Extruder and method for controlling an extruder

Abstract

The invention relates to an extruder comprising a discharge port in the form of an extrusion die (3) and a second discharge port (4) located upstream of the extrusion die (3). The invention is characterized in that the second discharge port (4) is in the form of a pressure control device for controlling the pressure at the extrusion die (3). The invention also relates to a method for controlling the pressure at an extrusion die (3) of an extruder. The invention allows use of optimized extrusion dies in extruders for high-pressure applications.

Description

[0001] EXTRUDER AND METHOD FOR CONTROLLING AN EXTRUDER

[0002] The invention relates to an extruder for extruding a material, in particular food or animal feed, comprising an inlet for feeding the material, a processing area for increasing the pressure of the material, and an outlet designed as a die for extruding the material, wherein a second outlet is arranged between the inlet and the die. The invention also relates to a method for regulating the pressure at a die of an extruder, wherein material, in particular food or animal feed, is fed to the extruder via an inlet, the pressure of the material is increased in a processing area of ​​the extruder, and the material is extruded through an outlet designed as a die.

[0003] In the food and feed industries, extruders are used to condition and shape the material, with the material being continuously forced out of the extruder outlet - the die - under pressure. Screw extruders or screw presses are a typical design. The material is continuously fed into the extruder's processing area via an inlet and conveyed by the screw in an axial direction of the extruder to the outlet - or die. In the processing area, the material is compressed between the screw and the barrel and brought to the pressure required for extrusion. In the outlet area, the focus is on homogeneous discharge, which is achieved by the die. Extruders are typically designed for high nominal pressures, e.g. 150 bar, and the individual components of the extruder must be able to withstand these loads.These highest loads occur particularly on the die, whereby additional qualitative expectations are placed on the die with regard to the extrudate produced.

[0004] EP3539748A1 discloses a screw press for extruding food or animal feed, wherein the material is extruded through a die and discharged by a knife unit. The extruder further comprises a sanitary start-up and discharge system (SSDS), wherein a valve is arranged within the barrel downstream of the extruder's processing area and upstream of the die. When starting up or shutting down the extruder, the valve is completely closed, and all material is discharged from the extruder through a bypass outlet. During operation, all material is passed through the valve and the die, but no material is passed through the bypass outlet. To build up a controlled pressure in the processing area, the valve can also be partially closed during operation, thus regulating not only the pressure in the processing area but also the specific mechanical energy.

[0005] DE102021110843A1 discloses an additive manufacturing device for the extrusion-based production of a molded body, wherein building material can be guided from an outlet of the plasticizing device to the outlet opening of the printing nozzle via a first connecting channel and building material can be guided to a receiving area which does not correspond to the outlet opening of the printing nozzle via a further connecting channel.

[0006] DE202009011114U1 discloses a granulating device and start-up valve with a movably mounted valve body for controlling, blocking and / or diverting the flow of melt through a melt channel, wherein the valve body has at least one passage section which blocks the melt channel more or less depending on the position of the valve body.

[0007] DE1231001 B is devoted to an extrusion head of screw extrusion presses for processing thermoplastic materials, wherein the extrusion head is provided with a branch channel leading to the injection nozzle and a closable secondary outlet, wherein a switching and throttling device is installed which, in one end position, closes the branch channel leading to the injection nozzle and at the same time keeps the secondary outlet open, while in the other end position, conversely, the branch channel leading to the injection nozzle is open and the branch channel to the secondary outlet is closed.

[0008] DE102018216152A1 relates to a control and closure device for extruded plastically deformable material, wherein a first piston and a second piston are guided into a channel from two opposite sides. An opening is formed in one of the pistons, which opens into a channel guided through this piston, which opens into a bypass nozzle.

[0009] The aim of the invention is an extruder that allows improved pressure control at the outlet or at the die, while being compact, robust in operation, and easy to retrofit. In particular, the invention is intended to enable energy-efficient pressure control. The flexible use of different dies and the production of a high-quality extrudate, especially with a small diameter, are also aims of the invention, with the reliable operation of the extruder or dies being important.

[0010] This is achieved according to the invention in that the second outlet is designed as a pressure control device for controlling the pressure at the die, wherein a partial flow of the material can be discharged from the extruder through the second outlet to regulate the pressure at the die. The second outlet allows the pressure at the die to be regulated, particularly during operation of the extruder. The second outlet is arranged between the inlet and the die, in particular between the processing area and the die. The extruder comprises a screw surrounded by a drum, wherein the screw comprises a helix and is arranged so as to be rotatable in the drum. In the processing area formed between the drum and the screw, the material is compressed and brought to the pressure required for extrusion.The option of directing a partial flow of material through the second outlet during extruder operation means that the pressure at the die can be controlled in a targeted manner. If an undesirably high pressure occurs at the die, the second outlet is opened to discharge a partial flow of material, or the partial flow directed via the second outlet is further increased. Conversely, if the second outlet is open and the pressure at the die falls below the desired level, the partial flow directed via the second outlet can be reduced until the desired pressure at the die is reached again. The solution according to the invention is particularly compact and easy to retrofit, as the effect is achieved via the second outlet and, in particular, no installations are required upstream of the die within the drum. The solution is robust, as the second outlet is only activated or deactivated when control is required.a partial flow is carried out through it and not all of the material flows through it permanently. This also results in the advantageous energy efficiency of the solution according to the invention - the material guided through the outlet, in particular the die, does not experience any additional pressure loss, since no internals in front of the die that would cause a pressure loss are required within the drum. The solution according to the invention thus makes it possible to reliably and constantly set a wide variety of desired operating pressures, independent of and in particular far from a nominal pressure, i.e. maximum permissible pressure, of the extruder. The desired operating pressure can, for example, correspond to the nominal pressure of optimized dies. Since different dies used can have different nominal pressures, the solution according to the invention enables reliable operation of the extruder at the respective nominal pressure of the die, even well below the nominal pressure of the extruder.During extrusion, material is pressed through openings in the die, e.g. holes, whereby the openings have a diameter and extrudate with a corresponding diameter is formed. Die thickness is essentially the length of the die openings in the extrusion direction. Surprisingly, it was found that the quality of the extrudate, e.g. density, strength, water resistance, etc., depends on the ratio of the die thickness to the diameter of the extrudate pressed through the die. It was therefore found that in order to maintain quality, a die with a decreasing die thickness should be used as the diameter of the extrudate or the die openings decreases. However, this is accompanied by a decreasing die strength and an increasing importance of regulating the operating pressure and, in particular, limiting the operating pressure to match the nominal pressure of the die.

[0011] An extruder has also proven advantageous in which the second outlet is arranged on the circumference of the extruder, the pressure control device comprises a control surface through which the partial flow can flow, and the size of the control surface for controlling the partial flow is adjustable. The arrangement of the second outlet on the circumference of the extruder is particularly compact and easy to retrofit, for example by arranging the advantageous pressure control device between the processing area and the die. In particular, internal components upstream of the die are omitted within the drum, which enables energy-efficient and robust operation. Furthermore, the pressure control device comprises a control surface through which the partial flow can flow, wherein the size of the control surface for controlling the partial flow is adjustable. Adjusting the size of the control surface allows the partial flow guided through the second outlet to be directly adjusted.When the control surface is fully open, a maximum partial flow is directed through the second outlet. However, when the control surface is completely closed, no partial flow can be directed through the second outlet. Advantageously, the pressure control device is designed as a fitting, particularly a valve, slide, or flap, and allows for simple and precise adjustment of the size of the control surface of the pressure control device.

[0012] In one possible embodiment of the invention, the control surface is directly enclosed by the second outlet. For example, a slide valve can be used to cover the second outlet completely, partially, or not at all, thus creating a control surface whose size can be adjusted.

[0013] In a further embodiment of the invention, the control surface is formed separately from the second outlet. In a particularly advantageous embodiment, the pressure control device comprises a movable piston, which piston is movable in particular in a radial direction of the extruder and which piston is designed to close the second outlet in the barrel of the extruder in a first position and to open the second outlet in a second position, wherein the size of the control surface for controlling the partial flow can be adjusted by positioning the piston between the first position and the second position. The control surface is formed, for example, by an intersection of the piston with a channel arranged in particular tangentially to the extruder, wherein the particularly radial movement of the piston from the first position to the second position enables an increasing partial flow to be discharged from the extruder through the channel.This arrangement is compact and allows for more efficient execution of even larger partial flows from the extruder.

[0014] An extruder is advantageous in which the size of the control surface is dependent on the pressure at the second outlet and a counteracting force generated in the pressure control device, in particular by a spring, a spindle, hydraulically, pneumatically or via actuators. In this case, a force counteracting the pressure acting at the second outlet is generated or set in the pressure control device, for example by a spring, a spindle, hydraulically, pneumatically or via actuators. With a low pressure at the second outlet and a given force - counteracting and exceeding the pressure - it is ensured that no partial flow escapes from the second outlet, or that the size of the control surface is minimal or the control surface is closed. As the pressure at the second outlet increases, the pressure at the second outlet reaches a response pressure of the pressure control device orexceed the counteracting force generated in the pressure control device. This subsequently leads to the escape of a partial flow through the second outlet or to the opening or enlargement of the control surface. In one embodiment of the invention, the pressure control device comprises, for example, a cylinder which is arranged such that it can move radially to the extruder and on which, on the one hand, a force generated in the pressure control device, for example by a spring, hydraulically, pneumatically or via an actuator, and, on the other hand, the pressure at the second outlet acts. The cylinder closes the second outlet as long as the force generated exceeds the pressure at the second outlet. Or the cylinder at least partially releases the second outlet or the control surface as soon as the pressure acting on the cylinder at the second outlet exceeds the counteracting force.Advantageously, the size of the control surface is formed automatically in this way, whereby only the desired counteracting force and thus the response pressure needs to be set.

[0015] Equally advantageous is an extruder wherein the pressure control device has a set pressure, in particular one that is adjustable, and at a pressure, in particular at the die or at the second outlet, below the set pressure, no material can be discharged through the second outlet, and at a pressure equal to or greater than the set pressure, at least a partial flow of the material can be discharged through the second outlet. By virtue of a set pressure, in particular one that is adjustable, the pressure control device can be optimally adapted to the use of dies with different nominal pressures, which ensures improved operational reliability of the extruder. Advantageously, the pressure is measured at the die, thus measuring the directly relevant pressure for the safe operation of dies with different nominal pressures.The pressure at the die can, for example, be fed back to the pressure control device as a controlled variable to adjust the response pressure accordingly. Likewise, the pressure at the second outlet can advantageously be measured, whereby the pressure at the second outlet can serve as a measure of the pressure at the die. Control based on the pressure at the second outlet enables advantageous independent control of the pressure control device.

[0016] An extruder is particularly advantageous in which the die comprises an identifier for designating a nominal pressure and the extruder comprises a reading device for reading the nominal pressure, wherein the response pressure of the pressure control device can be adjusted according to the read nominal pressure. This allows particularly safe operation of the extruder with dies whose nominal pressure deviates significantly from the nominal pressure of the extruder. By directly reading the permissible nominal pressure and processing this information into a response pressure of the pressure control device, incorrect operation of the extruder due to excessive pressures is excluded. The identifier on the die can be implemented, for example, as a serial number, barcode, RFID, or similar. The automated setting of the response pressure of the pressure control device is particularly advantageous, e.g.by automatically setting the counteracting force to be generated in the pressure control device.

[0017] Equally advantageous is an extruder in which the pressure regulating device is arranged between the inlet and a valve plate arranged in front of the die, or in particular between the processing area and the valve plate. The valve plate can be designed as a Venturi plate, for example. By arranging the second outlet or the pressure regulating device in front of the Venturi plate, a particularly even distribution of the material downstream of the Venturi plate and upstream of the die is ensured. Another particularly advantageous extruder is in which a closing device for closing the valve plate is arranged between the valve plate and the die. This ensures that no material can be fed to the die, which enables safe work on the die, e.g. during servicing.

[0018] The invention also relates to a method for regulating the pressure at a die of an extruder, wherein material, in particular food or animal feed, is fed to the extruder via an inlet, the pressure of the material is increased in a processing area of ​​the extruder and the material is extruded through an outlet designed as a die, characterized in that a partial flow of the material between the inlet and the die is discharged via a second outlet designed as a pressure regulating device. In particular, the partial flow of the material can also be discharged between the processing area and the die via a second outlet designed as a pressure regulating device. The method according to the invention allows safe operation of the extruder since compliance with the nominal pressures of the extruder orof the dies is ensured, whereby, according to the invention, a partial flow is discharged from the extruder via the pressure control device only when necessary. This allows for efficient operation according to the invention, since no additional pressure loss is caused within the drum and, in particular, no internal components upstream of the die that cause a pressure loss are required within the drum.

[0019] According to a further advantageous embodiment of the method, the partial flow of material discharged through the second outlet is adjusted by the size of a control surface through which the partial flow flows. This allows the partial flow directed through the second outlet to be directly adjusted. When the control surface is fully open, a maximum partial flow is directed through the second outlet, while when the control surface is completely closed, no partial flow is directed through the second outlet.

[0020] A method is particularly favorable in which the pressure regulating device closes the second outlet at a pressure, in particular at the die or at the second outlet, less than a particularly adjustable set pressure, and at least partially opens the second outlet at a pressure, in particular at the die or at the second outlet, equal to or greater than the set pressure. In this case, operation of the die remains completely unaffected at pressures less than the particularly adjustable set pressure. At the same time, it is ensured that, if the set pressure is exceeded, the pressure, in particular at the die or at the second outlet, is specifically reduced in order to prevent extruder failure due to excessively high operating pressures. Advantageously, the set pressure of the pressure regulating device is adjusted as a function of a nominal die pressure.The die typically represents a pressure-limiting component of the extruder, making it particularly advantageous to protect the extruder beyond the nominal pressure of the die. Equally advantageous is a process in which, when the set pressure is exceeded, the mass flow of the material and / or the viscosity of the material are reduced, for example, by increasing the moisture content of the material, particularly by adding water to the material. This allows for particularly rapid adjustment of the desired pressures, especially at the die or the second outlet, as well as an increased control range of the pressure control device.

[0021] The invention will now be described by way of example with reference to the drawings.

[0022] Fig. 1 shows a prior art extruder. Fig. 2 shows a prior art die.

[0023] Fig. 3 shows a section through an extruder according to the invention.

[0024] Fig. 4 shows a further section through an extruder according to the invention.

[0025] Fig. 1 shows a prior art extruder, wherein a material, in particular food or animal feed, is fed into the extruder via inlet 1. The extruder further comprises a processing section 2 formed between a drum 8 and a screw 9, wherein the material is compacted in the processing section and brought to the pressure required for extrusion. The compacted material is fed downstream of the processing section to a valve plate 10, which ensures uniform distribution of the material upstream of the die and ultimately extrudes it through the die 3.

[0026] Fig. 2 shows a die 3 according to the prior art, wherein the material compacted in the processing area 2 of the extruder is pressed through the die openings, e.g., holes. An extrudate with a corresponding diameter is formed according to the diameter of the openings. The die thickness essentially refers to the length of the die openings in the extrusion direction. Fig. 2 shows that the die thickness defined in this way refers to the smallest thickness of the die. The die thickness is of key importance for the strength of the die and determines the permissible nominal pressure for the die.

[0027] Fig. 3 shows a section through an extruder according to the invention, wherein the second outlet 4 is designed as a pressure control device for controlling the pressure at the die 3, and in order to regulate the pressure at the die 3, a partial flow of the material can be discharged through the second outlet 4. The second outlet 4 is arranged on the circumference of the extruder in the drum 8, wherein the pressure control device comprises a control surface 12 through which the partial flow can flow, and the size of the control surface 12 is adjustable. In Fig. 3, the pressure control device comprises a movable piston 5, which piston 5 is movable in particular in a radial direction of the extruder and which piston 5 is designed to close the second outlet 4 in a first position 6, which is shown in the upper image of Fig. 3, and to close the second outlet 4 in a second position 7, which is shown in the lower image of Fig.3 is shown - to release the second outlet 4, wherein the size of the control surface 12 for controlling the partial flow can be adjusted by positioning the piston 5 between the first position 6 and the second position 7. Thus, by moving the piston 5 from the first position 6 towards the second position 7, increasing material can be guided through the second outlet 4, wherein the control surface 12 is increasingly opened or released. The control surface 12 is formed by an intersection of the piston 5 with a channel 13 arranged in particular tangential to the extruder. The size of the control surface 12 is formed in particular as a function of the pressure at the second outlet 4 and a counteracting force generated in the pressure control device, in particular hydraulically or pneumatically. As the pressure at the second outlet 4 increases, this will increase the response pressure of the pressure control device orexceed the counteracting force generated in the pressure control device. This subsequently leads to the opening or enlargement of the control surface. Advantageously, the size of the control surface develops automatically, with only the desired counteracting force or set pressure being adjusted. The adjustability of the set pressure allows the pressure control device to be optimally adapted to the use of dies with different nominal pressures.

[0028] Fig. 4 shows a further section through an extruder according to the invention, or rather a section through the extruder shown in Fig. 3 normal to the longitudinal axis of the extruder through the second outlet 4. The upper image in Fig. 4 shows the first position 6 of the piston 5, wherein the piston 5 closes the second outlet 4. The lower image in Fig. 4 shows the second position 7, wherein the piston 5 opens the second outlet 4. In the lower image in Fig. 4, the piston 5 completely opens the second outlet 4 and the control surface 12 is also maximally open in order to guide the maximum partial flow through the second outlet 4.

[0029] The present invention offers numerous advantages. It allows for improved and, in particular, energy-efficient control of the pressure at the outlet or at the die. The pressure control device is compact, robust in operation, and easy to retrofit.

[0030] Reference symbol Inlet Processing area Die Second outlet Piston First position Second position Drum Screw Valve plate Closing device Control surface Channel

Claims

Patent claims 1. An extruder for extruding a material, in particular food or animal feed, comprising an inlet (1) for feeding the material, a processing area (2) for increasing the pressure of the material, and an outlet designed as a die (3) for extruding the material, wherein a second outlet (4) is arranged between the inlet (1) and the die (3), the second outlet (4) being designed as a pressure control device for controlling the pressure at the die (3), wherein, for controlling the pressure at the die (3), a partial flow of the material can be discharged from the inside to the outside of the extruder through the second outlet (4), the pressure control device comprises a control surface (12) through which the partial flow can flow, and the size of the control surface (12) is adjustable for controlling the partial flow, characterized in that the pressure control device comprises a movable piston (5), the piston (5) is designed,to close the second outlet (4) in a first position (6) and to release the second outlet (4) in a second position (7), the size of the control surface (12) for controlling the partial flow is adjustable by positioning the piston (5) between the first position (6) and the second position (7), wherein the second outlet (4) is arranged on the circumference of the extruder and the piston (5) is arranged outside the second outlet (4).

2. Extruder according to claim 1, wherein the piston (5) is movable in a radial direction of the extruder.

3. Extruder according to one of claims 1 to 2, wherein the size of the control surface (12) is formed as a function of the pressure at the second outlet and a counteracting force formed in the pressure control device, in particular by a spring, a spindle, hydraulically, pneumatically or via actuators.

4. Extruder according to one of the preceding claims, wherein the pressure control device has a particularly adjustable response pressure, and at a pressure, in particular at the die or at the second outlet, less than the response pressure, no material can be discharged through the second outlet (4) and at a pressure equal to or greater than the response pressure, at least a partial flow of the material can be discharged through the second outlet (4).

5. Extruder according to claim 4, wherein the die (3) has an identifier for designating a nominal pressure and the extruder has a read-out means for Reading of the nominal pressure, wherein the response pressure of the pressure control device can be adjusted according to the read nominal pressure.

6. Extruder according to one of the preceding claims, wherein the extruder comprises a drum (8) and a screw (9), the screw (9) is rotatably arranged in the drum (8) and the processing area (2) is formed between the drum (8) and the screw (9).

7. Extruder according to one of the preceding claims, wherein the pressure control device is arranged between the inlet (1) and a valve plate (10) or Venturi plate arranged in front of the die (3).

8. Extruder according to claim 7, wherein a closing device (11) for closing the valve plate (10) or Venturi plate is arranged between the valve plate (10) and the die (3).

9. Extruder according to one of claims 1 to 8, wherein the piston (5) is arranged outside the second outlet (4) in the first position (6) and in the second position (7).

10. Extruder according to one of claims 1 to 9, wherein the piston (5) for closing the second outlet (4) can be guided from the outside against the second outlet (4) and the piston (5) for releasing the second outlet (4) can be guided outwards away from the second outlet 11. A method for regulating the pressure on a die (3) of an extruder according to one of claims 1 to 10, wherein material, in particular food or animal feed, is fed to the extruder via an inlet (1), the pressure of the material is increased in a processing area (2) of the extruder and the material is extruded through an outlet designed as a die (3), characterized in that a partial flow of the material between the inlet (1) and the die (3) is discharged via a second outlet (4) designed as a pressure regulating device.

12. The method according to claim 11, wherein the partial flow of the material discharged via the second outlet (4) is adjusted via the size of a control surface (12) through which the partial flow flows.

13. Method according to one of claims 11 to 12, wherein the pressure control device closes the second outlet (4) at a pressure, in particular at the die or at the second outlet, less than a particularly adjustable response pressure and at a pressure, in particular at the die or at the second Outlet, equal to or greater than the response pressure, at least partially opens the second outlet (4).

14. The method according to claim 13, wherein the response pressure of the pressure control device is set as a function of a nominal pressure of the die (3).

15. The method according to one of claims 13 to 14, wherein when the response pressure, the mass flow of the material and / or the viscosity of the material is reduced, for example by increasing the moisture content of the material, in particular by adding water to the material.

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