatus for degassing a polymer melt using a multi-screw system comprising a main screw and several satellite screws. The satellite screws have a helical gear at one end, which engages with a helical gear located on the inside of a ring. The outside of the ring is connected to the cylinder containing the main screw via a worm gear. This design is intended to reduce the energy consumption of the multi-screw system and increase its throughput.

[0010] WO 2020 / 099 684 A1 describes a method and apparatus for a degassing extruder with a multi-screw unit consisting of a rotor element comprising a main screw web and at least one satellite screw. The primary objective is to generate a large polymer surface area and / or achieve high surface exchange in the polymer melt. To this end, the enclosure ratio of the satellite screw within the main screw web is to be greater than in the intervening passages and should be a maximum of 95%. WO 2020 / 099 684 A1 does not aim to achieve an adjustment of the conveying capacity of the main screw web and the satellite screw. Rather, the conveying effect of the satellite screw is to be significantly reduced or even negligible.

[0011] Neither DE 101 50 627 A1, nor DE 10 2013 008 201 A1, DE 10 2013 008 202 A1, DE 10 2018 128 884 A1, CN 1 01 837 633 B, nor WO 2020 / 099 684 A1 contain a description of peripheral mixing and are therefore not considered relevant. Furthermore, nowhere is it mentioned what promotes an improvement in peripheral mixing. The combination of improved conveying with improved peripheral mixing is also not addressed in these documents. Finally, none of the documents describe how to equalize the conveying capacity of the main and auxiliary screws. Nor is it mentioned anywhere what promotes an equalization of the conveying capacity of the main and auxiliary screws. Therefore, this adjustment of funding is considered irrelevant.Nowhere is the ratio of the number of threads between main and auxiliary screws mentioned, and this ratio is therefore also considered irrelevant. The same applies to the ratio of the thread pitches between main and auxiliary screws, the channel widths between main and auxiliary screws, and the web widths between main and auxiliary screws.

[0012] DE 20 2006 020 302 U1 describes a screw conveyor device with a mixer comprising at least two mixing elements. In particular, improved mixing performance is to be achieved. For this purpose, mixing elements are to be used whose number, spacing, and / or shape vary from one mixing element to the next. A change in shape within a single mixing element is not provided for.

[0013] The invention is based on the objective of providing an improvement or an alternative to the prior art.

[0014] The main objective of the proposed designs and arrangement of the main screw and auxiliary screws is to adjust their conveying capacity. Preferably, the conveying capacity of the main screw and auxiliary screws should be matched according to their respective diameters to achieve more uniform conveying of the material in the multi-screw zone. In addition to this matching, a specific conveying capacity ratio is also conceivable, depending on the material being processed and / or the product being manufactured. Furthermore, areas where there is no or only below-average conveying effect, and thus potentially above-average residence times and above-average material degradation, should be reduced.Another task lies in improved homogenization of the processing material in the circumferential direction, i.e., an improvement in the transfer of at least a part of the processing material from one auxiliary screw towards another auxiliary screw and / or to the main screw and vice versa.

[0015] These tasks are solved by the measures of claim 1 and the dependent or subordinate claims.

[0016] First, it should be expressly noted that, within the context of this document, indefinite articles and numerical specifications such as "one", "two", etc., are generally to be understood as "at least" specifications, i.e., as "at least one...", "at least two...", etc., unless it is expressly clear from the respective context or it is obvious or technically necessary for the person skilled in the art that only "exactly one...", "exactly two...", etc., can be meant.

[0017] This document frequently refers to an axial direction. The axial direction refers to the discharge direction along the extruder. The discharge direction of the extruder, and thus the axial direction, is the direction of the longitudinal axis of the main screw from the main feed zone to the main discharge zone. The axial direction is exemplified in Fig. 1 marked with the arrow 110.

[0018] A "longitudinal axis" refers to the respective axis of rotation of the main screw and the auxiliary screws, around which the respective screw rotates on its own axis.

[0019] When reference is made in this document to a length, location, beginning or end of positions, places, sections, areas, zones, regions or parts, this shall be understood to mean the length, location, beginning or end of positions, places, sections, areas, zones, regions or parts in the axial direction, unless it is expressly clear from the respective context or it is obvious or technically necessary for the person skilled in the art that a different reference is meant.

[0020] The following descriptions refer to the Fig. Reference is made to Figure 1, which schematically and not to scale depicts an extruder with a screw.

[0021] The length of, for example, zone 122 is, according to the above explanations, the axial length of zone 122 along the axial direction 110. The same terminology also applies to the length of locations, sections, areas, regions, and parts.

[0022] Zones 123 and 124 lie axially after or behind zone 122. Zones 122 and 123 lie axially in front of zone 124. Zone 123 lies axially directly after zone 122 and directly in front of zone 124. The same terminology applies to positions, locations, sections, areas, regions, and parts.

[0023] Zone 123 begins at the dashed line 104, which coincides with the end of Zone 122, and Zone 123 ends at the dashed line 105, which coincides with the beginning of Zone 124. This also means that the end of Zone 122 coincides with the beginning of Zone 123, i.e., they are located at the same axial position. The same terminology applies to the beginning and end of sections, areas, regions, and parts.

[0024] The extruder according to the invention has exactly one main screw, wherein the main screw has at least one multi-screw zone with several auxiliary screws.

[0025] For the purposes of this document, the term "extruder" refers to all devices in which exactly one main screw with at least one multi-screw section rotates within a housing, conveying and / or plasticizing and / or melting and / or cooling and / or homogenizing a processing material. This explicitly includes blown film lines, thermoforming film lines, injection molding units, rubber machines, rubber extruders, blow molding machines, or similar devices containing at least one extruder with a main screw featuring at least one multi-screw section.

[0026] The main screw of the extruder is installed in a cylinder within a cylinder bore during operation. When this document refers to a cylinder wall, it means the inner wall of this cylinder, which typically comes into contact with the material being processed during extruder operation, or can come into contact with it; in other words, the wall of the cylinder bore.

[0027] The cylinder can consist of several parts. The cylinder can have different inner and outer diameters along the axial direction. Preferably, the cylinder has a larger inner diameter in the multi-screw section than before and / or after the multi-screw section. Preferably, the cylinder also has a larger outer diameter in the multi-screw section.

[0028] The cylinder does not necessarily have to be round on the outside; it can, for example, have a square or rectangular shape. However, a round cylinder is usually the most cost-effective to manufacture and is also generally the easiest to equip with components such as heating or cooling units for the outer surface. When a cylinder is described in this document, this also includes all shapes that the extruder housing can have to accommodate the main screw and the multi-screw section. Similarly, when a cylinder bore is described in this document, this also includes all shapes that the housing can have on the inside to accommodate the main screw and the multi-screw section.

[0029] A "multi-screw zone" refers to the axial portion of the main screw in which several auxiliary screws are rotatably mounted, with all auxiliary screws of a multi-screw zone overlapping in at least one axial portion of the main screw. Viewed axially, the multi-screw zone begins with the first auxiliary screw and ends with the last. The auxiliary screws are aligned parallel to the longitudinal axis of the main screw and distributed circumferentially around it. In other words, the longitudinal axes of the auxiliary screws are parallel to the longitudinal axis of the main screw. The auxiliary screws are located in auxiliary bores that are machined into the main screw, with the auxiliary bores partially penetrating the screw base. As a result, all auxiliary screws are only partially embedded in the main screw.This means that a portion of each auxiliary snail protrudes from the base of the main snail. In other words, the sum of the distance between the longitudinal axis of each auxiliary snail and the longitudinal axis of the main snail (first term) and the base radius of the auxiliary snail (second term) is greater than the base radius of the main snail. Furthermore, the longitudinal axis of each auxiliary snail lies between the longitudinal axis of the main snail and the base of the main snail. In other words, the distance between the longitudinal axis of each auxiliary snail and the longitudinal axis of the main snail is less than the base radius of the main snail.

[0030] A "thrust radius" refers to the maximum distance of the thrust head of a screw to the longitudinal axis of the respective screw at an axial position.

[0031] A "flight head" refers to the outer surface of a screw flight at an axial position when viewed in the radial direction of the respective screw, in other words the part of the screw flight that has the largest radius when viewed in the radial direction of the respective screw at an axial position.

[0032] A "basic radius" refers to the minimum distance of the base of a screw to the longitudinal axis of the respective screw at an axial position.

[0033] A "circle" refers to the circle of a screw that a point at the distance of the maximum tang radius at an axial position of the respective screw to the longitudinal axis of the respective screw generates with a 360° rotation around the longitudinal axis of the respective screw at the axial position.

[0034] On the main screw and the auxiliary screws, screw flights and screw channels run helically around the screw, at least in some sections. The helix can have the same pitch at all axial positions, meaning it runs monotonically around the screw. Alternatively, the helix can also have different pitches at different axial positions, meaning it does not run monotonically around the screw.

[0035] Each screw can have one web running helically around it, or several webs can run helically around it in at least one section. If several webs run helically around the screw in one section, the number of webs is called the number of flights.

[0036] A snail channel is bordered on both sides by a snail bridge. These snail bridges are referred to as surrounding snail bridges in relation to the snail channel.

[0037] The channel depth of a worm gear at an axial position is calculated by subtracting the base radius of the worm gear at the axial position from the maximum stem radius at the axial position.

[0038] The pitch of the helical webs and / or channels in extruder screws is usually referred to as the thread pitch. This pitch is often expressed as a dimensionless value, namely the pitch of the helix divided by the diameter of the cylinder bore. This is also the format used in this document.

[0039] In this document, the pitch of the main screw at an axial position is therefore the pitch of the helical webs of the main screw at that axial position divided by the diameter of the cylinder bore at that axial position. The pitch of the respective auxiliary screw at an axial position is the pitch of the helical webs of the respective auxiliary screw at that axial position divided by the diameter of the respective auxiliary bore at that axial position.

[0040] With a pitch of 1, for example, the flight of a main screw has a pitch equal to one cylinder bore diameter. This corresponds approximately to a pitch angle of 17.6°. With a pitch of 2, the pitch angle is approximately 32.5°. If the axial distance, for example, between the active flanks of axially adjacent flight webs is less than the pitch, the number of threads is greater than 1. If this distance is, for example, half the pitch, the number of threads is 2; at one-third, the number of threads is 3; at one-quarter, the number of threads is 4, and so on.

[0041] The active flank of a web is the flank of the web that points in the direction of rotation of the respective screw. The distances described above can vary by normal manufacturing tolerances.

[0042] It should be explicitly noted that if a component is rotationally fixed to the main screw, this component is considered to belong to the main screw. For example, if screw flights are present on this component, these screw flights are considered to be screw flights of the main screw. Similarly, if auxiliary bores are incorporated into this component, these auxiliary bores are considered to be incorporated into the main screw.

[0043] An "auxiliary opening" refers to the portion of the main screw's base that is penetrated by the auxiliary bores. Viewed circumferentially, the base of the main screw is present both before and after the auxiliary opening. For example, when this document refers to the base radius of the main screw in the area of ​​the auxiliary opening at an axial position, it means the base radius of the main screw that is present before and after the auxiliary opening at that axial position. In other words, the auxiliary opening runs along the base of the main screw that existed before the auxiliary bore was inserted and was removed by the auxiliary bore, or that would exist if the auxiliary bore were not present.If, viewed in the circumferential direction, different basic radii exist before and after the auxiliary opening at an axial position, the basic radius of the auxiliary opening at the axial position is determined by the arithmetic mean.

[0044] The "opening length" refers to the length of an auxiliary opening circumferentially around the main screw. The decisive factor is the position of the base of the main screw, not the position of any screw bridges that may be present. In other words, any screw bridges that may be present do not affect the opening length.

[0045] An "intermediate part" refers to the part of the main screw that, viewed in the circumferential direction of the main screw, lies between two auxiliary bores.

[0046] An "intermediate surface" refers to the base of the main screw, which rests on an intermediate section. If the intermediate section has screw flights, the intermediate surface extends through these flights at the level of the base radius. For example, when this document refers to the base radius of the main screw in the area of ​​the intermediate surface at an axial position, it means the base radius of the main screw as it exists at that axial position on the intermediate surface. If, viewed circumferentially, different base radii exist at an axial position on the intermediate surface, the base radius of the intermediate surface at that axial position is the arithmetic mean.

[0047] An "intermediate length" refers to the length of an intermediate surface in the circumferential direction around the main snail. The decisive factor here is the position of the base of the main snail, and not the position of any snail bridges that may be present. In other words, any snail bridges that may be present do not affect the intermediate length.

[0048] The main screw has at least one screw web, preferably several screw webs, in at least one multi-screw zone, preferably in all multi-screw zones, on at least one intermediate part, preferably on at least 50% of the intermediate parts, and particularly preferably on all intermediate parts.

[0049] Preferably, in at least one multi-screw zone, the screw flights of at least two intermediate sections, and more preferably of all intermediate sections, are located on at least one helix that runs around the screw with exactly one pitch. Particularly preferably, the screw flights of at least two intermediate sections, and more preferably of all intermediate sections, are located on several helixes that run around the screw with exactly one pitch and preferably at equal distances from each adjacent helix, the number of helixes being referred to as the number of flights.

[0050] In a preferred embodiment, there is no screw web after the auxiliary opening when viewed in the radial direction of the main screw.

[0051] In an alternative embodiment, at least one screw web of the main screw is present at least partially in the radial direction downstream of the auxiliary opening. In other words, a screw web is partially present in the region of the auxiliary opening. Preferably, at least one screw web of the main screw is present continuously in the radial direction downstream of the auxiliary opening. In other words, a continuous screw web is present in the region of the auxiliary opening. Preferably, in at least one multi-screw zone, the screw webs of at least two intermediate sections and one auxiliary opening, and more preferably those of all intermediate sections and all auxiliary openings, are located in at least a portion of the multi-screw zone on at least one helix that runs around the screw with exactly one pitch.Particularly preferably, the screw flights of at least two intermediate parts and an auxiliary opening, preferably of all intermediate parts and all auxiliary openings, are located in at least one part of the multi-screw zone on several helixes that run around the screw with exactly one pitch and at the same distance to the respective adjacent helixes, wherein the number of helixes is referred to as the number of flights.

[0052] Each auxiliary screw has at least one gear-shaped section that is integrated into the auxiliary screw, or is rotationally fixed to the auxiliary screw, or is rotationally fixed to a component that is in turn rotationally fixed to the auxiliary screw. In other words, there is no rotational movement between the gear and the auxiliary screw. The gear engages with at least one internally toothed ring that is integrated into the cylinder, or is rotationally fixed to the cylinder, or is rotationally fixed to a component that is in turn rotationally fixed to the cylinder. In other words, there is no rotational movement between the toothed ring and the extruder cylinder.At least 50%, preferably at least 70%, and particularly preferably at least 80% of the axial length of each auxiliary screw is free of any gear meshing with a toothed ring of the cylinder. The auxiliary screws rotate about the longitudinal axis of the main screw and, additionally, about their own longitudinal axis due to the meshing of their gears with the toothed ring. In other words, the main screw conveys and / or homogenizes the material by rotating about its own longitudinal axis, and the auxiliary screws convey and / or homogenize the material by rotating their longitudinal axis about the longitudinal axis of the main screw and by rotating about their own longitudinal axis.

[0053] The auxiliary screws and the main screw are not interlocked. In other words, there is no interlocking connection between the auxiliary screws and the main screw. Put another way, the auxiliary screws could rotate freely if there were no interlocking connection between the auxiliary screws and the cylinder wall.

[0054] Preferably, each auxiliary screw has at least two areas designed as gears. Particularly preferably, the distance of these areas to the beginning or end of the auxiliary screw is smaller than the distance to the center of the auxiliary screw.

[0055] A "channel ratio" refers to the quotient of the width of the screw channel perpendicular to the screw flights over the maximum channel depth of the screw channel at an axial position.

[0056] For both the main screw and the auxiliary screws, the width of a screw channel is determined by the distance between the surrounding screw webs at the web head, measured perpendicular to the channel pitch. If at least one screw web has at least one opening or mixing opening along its helical path, for example, the main screw above an auxiliary opening, and the surrounding screw webs are located before and after the opening, the screw channel will have the same width during the opening as it does before and after the opening. If the screw channel widths differ before and after the opening along its helical path, the width of the screw channel during the opening is the arithmetic mean of these two widths.The width of the screw channel at an axial position is the width of the screw channel, exactly half of which lies before the axial position and exactly the other half of which lies after the axial position.

[0057] The "main feed zone" is the axial zone of the extruder where, typically, the majority of the meltable or molten components of the material being processed, or even all of the material, is fed into the extruder. For this purpose, an opening, such as a bore, is located in the screw barrel within this zone. The axial dimensions of this opening define the axial length of the main feed zone. An extruder has exactly one main feed zone.

[0058] The "main discharge zone" is the axial zone through which at least a portion, preferably at least a large portion, and most preferably all of the material being processed is discharged for further processing, e.g., into a shaping extrusion die or injection mold. The main discharge zone is usually located at the end of the extruder, but in special cases, it can also be an axial zone of the extruder in which at least one screw is present. If the main discharge zone is located at the end of the extruder, it begins directly after the end of the screw that terminates last in the axial direction and ends at the end of the extruder. If the extruder contains at least one screw that is partially located at its end in a component following the extruder, such as a screen changer, then the main discharge zone begins and ends at the end of the last screw.If the main discharge zone is located in an axial part of the extruder where at least one screw is present, an opening, such as a bore, is located in the screw cylinder for the purpose of discharge. The axial dimensions of the opening define the axial length of the main discharge zone. An extruder has exactly one main discharge zone.

[0059] A "secondary discharge zone" is the axial zone of the extruder in which at least one screw is present and in which a portion of the processed material and / or at least a portion of at least one component of the processed material is discharged from the extruder. This can involve solid, liquid, molten, and / or gaseous components of at least one component of the processed material. For this purpose, an opening, such as a bore, is located in the cylinder of this zone. The shape of the opening in the axial direction defines the area of ​​the secondary discharge zone. An extruder can have zero, one, or multiple secondary discharge zones.

[0060] A "process zone" is the zone of a screw where the screw typically comes into contact with the material being processed. If the screw has a return thread, toothing, or a screw shaft, these zones are not considered part of the screw's process zone, even if they come into contact with the material being processed, unless it is explicitly stated that these zones are part of the process zone.

[0061] The extruder according to the invention is designed to process any material. At least one component of the material is meltable and is at least partially melted in the extruder and / or fed to the extruder in a molten state. This component is usually present in a solid state, at least partially, after optional shaping, e.g., but not exclusively, after an extrusion die or in an injection mold, and cooling methods appropriate to the respective process. Alternatively, the extruder can transfer the material in a molten state to another unit, e.g., another extruder. In addition to the meltable components, non-meltable materials, e.g., wood, calcium carbonate, fibers (e.g., carbon fibers), carbon black, mineral substances, or similar materials, can also be components of the material.Other components can also be materials that melt only at very high temperatures, such as sand, glass beads or similar materials, hollow glass bodies, fibers, e.g., glass fibers or similar materials. As described, these components are also meltable, but typically remain solid in the extruder due to their high melting point. In this document, "meltable components" of the processing material refers to those components that are typically at least partially melted during the extrusion process. Preferably, the melting point of these meltable components is below 450°C, more preferably below 400°C, and most preferably below 350°C.

[0062] Preferably, at least one part of the processing material is a thermoplastic polymer. It is particularly preferred that the thermoplastic polymer is processed in the extruder together with additives and / or fillers.

[0063] Preferably, at least one part of the processing material is an elastomer and / or rubber and / or thermoset.

[0064] Preferably, at least part of the processing material is at least a meltable foodstuff.

[0065] Preferably, at least part of the processing material is a pharmaceutical active ingredient.

[0066] Preferably, a large proportion of the components of the processing material are fed to the extruder as a solid. In an alternative embodiment, a large proportion of the components of the processing material are fed to the extruder in an already molten and / or liquid and / or gaseous state.

[0067] Part of the material being processed can be discharged from the extruder before the main discharge zone. It is also possible to feed in solid and liquid materials that only become liquid or gaseous through further temperature adjustment, shearing, and / or pressure reduction, such as blowing agents. The material can be fed into the extruder at one or more points.

[0068] When calculating the average melting temperature of the processing material, only those components with melting temperatures below 450°C, preferably below 400°C, and particularly preferably below 350°C, are considered. These components are essentially, but not exclusively, meltable thermoplastic polymers or meltable foodstuffs. The basis for determining the average is the weight, not the volume, of the individual components. Components whose melting temperature is not considered are essentially, but not exclusively, glass components such as glass fibers or glass beads, as well as sand and other at least partially mineral fillers.

[0069] All of the following aspects are based on the same inventive idea: to use the extruder with a main screw and at least one multi-screw zone in advantageous designs to fulfill at least one of the tasks described above.

[0070] According to a first aspect of the invention, the above-mentioned problem is solved by an extruder for processing a material with a main screw and at least one multi-screw zone in which several auxiliary screws are located in auxiliary bores, wherein in at least 30% of the length of the multi-screw zone, preferably in at least 50% of the length of the multi-screw zone, particularly preferably in at least 70% of the length of the multi-screw zone, at all axial positions the minimum number of threads of the main screw in at least one intermediate section, preferably in all intermediate sections, is at least one greater than the maximum number of threads of at least one auxiliary screw, preferably of all auxiliary screws, preferably at least two greater, particularly preferably at least three greater.

[0071] In an advantageous embodiment, in at least 30% of the length of the multi-screw zone, preferably in at least 50% of the length of the multi-screw zone, particularly preferably in at least 70% of the length of the multi-screw zone, at all axial positions, the minimum number of threads of the main screw in at least one intermediate section, preferably in all intermediate sections, is at least 2 times as large as the maximum number of threads of at least one auxiliary screw, preferably of all auxiliary screws, preferably at least 3 times as large, particularly preferably at least 4 times as large.

[0072] Tests on several prototypes have shown that this achieves a more favorable distribution of conveying capacity between the main screw and auxiliary screws, and improves the conveying performance of the main screw in the intermediate sections. Areas where there is no or only minimal conveying effect, and thus potentially long residence times and material degradation, are thereby reduced. Furthermore, improved homogenization of the processed material is achieved in the circumferential direction of the main screw.

[0073] In an advantageous embodiment, the pitch of the main screw is at least 0.8, preferably at least 1, preferably at least 1.2, particularly preferably at least 1.4 at all axial positions in at least 30% of the length of the multi-screw zone, preferably at least 50% of the length of the multi-screw zone, and particularly preferably at least 70% of the length of the multi-screw zone.

[0074] In an advantageous embodiment, the channel ratio is at most 8, preferably at most 6, particularly preferably at most 5, in at least 30% of the length of the multi-screw zone, preferably at least 50% of the length of the multi-screw zone, and particularly preferably at least 70% of the length of the multi-screw zone at all axial positions in at least one intermediate section, preferably in all intermediate sections.

[0075] In an advantageous embodiment, the number of turns of the main screw is at least 2, preferably at least 3, preferably at least 4, particularly preferably at least 5, particularly preferably at least 6 in at least 30% of the length of the multi-screw zone, preferably at least 50% of the length of the multi-screw zone, and particularly preferably at least 70% of the length of the multi-screw zone at all axial positions.

[0076] According to a second aspect of the invention, the above-mentioned problem is solved by an extruder for processing a material with a main screw and at least one multi-screw zone in which several auxiliary screws are located in auxiliary bores. wherein the main screw has at least two intermediate parts and at least two auxiliary openings and in at least 30% of the length of the multi-screw zone, preferably in at least 50% of the length of the multi-screw zone, particularly preferably in at least 70% of the length of the multi-screw zone at all axial positions the quotient of the minimum intermediate length of at least one intermediate part, preferably of all intermediate parts over the maximum opening length of at least one auxiliary opening, preferably of all auxiliary openings is at least 0.8, preferably at least 0.9, preferably at least 1, particularly preferably at least 1.1, particularly preferably at least 1.2.

[0077] Tests on several prototypes have shown that this achieves a more favorable distribution of conveying capacity between the main screw and auxiliary screws, and improves the conveying performance of the main screw in the intermediate sections. Areas where there is no or only minimal conveying effect, and thus potentially long residence times and material degradation, are thereby reduced. Furthermore, improved homogenization of the processed material is achieved in the circumferential direction of the main screw.

[0078] It should be expressly noted that the subject matter of the second aspect can be advantageously combined with the subject matter of the first aspect of the invention, either individually or cumulatively in any combination, provided that the subject matter of the aspects is not technically mutually exclusive for the person skilled in the art.

[0079] According to a third aspect of the invention, the above-mentioned problem is solved by an extruder for processing a material with a main screw and at least one multi-screw zone in which several auxiliary screws are located in auxiliary bores. wherein the main screw has at least two intermediate parts and at least two auxiliary openings and in at least 30% of the length of the multi-screw zone, preferably in at least 50% of the length of the multi-screw zone, particularly preferably in at least 70% of the length of the multi-screw zone at all axial positions the width of at least one screw channel in at least one intermediate part, preferably in all intermediate parts, is at most 2.5 times as large as the intermediate length of the intermediate part, preferably at most 2 times as large, particularly preferably at most 1.5 times as large.

[0080] Tests on several prototypes have shown that this achieves a more favorable distribution of conveying capacity between the main screw and auxiliary screws, and improves the conveying performance of the main screw in the intermediate sections. Areas where there is no or only minimal conveying effect, and thus potentially long residence times and material degradation, are thereby reduced. Furthermore, improved homogenization of the processed material is achieved in the circumferential direction of the main screw.

[0081] It should be expressly pointed out that the subject matter of the third aspect can be advantageously combined with the subject matter of the preceding aspects of the invention, either individually or cumulatively in any combination, provided that the subject matter of the aspects is not technically mutually exclusive for the person skilled in the art.

[0082] According to a fourth aspect of the invention, the above-mentioned problem is solved by an extruder for processing a material with a main screw and at least one multi-screw zone in which several auxiliary screws are located in auxiliary bores. wherein the passage depth of at least one auxiliary screw changes along the longitudinal axis of the auxiliary screw and has at least 2 local minima and / or 2 local maxima, preferably has at least 3 local minima and / or 3 local maxima, especially preferably has at least 4 local minima and / or 4 local maxima.

[0083] Tests on several prototypes have shown that this results in improved homogenization of the processing material in the circumferential direction of the main screw.

[0084] In an advantageous embodiment, the passage depth of at least 50% of the auxiliary screws, preferably of all auxiliary screws, changes along the longitudinal axis of the respective auxiliary screw, wherein the respective auxiliary screw has at least 2 local minima and / or 2 local maxima, preferably at least 3 local minima and / or 3 local maxima, and particularly preferably at least 4 local minima and / or 4 local maxima.

[0085] It should be expressly pointed out that the subject matter of the fourth aspect can be advantageously combined with the subject matter of the preceding aspects of the invention, either individually or cumulatively in any combination, provided that the subject matter of the aspects is not technically mutually exclusive for the person skilled in the art.

[0086] According to a fifth aspect of the invention, the above-mentioned problem is solved by an extruder for processing a material with a main screw and at least one multi-screw zone in which several auxiliary screws are located in auxiliary bores, wherein at least one auxiliary screw has a different geometry than at least one other auxiliary screw and preferably at least one auxiliary screw, and more preferably at least 50% of the auxiliary screws, has different channel depths and / or different channel pitches along its longitudinal axis. In other words, the channel depth and / or the channel pitch changes on the respective auxiliary screw along its longitudinal axis.

[0087] Preferably, the different geometry of the auxiliary screw results at least from a different course of the passage depth along the longitudinal axis of the auxiliary screw.

[0088] Preferably, the channel depth of one auxiliary screw exhibits a local minimum at at least one axial position, while the channel depth of another auxiliary screw does not exhibit a local minimum at the same axial position. Preferably, the other auxiliary screw exhibits a local maximum at the same axial position.

[0089] Tests on several prototypes have shown that this results in improved homogenization of the processing material in the circumferential direction of the main screw.

[0090] Preferably, the different geometry of the auxiliary screw results at least from a different course of the channel slope along the longitudinal axis of the auxiliary screw.

[0091] In an advantageous embodiment, the number of threads changes on at least one auxiliary screw.

[0092] Preferably, the number of auxiliary snails should be an even number.

[0093] Preferably, the auxiliary snails are divided into at least two groups, wherein the auxiliary snails in one group have the same geometry and auxiliary snails from different groups have different geometries.

[0094] There are exactly two groups of auxiliary snails that are particularly prevalent.

[0095] Preferably, all auxiliary snails have direct neighbors from a different group than their own. In other words, auxiliary snails from a different group are located both upstream and downstream of an auxiliary snail belonging to one group.

[0096] It should be expressly pointed out that the subject matter of the fifth aspect can be advantageously combined with the subject matter of the preceding aspects of the invention, either individually or cumulatively in any combination, provided that the subject matter of the aspects is not technically mutually exclusive for the person skilled in the art.

[0097] According to a sixth aspect of the invention, the above-mentioned problem is solved by an extruder with a main screw and at least one multi-screw zone with several auxiliary screws for processing a material, wherein in at least 30% of the length of the multi-screw zone, preferably in at least 50% of the length of the multi-screw zone, particularly preferably in at least 70% of the length of the multi-screw zone at all axial positions, the quotient of the maximum width of the screw channels of the main screw over the minimum width of the screw channels of at least one auxiliary screw, preferably all auxiliary screws, is at most 1.8, preferably at most 1.6, particularly preferably at most 1.5.

[0098] Tests on several prototypes have shown that this achieves a more favorable distribution of conveying capacity between the main screw and auxiliary screws, and improves the conveying performance of the main screw. Areas where there is no or only minimal conveying effect, and thus potentially long residence times and material degradation, are reduced. Furthermore, improved homogenization of the processed material is achieved in the circumferential direction of the main screw.

[0099] It should be expressly pointed out that the subject matter of the sixth aspect can be advantageously combined with the subject matter of the preceding aspects of the invention, either individually or cumulatively in any combination, provided that the subject matter of the aspects is not technically mutually exclusive for the person skilled in the art.

[0100] According to a seventh aspect of the invention, the above-mentioned problem is solved by an extruder for processing a material with a main screw and at least one multi-screw zone in which several auxiliary screws are located in auxiliary bores. wherein in at least 30% of the length of the multi-screw zone, preferably in at least 50% of the length of the multi-screw zone, particularly preferably in at least 70% of the length of the multi-screw zone, at all axial positions the minimum distance of the circumscribed circle of the main screw to the cylinder wall of the extruder is smaller than the minimum distance of the circumscribed circle of at least one auxiliary screw to the cylinder wall of the extruder, preferably the minimum distance of the circumscribed circles of all auxiliary screws to the cylinder wall of the extruder.

[0101] Tests on several prototypes have shown that this results in improved material exchange at the extruder cylinder wall and also reduces areas where there is little or no conveying effect, thus preventing long residence times and material degradation. Furthermore, improved homogenization of the material being processed is achieved in the circumferential direction of the main screw.

[0102] In an advantageous embodiment, in at least a part of the multi-screw zone, preferably in at least 50% of the length of the multi-screw zone, particularly preferably in at least 70% of the length of the multi-screw zone, at all axial positions, the minimum distance of the circumscribed circle of the main screw to the cylinder wall of the extruder is at most 0.5 times, particularly preferably at most 0.3 times, as the minimum distance of the circumscribed circle of at least one auxiliary screw, preferably all auxiliary screws, to the cylinder wall of the extruder.

[0103] It should be expressly pointed out that the subject matter of the seventh aspect can be advantageously combined with the subject matter of the preceding aspects of the invention, either individually or cumulatively in any combination, provided that the subject matter of the aspects is not technically mutually exclusive for the person skilled in the art.

[0104] According to an eighth aspect of the invention, the above-mentioned problem is solved by an extruder for processing a material with a main screw and at least one multi-screw zone in which several auxiliary screws are located in auxiliary bores. wherein in at least 30% of the length of the multi-screw zone, preferably in at least 50% of the length of the multi-screw zone, particularly preferably in at least 70% of the length of the multi-screw zone, at all axial positions the web width of the main screws is at most 1.5 times as large, preferably at most 1.3 times as large, particularly preferably at most 1.1 times as large as the maximum web width of at least one auxiliary screw, preferably all auxiliary screws.

[0105] Preferably, in at least one multi-screw zone on at least one auxiliary screw, the angle between the web flank and the web head changes along at least one web on at least one side of the web, wherein at least two axial regions are present where the angle is greater than 90° and at least one further axial region exists between these regions where the angle is less than 90°. Preferably, the angle is greater than 90° for at least 30% of the axial length of the web. Preferably, the angle is less than 90° for at least 30% of the axial length of the web.

[0106] Tests on several prototypes have shown that this results in a more favorable distribution of the conveying capacity between the main screw and auxiliary screws, and improves the conveying performance of the main screw in the intermediate sections. Furthermore, improved homogenization of the material being processed is achieved in the circumferential direction of the main screw.

[0107] It should be expressly pointed out that the subject matter of the eighth aspect can be advantageously combined with the subject matter of the preceding aspects of the invention, either individually or cumulatively in any combination, provided that the subject matter of the aspects is not technically mutually exclusive for the person skilled in the art.

[0108] The following embodiments can be advantageously combined individually or cumulatively with one or more of the preceding aspects of the invention, provided that the subject matter of the aspects and / or embodiments is not technically mutually exclusive for the person skilled in the art.

[0109] Preferably, in at least one multi-screw zone, all auxiliary screws have the same direction of rotation when viewed in the axial direction, and the main screw has a direction of rotation that is opposite to the direction of rotation of the auxiliary screws when viewed along the axial direction.

[0110] In an advantageous embodiment, the surface of at least one auxiliary screw, preferably all auxiliary screws, which are directed towards the cylinder wall of the extruder, in other words, the surface of the respective auxiliary screw which is closest to the cylinder wall of the extruder, has a lower relative velocity to the surface of the cylinder wall than the relative velocity of the surface of the main screw to the surface of the cylinder wall.

[0111] Preferably, at least one multi-screw zone of the extruder is located, viewed in the axial direction, after the main feed zone and before the main discharge zone.

[0112] Preferably, the processing material is fed to the extruder in the main feed zone at least mostly in molten form under pressure.

[0113] Preferably, the area of ​​at least one multi-screw zone overlaps at least partially with the area of ​​a secondary discharge zone.

[0114] The invention will be explained below using various figures. Fig. Figure 1 shows a schematic, and not to scale, extruder with a screw. Fig. Figure 2 shows a schematic, and not to scale, section through a multi-screw zone at an axial position. Fig. Figure 3 shows a schematic, and not to scale, perspective view of a section through the multi-screw zone, which was already shown in Fig. 2 is shown. Fig. Figure 4 shows a schematic, and not to scale, perspective view of a section through a multi-screw zone, which contains a similar main screw as Fig. 3. Fig. Figure 5 shows a schematic, and not to scale, section of the in Fig. 4 multi-snail zone shown. Fig. Figure 6 shows schematically and not to scale the passage depth profile of two auxiliary worms. Fig. Figure 7 shows a schematic, and not to scale, section through an auxiliary screw at an axial position. Fig. Figure 8 shows a schematic, and not to scale, section through an auxiliary screw at an axial position. Fig. Figure 9 shows a schematic, and not to scale, section through an auxiliary screw at an axial position.

[0115] If the description of a character indicates that something is moving downwards, upwards, to the right, or to the left, this always refers to the character's orientation. The character's orientation is determined by the orientation of the text or the reference marks.

[0116] Fig. Figure 1 shows a schematic, not-to-scale, extruder with a main screw 112 that has a multi-screw section 123. The discharge direction of the extruder, and thus the axial direction 110, results from the direction of the longitudinal axis of the main screw 112 from the main feed section 121 to the main discharge section 125. The direction of rotation 111 of the main screw 112 is downwards on the front side of the figure. The dashed line 101 marks the beginning and the dashed line 102 the end of the main feed section 121 in the axial direction. The dashed line 103 marks the beginning of the multi-screw zone 123 and the dashed line 104 marks the end of the multi-screw zone 123. Zone 122 lies directly after the main feed zone 121 and directly before the multi-screw zone 123.

[0117] The axial end of the main screw 112 and the extruder is marked by the dashed line 105. The dashed line 105 therefore simultaneously marks the beginning and the end of the main discharge zone 125 in the axial direction. Zone 124 lies directly after the multi-screw zone 123 and directly before the main discharge zone 125.

[0118] The length of, for example, the multi-screw zone 123 is the axial length dimension of zone 123 along the axial direction 110.

[0119] Zones 123 and 124 lie axially after or behind zone 122. Zones 122 and 123 lie axially in front of zone 124. Zone 123 lies axially directly after zone 122 and directly in front of zone 124.

[0120] Contrary to the depicted direction of rotation 111 of the main screw 112, in an alternative embodiment the direction of rotation of the main screw 112 can also be in the opposite direction.

[0121] Fig. Figure 2 shows a schematic, not-to-scale, section through a multi-screw section at an axial position. The axial direction 210 extends into the plane of the image. The main screw 202 is located inside the cylinder 201. The main screw 202 contains eight auxiliary bores 205, of which, for clarity, only one auxiliary bore 205 is labeled. The auxiliary bores 205 are distributed around the circumference of the main screw 202. Seven of the eight auxiliary bores 205 contain auxiliary screws 203, of which, for clarity, only one auxiliary screw 203 is labeled. In a production extruder, auxiliary screws 203 are present in all auxiliary bores 205. The illustration of one auxiliary screw 203 has been omitted to better demonstrate the auxiliary bore 205 in the figure. Fig. 2 waived.

[0122] The auxiliary bores 205 create auxiliary openings at the base of the main screw 202, the opening length 207 of which is measured circumferentially along the base of the main screw 202. In other words, the auxiliary opening runs along the base of the main screw 202 that existed before the auxiliary bore was created and was removed by the auxiliary bore, or that would exist if the auxiliary bore were not present.

[0123] Viewed in the circumferential direction of the main screw 202, intermediate sections 206 are located between two auxiliary openings 205. The intermediate length 208 of these intermediate sections is measured circumferentially along the base of the main screw 202. For measuring the intermediate length 208, it is irrelevant whether or not a screw web 204 is located on the intermediate section 206. For the sake of clarity, only one intermediate section 206 and one screw web 204 are designated with a reference symbol.

[0124] The auxiliary screws 203 are rotatably mounted in the auxiliary bores 205. The direction of rotation 212 is indicated on each auxiliary screw 203, with only one direction of rotation 212 being marked with a reference symbol for clarity. The auxiliary screws 203 are aligned parallel to the longitudinal axis of the main screw 202. The main screw 202 is rotatably mounted in the cylinder 201. The direction of rotation 211 is indicated on the main screw 202. The direction of rotation 211 of the main screw 202 is the opposite of the direction of rotation 212 of the auxiliary screws 203.

[0125] Contrary to the depicted direction of rotation 211 of the main screw 202, in an alternative embodiment the direction of rotation of the main screw 202 can also point in the opposite direction. In this case, the auxiliary screws 203 also have a direction of rotation that is opposite to the depicted direction of rotation 212 of the auxiliary screws 203. In other words, in the alternative embodiment as well, the direction of rotation of the main screw 202 is opposite to the direction of rotation of the auxiliary screws.

[0126] The main screw 202 has 10 screw flights 204, which are also located radially after the auxiliary openings. For clarity, only one screw flight 204 is marked with a reference symbol. The main screw thus has a number of flights of 10. All auxiliary screws 203 have two screw flights each. All auxiliary screws 203 thus have a number of flights of 2.

[0127] Arrow 214 indicates the passage depth of a screw channel of the main screw 202, which results from the ridge radius minus the base radius of the screw channel of the main screw 202.

[0128] Arrow 218 indicates the passage depth of a screw channel of an auxiliary screw 203, which results from the stem radius minus the base radius of the screw channel of the auxiliary screw 203.

[0129] Dimension arrow 216 indicates the distance of the circumscribed circle of the main screw 202 to the cylinder wall, and dimension arrow 217 indicates the minimum distance of the circumscribed circle of an auxiliary screw 203 to the cylinder wall. In this case, the distance of the circumscribed circle of the main screw 202 to the cylinder wall is less than the minimum distance of the circumscribed circle of the auxiliary screw 203 to the cylinder wall.

[0130] Fig. Figure 3 shows a schematic, and not to scale, perspective view of a section through the multi-screw zone, which was already shown in Fig. Figure 2 shows the main screw 302 located inside the cylinder 301. The main screw 302 contains eight auxiliary bores 305, but for clarity, only one auxiliary bore 305 is labelled. The auxiliary bores 305 are distributed around the circumference of the main screw 302. Auxiliary screws 303 are present in all auxiliary bores 305, but for clarity, only one auxiliary screw 303 is labelled.

[0131] The auxiliary screws 303 are rotatably mounted in the auxiliary bores 305. The main screw 302 is rotatably mounted in the cylinder 301.

[0132] The main screw 302 has 10 screw flights 304, although for clarity only one screw flight 304 is labelled. The main screw thus has a number of flights 10. The screw flights 304 run helically around the main screw 302 and are also located radially after the auxiliary openings. All auxiliary screws 303 have two screw flights that run helically around their respective auxiliary screws 303. All auxiliary screws 303 thus have a number of flights 2.

[0133] Fig. Figure 4 shows a schematic and not to scale perspective view of a section through a multi-screw zone, which contains a main screw similar to 402. Fig. 3. The only difference is that the screw flights 404 of the main screw 402 are interrupted after the auxiliary openings of the auxiliary bores 405 when viewed radially. The screw flights 404 are present on all intermediate parts 406. For the sake of clarity, only a portion of a screw flight 404, an auxiliary bore 405, and an intermediate part 406 are provided with a reference numeral.

[0134] The helical webs 404, with the described interruptions, run helically around the main helical web 402. To clarify the helical course, the parts of a helical web that lie on a helical path are marked with the reference symbol 415. From this, it can be seen that the main helical web 402 has a number of turns of 10, like the main helical web 302 of the Fig. 3.

[0135] Fig. Figure 5 shows a schematic, and not to scale, section of the in Fig. 4 multi-screw zone shown. Arrow 509 indicates the width of a screw channel 510 of the main screw 502 in the intermediate section 506. Arrow 511 indicates the width of a screw channel 512 of an auxiliary screw 503. Arrow 518 indicates the web width of a screw web 517 of the main screw 502 in the intermediate section 506, and arrow 520 indicates the web width of a screw web 519 of an auxiliary screw 503.

[0136] Fig. Figure 6 shows, schematically and not to scale, the channel depth profile of two auxiliary screws 631 and 634. The dashed lines 601 and 602 indicate axial positions. The arrow 610 indicates the discharge direction of the extruder and thus the axial direction. The channel depth of auxiliary screw 631 exhibits several local minima 632 and local maxima 633. The channel depth profile of auxiliary screw 631 differs from that of auxiliary screw 634. For example, the channel depth of auxiliary screw 631 has a local maximum 633 at the axial position indicated by the dashed line 601, while auxiliary screw 634 has a local minimum 635 at this position. At the axial position, which is marked by the dashed line 602, the passage depth of the auxiliary screw 631 has a local minimum 632, while the auxiliary screw 634 has a local maximum 636 at this position.

[0137] Fig. Figure 7 shows a schematic, not-to-scale, section through an auxiliary screw 703 at an axial position. The axial direction 710 extends into the plane of the image. The angle 744 between the right flank 742 (viewed in the axial direction) and the web head 741 of the web 717 is 90° in the illustrated case. The angle 745 between the web head 741 and the left flank 743 (viewed in the axial direction) is also 90° in the illustrated case.

[0138] Fig. Figure 8 shows a schematic, not to scale, section through an auxiliary screw 803 at an axial position. The axial direction 810 extends into the plane of the image. The angle 844 between the right flank 842 (viewed in the axial direction) and the web head 841 of the web 817 is less than 90° in the illustrated case.

[0139] Fig.Figure 9 shows a schematic, not to scale, section through an auxiliary screw 903 at an axial position. The axial direction 910 extends into the plane of the image. The angle 944 between the right flank 942 (viewed in the axial direction) and the web head 941 of the web 917 is greater than 90° in the illustrated case. List of reference symbols used 101 Dashed line (dividing line) 102 Dashed line (dividing line) 103 Dashed line (dividing line) 104 Dashed line (dividing line) 105 Dashed line (dividing line) 110 Axial direction 111 Direction of rotation of a worm 112 Main snail 121 Main feed zone 122 Zone in one extruder 123 Multi-snail zone 124 zones in one extruder 125 Main discharge zone 201 cylinders 202 Main snail 203 Auxiliary snail 204 Snail bridge of an auxiliary snail 205 Auxiliary borehole 206 Intermediate part 207 Opening length of an auxiliary opening of an auxiliary bore 208 Intermediate length of an intermediate surface of an intermediate part 210 Axial direction 211 Direction of rotation of the main screw 212 Direction of rotation of an auxiliary screw 214 Passage depth of a screw channel of the main screw 216 Distance of the circumcircle of the main screw to the cylinder wall 217 Minimum distance of the circumcircle of an auxiliary screw to the cylinder wall 218 Passage depth of a screw channel of an auxiliary screw 301 cylinders 302 Main snail 303 Auxiliary snail 304 Snail bridge of an auxiliary snail 305 Auxiliary borehole 306 Intermediate part 401 cylinders 402 Main snail 403 Auxiliary screw 404 Snail ramp of an auxiliary snail 405 Auxiliary borehole 406 Intermediate part 415 parts of a snail's web 502 Main snail 503 Auxiliary snail 506 Intermediate part 509 Width of a screw channel of the main screw 510 Screw channel of the main screw 511 Width of a screw channel of an auxiliary screw 512 Screw channel of an auxiliary screw 517 Snail bridge of the main snail 518 Bridge width of a snail bridge of the main snail 519 Snail bridge of an auxiliary snail 520 web width of a screw thread of an auxiliary screw 601 Dashed line (axial position) 602 Dashed line (axial position) 610 Axial direction 631 Auxiliary screw 632 Local minimum of the passage depth of an auxiliary screw 633 Local maximum of the passage depth of an auxiliary screw 634 Auxiliary screw 635 Local minimum of the passage depth of an auxiliary screw 636 Local maximum of the passage depth of an auxiliary screw 703 Auxiliary screw 710 Axial direction 717 Schneckensteg 741 Bridge head 742 Flank of Schneckensteg 743 Flank of Schneckensteg 744 Angle between flank and bridge head 745° angle between bridge head and flank 803 Auxiliary screw 810 Axial direction 817 Schneckensteg 841 Bridge head 842 Flank of Schneckensteg 844 Angle between flank and bridge head 903 Auxiliary screw 910 Axial direction 917 Schneckensteg 941 Bridge head 942 Flank of Schneckensteg 944 Angle between flank and bridge head

Claims

[1] Extruder for processing a processing material with a main screw 202 and at least one multi-screw zone 123 in which several auxiliary screws 203 are present in auxiliary bores 205, wherein the auxiliary bores 205 partially penetrate the screw base of the main screw 202. characterized by , that in at least 30% of the length of the multi-screw zone 123 at all axial positions, the minimum number of flights of the main screw 202 in at least one intermediate part 206 is at least 3 greater than the maximum number of flights of at least one auxiliary screw 203. [2] Extruder according to claim 1 characterized by , that in at least 30% of the length of the multi-screw zone 123 at all axial positions, the channel ratio in at least one intermediate part 506 is a maximum of 8, where the channel ratio denotes the quotient of the width 509 of a screw channel 510 transverse to the screw flights over the maximum flight depth 214 of the screw channel 510 at an axial position. [3] Extruder according to claim 1 or 2 characterized by that the main screw 202 has at least two intermediate parts 206 and at least two auxiliary openings 205 and in at least 30% of the length of the multi-screw zone 123 at all axial positions the quotient of the minimum intermediate length 208 of at least one intermediate part 206 over the maximum opening length 207 of at least one auxiliary opening 205 is at least 0.

8. [4] Extruder according to one of claims 1 to 3 characterized bythat the main screw 202 has at least two intermediate parts 206 and at least two auxiliary openings 205 and in at least 30% of the length of the multi-screw zone 123 at all axial positions the width 509 of at least one screw channel 510 in at least one intermediate part 206 is at most 2.5 times as large as the intermediate length 208 of the intermediate part 206. [5] Extruder for processing a processing material with a main screw 202 and at least one multi-screw zone 123 in which several auxiliary screws 203 are present in auxiliary bores 205, wherein the auxiliary bores 205 partially penetrate the screw base of the main screw 202. characterized by , that the flight depth 218 of at least one auxiliary screw 203 changes along the longitudinal axis of the auxiliary screw 203 and has at least 3 local minima 632 and / or 3 local maxima 633. [6] Extruder for processing a processing material with a main screw 202 and at least one multi-screw zone 123 in which several auxiliary screws 203 are present in auxiliary bores 205, wherein the auxiliary bores 205 partially penetrate the screw base of the main screw 202. characterized by , that at least one auxiliary screw 631 has a different geometry than at least one other auxiliary screw 634 and preferably at least one auxiliary screw 631 has different flight depths 218 and / or different flight pitches along its longitudinal axis. [7] Extruder for processing a processing material with a main screw 202 and at least one multi-screw zone 123 in which several auxiliary screws 203 are present in auxiliary bores 205, wherein the auxiliary bores 205 partially penetrate the screw base of the main screw 202. characterized by , that in at least 30% of the length of the multi-screw zone 123 at all axial positions, the quotient of the maximum width 509 of the screw channels 510 of the main screw 502 over the minimum width 511 of the screw channels 512 of at least one auxiliary screw 502 is a maximum of 1.8, and in at least 30% of the length of the multi-screw zone 123, the pitch of the main screw 202 in at least one intermediate part 206 is at least 0.8 at all axial positions. [8] Extruder according to one of the preceding claims characterized by that in at least 30% of the length of the multi-screw zone 123 at all axial positions the minimum distance of the envelope circle 216 of the main screw 202 to the cylinder wall of the extruder is smaller than the minimum distance of the envelope circle 217 of at least one auxiliary screw 203 to the cylinder wall of the extruder. [9] Extruder for processing a processing material with a main screw 202 and at least one multi-screw zone 123 in which several auxiliary screws 203 are present in auxiliary bores 205, wherein the auxiliary bores 205 partially penetrate the screw base of the main screw 202. characterized by , that in at least 30% of the length of the multi-screw zone 123 at all axial positions, the flight width 518 of the main screws 502 is a maximum of 1.5 times as large as the maximum flight width 520 of at least one auxiliary screw 503. [10] Extruder for processing a processing material with a main screw 202 and at least one multi-screw zone 123 in which several auxiliary screws 203 are present in auxiliary bores 205, wherein the auxiliary bores 205 partially penetrate the screw base of the main screw 202. characterized by , that in at least one multi-screw zone 123 on at least one auxiliary screw 703 along at least one web 717 on at least one side of the web, the angle between the web flank and the web head changes, wherein there are at least two axial regions in which the angle is greater than 90° and between these regions there is at least one further axial region in which the angle is less than 90°.

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