EXTRUSION DEVICE AND METHOD FOR PRODUCE AN OBJECT CONTAINING A CAVITARY

Description

[0001] The invention relates to an extrusion device, in particular a blown film extrusion device, according to the preamble of claim 1 and a method for producing an article having a cavity according to the preamble of claim 14.

[0002] It is well known that in extrusion, for example in the production of blown film or hoses, inflation systems are used that use excess pressure to create a bubble or a cavity in the resulting strand. In this process, so-called supporting air is blown into the interior of the resulting object.

[0003] DE102017008803A1 discloses a device for producing and filling container products, in which a tube of plasticized plastic material is extruded from an extrusion head along a tube guide into a mold. Process gas is introduced into the interior of the tube by means of a process gas supply device.

[0004] US 2002 / 076459 A1 discloses a system for starting up an extruded film tube in a blown film extrusion apparatus, comprising a subsystem for changing an air quantity in the extruded film and a subsystem for executing program instructions that control the operation of the subsystem for changing an air quantity.

[0005] US 4 402 656 A discloses an internally cooled blown film system for producing plastic hoses, in which the flow rate of the continuous stream of internal cooling air is made directly dependent on the positional deviation of the hose wall by contactless energy beam sensor means.

[0006] State-of-the-art extrusion blow molding and blown film systems, especially those with low blow volumes, have the disadvantage that the valve control (sometimes manual) leads to inaccurate, varying, and only poorly reproducible properties of the resulting products (especially dimensions such as diameter, thickness, etc.). This often leads to defects or undesirable effects, such as bubble oscillation or even bubble breakout in areas of the strand that have not yet solidified, especially with high-precision components.

[0007] The objective of the present invention was to overcome the disadvantages of the prior art and to provide a device and method that would sustainably improve the quality and precision of the resulting products through targeted manipulation of the support gas flow. Properties, particularly dimensions such as (outer) diameter or wall thickness, should be consistent and reproducible along the extruded strand. The solution should be reliable and cost-effective, and enable simplified application.

[0008] This object is achieved by an extrusion device and a method for producing an article having a cavity according to the claims.

[0009] According to the invention, the extrusion device for producing an article having a cavity, in particular a hose or a container, a material supply which opens into an extrusion nozzle and a supporting gas supply which opens into an injection opening for introducing Supporting gas, preferably air, into the interior of the resulting object, wherein the supporting gas supply has at least one valve for regulating the supporting gas.

[0010] At least one valve for regulating the support gas is a proportional valve that can be controlled by a regulator.

[0011] On the one hand, the use of a proportional valve (particularly an electrically controllable one) ensures that the support gas flow is continuously adjustable, thus enabling precise control of the support gas flow. As a result, the pressure inside the resulting object or extrudate can correspond to the specific requirements of the process (e.g., it can be kept constant). On the other hand, the controller enables the proportional valve to be regulated rather than merely controlled. This allows automatic response to current conditions (support gas flow) and / or properties (extrudate). Deviations from a desired behavior can be immediately corrected or compensated for by (readjusting) the proportional valve.

[0012] Any suitable controller, in particular a PI controller, a PID controller and / or a non-linear controller, can be used as a controller for the proportional valve.

[0013] The supplied material can be any material that can be brought into a specific shape by the extrusion process, in particular plastic material that is plasticizable or liquefiable due to its (thermoplastic) properties and can be conveyed through an extrusion nozzle in this state.

[0014] The extrusion nozzle and the injection opening can be arranged in a common extrusion head. Here, the material flow and the support gas flow have essentially the same direction after exiting the extrusion head. The cross-section of the outlet opening of the extrusion nozzle is, in particular, circumferential, preferably annular, and encloses the area in which the injection opening is located.

[0015] The extrusion device is preferably a device in which the extrudate is a continuous product, in particular a (film) tube or a tube- or tubular structure, whereby the continuous product usually has no inherent dimensional stability. No further molds are used downstream of the extrusion die, i.e., after exiting the extrusion die, the extrudate is shaped or held in shape exclusively by the introduced support gas. The extrusion device is therefore preferably a blown film or blown tube extrusion device, although both terms are also used synonymously.

[0016] However, it is not excluded that the extrusion device downstream of the extrusion nozzle may have a mold into which the material can be extruded. In this case, the support gas can press the extrudate against the inner wall of the mold.

[0017] As already mentioned above, the invention is particularly suitable for the production of continuous products (e.g., hoses). There are no restrictions regarding dimensions either. Thus, thin hoses (e.g., film hoses or blown films) can be produced just as easily as hoses or tubular objects with greater wall thickness.

[0018] The extrusion device may comprise a (preferably heated) material reservoir from which the material supply extends to the extrusion nozzle.

[0019] A preferred embodiment is characterized in that the extrusion device for adjusting the proportional valve has a control loop comprising a controller, in which a detected actual value of a property of the object, in particular a diameter of the object, and / or an actual value of the support gas flow feeds back on the manipulated variable of the proportional valve. Due to the feedback of detected actual values ​​on the control loop, the proportional valve can be readjusted immediately, in particular in real time. This measure allows the proportional valve to be reliably controlled, thereby preventing effects such as the oscillation of the support gas (bubble) or the breakout of the support gas in areas of the extrudate that have not yet solidified.

[0020] A preferred embodiment is characterized in that the control loop's reference variable is a nominal diameter of the object and / or a nominal diameter of the object adjusted by a ramp generator. The diameter of the resulting object depends heavily on the support gas supply. The extrudate will swell or collapse if the support gas flow is not correctly adjusted. Thus, by measuring the diameter, a direct connection to the support gas is established.

[0021] The extrusion device is characterized by the fact that the proportional valve has a non-linear gas flow characteristic in at least one operating range. The invention enables, for example, the use of an electrically controlled proportional valve instead of one or more simple solenoid valves. However, these valves often do not exhibit a linear response. For example, with analog control (e.g., 0-10V), no linear volume or mass flows are achieved. However, such non-linearities can be compensated for by means of a controller.

[0022] The extrusion device is characterized in that the control loop has a pilot control superimposed on the controller, wherein the pilot control is preferably designed to compensate for a non-linear gas flow characteristic of the proportional valve. The pilot control not only improves the control behavior but also allows for the non-linearities often inherent in proportional valves to be addressed. In this case, it is a so-called linearized pilot control. For at least one control range, preferably for the entire operating range, of the proportional valve, the non-linear gas flow characteristic of the proportional valve can therefore be mapped – directly or indirectly – in the pilot control. The stability of the control and, consequently, the stability of the support gas flow or gas pressure within the resulting object can be significantly improved by this measure.The non-linear characteristic of the proportional valve can be compensated by such a linearized pilot control.

[0023] The characteristic curve of the valve behavior can, for example, either be linearized by one or more support points or be determined via an identification run.

[0024] Optionally, the (additional) valve(s) can also be controlled manually via the controller. A dedicated mode can be used to adjust the controller, in which the flow rate is set to a defined value.

[0025] A preferred embodiment is characterized by the fact that a ramp generator for setpoint adjustment is connected upstream of the controller, with the target diameter and the actual diameter of the object preferably serving as input variables for the ramp generator. To achieve large target diameter changes, the diameter change can optionally be stepped or extended over time using a ramp generator or similar device.

[0026] A preferred embodiment is characterized in that at least one sensor for detecting a property of the supporting gas flow, preferably the volume flow and / or the mass flow and / or the gas pressure of the supporting gas, is arranged in the supporting gas supply, wherein the detected property(ies) of the supporting gas flow preferably serve as input variable(s) for the control loop and / or the pilot control. Since the gas flow is crucial for the properties and quality of the resulting object, the process can be significantly improved by a control loop that uses such sensors. Using the sensor data (e.g. volume flow or mass flow), the control characteristic of the proportional valve can be set linearly or according to a specific characteristic. This measure can therefore also be used to compensate for the non-linear behavior of a proportional valve.

[0027] A preferred embodiment is characterized in that the extrusion device comprises at least one sensor for detecting a property of the object, in particular the diameter of the object, wherein the detected property(ies) of the object preferably serve as input variable(s) for the control loop and / or the feedforward control. Here, a highly stable feedback loop is established directly based on the properties of the object and thus on the immediate consequences of a specific gas flow.

[0028] A preferred embodiment is characterized in that a discharge line for discharging support gas branches off from the support gas supply, wherein the discharge line is preferably connected to a vacuum generator, in particular a vacuum pump. This allows excess support gas to be discharged if necessary. This expands the control range and reduces the time latency of the control when excessive pressure is present inside the extrudate.

[0029] A preferred embodiment is characterized in that the discharge line is connected to the support gas supply via the proportional valve, with the discharge line being decoupled from the support gas supply in a first control range of the proportional valve and coupled to the support gas supply in a second control range of the proportional valve. This preferred measure allows the proportional valve to perform an additional function, namely the discharge of support air. This expands the operating range as well as the stability and reliability of the manufacturing process.

[0030] In an alternative embodiment, the discharge line opens into the support gas supply in a region between the proportional valve and the injection opening. A separate valve can be provided in the discharge line to regulate the discharged support gas.

[0031] A preferred embodiment is characterized in that the control circuit is designed such that in a region of the control range, preferably starting in the region of the middle of the control range, support gas is discharged by coupling the discharge line to the support gas supply, whereby the pressure inside the object being produced is preferably reduced and / or maintained at a desired value.

[0032] A preferred embodiment is characterized in that the discharge line is connected to a vacuum generator, in particular a vacuum pump, wherein the vacuum generator is preferably controlled by the controller of the control circuit.

[0033] A preferred embodiment is characterized in that the support gas supply comprises a gas pressure source. The gas pressure source can be, for example, a pressurized gas reservoir or a device for generating (or increasing) the gas pressure, in particular a blower or a compressor.

[0034] A preferred embodiment is characterized in that, in at least one position, preferably in one adjustment range, of the proportional valve, both a section of the support gas supply extending between the proportional valve and the gas pressure source and the discharge line are fluidically coupled to the injection opening. In this way, the support gas flow passing through the injection opening can be very precisely regulated.

[0035] A preferred embodiment is characterized in that, in at least one operating state of the extrusion device, both the gas pressure source via the at least partially open proportional valve and the vacuum generator - preferably via at least one at least partially open valve - are fluidly coupled to the injection opening, so that support gas can be supplied via the support gas supply and discharged via the discharge line simultaneously, wherein the ratio between the supplied support gas and the discharged support gas can preferably be controlled by means of the proportional valve and / or a valve connected in the discharge line and / or a controllable vacuum generator. This measure allows the support gas flowing through the injection opening into the extrudate to be controlled particularly precisely.By simultaneously removing gas, not only can the control range be extended, but the flow parameters can also be adjusted particularly quickly in order to prevent deviations from the ideal state of the extrudate or to quickly compensate for them.

[0036] A preferred embodiment is characterized by the fact that at least one valve – preferably manually controllable and / or controlled by a separate regulator – is installed in the discharge line to control the support gas discharge. These measures allow the (negative) pressure present in the discharge line to be switched on or off or preset to a specific value, particularly for special applications.

[0037] A preferred embodiment is characterized in that, in addition to the proportional valve, the support gas supply has at least one further valve—preferably manually and / or controllable by a separate regulator—for controlling the support gas. Preferably, the further valve is connected between the proportional valve and the gas pressure source. These measures allow the (over)pressure present in the support gas supply—upstream of the proportional valve—to be switched on or off or preset to a specific value, particularly for special applications.

[0038] A preferred embodiment is characterized by the fact that the extrusion nozzle and the injection opening are integrated into one extrusion head. The material flow and the gas flow essentially point in the same direction.

[0039] The aim is also achieved with a method for producing an object having a cavity, in particular a hose or a container, by means of an extrusion device, wherein material is fed to an extrusion nozzle via a material feed and supporting gas is introduced into the interior of the resulting object via an injection opening by means of a supporting gas feed, wherein the supporting gas feed has at least one valve for regulating the supporting gas, characterized in that at least one valve for regulating the supporting gas supply is a proportional valve that can be regulated by a controller. A preferred embodiment is characterized in that the setting of the proportional valve is carried out by a control circuit comprising a controller, in which a detected actual value of a property of the object, in particular a diameter of the object,and / or an actual value of the support gas flow affects the control variable of the proportional valve.

[0040] The method is characterized in that the control loop has a pilot control superimposed on the controller, wherein a non-linear gas flow characteristic of the proportional valve is preferably compensated by means of the pilot control.

[0041] A preferred embodiment is characterized in that a discharge line for discharging support gas is connected to the support gas supply via the proportional valve, wherein for regulating the support gas flow the proportional valve is regulated between a first control range in which the discharge line is decoupled from the support gas supply and a second control range in which the discharge line is coupled to the support gas supply,

[0042] A preferred embodiment is characterized in that in a region of the control range, preferably starting in the region of the middle of the control range, support gas is discharged by coupling the discharge line to the support gas supply, whereby the pressure inside the object being produced is preferably reduced and / or maintained at a desired value.

[0043] It is therefore preferable that – approximately in the middle of the control range – a counterflow is established through the discharge line (e.g., using a vacuum pump), which equalizes the pressure relative to the bladder to 0 bar or another setpoint. If the valve is then opened further, inflation occurs. If it is closed further, suction occurs, as the applied negative pressure (vacuum) then predominates. All valves can be finely adjusted using additional manual valves.

[0044] A preferred embodiment is characterized in that, in at least one operating state of the extrusion device, both the gas pressure source via the at least partially open proportional valve and the vacuum generator - preferably via at least one at least partially open valve - are fluidly coupled to the injection opening, so that support gas is simultaneously supplied via the support gas supply and discharged via the discharge line, wherein the ratio between the supplied support gas and the discharged support gas is preferably regulated by means of the proportional valve and / or a valve connected in the discharge line and / or a controllable vacuum generator. This measure allows the support gas flowing through the injection opening into the extrudate to be regulated particularly precisely. The control range can be expanded by simultaneously discharging gas.

[0045] A preferred embodiment is characterized in that the extrusion device is designed according to the invention.

[0046] The controller either controls the optional vacuum generator (e.g., vacuum pump) permanently or switches depending on the desired operating point. This allows for a very wide control range. The control of the support gas supply can be superimposed on this. Both simple PID controllers and nonlinear controllers can be used. As already mentioned, a feedforward control, which can also depend on the desired operating point, can be superimposed on the controller for dynamic and precise control.

[0047] For a better understanding of the invention, it is explained in more detail using the following figures.

[0048] They show in a highly simplified, schematic representation: Fig. 1 a schematic representation of an extrusion device Fig. 2 a schematic representation of the control circuit of an embodiment of the extrusion device Fig. 3 an embodiment of an extrusion device

[0049] By way of introduction, it should be noted that in the variously described embodiments, identical parts are provided with identical reference symbols or component designations. The disclosures contained throughout the description can be applied analogously to identical parts with identical reference symbols or component designations. Furthermore, the positional information chosen in the description, such as top, bottom, side, etc., refers to the directly described and illustrated figure, and these positional information must be applied analogously to the new position in the event of a change in position. FIGURE DESCRIPTION

[0050] The embodiments show possible embodiments, whereby it should be noted at this point that the invention is not limited to the specifically illustrated embodiments thereof, but rather various combinations of the individual embodiments with each other are also possible and this possibility of variation lies within the skill of the person skilled in the art in this technical field due to the teaching of technical action by means of the objective invention.

[0051] The scope of protection is determined by the claims. However, the description and drawings must be used to interpret the claims. Individual features or combinations of features from the various embodiments shown and described may represent independent inventive solutions. The problem underlying these independent inventive solutions can be derived from the description.

[0052] All information on value ranges in this description is to be understood as including any and all sub-ranges thereof, e.g. the information 1 to 10 is to be understood as including all sub-ranges starting from the lower limit of 1 and the upper limit of 10, ie all sub-ranges begin with a lower limit of 1 or greater and end with an upper limit of 10 or less, e.g. 1 to 1.7, or 3.2 to 8.1, or 5.5 to 10.

[0053] For the sake of clarity, it should finally be pointed out that, in order to better understand the structure, some elements have been shown out of scale and / or enlarged and / or reduced in size.

[0054] Fig. 1shows an extrusion device 1 in the form of a blown film extrusion device for producing an object 2 having a hollow space, in particular a hose, a blown film, or a container, preferably made of plastic. This produces a continuous product which has specific requirements regarding diameter, wall thickness, etc. A material supply 3, which originates from a material reservoir (not shown), opens into an extrusion nozzle 4 of the extrusion head 18. A supporting gas supply 5, which opens into an injection opening 6, serves to introduce supporting gas into the interior of the resulting object 2 (extrudate). The supporting gas supply 5 has at least one valve 7, 16 for regulating the supporting gas, wherein at least one valve for regulating the supporting gas is a proportional valve 7 that can be regulated by a regulator 9.

[0055] In Fig. 1It can also be seen that the support gas supply 5 has a gas pressure source 17 – here in the form of a compressor. The gas pressure source 17 does not necessarily have to be part of the extrusion device, but could also be available externally and simply connected to the support gas supply.

[0056] The extrusion nozzle 4 and the injection opening 6 are integrated in an extrusion head 18.

[0057] In the preferred embodiment shown, the extrusion device 1 for setting the proportional valve 7 has a control circuit 8 comprising a controller 9, in which a detected actual value of a property of the object 2, in particular a diameter of the object 2, and / or an actual value of the support gas flow acts on the control variable of the proportional valve 7 (see also Fig. 2 ).

[0058] As from Fig. 2As can be seen, the reference variable of the control loop 8 can be a nominal diameter of the object and / or a nominal diameter of the object 2 adjusted by a ramp generator 11. 6. In the case of a ramp generator 11 connected upstream of the controller 9 for adjusting the nominal value, the specified nominal diameter and the actual diameter of the object can be input variables of the ramp generator 11.

[0059] Since the proportional valve 7 has a non-linear gas flow characteristic in at least one operating range, the control circuit 8 has a pilot control 10 superimposed on the controller 9. This is designed to compensate for a non-linear gas flow characteristic of the proportional valve 7, either completely or partially. The control circuit 8 is described in detail in Fig. 2 shown.

[0060] It is preferred if - as in Fig. 1shown - at least one sensor 15 for detecting a property of the supporting gas flow, preferably the volume flow and / or the mass flow and / or the gas pressure of the supporting gas, is arranged in the supporting gas supply 5. The detected property(ies) of the supporting gas flow can serve as input variable(s) for the control circuit 8 and / or the pilot control 10.

[0061] Alternatively or additionally, the extrusion device 1 can have at least one sensor 19 (e.g., in the form of a camera or a light barrier sensor) for detecting a property of the object 2, in particular the diameter of the object 2. The detected property(ies) of the object 2 can then serve as input variable(s) for the control loop 8 and / or the feedforward control 10.

[0062] As in Fig. 1As shown, a discharge line 12 for discharging support gas can branch off from the support gas supply. In the illustrated embodiment, the discharge line 12 is connected to a vacuum generator 13, in particular a vacuum pump. The vacuum generator 13 can also be controlled by the controller 9 of the control circuit 8 or by a separate control device.

[0063] The discharge line 12 can be connected to the support gas supply 5 via the proportional valve 7, wherein the discharge line 12 is decoupled from the support gas supply in a first control range of the proportional valve 7 and coupled to the support gas supply 5 in a second control range of the proportional valve 7. If the pressure inside the extrudate is too high, the discharge line can be activated by adjusting the valve, thereby causing an immediate pressure reduction.

[0064] The control circuit 8 can thus be designed such that in a region of the control range, preferably starting in the region of the middle of the control range, support gas is discharged by coupling the discharge line 12 to the support gas supply 5, whereby the pressure inside the object 2 being produced is preferably reduced and / or maintained at a desired value.

[0065] In a particular embodiment of the proportional valve, in at least one position, preferably in one adjustment range, of the proportional valve 7, both a section of the support gas supply 5 extending between the proportional valve 7 and the gas pressure source 17 and the discharge line 12 are fluidically coupled to the injection opening 6. This allows a particularly large and finely controllable operating range with regard to the support gas to be achieved.

[0066] In the discharge line 12, at least one valve 14 can additionally be connected to control the support gas discharge—preferably manually and / or by a separate controller. Likewise, the support gas supply 5 can have, in addition to the proportional valve 7, at least one further valve 16 to control the support gas. In the illustrated embodiment, this further valve 16 is connected between the proportional valve 7 and the gas pressure source 17.

[0067] In another, in Fig. 3 In the embodiment shown, the discharge line 12 opens into the support gas supply 5 in an area between the proportional valve 7 and the injection opening 4. In this case, the connection to the vacuum generator 13 takes place by means of the valve 14 for controlling the support gas discharge.

[0068] In the method for producing an object 2 having a cavity using an extrusion device 1, material is fed to an extrusion nozzle 4 via a material feed 3. The means provided for this purpose (material reservoir, heating, conveying device, etc.) are well known from the prior art. Support gas is then introduced into the interior of the resulting object 2 via an injection opening 6 by means of the support gas supply 5. As already explained in detail, a proportional valve 7 controlled by a regulator is used to regulate the support gas.

[0069] Fig. 2shows in detail how such a control loop can be designed. The setting of the proportional valve 7 is therefore carried out by a control loop 8 comprising a controller 9, in which a detected actual value of a property of the object 2, in particular an actual diameter of the object 2, has a feedback effect. Additionally or alternatively, an actual value of the support gas flow can also have a feedback effect on the control variable of the proportional valve 7. The control loop 8 consists of Fig. 2 has a pilot control 10 superimposed on the controller 9, by means of which a non-linear gas flow characteristic of the proportional valve 7 is compensated - at least partially, preferably completely. By controlling the manipulated variable for the proportional valve 7 in this way, a high and sustainable stability of the support gas flow can be achieved.

[0070] In the illustrated embodiment, the proportional valve 7 can be controlled by the control circuit 8 in "automatic" mode. However, it can also be operated in "injection" or "vacuum adjustment" mode. In the latter two modes, a separate controller (e.g., manually) can take over the operation of the proportional valve. This provides all the options for reliable operation of the support gas supply 5.

[0071] The Fig. 2 The indicated valves 14 (for suction) and 16 (for injection) can also be controlled by control circuit 8 or a separate controller (see "Automatic Operation") or can be set manually in another operating mode. Valves 14 and 16 (see also Fig. 1 ) can be, for example, solenoid valves. Reference symbol list

[0072] 1Extrusion device 2Object 3Material supply 4Extrusion nozzle 5Support gas supply 6Injection opening 7Proportional valve 8Control circuit 9Controller 10Pre-control 11Ramp generator 12Discharge line 13Vacuum generator 14Valve 15Sensor 16Valve 17Gas pressure source 18Extrusion head 19Sensor

Claims

1. An extrusion device (1), in particular a blown film extrusion device, for producing an object (2), in particular a tube, a blown film or a container, having a cavity, comprising - a material feed (3) which opens into an extrusion die (4), and - a supporting gas supply (5), which opens into an injection opening (6), for introducing supporting gas into the interior of the object (2) being formed, wherein the supporting gas supply (5) has at least one valve for controlling the supporting gas, characterized in that at least one valve for controlling the supporting gas is a proportional valve (7) which can be controlled by a controller (9), that the proportional valve (7) has a non-linear gas flow characteristic in at least one operating range and that the control circuit (8) has a pilot control (10) - which is superimposed on the controller (9) -, wherein the pilot control (10) is configured to compensate for a non-linear gas flow characteristic of the proportional valve (7).

2. The extrusion device according to claim 1, characterized in that the extrusion device (1) has a control circuit (8) - comprising a controller (9) - for adjusting the proportional valve (7), in which control circuit (8) a detected ACTUAL value of a property of the object (2), in particular a diameter of the object (2), and / or an ACTUAL value of the supporting gas flow acts back on the manipulated variable of the proportional valve (7).

3. The extrusion device according to claim 2, characterized in that the reference variable of the control circuit (8) is a TARGET diameter of the object and / or a TARGET diameter of the object adapted by a ramp generator (11).

4. The extrusion device according to one of claims 2 or 3, characterized in that a ramp generator (11) is connected upstream of the controller (9) for target value adaption, wherein preferably the TARGET diameter and the ACTUAL diameter of the object are input variables of the ramp generator (11).

5. The extrusion device according to one of the preceding claims, characterized in that at least one sensor (15) is arranged in the supporting gas supply (5) for detecting a property of the supporting gas flow, preferably the volume flow rate and / or the mass flow rate and / or the gas pressure of the supporting gas, wherein preferably the detected property or properties of the supporting gas flow serve(s) as input variable or variables for the control circuit (8) and / or the pilot control (10), and / or that the extrusion device (1) has at least one sensor (19) for detecting a property of the object (2), in particular the diameter of the object (2), wherein preferably the detected property or properties of the object (2) serve(s) as input variable or variables for the control circuit (8) and / or the pilot control (10).

6. The extrusion device according to one of the preceding claims, characterized in that a discharge line (12) for discharging supporting gas branches off from the supporting gas supply, wherein preferably the discharge line (12) is connected to a vacuum generator (13), in particular a vacuum pump.

7. The extrusion device according to one of the preceding claims, characterized in that the discharge line (12) is connected to the supporting gas supply (5) via the proportional valve (7), wherein the discharge line (12) is decoupled from the supporting gas supply in a first adjustment range of the proportional valve (7) and is coupled to the supporting gas supply (5) in a second adjustment range of the proportional valve (7), and / or that the discharge line (12) opens into the supporting gas supply (5) in a region between the proportional valve (7) and the injection opening (4).

8. The extrusion device according to one of the preceding claims, characterized in that the control circuit (8) is configured such that supporting gas is discharged in a region of the control range, preferably starting in the region of the center of the control range, by coupling the discharge line (12) to the supporting gas supply (5), whereby the pressure inside the object (2) being formed is preferably reduced and / or maintained at a target value.

9. The extrusion device according to one of the preceding claims, characterized in that the discharge line (12) is connected to a vacuum generator (13), in particular a vacuum pump, wherein preferably the vacuum generator (13) is controlled by the controller (9) of the control circuit (8), and / or that the supporting gas supply (5) has a gas pressure source (17).

10. The extrusion device according to one of the preceding claims, characterized in that in at least one position, preferably in an adjustment range, of the proportional valve (7), both a section of the supporting gas supply (5) extending between the proportional valve (7) and the gas pressure source (17) and the discharge line (12) are flow-coupled to the injection opening (6), and / or that, in at least one operating state of the extrusion device (1), both the gas pressure source (17) via the at least partially open proportional valve (7) and the vacuum generator (13) - preferably via at least one at least partially open valve (7, 14) - are flow-coupled to the injection opening (4), so that supporting gas can be simultaneously supplied via the supporting gas supply and discharged via the discharge line (12), wherein preferably the ratio between the supplied supporting gas and the discharged supporting gas is controllable by means of the proportional valve (7) and / or a valve (14) connected in the discharge line and / or a controllable vacuum generator (13).

11. The extrusion device according to one of claims 6 to 10, characterized in that at least one valve (14) - which can preferably be controlled manually and / or by a separate controller - is connected in the discharge line (12) to control the support gas discharge.

12. The extrusion device according to one of the preceding claims, characterized in that the supporting gas supply (5) has, in addition to the proportional valve (7), at least one further valve (16) - which can preferably be controlled manually and / or by a separate controller - for controlling the supporting gas, wherein preferably the further valve (16) is connected between the proportional valve (7) and the gas pressure source (17).

13. The extrusion device according to one of the preceding claims, characterized in that the extrusion nozzle (4) and the injection opening (6) are integrated in an extrusion head (18).

14. A method for producing an object (2), in particular a tube, a blown film or a container, having a cavity, by means of an extrusion device (1), in particular a blown film extrusion device, wherein material is fed to an extrusion nozzle (4) via a material feed (3) and supporting gas is introduced into the interior of the object (2) being formed via an injection opening (6) by means of a supporting gas supply (5), wherein the supporting gas supply (5) has at least one valve for controlling the supporting gas, characterized in that at least one valve for controlling the supporting gas supply is a proportional valve (7) which can be controlled by a controller, in that the proportional valve (7) has a non-linear gas flow characteristic in at least one operating range, and in that the control circuit (8) has a pilot control (10) which is superimposed on the controller (9), a non-linear gas flow characteristic of the proportional valve (7) being compensated for by means of the pilot control (10).

15. The method according to claim 14, characterized in that the proportional valve (7) is adjusted by a control circuit (8) - comprising a controller (9) - in which a detected ACTUAL value of a property of the object (2), in particular a diameter of the object (2), and / or an ACTUAL value of the supporting gas flow acts back on the adjusted variable of the proportional valve (7).

16. The method according to one of claims 14 to 15, characterized in that a discharge line (12) for discharging supporting gas is connected to the supporting gas supply (5) via the proportional valve (7), wherein the proportional valve (7) is controlled between a first adjustment range, in which the discharge line (12) is decoupled from the supporting gas supply (5), and a second adjustment range, in which the discharge line (12) is coupled to the supporting gas supply (5), in order to control the supporting gas flow, and / or that in a region of the control range, preferably starting in the region of the center of the control range, by coupling the discharge line (12) to the supporting gas supply (5), whereby the pressure inside the object (2) being formed is preferably reduced and / or maintained at a target value, and / or that, in at least one operating state of the extrusion device (1), both the gas pressure source (17) via the at least partially open proportional valve (7) and the vacuum generator (13) - preferably via at least one at least partially open valve (7, 14) - are flow-coupled to the injection opening (4), so that supporting gas is simultaneously supplied via the supporting gas supply and discharged via the discharge line (12), wherein preferably the ratio between the supplied supporting gas and the discharged supporting gas is controlled by means of the proportional valve (7) and / or a valve (14) connected in the discharge line and / or a controllable vacuum generator (13).

17. The method according to one of claims 14 to 16, characterized in that the extrusion device (1) is configured according to one of claims 1 to 13.