EXTRUDER WITH SEALING ELEMENT AND METHOD FOR PRODUCING A FOOD

Description

[0001] 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.

[0002] As can be seen from the documents US 4 521 026 A and US 3 522 214 A, 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 shaft, each of the extruder screw shafts having a set of extruder screw elements mounted on a support shaft. The extruder screw shafts are housed in a cylinder called a barrel. An extruder usually comprises several barrels that are 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, dosing and the like.Within the barrel(s) is the extruder's process zone, i.e., the area in which the extruder screw shafts are movably arranged and, through their movement, process the material introduced into the process zone. The material to be processed can be introduced into the process zone through an inlet. The inlet is usually located at the machine-side end of the process zone (i.e., opposite the extruder outlet) and is usually arranged such that the material can be introduced into the process zone from above using gravity.

[0003] Such an extruder is shown in DE 20 2010 003 416 U1. The extruder screw shaft is characterized by a support shaft with external teeth running parallel to the shaft axis. Screw elements and kneading elements with internal teeth can be positively mounted on this support shaft by the internal teeth engaging the external teeth of the support shaft.

[0004] The extruder screw shaft is connected via a gear to a motor, which can set the extruder screw shaft in rotating motion. The motor and gear are located 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. The partition wall must have an opening through which the support shaft from the gearbox is guided into the process zone.

[0005] This opening cannot be sealed tightly, as the support shaft must be able to rotate within the opening. This means that during extended extruder operation, extruded material can enter the intermediate housing and contaminate it. In addition to the unwanted material loss, this requires disassembly of the extruder for cleaning.

[0006] This problem has not yet been satisfactorily resolved.

[0007] In conventional extruders, the support shaft is typically guided through a so-called 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. This known system is disadvantageous from a hygiene perspective.

[0008] In the food or animal feed industry, a preferred solution is one in which the support shaft is mounted in a sliding mount, free of lubrication oil. However, this sliding mount also does not seal the intermediate housing from the extruder's process zone, thus also resulting in the problem described above.

[0009] 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.

[0010] This problem is solved by the features of claim 1.

[0011] According to the invention, it has been found that the passage of material to be extruded through the opening in the partition 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 dam element. The dam element prevents the conveyance of material to be extruded toward the partition 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 partition through which the support shaft of the extruder screw is guided.

[0012] The damming 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 leading 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.

[0013] 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.

[0014] It is further preferred according to the invention that the dam element has a length of 30-90 mm, preferably 40-80 mm.

[0015] 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.

[0016] Due to its large gradient, the dam element according to the invention does not convey material to be extruded and thus prevents such material from moving towards the opening in the partition wall between the process zone and the intermediate housing.

[0017] Screw elements with such a large pitch are known, for example, from D1 10-2004 052 055 B4. This document shows a one-piece screw element in which a conveyor screw segment and a working segment with a larger 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 a section of the one-piece screw element has a pitch corresponding to the pitch of the dam element according to the invention.

[0018] 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, 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.

[0019] The dam element according to the invention 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.

[0020] 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 such that a gap of 1 to 5 mm, preferably 1 to 4 mm, exists between the end of the baffle element facing the opening and the opening. According to the invention, this is preferably achieved by the baffle element having 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 enters 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.

[0021] 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.

[0022] According to one embodiment of the invention, the dam element is arranged on the support shaft such that its end facing the extruder inlet is flush with the boundary of the inlet, which faces the opening in the partition wall between the intermediate housing and the process zone. In other words, according to this embodiment, the dam element does not protrude into the area of ​​the process zone located below the inlet. Preferably, however, there is also no gap between the area of ​​the process zone located below the inlet and the position of the dam element. The dam element is thus arranged downstream of the extruder inlet.

[0023] 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 region of the process zone located below the inlet. However, it is essential that the dam element does not extend over the entire region of the process zone located below the inlet. In this embodiment, the dam element according to the invention preferably extends into the region 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 region (i.e., projects into this region).

[0024] The baffle element described above can be used in any conventional extruder.

[0025] The extruder screw described here comprises a support shaft and at least one dam element, wherein the dam element has a pitch of 5 to 30 mm, preferably 10 to 20 mm.

[0026] The dam element can be designed as described above.

[0027] 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 multiple dam elements. For example, one to three dam elements could be arranged one behind the other on a support shaft and together constitute a dam element according to the invention.

[0028] 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 each other is particularly preferred. In this way, the sealing effect of the baffle elements is enhanced and, preferably, a self-cleaning effect is also achieved.

[0029] 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 particularly preferably at 250 to 350 rpm.

[0030] The extruder according to the invention comprises a motor with a gearbox to drive 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 conventionally known manner.

[0031] The extruder according to the invention further comprises an extruder barrel with a process zone located within the barrel and an inlet and outlet. The extruder barrel 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 barrel.

[0032] The extruder barrel (or each of the barrels comprising the extruder barrel) has a through-bore. The through-bore runs axially through the entire length of the extruder barrel. The extruder's processing zone is located within this through-bore.

[0033] 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.

[0034] The extruder inlet is used to introduce raw materials into a first section of the extruder. This inlet opens into the process zone. The inlet is usually and preferably located on the extruder barrel, allowing material to enter the extruder barrel, or more precisely, the process zone, under the influence of gravity.

[0035] The material to be extruded can be fed directly into the process zone through the inlet. A metering device is preferably 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.

[0036] 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.

[0037] The extruder typically also has a water, oil and possibly a steam supply line.

[0038] The extruder according to the invention further comprises an intermediate housing (also called a gearbox lantern), which is 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 in this section, no screw elements are arranged on the support shaft.

[0039] Preferably, the end of the intermediate housing facing the extruder housing forms a partition; however, a separate partition can also be provided. This partition separates the intermediate housing from the process zone located within the extruder housing. This partition contains 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 corresponds to the number of extruder screws. This is conventionally known.

[0040] The transition area between the intermediate housing and the process zone is preferably lubricant-free 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 the support shaft of the extruder screw is guided.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] These additional screw elements can be arranged in the desired order on the support shaft.

[0045] 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.

[0046] According to the invention, it is preferred that the additional screw elements have internal gearing and the support shaft has external gearing, wherein the gearings are positively connected to one another. This is known, for example, from DE 20 2010 003 416 U1 or WO 2013 / 030322 A1. According to the invention, the extruder is preferably a twin-screw extruder with two extruder screws, wherein each extruder screw has at least one damming element according to the invention. Each damming element is arranged on a support shaft of the twin-screw extruder as described above.

[0047] Particularly preferred is an arrangement in which damming elements and additional screw elements located on different support shafts interlock.

[0048] According to a preferred embodiment of the present invention, a cooling tool, such as a cooling nozzle, can be provided at the outlet of the extruder. Cooling tools for extruders are well known. A known distributor unit can preferably be arranged between the extruder and the cooling tool.

[0049] The extruder according to the invention has the advantage that it can be operated without unnecessary material loss and, in particular, under very good hygienic conditions. This makes it particularly suitable for the production of food or animal feed.

[0050] The present invention thus also relates to a method for producing a food or animal feed using an extruder according to the invention as claimed in claim 1, comprising the step of introducing a material for producing the food 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.

[0051] As described above, this is achieved by providing a dam element according to the invention, which prevents material from being conveyed toward the opening in the partition wall between the intermediate housing and the process zone. 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 dam element according to the invention, and no measures such as the provision of a stuffing box with oil lubrication are required. The present invention thus also relates to the use of an extruder according to the invention according to claim 1 for producing a food or animal feed.

[0052] According to the invention, all food or animal feed products that are conventionally produced by extrusion can be produced. Examples include protein-containing mixtures for the production of food products, including cereals, snacks, animal feed, and alternative foods (such as alternative meat and fish products).

[0053] The present invention will be described in more detail below using non-limiting exemplary embodiments with reference to the figures. In the figures, like reference numerals denote like elements. They show: Fig. 1 a schematic representation of an embodiment of two damming elements according to the invention Fig. 2 a cross-sectional view through the damming elements according to the invention according to Fig. 1 Fig. 3 a schematic representation of an embodiment of a dam element with passage-free sections Fig. 4 a schematic representation of an embodiment of a support shaft with external teeth Fig. 5 a schematic representation of an embodiment of an extruder according to the invention

[0054] In Fig. 1 A schematic representation of an embodiment of two damming elements 1 according to the invention is shown. However, the following explanations apply analogously to a single damming element.

[0055] The damming element 1 according to the invention comprises a central section 3 and spirals (turns) 2 arranged thereon in a helical manner. In this embodiment, each damming element 1 according to the invention has four spirals 2, which have a preferred large pitch of 10 mm. Each damming element 1 according to the invention according to Fig. 1 has a length of 40 mm.

[0056] In Fig. 1 It can also be seen how two dam elements 1 according to the invention can interlock. This can be realized, for example, in a twin-screw extruder in which one dam element 1 is arranged on each of the two support shafts.

[0057] In Fig. 2 is a cross-sectional view through the inventive damming elements 1 according to Fig. 1 shown. It can be seen that each dam element 1 according to the invention has an internal toothing 4, which can be positively connected to an external toothing (not shown here) of a support shaft 5.

[0058] In Fig. 3 is a schematic representation of an embodiment of a damming element 1 with passage-free sections. As in the embodiment according to Fig. 1 comprises the inventive damming element 1 in the embodiment according to Fig.3 a central section 3 and spirally arranged threads (turns) 2.

[0059] In this embodiment, each dam element 1 according to the invention has four flights 2, which have a preferred large pitch of 10 mm. The dam element 1 according to the invention Fig. 3 has a length of 40 mm. At both ends of the baffle element 1 there is a section 3a, 3b which is free of any aisles. 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 of 1 to 3 mm and corresponds to the section 3a, 3b. If material enters 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.

[0060] In Fig. 4 A schematic representation of an embodiment of a support shaft 5 with external toothing 5a is shown. The external toothing of the support shaft 5 can be positively connected to the internal toothing 4 of a dam 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 threads than the dam element 1.

[0061] In Fig. 5 is 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 Fig. 5 The embodiment shown 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).

[0062] 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.

[0063] Arranged within the process zone 9 is an extruder screw, which is constructed from a support shaft 5, a dam element 1 arranged thereon, and several 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.

[0064] The intermediate housing 13 is arranged between the gear unit 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. An opening 16 is located in the partition wall 15, through which the support shaft 5 of the extruder screw is guided.

[0065] 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.

[0066] According to the invention, the gap between the dam element and the partition wall 15 is preferably formed by using a dam element 1 according to Fig. 3realized, 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 preferably has a width in the range of 1 to 4 mm. If material enters 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 1 remains completely intact.

Claims

1. Extruder, comprising a motor (14) with a gearbox (12), at least one extruder housing (8) with a process zone (9) located in the housing (8) and an inlet (10) and an outlet (11), an intermediate housing (13), which is arranged between the extruder housing (8) and the gearbox (12) and is separated from the process zone by a partition wall (15), an opening (16) being located in the partition wall (15), a support shaft (5), which is arranged in the extruder (7), wherein screw elements (6) are arranged on at least one 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 retaining element (1) is arranged on a section of the support shaft (5) which is located in the process zone (9), characterized in that the opening (16) in the partition wall (15) between the intermediate housing (13) and the process zone (9) is sealed by the at least one retaining element (1), the retaining element (1) having a pitch of 5 to 30 mm, preferably 10 to 20 mm.

2. Extruder according to claim 1, characterized in that the retaining 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 retaining 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 retaining 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 retaining element (1) has a flight-free section (3a, 3b) at each end.

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 retaining element (1) and are separate from the latter.

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

8. Extruder according to one of the preceding claims, characterized in that the retaining element (1) is arranged downstream of the inlet (10) of the extruder (7) and does not project 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 retaining 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 the intermediate housing (13) and the process zone (9) is lubricant-free.

11. A method for producing a food product or an animal feed with an extruder (7) according to any one of claims 1 to 10, comprising the step of introducing a material for producing the food product 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).

12. Method according to claim 11, characterized in that the material is conveyed in the process zone (9) under lubricant-free conditions.

13. Method according to claim 11 or 12, characterized in that the conveying 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 retaining element (1), the retaining element (1) having a pitch of 5 to 30 mm, preferably 10 to 20 mm.

14. Use of an extruder (7) according to any one of claims 1 to 10 for the manufacture of a food product or animal feed.