Extruder with sealing element, and method for producing a food product

Abstract

The present invention relates to an extruder, comprising an intermediate housing (13), which is arranged between the extruder housing (8) and the gearing (12), and a supporting shaft (5) of an extruder screw, which supporting shaft is arranged in the extruder (7), wherein at least one restriction element (1) is arranged on a portion of the supporting shaft (5) that is located in the process area (9) of the extruder (7), the restriction element sealing off the intermediate housing (13) from the process area (9), the restriction element (1) having a pitch from 5 to 30 mm, in particular 10 to 20 mm. The present invention furthermore relates to a method for producing a food product or animal feed with an extruder (7) of this type, wherein the material introduced into the process area (9) is conveyed exclusively in the direction of the outlet (11) of the extruder (7).

Description

[0001] EXTRUDER WITH SEALING ELEMENT AND METHOD FOR PRODUCING A FOOD

[0002] The present invention relates to an extruder, in particular for producing a food or animal feed, which has an improved sealing of the process zone.

[0003] Extruders are machines in which materials such as polymers, elastomers or protein-containing mixtures can be treated under desired pressure and temperature conditions for the production of food products including cereals, snacks, pet food and alternative foods. A typical extruder comprises at least one extruder screw, each of the extruder screws having a set of extruder screw elements mounted on a support shaft. The extruder screws are housed in a cylinder called a barrel. An extruder usually comprises several barrels connected end to end. Several barrels are required to carry out the various processes to be carried out in the extruder such as conveying, kneading, mixing, devolatilization, metering and the like.

[0004] The process zone of the extruder is located within the barrel or barrels, i.e. the area in which the extruder screw shafts are arranged to be movable and whose movement causes the material introduced into the process zone to be processed. The material to be processed can be introduced into the process zone through an inlet. The inlet is usually located at an end of the process zone on the machine side (i.e. opposite the extruder outlet) and is usually arranged in such a way that the material can be introduced into the process zone from above with the aid of gravity. An extruder of this type is shown in DE 20 2010 003 416 U1. The extruder screw shaft is characterized in that it has a support shaft with a toothing with external teeth running parallel to the shaft axis.Screw elements and kneading elements with internal teeth can be positively attached to this support shaft by the internal teeth engaging with the external teeth of the support shaft.

[0005] The extruder screw shaft is connected via a gear to a motor, which can set the extruder screw shaft in a rotating motion. The motor and gear are arranged on the machine side, with an intermediate housing (also known as a gearbox lantern) located between the process zone and the gear. The intermediate housing is separated from the process zone by a partition wall, which must have an opening through which the support shaft is guided from the gearbox into the process zone.

[0006] This opening cannot be sealed, as the support shaft must be able to rotate within the opening. This means that during extended extruder operation, material to be extruded can enter the intermediate housing and contaminate it. In addition to the unwanted loss of material, this necessitates disassembling the extruder for cleaning.

[0007] This problem has not yet been satisfactorily resolved.

[0008] In conventional extruders, the support shaft is typically guided through a stuffing box, in which the support shaft rotates with the aid of oil lubrication. However, such a stuffing box does not seal the intermediate housing from the extruder's process zone, leading to the contamination problem described above during extended extruder operation. Furthermore, oil used for lubrication can enter the process zone, which is undesirable in extruders used to produce food or animal feed.

[0009] This known system is disadvantageous from a hygiene point of view.

[0010] In the food or animal feed industry, a preferred solution is one in which the support shaft is mounted in a sliding mount, free from lubricating oil. However, this sliding mount does not seal the intermediate housing from the extruder's processing zone, thus resulting in the problem described above.

[0011] It was the object of the present invention to provide an extruder in which the intermediate housing of the extruder is reliably sealed from the process zone of the extruder.

[0012] This object is achieved by the present invention.

[0013] In detail, the present invention relates to an extruder, comprising a motor with a gear, an extruder housing with a process zone located in the housing and an inlet and outlet, an intermediate housing which is arranged between the extruder housing and the gear, a support shaft which is arranged in the extruder, wherein screw elements are arranged on at least a section of the support shaft and form an extruder screw with the support shaft, wherein the extruder screw is movably arranged in the extruder housing, wherein at least one baffle element is arranged on a section of the support shaft which is located in the process zone, characterized in that the intermediate housing is sealed off from the process zone by the at least one baffle element, wherein the baffle element has a pitch of 5 to 30 mm, preferably 10 to 20 mm.

[0014] According to the invention, it has been found that the passage of material to be extruded through the opening in the dividing wall between the process zone and the intermediate housing of an extruder can be reliably prevented by arranging a special screw element on the process zone side of the support shaft. This screw element is referred to according to the invention as a damming element. The damming element prevents the material to be extruded from being conveyed in the direction of the dividing wall between the process zone and the intermediate housing; instead, the material to be extruded is dammed and prevented from passing through the opening in the dividing wall through which the support shaft of the extruder screw is guided.

[0015] The solution according to the invention is characterized in that the extruder can be operated without lubricant, which significantly improves the hygiene of the extruder with regard to the production of food or animal feed. Since the intermediate housing is sealed off from the process zone by the at least one baffle element, a stuffing box operated with lubricant (as used in the prior art) can be dispensed with. In particular, the use of oil, water or air for lubrication or sealing purposes can preferably be dispensed with, which results in advantages in terms of apparatus and process technology. The baffle element according to the invention has a pitch of 5 to 30 mm, preferably 10 to 20 mm. The pitch of a screw element of an extruder screw describes the steepness of the flights (turns) of the screw element. These flights wind helically around a central section of the screw element.The greater the pitch, the more the flights in a position are aligned perpendicular to the central longitudinal axis of the screw element (i.e., the axis running longitudinally through the center of the screw element). The pitch describes the distance between two flight positions that are at a maximum distance from the central longitudinal axis of the screw element. The smaller this distance, the greater the pitch of the screw element.

[0016] Due to the steep pitch, the dam element has a comparatively large number of turns (windings) over a comparatively short axial length of the dam element. According to the invention, it is preferred that the dam element has 2 to 10, preferably 3 to 4, helical turns.

[0017] It is further preferred according to the invention that the dam element has a length of 30-90 mm, preferably 40-80 mm.

[0018] Thus, the dam element according to the invention can, for example, have 4 threads over a length (i.e. axial length) of 40 mm with a pitch of 10 mm.

[0019] Due to its large pitch, the baffle element according to the invention does not convey any material to be extruded and thus prevents such material from moving towards the opening in the dividing wall between the process zone and the intermediate housing. Screw elements with such a large pitch are known, for example, from Dl 10-2004 052 055 B4. There, a one-piece screw element is shown in which a conveyor screw segment and a working segment with a greater pitch than the conveyor screw segment are arranged one behind the other. There is no gap with a width of approximately 1 to 3 mm between these segments and, for manufacturing reasons, one cannot be provided. This element is not proposed for sealing a process zone. Furthermore, only one section of the one-piece screw element has a pitch which corresponds to the pitch of the baffle element according to the invention.

[0020] The dam element according to the invention can be arranged in a known manner on a support shaft of an extruder screw. According to the invention, it is preferred that the dam element has internal teeth and the support shaft has external teeth, the teeth being positively connected to one another. This is known, for example, from DE 20 2010 003 416 U1 or WO 2013 / 030322 A1.

[0021] The inventive baffle element is arranged on a section of the extruder screw support shaft located in the process zone. This section is located between the inlet to the process zone and the opening in the partition wall between the process zone and the intermediate housing and prevents product from escaping from the process chamber into the intermediate housing.

[0022] According to one embodiment of the invention, the baffle element can rest against the opening in the partition wall between the intermediate housing and the process zone. According to another embodiment of the invention, the baffle element is arranged on the support shaft in such a way that a gap of 1 to 5 mm, preferably 1 to 4 mm, is present between the end of the baffle element facing the opening and the opening. According to the invention, this is preferably achieved in that the baffle element has a section on each side in which no flight is present. In this way, in the installed state, a gap is formed on each side of the baffle element, which gap preferably has a width in the range of 1 to 5 mm. If material gets into such a gap during operation of the extruder, it is conveyed back by the rotation of the support shaft. The screw flight of the baffle element is fully retained.

[0023] There is no other screw element between the inventive baffle element and the opening in the partition wall between the intermediate housing and the process zone.

[0024] According to one embodiment of the invention, the baffle element is arranged on the support shaft in such a way that its end facing the extruder inlet is flush with the boundary of the inlet, which borders the opening in the partition wall between the intermediate housing and the process zone. In other words, according to this embodiment, the baffle element does not protrude into the area of ​​the process zone located below the inlet. However, there is preferably also no gap between the area of ​​the process zone located below the inlet and the position of the baffle element. The baffle element is thus arranged downstream of the extruder inlet.

[0025] According to another embodiment of the invention, the dam element can also be arranged on the support shaft in such a way that it projects into the area of ​​the process zone which is located below the inlet. This has the advantage that no dead space is formed in the process zone in which material can remain. However, it is essential that the dam element does not extend over the entire area of ​​the process zone which is located below the inlet. Preferably, in this embodiment, the dam element according to the invention extends into the area of ​​the process zone which is located below the inlet in such a way that it occupies a maximum of 10%, more preferably a maximum of 5% of the axial length of this area (i.e. projects into this area).

[0026] The baffle element described above can be used in any conventional extruder.

[0027] The present invention further relates to an extruder screw comprising a support shaft and at least one baffle element, wherein the baffle element has a pitch of 5 to 30 mm, preferably 10 to 20 mm and the ratio D / L s from the diameter of the extruder screw D to the length of the baffle element L s in the range of 1.35 to 1.6, preferably 1.45 to 1.55.

[0028] The dam element can be designed as described above. As stated above, this dam element has a steep gradient and thus a comparatively large number of turns (windings) over a comparatively short axial length L s of the dam element. According to the invention, it is preferred that the dam element has 2 to 10, preferably 3 to 4 helical threads. According to the invention, the ratio D / L is s from the diameter of the extruder screw D to the length of the baffle element L sin the range of 1.35 to 1.6, preferably 1.45 to 1.55.

[0029] According to the invention, extruder screws with a diameter D can be used over a wide range from 30 mm to 180 mm, preferably 40 mm to 160 mm, and particularly preferably 60 mm to 130 mm. Accordingly, a dam element with a length L s in the range of 20 mm to 120 mm, preferably 25 mm to 100 mm, more preferably 30 mm to 90 mm, and particularly preferably 40 mm to 80 mm.

[0030] According to the present invention, the baffle element is the first screw element on the support shaft of the extruder screw. An extruder screw is produced by applying the required screw elements one after the other in a desired order to the support shaft. According to the invention, the at least one baffle element is applied as the first element to the support shaft of the extruder screw and is thus the first screw element on the support shaft of the extruder screw. This has the result that, when installed in the extruder, the baffle element is the screw element that is closest to the opening in the dividing wall between the intermediate housing and the process zone of the extruder.

[0031] According to the invention, the dam element is preferably arranged detachably on the support shaft of the extruder screw.

[0032] According to an embodiment of the invention, the dam element is arranged on the support shaft of the extruder screw in such a way that, when installed in the extruder, it rests against the opening in the partition wall between the intermediate housing and the process zone of the extruder.

[0033] According to another embodiment of the invention, the baffle element is arranged on the support shaft of the extruder screw in such a way that, when installed in the extruder, a gap of 1 to 5 mm, preferably 1 to 4 mm, is present between the end of the baffle element facing the opening in the dividing wall between the intermediate housing and the process zone of the extruder and the opening. According to the invention, this is preferably achieved in that the baffle element has a section on each side in which no flight is present. In this way, a gap is formed on each side of the baffle element in the installed state, which gap preferably has a width in the range of 1 to 5 mm.

[0034] According to another embodiment of the invention, the baffle element is arranged on the support shaft of the extruder screw in such a way that, when installed in the extruder, there is no other screw element between the baffle element according to the invention and the opening in the partition wall between the intermediate housing and the process zone.

[0035] According to another embodiment of the invention, the baffle element is arranged on the support shaft of the extruder screw in such a way that, when installed in the extruder, the end of the baffle element facing the extruder inlet is flush with the boundary of the inlet, which border faces the opening in the dividing wall between the intermediate housing and the process zone. In other words, according to this embodiment, the baffle element does not protrude into the area of ​​the process zone which is located below the inlet. However, there is preferably also no gap between the area of ​​the process zone which is located below the inlet and the position of the baffle element. The baffle element is thus arranged downstream of the extruder inlet.

[0036] According to another embodiment of the invention, the dam element is arranged on the support shaft of the extruder screw in such a way that, when installed in the extruder, it projects into the area of ​​the process zone located below the inlet. However, it is essential that the dam element does not extend over the entire area of ​​the process zone located below the inlet. In this embodiment, the dam element according to the invention preferably extends into the area of ​​the process zone located below the inlet in such a way that it occupies a maximum of 10%, more preferably a maximum of 5% of the axial length of this area (i.e., projects into this area).

[0037] According to the present invention, at least one dam element as described above is provided. However, it is also possible, and in the case of multi-screw extruders, preferred, to provide several dam elements. For example, 1 to 3 dam elements could be arranged one behind the other on a support shaft and together constitute a dam element according to the invention.

[0038] In the case of multi-screw extruders, a baffle element according to the invention, as described above, is preferably arranged on each support shaft of each extruder screw. An arrangement in which baffle elements located on different support shafts interlock with one another is particularly preferred. In this way, the sealing effect of the baffle elements is enhanced and, preferably, a self-cleaning effect is also achieved.

[0039] Extruders are well known. Reference is made, for example, to WO 2012 / 158023 A1 or to the extruders, in particular twin-screw extruders, from Bühler. Such extruders preferably have an L / D ratio (total length to screw diameter) in the range of 12 to 60, preferably 20 to 40. According to the invention, the extruders are preferably operated at 100 to 1000 rpm, more preferably at 200 to 600 rpm, and most preferably at 250 to 350 rpm.

[0040] The extruder according to the invention comprises a motor with a gearbox for driving the extruder screws. For this purpose, the support shaft of each extruder screw is operatively connected to the gearbox. This can be done in a conventional manner.

[0041] The extruder according to the invention further comprises an extruder housing with a process zone located within the housing and an inlet and outlet. The extruder housing preferably comprises 2 to 20 barrels, more preferably 2 to 15 barrels. The barrels are preferably connected to one another at the end faces and together form the extruder housing.

[0042] The extruder barrel (or each of the barrels comprising the extruder barrel) has a through-bore. The through-bore runs axially through the extruder barrel throughout its entire length. The extruder's processing zone is located within this through-bore.

[0043] The extruder housing is preferably temperature-controlled. The material to be extruded is kneaded under pressure (usually 1 to 400 bar, preferably 1 to 200 bar) to form a homogeneous mixture. This typically requires an energy consumption of 10 to 150 Wh / kg, preferably 10 to 120 Wh / kg, and particularly preferably 15 to 30 Wh / kg.

[0044] The extruder inlet is used to introduce raw materials into a first section of the extruder. This inlet leads into the process zone. The inlet is usually and preferably located on the extruder barrel, so that material can flow into the extruder barrel, or more precisely, into the extruder's process zone, under the influence of gravity.

[0045] The material to be extruded can be fed directly into the process zone through the inlet. Preferably, a metering device is located above the inlet, with which the material to be extruded is metered and, if necessary, mixed before it is fed through the inlet. According to the invention, the material to be extruded can preferably be pretreated in a conventional preconditioner and fed from there to the inlet, for example, by means of a conventional screw conveyor.

[0046] At the end of the process zone farther from the inlet is an outlet through which the extruded material leaves the extruder. The outlet is connected to the process zone.

[0047] The extruder typically also has a water, oil and possibly a steam supply line.

[0048] The extruder according to the invention further comprises an intermediate housing (also called a gearbox lantern) arranged in a conventional manner between the extruder housing and the gearbox. The support shaft of the extruder screw is guided through this intermediate housing, but no screw elements are arranged on the support shaft in this section.

[0049] Preferably, the end of the intermediate housing facing the extruder housing forms a partition wall; however, a separate partition wall can also be provided. This partition wall separates the intermediate housing from the process zone, which is located in the extruder housing. In this partition wall there is an opening through which the support shaft of the extruder screw is guided. In the case of a multi-screw extruder, the number of openings in the partition wall corresponds to the number of extruder screws. This is conventionally known. The transition region between the intermediate housing and the process zone is preferably free of lubricant in order to improve the hygiene of the extruder with regard to the production of food or animal feed. According to a preferred embodiment of the present invention, a sleeve is arranged in the opening in the partition wall, through which sleeve the support shaft of the extruder screw is guided.Since the intermediate housing is sealed from the process zone by at least one dam element, a stuffing box operated with lubricant (as used in the prior art) is no longer necessary. In particular, the use of oil, water, or air for lubrication or sealing purposes can be dispensed with, which offers advantages in terms of equipment and process technology.

[0050] According to a further preferred embodiment of the present invention, a bearing is provided on the partition wall or in the opening in the partition wall in order to support the support shaft and, if appropriate, a provided sleeve.

[0051] Within the process zone, in addition to the baffle element arranged as described above, additional screw elements are arranged on at least one section of the support shaft and, together with the support shaft, form an extruder screw. These additional screw elements are distinct from the baffle element and are separated from it. This separation increases the flexibility in arranging different screw elements on the support shaft in the desired sequence.

[0052] Preferably, the additional screw elements are selected from the group consisting of conveyor screw elements, mixing elements, barrier elements, and kneading screw elements. Screw elements with an Erdmenger profile are particularly preferred. These additional screw elements can be arranged in the desired order on the support shaft.

[0053] As stated above with regard to the damming elements according to the invention, the additional screw elements can also be arranged in a known manner on a support shaft of an extruder screw. According to the invention, it is preferred that the additional screw elements have internal teeth and the support shaft have external teeth, with the teeth being positively connected to one another. This is known, for example, from DE 20 2010 003 416 U1 or WO 2013 / 030322 A1.

[0054] According to the invention, the extruder is preferably a twin-screw extruder with two extruder screws, each extruder screw having at least one dam element according to the invention. Each dam element is arranged on a support shaft of the twin-screw extruder as described above.

[0055] Particularly preferred is an arrangement in which damming elements located on different support shafts and additional screw elements intermesh with each other.

[0056] According to a preferred embodiment of the present invention, a cooling tool, such as a cooling nozzle, can be provided at the extruder outlet. Cooling tools for extruders are well known. A known distribution unit can preferably be arranged between the extruder and the cooling tool.

[0057] The extruder according to the invention has the advantage that it can be operated without unnecessary material loss and, in particular, preferably under very good hygienic conditions. This makes it particularly suitable for the production of a foodstuff or animal feed. The present invention thus also relates to a method for producing a foodstuff or animal feed using an extruder according to the invention, comprising the step of introducing a material for producing the foodstuff or animal feed through the inlet of the extruder into the process zone of the extruder, wherein the material introduced into the process zone is conveyed exclusively in the direction of the outlet of the extruder.

[0058] As described above, this is achieved by providing a dam element according to the invention which prevents material from being conveyed in the direction of the opening in the partition wall between the intermediate housing and the process zone.

[0059] According to the invention, the material is preferably conveyed in the process zone under lubricant-free conditions. This is possible because the opening in the partition wall between the intermediate housing and the process zone is sealed by the inventive baffle element, and no measures such as the provision of a stuffing box with oil lubrication are required. In particular, the use of oil, water, or air for lubrication or sealing purposes can preferably be dispensed with, which results in advantages for the equipment and process.

[0060] The present invention thus also relates to the use of an extruder according to the invention for producing a food or animal feed.

[0061] According to the invention, all foodstuffs or animal feeds that are conventionally produced by extrusion can be produced. Examples include protein-containing mixtures for the production of foodstuffs, including cereals, snacks, animal feed, and alternative foodstuffs (such as alternative meat and fish products).

[0062] The present invention will now be described in more detail using non-limiting exemplary embodiments with reference to the figures. In the figures, like reference numerals designate like elements. They show:

[0063] Fig. 1 is a schematic representation of an embodiment of two dam elements according to the invention

[0064] Fig. 2 is a cross-sectional view through the inventive dam elements according to Fig. 1

[0065] Fig. 3 is a schematic representation of an embodiment of a dam element with passage-free sections

[0066] Fig. 4 is a schematic representation of an embodiment of a support shaft with external teeth

[0067] Fig. 5 is a schematic representation of an embodiment of an extruder according to the invention

[0068] Fig. 1 shows a schematic representation of an embodiment of two damming elements 1 according to the invention. However, the following explanations apply analogously to a single damming element.

[0069] The damming element 1 according to the invention comprises a central section 3 and threads (turns) 2 arranged helically thereon. In this embodiment, each damming element 1 according to the invention has four threads 2 which have a large pitch of 10 mm, which is preferred according to the invention. Each damming element 1 according to the invention according to Fig. 1 has a length of 40 mm. Fig. 1 also shows how two damming elements 1 according to the invention can interlock. This is feasible, for example, in a twin-screw extruder in which one damming element 1 is arranged on each of the two support shafts.

[0070] Fig. 2 shows a cross-sectional view through the inventive dam elements 1 according to Fig. 1. It can be seen that each inventive dam element 1 has an internal toothing 4, which can be positively connected to an external toothing (not shown here) of a support shaft 5.

[0071] Fig. 3 shows a schematic representation of an embodiment of a dam element 1 with passage-free sections. As in the embodiment according to Fig. 1, the dam element 1 according to the invention in the embodiment according to Fig. 3 comprises a central section 3 and passages (turns) 2 arranged helically thereon.

[0072] In this embodiment, each dam element 1 according to the invention has four flights 2, which have a preferred large pitch of 10 mm according to the invention. The dam element 1 according to the invention according to Fig. 3 has a length L sof 40 mm. At both ends of the baffle element 1 there is a section 3a, 3b which is free of any flights. In this way, in the installed state, a gap is formed on each side of the baffle element 1, which preferably has a width b, b' in the range from 1 to 3 mm and corresponds to the section 3a, 3b. If material gets into such a gap during operation of the extruder, it is fed back by the rotation of the support shaft. The screw flight of the baffle element is fully retained. Fig. 4 shows a schematic representation of an embodiment of a support shaft 5 with diameter D and external toothing 5a. The external toothing of the support shaft 5 can be connected in a form-fitting manner to the internal toothing 4 of a baffle element 1 according to the invention or (as shown here) to an additional screw element 6 with corresponding internal toothing.The additional screw element 6 has a lower pitch of the flights than the dam element 1 .

[0073] Fig. 5 shows a schematic representation of an embodiment of an extruder 7 according to the invention. The extruder 7 comprises an extruder housing 8, which in the embodiment shown in Fig. 5 consists of four barrels. Within the extruder housing 8 is a process zone 9, which is realized by an axial through-bore through the extruder housing 8 (or the barrel forming it).

[0074] The extruder 7 has an inlet 10 through which material can be introduced into the process zone 9. At the opposite end of the process zone 9 there is an outlet 11 through which extruded or mixed material can leave the extruder 7.

[0075] Within the process zone 9, an extruder screw is arranged, which consists of a support shaft 5 with a diameter D, a baffle element 1 arranged thereon with a length L s and a plurality of additional screw elements 6 arranged on the support shaft 5. The support shaft 5 extends through an intermediate housing 13 to a gear 12, which in turn is operatively connected to a motor 14 (not shown). The support shaft 5 can be set in rotation by the motor 14 via the gear 12. The intermediate housing 13 is arranged between the gear 12 and the extruder housing 8 or the process zone 9 located therein. The intermediate housing 13 is separated from the extruder housing 8 or the process zone 9 located therein by a partition wall 15. In the partition wall 15 there is an opening 16 through which the support shaft 5 of the extruder screw is guided.

[0076] The dam element 1 is arranged in the area between the inlet 10 and the opening 16, with a gap preferably being present between the dam element 1 and the partition wall 15, which gap is approximately 4 mm in this embodiment. In this embodiment, the dam element 1 does not extend into the area of ​​the process zone 9 below the inlet 10.

[0077] According to the invention, the gap between the baffle element and the partition wall 15 is preferably realized by using a baffle element 1 according to Fig. 3, which has a section on each side in which no flight is present. In this way, in the installed state, a gap is formed on each side of the baffle element 1, which gap preferably has a width in the range of 1 to 4 mm. If material gets into such a gap during operation of the extruder, it is fed back by the rotation of the support shaft. The screw flight of the baffle element 1 is completely retained.

Claims

Patent claims 1. Extruder, comprising a motor (14) with a gear (12), at least one extruder housing (8) with a process zone (9) located in the housing (8) and with an inlet (10) and an outlet (11), an intermediate housing (13) which is arranged between the extruder housing (8) and the gear (12), a support shaft (5) which is arranged in the extruder (7), wherein screw elements (6) are arranged on at least a section of the support shaft (5) and form an extruder screw with the support shaft (5), wherein the extruder screw is movably arranged in the extruder housing (8), wherein at least one baffle element (1) is arranged on a section of the support shaft (5) which is located in the process zone (9), characterized in that the intermediate housing (13) is sealed off from the process zone (9) by the at least one baffle element (1), wherein the baffle element (1) has a Pitch of 5 to 30 mm, preferably 10 to 20 mm.

2. Extruder according to claim 1, characterized in that the dam element (1) has 2 to 10, preferably 3 to 4 helical flights (2).

3. Extruder according to claim 1 or 2, characterized in that the dam element (1) has an internal toothing (4) and the support shaft (5) has an external toothing (5a), wherein the toothings (4, 5a) are positively connected to one another.

4. Extruder according to one of the preceding claims, characterized in that the dam element (1) has a length of 30-90 mm, preferably 40-80 mm.

5. Extruder according to one of the preceding claims, characterized in that the dam element (1) has a passage-free section (3a, 3b) at each of its ends.

6. Extruder according to one of the preceding claims, characterized in that additional screw elements (6) are arranged on the support shaft (5) in the process zone (9), which screw elements are different from the dam element (1) and are separate from it.

7. Extruder according to claim 5, characterized in that the additional screw elements (6) are selected from the group consisting of conveyor screw elements, mixing elements, barrier elements and kneading screw elements.

8. Extruder according to one of the preceding claims, characterized in that the dam element (1) is arranged downstream of the inlet (10) of the extruder (7) and does not protrude into a region of the process zone (9) below the inlet (10).

9. Extruder according to one of the preceding claims, characterized in that the extruder (7) is a twin-screw extruder with two extruder screws, each extruder screw having at least one baffle element (1) according to one of claims 1 to 8.

10. Extruder according to one of the preceding claims, characterized in that the transition region (16) between Intermediate housing (13) and process zone (9) are free of lubricant.

11. Extruder screw, comprising a support shaft (5) and at least one baffle element (1), wherein the baffle element (1) has a pitch of 5 to 30 mm, preferably 10 to 20 mm and the ratio D / L s from the diameter of the extruder screw D to the length of the baffle element L s in the range of 1.35 to 1.6, preferably 1.45 to 1.

55.

12. A method for producing a food or animal feed using an extruder (7) according to any one of claims 1 to 10, comprising the step of introducing a material for producing the food or animal feed through the inlet (10) of the extruder (7) into the process zone (9) of the extruder (7), wherein the material introduced into the process zone (9) is conveyed exclusively in the direction of the outlet (11) of the extruder (7).

13. Method according to claim 12, characterized in that the conveyance of the material in the process zone (9) takes place under lubricant-free conditions.

14. The method according to claim 12 or 13, characterized in that the conveyance of the material in the process zone (9) is achieved exclusively in the direction of the outlet (11) of the extruder (7) by at least one damming element (1), wherein the damming element (1) has a gradient of 5 to 30 mm, preferably 10 to 20 mm.

15. Use of an extruder (7) according to one of claims 1 to 10 for producing a food or animal feed.

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