Paddle mixing device and method for cleaning same

Abstract

The invention relates to a paddle mixing device (1), in particular a preconditioner, comprising a cylindrical mixing unit (2) with a shaft arranged in the mixing unit, wherein the shaft has paddles and the mixing unit has a base surface (2b), characterised in that closable openings (2c) for introducing a cleaning apparatus into the mixing unit (2) are provided in the base surface (2b). The present invention also relates to an extruder (7), comprising such a paddle mixing device (1), and to a method for cleaning such a paddle mixing device (1).

Description

[0001] The present invention relates to a paddle mixing device, in particular a preconditioner, for an extruder for producing a food or animal feed.

[0002] Extruders are machines in which materials such as polymers, elastomers, or protein-containing mixtures can be processed 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 which has 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 typically comprises several barrels connected end-to-end. Multiple barrels are required to perform the various processes performed in the extruder, such as conveying, kneading, mixing, devolatilization, dosing, and the like.

[0003] Preconditioners are often used in combination with extruders or other equipment for the preparation and mixing of food and feed products. For example, one or more flours or a concentrate / isolate are treated with water / steam and / or other additives for subsequent extrusion. In the preconditioner, the materials to be treated are first mixed with water and then treated with steam before entering the extruder.

[0004] A suitable preconditioner is known, for example, from DE 197 43 470 A1. This preconditioner comprises a mixing unit and a dwell unit, with the mixing unit located above the dwell unit. Both units contain at least one shaft with attached paddles to convey material through the corresponding unit. By separating the mixing unit from the dwell unit, optimal, intensive mixing of the material can be achieved at high shaft rotation speed, while also allowing the material to remain in the dwell unit under gentle conditions at a slow shaft rotation speed.

[0005] After the material has passed through both units, it enters a material inlet of the extruder via a material outlet located at the lower end of the dwell unit. A screw conveyor may be provided to transport the material from the material outlet of the dwell unit to the material inlet of the extruder.

[0006] In this well-known preconditioner, the mixing unit and the dwell unit are equipped with doors on both sides that can be folded up, thus making the interior of both units accessible for cleaning purposes. This is still not optimal.

[0007] EP-3 656 462 A1 describes a dosing and mixing device according to the preamble of claim 1. It is a swing door entlang der Mittelachse of the mixing container, which can be opened for cleaning purposes.

[0008] EP-1 990 085 A2 shows a mixer which has an outlet in its end face which can be closed by a rotatable plate.

[0009] It was the object of the present invention to provide a paddle mixing device which can be cleaned in an advantageous manner.

[0010] This object is solved by the present invention.

[0011] In detail, the present invention relates to a paddle mixing device, in particular a preconditioner, comprising a cylindrical mixing unit with a shaft arranged in the mixing unit, wherein the shaft has paddles and the mixing unit has a base area, characterized in that closable openings are provided in the base area for introducing a cleaning device into the mixing unit.

[0012] The present invention is based on the idea of ​​providing openings in the base area of ​​a cylindrical unit of a paddle mixing device through which a cleaning device can be introduced into the interior of the unit in order to clean it.

[0013] In the simplest embodiment, the paddle mixing device comprises a cylindrical mixing unit. Such mixing units are known and include a material inlet through which material can be introduced into the mixing unit. The material inlet is typically arranged such that material can be introduced into the mixing unit by gravity. A shaft is provided in the mixing unit, which extends over the entire length of the mixing unit and on which paddles are arranged. With the aid of a drive such as an electric motor, the shaft can be set in a rotary motion and convey material contained in the mixing unit through the mixing unit.

[0014] The mixing unit further comprises one or more additional inlets for introducing a liquid such as water and / or a gas such as water vapor into the mixing unit.

[0015] The cylindrical mixing unit further comprises a base surface facing away from the side on which the drive is located. This base surface provides closable openings for introducing a cleaning device into the mixing unit. It would also be conceivable to provide closable openings in the base surface on which the drive is located for introducing a cleaning device into the mixing unit.

[0016] This is preferably a round opening with a diameter that allows the insertion of a conventional cleaning device such as a spray lance (for example, from Kärcher). Such cleaning devices are known and not the subject of the present invention. The diameter of the opening is preferably in the range of 10-80 mm, preferably in the range of 10-45 mm, and more preferably 15 to 30 mm.

[0017] According to the invention, the diameter of the opening is preferably selected in relation to the diameter of a spray lance used for cleaning such that the ratio r (d(opening) / d(spray lance) is in the range from 4 to >1, preferably 3 to >1, more preferably 2 to >1, and particularly preferably 1.5 to >1. Thus, with a lance diameter of 16 mm, a bore diameter of 17 mm could be selected. In this way, it is prevented that too much cleaning fluid escapes from the opening during a cleaning process.

[0018] According to the invention, this opening is preferably provided with a fastening device such as a thread to securely close the opening, for example, with a closed screw nut. The opening should be closed during operation of the mixing unit.

[0019] According to the invention, the opening can preferably be additionally sealed with a plug, optionally in combination with an O-ring seal. The plug and O-ring seal are preferably made of an elastic material such as rubber.

[0020] According to the invention, the elements for closing the opening(s) can preferably be installed and removed without tools, for example by using blind plugs.

[0021] According to one embodiment of the present invention, it is preferred that the base has 2-8, preferably 2-6, more preferably 3-6, and particularly preferably 4 closable openings for inserting a cleaning device. In a conventional design of a shaft with paddles, the interior of the mixing unit is divided into four segments, each of which occupies approximately a quarter of the cross-section of the cylindrical mixing unit. To completely or optimally clean the mixing unit, the cleaning device is inserted successively into four openings assigned to the corresponding segments, with one opening opening into each of these segments.

[0022] According to one embodiment of the present invention, it is preferred for safety reasons that the base is covered with a cover. This conceals the closable openings arranged in the base from the outside and prevents them from being accidentally opened during operation, for example.

[0023] According to a preferred embodiment of the present invention, the opening(s) are of such a length that, even if the opening in question is not closed, reaching through the opening to a shaft rotating during operation is not possible (ISO 13857). Monitoring of open openings is then unnecessary.

[0024] According to a preferred embodiment of the present invention, a cylindrical dwelling unit with a shaft arranged in the dwelling unit is additionally provided with the mixing unit, wherein the shaft has paddles and the dwelling unit has a base area, wherein the dwelling unit is preferably arranged below the mixing unit, wherein closable openings for introducing a cleaning device into the dwelling unit are provided in the base area of ​​the cylindrical dwelling unit.

[0025] Retention devices are known from conventional preconditioners, as described above. A shaft is provided in the retention unit, extending the entire length of the retention unit and on which paddles are arranged. With the aid of a drive such as an electric motor, the shaft can be set in rotation and convey material contained in the retention unit through the retention unit.

[0026] In a preconditioner as described above, the material is transferred to a separate holding unit after leaving the mixing unit. According to the invention, the mixing unit and holding unit are preferably arranged one above the other, with the mixing unit above the holding unit, in order to transfer the material from the mixing unit to the holding unit by gravity.

[0027] According to the invention, the mixing unit and the dwell unit are particularly preferably connected to each other by a closed line, with this line preferably being arranged at the end of the mixing unit furthest from the material inlet. In this way, the material is first conveyed through the entire length of the mixing unit and processed there before being transferred through the line to the dwell unit.

[0028] The above statements regarding the openings of the mixing unit also apply analogously to the retention unit, i.e. the information regarding the number and position of the openings, their diameter, closability and clogability, as well as the covering of the openings with a cover apply analogously.

[0029] The dwell unit also has a material outlet. This is preferably located on the underside of the dwell unit so that the material can be transferred by gravity from the dwell unit into a screw conveyor unit or directly into the extruder.

[0030] According to the invention, the dwell unit and the screw conveyor unit or extruder are particularly preferably connected to one another by a closed line, with this line preferably being arranged at the end of the dwell unit that is furthest from the connecting line to the mixing unit. In this way, the material is first conveyed through the entire length of the dwell unit and processed there before being transferred through the line to the screw conveyor unit or the extruder.

[0031] According to the invention, a cylindrical screw conveyor unit connected to the dwell unit is additionally provided, with a shaft arranged in the screw conveyor unit, wherein the shaft has paddles and the screw conveyor unit has a base area, wherein the screw conveyor unit is preferably arranged below the dwell unit, wherein in the base area of ​​the cylindrical screw conveyor unit there are closable openings for introducing a cleaning device into the screw conveyor unit.

[0032] Conveyor screw units are familiar from conventional extruders with preconditioners. The conveyor screw unit features a shaft that extends the entire length of the conveyor screw unit and on which paddles are arranged. With the aid of a drive such as an electric motor, the shaft can be set in rotation, conveying material contained in the conveyor screw unit through the conveyor screw unit.

[0033] The above statements regarding the openings of the mixing unit also apply analogously to the screw conveyor unit, i.e. the information regarding the number and position of the openings, their closability and clogging capability, as well as the covering of the openings with a cover apply analogously.

[0034] The screw conveyor unit also has a material outlet. This is preferably located on the underside of the screw conveyor unit so that the material can be transferred from the screw conveyor unit into the extruder by gravity.

[0035] According to the invention, the conveyor screw unit and the extruder are particularly preferably connected to one another by a closed line, this line preferably being arranged at the end of the conveyor screw unit which is furthest away from the connecting line to the residence unit.

[0036] According to the invention, a bypass is preferably arranged on the conveyor screw unit, which bypass can be opened and closed with a flange plate arranged coaxially to the shaft provided in the conveyor screw unit.

[0037] A bypass is well known. A bypass is used to initially direct product out of the device via a bypass outlet when the device is started up, rather than into the product stream. This allows material that is formed during device start-up but does not yet meet the product specifications to be removed from the device to prevent contamination.

[0038] If the bypass according to the present invention is arranged on the screw conveyor unit, the preconditioning of the product can continue even in the event of a malfunction of the downstream extruder; the preconditioned product is then fed into a container through the bypass outlet.

[0039] In a conventional bypass, the bypass outlet is closed with a slide plate, which can preferably be moved horizontally back and forth pneumatically. The slide and the bypass outlet are usually located below the material inlet. However, due to the cylindrical shape of the screw conveyor unit and the necessarily curved shape of the slide plate, dead spaces are created in which large amounts of material can remain. This is undesirable for product safety reasons. Cleaning and sealing this bypass is also difficult.

[0040] According to a preferred embodiment of the present invention, the bypass is opened and closed by a flange plate arranged coaxially with the shaft provided in the screw conveyor unit. In other words, in this preferred embodiment, the bypass is opened and closed by moving a flange plate from a first position in the screw conveyor unit to a second position in the screw conveyor unit.

[0041] In the first position, the flange plate is located between the material inlet and the bypass outlet, separating the interior of the screw conveyor unit into two separate sections. One section contains the bypass outlet, and the other contains the material inlet and the remaining interior of the screw conveyor unit. Product introduced through the material inlet cannot enter the bypass outlet because the flange plate separates the interior of the screw conveyor unit into two separate sections that are not fluidically connected.

[0042] In the second position, the flange plate divides the interior of the screw conveyor unit into two other separate sections, with the bypass outlet and the material inlet located at least partially in one section. Product introduced through the material inlet can now flow into the bypass outlet.

[0043] The flange plate can be moved from the first to the second position by conventional means. Preferably, the flange plate is moved using one or more pneumatic cylinders.

[0044] This flange plate, which is arranged coaxially to the screw conveyor shaft, prevents dead spaces.

[0045] Preferably, the flange plate can be provided with seals such as O-rings made of an elastic material such as rubber.

[0046] When the device is started up, the flange plate is moved axially away from the material inlet into the second position described above. The screw conveyor rotates backward, and the incoming material is conveyed into the accessible bypass outlet. Once the desired product specifications are reached, the flange plate is moved back to the first position, separating the material inlet from the bypass outlet. The screw conveyor rotates forward, and material is conveyed into the extruder.

[0047] The bypass with flange plate according to the invention can generally be used for any paddle mixing device, in particular any preconditioner, or any extruder, and is not limited to the present device.

[0048] The paddle mixing device according to the invention, in particular preconditioner, can be arranged on any conventional extruder.

[0049] The present invention thus also relates to an extruder comprising a paddle mixing device according to the invention as described above, in particular a preconditioner.

[0050] 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.

[0051] 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 conventional manner.

[0052] 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.

[0053] The extruder barrel (or each of the barrels comprising the extruder barrel) has a through-bore. This through-bore runs axially through the entire length of the extruder barrel. The extruder's processing zone is located within this through-bore.

[0054] 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.

[0055] 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.

[0056] According to the invention, the inlet of the extruder is connected to the preconditioner described above, either to the material outlet of the residence unit or to the material outlet of the screw conveyor unit (if present).

[0057] 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.

[0058] 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.

[0059] The extruder typically also has a water, oil and possibly a steam supply line.

[0060] 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.

[0061] The present invention further relates to a method for cleaning a paddle mixing device according to the above description, comprising the steps: Opening a closable opening in a base area of ​​at least one unit selected from the group consisting of the mixing unit, the dwell unit, and the screw conveyor unit; introducing a cleaning device into the opened opening (2c, 3c, 4c); cleaning the at least one unit (2, 3, 4) with the introduced cleaning device.

[0062] The method can be carried out (and is preferably carried out) with any closable opening arranged on the unit. For example, the mixing unit, dwell unit, and conveyor screw unit of the paddle mixing device according to the invention can be cleaned simultaneously or sequentially, in particular through all openings arranged thereon.

[0063] If necessary, before inserting a cleaning device into one of the openings, a shaft located in the unit to be cleaned must be moved to a position that does not obstruct the insertion of the cleaning device into the unit to be cleaned. If necessary, the shaft can be moved to the desired position using the unit's motor or manually, for example, using a tool such as a screwdriver that can be inserted into a hole in the shaft.

[0064] According to the invention, the cleaning device preferably feeds a liquid into the unit to be cleaned, which liquid is at a pressure exceeding normal pressure. Preferably, this liquid is pressurized water.

[0065] For cleaning, a closable opening on one of the units (mixing unit, retention unit, screw conveyor unit) is opened. In a preferred embodiment of the present invention, the opening is closed with a closed screw nut (nut) or knurled nut, which is loosened from a thread to open the opening (manually or using known tools). If there is a plug in the opening, this must also be removed.

[0066] The cleaning device, for example, a commercially available cleaning lance, is inserted into the opening. According to the invention, it is preferred that the cleaning device has a tube whose length corresponds to the axial extent of the unit to be cleaned. With such a cleaning device, the corresponding unit can be cleaned across its entire axial extent.

[0067] Once the cleaning device has been inserted, a familiar cleaning process is carried out by introducing cleaning fluid.

[0068] The process is repeated with each desired opening if necessary.

[0069] To discharge the cleaning fluid fed into the unit to be cleaned from the paddle mixing device according to the invention, the bypass, which is preferably arranged on the screw conveyor unit as described above, is preferably opened. The cleaning fluid can then be discharged from the paddle mixing device through the bypass outlet.

[0070] 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 view of an embodiment of an extruder according to the invention with a paddle mixing device Fig. 2 a schematic view of an embodiment of a unit according to the invention with openings located in the base area Fig. 3 a schematic view of an embodiment of a unit according to the invention with a closed opening Fig. 4a a schematic view of an embodiment of a bypass according to the invention in the closed state Fig. 4b a schematic view of an embodiment of a bypass according to the invention in the open state

[0071] In Fig. 1 A schematic view of an embodiment of an extruder 7 according to the invention with a paddle mixing device 1 is shown. The product flow through the device is indicated by black arrows.

[0072] The paddle mixing device 1 comprises a cylindrical mixing unit 2 with a material inlet arranged on the mixing unit 2. The base area 2b ( Fig. 2 ) of the mixing unit 2 is covered with a cover 2a. A shaft (not shown) with paddles is arranged in the mixing unit 2, which can be set in a rotary motion by means of a drive (not shown).

[0073] Below the mixing unit 2, a cylindrical retention unit 3 is arranged, which is connected to the mixing unit 2 via a line. This line is arranged at the end of the mixing unit 2 remote from the material inlet, so that material flows through the entire length of the mixing unit 2 before it passes through this line into the retention unit 3 by gravity. The base area 3b ( Fig. 2 ) of the dwell unit 3 is covered with a cover 3a. A shaft (not shown) with paddles is arranged in the dwell unit 3, which can be set in a rotary motion by means of a drive (not shown).

[0074] Below the dwell unit 3, a cylindrical screw conveyor unit 4 is arranged, which is connected to the dwell unit 3 via a material outlet 5. This material outlet 5 is arranged at the end of the dwell unit 3 remote from the line from the mixing unit 2, so that material flows through the entire length of the dwell unit 3 before it reaches the screw conveyor unit 4 through this line by means of gravity. The base area 4b ( Fig. 2 ) of the screw conveyor unit 4 is covered with a cover 4a. In the screw conveyor unit 4, a (in Fig. 4a und 4b shown) shaft 4f with paddles 4g, which are arranged by means of a (in Fig. 4a und 4b shown) drive 11 can be set into a rotary movement.

[0075] At the end of the screw conveyor unit 4 facing away from the base surface 4b, a bypass 6 is arranged, which comprises a bypass outlet 6a. A preferred embodiment of this bypass 6 is described below with reference to Fig. 4a und 4b described.

[0076] The screw conveyor unit 4 is fluidically connected to an inlet of the extruder 7, so that material from the screw conveyor unit 4 can reach the process zone 9 of the extruder 7. In the process zone 9 of the extruder 7 (shown in dashed and transparent lines), a screw conveyor 9a is arranged, which can be set in a rotary motion by means of the drive 8 of the extruder 7 in order to convey material through the process zone 9. Further details of the extruder 7 are known and in Fig. 1 not shown.

[0077] In Fig. 2 A schematic view of an embodiment of a unit 2, 3, 4 according to the invention with openings 2c, 3c, 4c located in the base area 2b, 3b, 4b is shown. The explanations apply equally to a mixing unit 2, a dwell unit 3, and a screw conveyor unit 4.

[0078] In the base area 2b, 3b, 4b (ie the bottom surface of the cylindrical unit 2, 3, 4) are in the Fig. 2 In the embodiment shown, four openings 2c, 3c, 4c are arranged such that each of the openings 2c, 3c, 4c provides access to an area of ​​the unit 2, 3, 4. This area corresponds to a quarter of the cross-sectional area of ​​the unit 2, 3, 4. If a cleaning device (not shown) is inserted successively into each of the openings 2c, 3c, 4c, the unit 2, 3, 4 can be completely cleaned.

[0079] According to the Fig. 2 In the preferred embodiment shown, the openings 2c, 3c, 4c protrude from the base surface 2b, 3b, 4b and have a fastening element, such as a thread, in this protruding section. A screw nut 2d, 3d, 4d can be applied to this thread, for example, as shown in Fig. 3 described.

[0080] In Fig. 3 A schematic view of an embodiment of a unit 2, 3, 4 according to the invention with a closed opening 2c, 3c, 4c is shown. The explanations apply equally to a mixing unit 2, a dwell unit 3, and a screw conveyor unit 4 and all openings 2c, 3c, 4c arranged thereon.

[0081] In the Fig. 3 In the embodiment shown, an opening 2c, 3c, 4c arranged on the base surface 2b, 3b, 4b of the unit 2, 3, 4 has a thread in a region protruding from the base surface 2b, 3b, 4b, to which a screw nut 2d, 3d, 4d is fastened. A plug 2e, 3e, 4e is also present in the opening 2c, 3c, 4c to close the opening 2c, 3c, 4c. The plug 2e, 3e, 4e can be provided with an O-ring seal (not shown).

[0082] In Fig. 4a a schematic view of an embodiment of a bypass 6 according to the invention is shown in the closed state.

[0083] Material enters the screw conveyor unit 4 through the material outlet 5. A shaft 4f with paddles 4g located thereon is rotatably arranged in the screw conveyor unit 4. The Fig. 4a The shaft 4f with paddles 4g shown corresponds analogously to the shafts with paddles arranged in the mixing unit 2 and the dwell unit 3.

[0084] The shaft 4f can be set into a rotary movement by means of a drive 11.

[0085] A bypass 6 is arranged between the drive 11 and the material outlet 5. The bypass 6 includes a bypass outlet 6a through which material can be discharged from the screw conveyor unit 4 as needed without reaching the extruder 7.

[0086] The bypass 6 further comprises a flange plate 10, which is arranged coaxially to the shaft 4f in the screw conveyor unit 4 and by means of (in Fig. 4a und 4b two) pneumatic cylinders can be moved to the left and back again according to the dashed double arrow.

[0087] In Fig. 4a The flange plate 10 is in a position blocking access to the bypass outlet 6a. The shaft 4f is driven forward in the direction (shown by the dotted arrow) toward the extruder 7. Material entering the screw conveyor unit 4 through the material outlet 5 is conveyed toward the extruder 7 according to the thick arrows.

[0088] In Fig. 4b The flange plate 10 is in a position that allows access to the bypass outlet 6a. The flange plate 10 has been Fig. 4a moved to the left by means of the pneumatic cylinders 12. The shaft 4f is driven backward in the direction (indicated by the dotted arrow) toward the bypass outlet 6a. Material entering the screw conveyor unit 4 through the material outlet 5 is conveyed toward the bypass outlet 6a according to the thick arrows.

Claims

1. Paddle mixing device (1), in particular pre-conditioner, comprising a cylindrical mixing unit (2) with a shaft arranged in the mixing unit, wherein the shaft has paddles and the mixing unit has a base surface (2b), characterised in that closable openings (2c) are provided in the base surface (2b) for introducing a cleaning device into the mixing unit (2).

2. Paddle mixing device according to claim 1, characterised in that a cylindrical retention unit (3) connected to the mixing unit (2) and having a shaft arranged in the retention unit is additionally provided, wherein the shaft has paddles and the retention unit (3) has a base surface (3c), wherein the retention unit (3) is preferably arranged below the mixing unit (2), wherein closable openings (3c) are provided in the base surface (3b) of the cylindrical retention unit (3) for introducing a cleaning device into the retention unit (3).

3. Paddle mixing device according to claim 1 or 2, characterised in that a cylindrical feed screw unit (4) connected to the retention unit (3) is additionally provided with a shaft (4f) arranged in the feed screw unit (4), wherein the shaft (4f) has paddles (4g) and the feed screw unit (4) has a base surface (4b), wherein the feed screw unit (4) is preferably arranged below the retention unit (3), wherein closable openings (4c) are provided in the base surface (4b) of the cylindrical feed screw unit (4) are provided for introducing a cleaning device into the feed screw unit (4).

4. Paddle mixing device according to one of claims 1 to 3, characterised in that at least one unit selected from the group consisting of the mixing unit (2), the retention unit (3) and the feed screw unit (4), a base surface (2b, 3b, 4b) with 2-8, preferably 2-6, more preferably 3-6 and most preferably 4 closable openings (2c, 3c, 4c) for introducing a cleaning device is provided.

5. Paddle mixing device according to one of claims 1 to 4, characterised in that the closable openings (2c, 3c, 4c) are closed with a screw nut (2d, 3d, 4d).

6. Paddle mixing device according to one of claims 1 to 5, characterised in that a plug (2e, 3e, 4e) is arranged in the closable openings (2c, 3c, 4c).

7. Paddle mixing device according to one of claims 1 to 6, characterised in that a cover (2a, 3a, 4a) is arranged over the closable openings.

8. Paddle mixing device according to one of claims 3 to 4, characterised in that a bypass (6) is arranged at the feed screw unit (4), which can be opened and closed by means of a flange plate (10) arranged coaxially with the shaft (4f) provided in the feed screw unit (4).

9. Extruder (7), comprising a paddle mixing device (1) according to one of claims 1 to 8.

10. Method for cleaning a paddle mixing device (1) according to one of claims 1 to 8, comprising the steps: - opening a closable opening (2c, 3c, 4c) in a base surface (2b, 3b, 4b) of at least one unit selected from the group consisting of the mixing unit (2), the retention unit (3) and the feed screw unit (4); - Inserting a cleaning device into the opened opening (2c, 3c, 4c); - cleaning the at least one unit (2, 3, 4) with the inserted cleaning device.

11. Method according to claim 10, characterised in that the method can be carried out with each closable opening (2c, 3c, 4c) arranged at the unit (2, 3, 4).

12. Method according to claim 10 or 11, characterised in that a liquid is fed through the cleaning device into the unit (2, 3, 4) to be cleaned, which liquid is at a pressure exceeding normal pressure.

13. Method according to one of claims 10 to 12, characterised in that the cleaning device has a pipe whose length corresponds to the axial extension of the unit (2, 3, 4) to be cleaned.

14. Method according to one of claims 10 to 13, characterised in that a bypass (6) arranged at the feed screw unit is opened in order to discharge the liquid fed into the unit (2, 3, 4) to be cleaned from the paddle mixing device (1).

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