Method and film-blowing installation for regulating a film-blowing installation

Abstract

The invention relates to a method for subsequently controlling the temperature of a film tube extruded by means of a film blowing installation, the method having the following method steps: - ejecting a film tube (1) of plasticised thermoplastic material in a drawing direction along a longitudinal axis (L) of the film blowing installation by means of a film blowing die (6), - flowing cooling gas onto the film tube (1) in the drawing direction downstream of the film blowing die (6) by means of at least one cooling gas ring (10) such that the film tube (1) hardens under the effect of the cooling gas at a frost line (14), - subsequently controlling the temperature of the film tube (1) by means of a subsequent temperature control unit (20) downstream of the frost line (14), wherein the subsequent temperature control unit (20) has a plurality of adjustable blowing elements (22) for blowing temperature control gas onto the film tube (1), the blowing elements forming a through-opening for the film tube (1), - adapting a diameter (D) of the through-opening formed by the blowing elements (22) to a diameter of the film tube (1) by adjusting the blowing elements (22), - measuring the actual temperature of the film tube (1) downstream of at least one of the blowing elements (22), and - regulating the temperature of the film tube (1) downstream of the at least one blowing element (22) to a target temperature by blowing temperature control gas onto the film tube (1) by means of the subsequent temperature control unit (20).

Description

[0001] Method and film blowing system for controlling a film blowing system

[0002] Description

[0003] The invention relates to a method and a film blowing system for producing a film tube made of plasticized thermoplastic material in a draw-off direction along a longitudinal axis of the film blowing system by means of a blowing head. Cooling gas is applied to the film tube in the draw-off direction downstream of the blowing head by means of at least one cooling gas ring, so that the film tube hardens at a freezing point under the effect of the cooling gas.

[0004] EP 1 491 319 A1 shows a film blowing system that comprises, downstream of the calibration basket, a gas extraction device enclosing the film tube with essentially annularly arranged extraction nozzles for extracting monomer-containing outgassing. Immediately above, i.e., downstream of the gas extraction device, a post-temperature control unit in the form of another cooling gas ring is arranged outside the film tube. This cooling gas ring is designed as a rigid ring with a fixed, unchangeable inner diameter for guiding the film tube through.

[0005] Above or downstream of the further cooling ring, the film tube enters a flattening unit, which compresses it flat. Downstream of the flattening unit, the film tube is removed by a puller. The flattened film tube is then wound onto a reel.

[0006] The still relatively warm film tube can be cooled with the additional cooling gas ring before entering the flattening unit, thus reducing the risk of the film layers clogging (sticking together) in the pull-off unit after the film tube has been folded together. This means that the film layers cannot be separated from one another for winding onto multiple reels or during later processing, or can only be separated with difficulty. During the extrusion of film tubes, certain recipes and products can lead to so-called flatness defects in the produced film. Such flatness defects include, for example, waves with an uneven distribution, sagging in the edge area, and so-called bowing.

[0007] Such defects are clearly visible when the film is unrolled from the finished roll and unrolled without tension on the floor. Simply put, flatness defects are local length deviations of individual film sections across the web width.

[0008] These defects can often be visually identified in the film web under tension on its way from the take-off to the winder or within the winder.

[0009] Measuring devices are known that measure the flatness of the web in the transverse direction between guide rollers on the way from the take-off to the winder or within the winder. Furthermore, measuring devices are known that measure the geometric quality of the developing lap. This is intended to ensure that poor flatness is detected at an early stage.

[0010] Control circuits are also proposed in which such measuring devices are coupled with stretching devices, which are intended to improve the flatness by heating and re-stretching the film tube after withdrawal.

[0011] For the still-round film tube, heating tunnel systems are known that reheat the film tube above the freezing point using infrared heaters positioned along its diameter to improve the flatness of the subsequently flattened film. This utilizes the effect that uneven stress distributions caused by different molecular orientations around the circumference of the film tube and resulting local length differences are reduced by reheating, thus significantly reducing or even completely preventing flatness defects in the flattened film.The uneven stress distributions are mainly caused by flow effects in the extrusion nozzle of the die head, for example due to a flow channel design that is not optimally suited to the raw material, due to an unsuitable heating profile of the extrusion nozzle, or due to an uneven circumferential temperature distribution and / or circumferential quantity distribution of the melt within and at the exit from the extrusion nozzle.

[0012] In addition, a calibration basket that is set at an inappropriate height to the freezing limit of the film tube, an excessive contact pressure (filling level) in the calibration basket or a calibration basket that is slightly off-center to the extrusion nozzle can also cause flatness errors.

[0013] Flatness errors that occur during the flattening process itself are of minor importance if the film tube enters the process as unstressed as possible by previously occurring flatness errors.

[0014] State-of-the-art cross-profile control systems, which intervene to correct the cooling of the bubble in the tube formation zone between the extrusion die and the freezing point, can significantly improve the problems mentioned, but cannot completely prevent them in many flatness-sensitive products.

[0015] A disadvantage of heating tunnel systems is the rigid arrangement of the heaters, as a wide range of different bubble diameters is typically produced. The variable distance between the film and the heating tunnel is an additional, highly influential parameter in addition to the actual production parameters, making the construction of automatic control loops difficult.

[0016] US 3,930,781 A shows a post-cooling device attached to a calibration basket. The post-cooling device has a cooling air ring arranged beyond the film solidification line with air outlet openings directed toward the film tube. The cooling air ring consists of a number of individual blowing elements, each connected in pairs at their adjacent ends so as to be pivotable about horizontal axes and radially adjustable with respect to the tube axis, forming a uniform polygon.

[0017] The object of the present invention is to provide a film blowing plant which has a post-temperature control unit downstream of the freezing point which is as effective and variable as possible.

[0018] The object is achieved by a method for post-tempering a film tube extruded by means of a film blowing system, wherein the method comprises the following process steps:

[0019] - Ejecting a film tube made of plasticized thermoplastic material in a withdrawal direction along a longitudinal axis of the film blowing machine by means of a blowing head,

[0020] - Cooling gas is applied to the film tube in the discharge direction downstream of the blow head by means of at least one cooling gas ring, so that the film tube hardens at a freezing point under the effect of the cooling gas,

[0021] - post-tempering of the film tube by means of a post-tempering unit downstream of the freezing point, wherein the post-tempering unit has several adjustable blowing elements for blowing the film tube with tempering gas, which form a through-opening for the film tube,

[0022] - Adjusting the diameter of the through-opening formed by the blowing elements to the diameter of the film tube by adjusting the blowing elements,

[0023] - measuring the actual temperature of the film tube downstream of at least one of the blowing elements, and

[0024] - Regulating the temperature of the film tube downstream of the at least one blowing element to a target temperature by blowing the film tube with tempering gas by means of the post-tempering unit.

[0025] The actual temperature of the film tube can be measured at any point downstream of at least one of the blowing elements, i.e., in an area of ​​the film tube where it is round, or in an area where the film tube is no longer round, for example, in a flattening unit or behind it, i.e., in or behind a peeling unit. Accordingly, the actual temperature can also be measured in an area that is no longer in line with the longitudinal axis of the film blowing system.

[0026] By precisely regulating the temperature of the film tube, excessive subsequent cooling or heating is avoided, thus increasing energy efficiency.

[0027] Furthermore, a high level of process consistency is ensured. Changes in ambient conditions, such as ambient temperature and / or humidity, can lead to significant changes in the temperature of the film tube even when machine parameters remain the same. In the worst case, this can result in blockages or film defects. Fluctuations in machine parameters, such as the output quantity of the plasticized material and / or the output speed, also lead to temperature changes in the film tube. Adjusting the film tube to a target temperature results in greater process consistency and thus a higher quality of the produced film tube.

[0028] The post-temperature control unit can have a plurality of guide elements which are adjustably hinged to the frame for guiding the film tube and which form a guide opening for passing the film tube, wherein a diameter of the guide opening is adapted to a diameter of the film tube by adjusting the guide elements.

[0029] The actual temperature profile of the film tube can be measured over the circumference, or at least over at least one circumferential area, of the film tube, whereby temperatures and / or volume flows of the tempering gas of the blowing elements distributed over the circumference are each adjusted depending on the difference between the actual temperature in the respective circumferential area of ​​the film tube of the respective blowing element and the target temperature in the respective circumferential area of ​​the film tube. To prevent blocking, the film tube can be cooled at least in sections around the circumference downstream of the freezing point. To increase the flatness quality, the film tube can be heated at least in sections around the circumference downstream of the post-temperature control unit.

[0030] The actual temperature of the film tube can be measured in an area of ​​an outlet of the post-temperature control unit from which the film tube exits the post-temperature control unit.

[0031] Here, a temperature and / or a volume flow of the tempering gas can be set depending on the difference between the measured temperature of the film tube and the target temperature of the film tube. The target temperature can be a specific absolute temperature value. Alternatively, the target temperature can also be determined from a difference value based on the actual temperature of the film tube before passing through the post-temperature control unit. In this case, the target temperature is calculated from the actual temperature of the film tube before passing through the post-temperature control unit plus or minus a fixed temperature difference value, if applicable.

[0032] The temperature sensor for measuring the temperature of the tubular film can be located anywhere downstream of the post-temperature control unit, for example, on the flattening unit. The temperature sensor can also be part of the post-temperature control unit, in which case the temperature sensor is located near an outlet of the post-temperature control unit.

[0033] In special applications, it may be necessary to influence the temperature profile differently across the circumference, for example, to set a constant temperature profile across the circumference based on local conditions, starting from a non-uniform temperature profile across the circumference. It may also be necessary to set a non-uniform temperature profile across the circumference.For this purpose, it can be provided that a temperature profile of the film tube downstream of the post-temperature control unit, in particular in an area of ​​the outlet of the post-temperature control unit from which the film tube exits the post-temperature control unit, is measured over the circumference and that temperatures and / or volume flows of the tempering gas of the blowing elements arranged distributed over the circumference are each set depending on the difference between the temperature in the respective circumferential area of ​​the film tube of the respective blowing element and the target temperature in the respective circumferential area of ​​the film tube.

[0034] The temperature of the tempering gas can be between 5 °C and 150 °C, in particular between 8 °C and 110 °C. The target temperature of the film tube downstream of the post-tempering unit can be between 35 °C and 110 °C, in particular between 45 °C and 80 °C.

[0035] Furthermore, an annular air curtain can be blown out essentially parallel to the longitudinal axis and around the tempering gas flow. The air curtain thus envelops the tempering gas flow and protects it from external influences and excessive mixing with ambient air, which has a different temperature than the tempering gas.

[0036] The film tube can be guided downstream of the at least one cooling gas ring and upstream of the freezing limit by means of a calibration basket with a plurality of calibration elements, wherein the calibration elements are designed to enclose the film tube and form a calibration opening, wherein the calibration elements are adjusted to set a diameter of the calibration opening.

[0037] The object is further achieved by a film blowing system comprising a blowing head for ejecting a film tube made of plasticized thermoplastic material in a withdrawal direction along a longitudinal axis of the film blowing system, at least one cooling gas ring downstream of the blowing head in the withdrawal direction for flowing cooling gas onto the film tube in order to allow the film tube to harden at a freezing point under the effect of the cooling gas. A post-temperature control unit for post-temperature control of the film tube is designed and intended to be arranged downstream of the freezing point. The post-temperature control unit has a plurality of blowing elements for blowing tempering gas onto the film tube, which are designed to enclose the film tube and form a through-opening for the film tube, wherein the blowing elements are adjustable for setting a diameter of the through-opening.A temperature sensor for detecting the temperature of the film tube is arranged downstream of at least one of the blowing elements, wherein the film blowing system has a control unit which is designed to regulate the temperature of the film tube downstream of the at least one blowing element by blowing the film tube with tempering gas by means of the post-tempering unit to a desired temperature.

[0038] The at least one cooling gas ring can form a central opening for the passage of the film tube and have at least one internal outlet nozzle for cooling gas.

[0039] The post-temperature control unit may comprise a plurality of guide elements configured to enclose the film tube and form a guide opening for guiding the film tube, wherein the post-temperature control unit comprises a frame to which the guide elements are adjustably hinged for adjusting a diameter of the guide opening.

[0040] The diameter of the calibration opening, the guide opening and the feed-through opening is to be understood as the largest possible diameter of an imaginary circle within the adjustable elements, i.e. the calibration elements of the calibration basket as well as the guide elements and the blowing elements of the post-temperature control unit.

[0041] If the post-temperature control unit has both blowing elements and guide elements, it is ensured that the film tube is fed as centrally as possible to a downstream unit, such as a flattening unit. The combination of blowing elements and guide elements in a single unit also enables a high flow velocity of the tempering gas onto the film tube without excessively affecting the position of the film tube or causing vibrations in the film tube. In addition, contact between the film tube and the blowing elements is avoided. Furthermore, the post-temperature control unit has a low installation height due to the combination of blowing elements and guide elements in a single unit. The high flow velocities that can be achieved also increase the tempering effect.Particularly when cooling the film tube, blowing a tempering gas at a high flow velocity enables efficient post-cooling, requiring a shorter post-cooling section for convection cooling after at least one cooling gas ring. The longer the post-cooling process, the longer the post-cooling section must be. This requires correspondingly taller film blowing systems. More effective temperature control during cooling allows for a shorter post-cooling section. The film blowing system thus has a more compact design and a lower height.

[0042] Furthermore, efficient and variable post-temperature control is enabled by the fact that the blowing elements are adjustable and hinged to the frame to adjust the diameter of the through-hole. This ensures that the blowing elements always maintain a constant distance from the film tube being produced, regardless of its diameter.

[0043] The post-temperature control unit can also be designed to heat and / or cool the film tube. For this purpose, the post-temperature control unit can have a cooling unit for cooling the temperature control gas and / or a heating unit for heating the temperature control gas. In order to reduce or prevent the films from sticking together (blocking) when folded, the film tube can be post-cooled. This allows the film blowing system to be operated at a higher output, i.e. a higher film tube draw-off speed, without running the risk of the film tube being fed into the flattening unit too warm and thus causing blocking. The output, i.e. the amount of film produced per unit time, can thus be increased. Furthermore, the use of additives in the plastic material to reduce the tendency for blocking can be reduced or possibly even avoided.In addition to cost savings, reducing additives can also have a positive impact on the service life of the extruder screw(s). Additives to reduce blocking tendencies usually include mineral fillers, which can lead to increased wear on extruder components, especially the screw. To improve the flatness of the film tube, however, the film tube can be reheated to reduce uneven stress distributions in the molecular structure. This improves the flatness or evenness of the film tube.

[0044] A particular advantage here is that one and the same post-heating unit is equally suitable for cooling tubular films made of blocking-sensitive materials and for heating tubular films made of flatness-sensitive materials. This means that the post-heating unit does not need to be replaced when switching between blocking-sensitive and flatness-sensitive materials.

[0045] To blow the film tube with tempering gas, the blowing elements can each have at least one inward-facing nozzle. The at least one nozzle can be designed as a slot in the circumferential direction around the film tube. Several short slots or openings can also be arranged one behind the other or next to each other in the circumferential direction. The at least one nozzle should be designed or arranged in such a way that a uniform flow of tempering gas onto the film tube is possible.

[0046] In one embodiment of the film blowing system, the blowing elements and / or an air distribution ring arranged radially outside the blowing elements and supplying them with tempering gas can each have at least one outlet nozzle pointing radially outside the at least one blowing nozzle at least substantially parallel to the longitudinal axis in order to generate an air curtain flowing out in a ring-shaped manner around the longitudinal axis, parallel to the axis. It is also conceivable to provide a separate ring for generating an air curtain. The air curtain envelops the tempering gas flow and protects it from external influences and from excessive mixing with ambient air at a different temperature.

[0047] It can be advantageous to arrange the blowing elements downstream of the guide elements. After exiting the at least one blowing nozzle, the tempering gas hits the film tube and is drawn along in the direction of the film tube's withdrawal. If the blowing elements are arranged downstream of the guide elements, at least a portion, preferably the majority, of the tempering gas does not hit the guide elements and is therefore not deflected or swirled. This allows the longest possible path over which the tempering gas can act on the film tube without being influenced.

[0048] In an exemplary embodiment, the blowing elements and the guide elements are adjustable synchronously. This ensures that, regardless of the diameter of the film tube, the blowing elements always maintain a constant distance from the film tube or that the blowing elements are radially offset from the guide elements by a constant amount.

[0049] To enable synchronous adjustment of the blowing elements and guide elements, the post-temperature control unit can, for example, have several supports distributed around the circumference, which are adjustably hinged to the frame. At least one of the blowing elements and at least one of the guide elements can then be attached to each of the supports.

[0050] If the blowing elements are arranged radially offset from the guide elements, the diameter of the guide opening of the post-temperature control unit, which is formed by the guide elements, is smaller than the diameter of the through-opening of the post-temperature control unit, which is formed by the blowing elements.

[0051] According to an exemplary embodiment, the film blowing system comprises a flattening unit for folding the film tube downstream of the post-temperature control unit. An area between the post-temperature control unit and the flattening unit is free of any elements that influence the film tube.

[0052] Downstream of the post-temperature control unit, an annular baffle arrangement can be arranged through which the film tube is guided. The baffle arrangement can consist of individual baffles, each connected to one of the supports of the blowing elements or the guide elements. The individual baffles are arranged next to one another around the circumference and together form a ring. The baffle arrangement serves to keep the tempering gas on the film tube over a certain length, protecting it from external influences and preventing excessive mixing with ambient air at a different temperature.

[0053] The post-temperature control unit can also have an extraction unit for at least partially extracting the tempering gas. If the blowing elements blow largely in the discharge direction, the extraction unit can be arranged downstream of the blowing elements. If the blowing elements blow largely opposite to the discharge direction, the extraction unit can be arranged upstream of the blowing elements. The extraction unit can be fluidly connected to a tempering gas supply for the blowing elements. This makes it possible, under certain conditions, to reduce the energy consumption for pre-tempering the tempering gas. In particular, a control system can be provided that regulates the volume flow of the recirculated tempering gas by means of the extraction unit in order to achieve the highest possible energy recovery.

[0054] In one embodiment, at least one temperature sensor for detecting the temperature of the film tube is arranged upstream of the blowing elements over the circumference around the longitudinal axis.

[0055] The film blowing system can also have a temperature sensor for detecting the temperature of the tempering gas.

[0056] This allows the temperature of the film tube to be measured and controlled downstream of the blowing elements. The temperature sensor can be located on the support for the blowing elements or the guide elements, on the frame near the outlet of the post-temperature control unit, or on any other element of the film blowing system downstream of the post-temperature control unit.

[0057] In one embodiment, the temperature of the film tube can be determined using the temperature sensor upstream of the blowing elements. For this purpose, the temperature sensor can be arranged on the support for the blowing elements or the guide elements, or on the frame near the inlet of the post-temperature control unit, or on any other element of the film blowing system upstream of the post-temperature control unit.

[0058] Depending on the temperature of the film tube upstream and / or downstream of the blowing elements or a temperature difference between the temperatures of the film tube upstream and downstream of the blowing elements and a difference between a target temperature and the actual temperature of the film tube downstream of the blowing elements, the temperature and / or the volume flow or the pressure of the tempering gas can be adjusted.

[0059] For this purpose, the film blowing system can also include a pressure sensor and / or a volume flow sensor for detecting the pressure or volume flow of the tempering gas. The pressure can be used to determine the volume flow of the tempering gas. The sensor is preferably located within a piping system for supplying the blowing elements with tempering gas. This means that the sensor can be positioned anywhere between a blower for pressure generation and the blowing nozzles of the blowing elements.

[0060] Exemplary embodiments are explained in more detail below with reference to the figures.

[0061] Figure 1 shows an overall view of a film blowing system with a first embodiment of a post-temperature control unit,

[0062] Figure 2 is an enlarged view of a film blowing system in the area of ​​a second embodiment of a post-temperature control unit,

[0063] Figure 3 is an enlarged view of a film blowing system in the area of ​​a third embodiment of a post-temperature control unit,

[0064] Figure 4 is an enlarged view of a film blowing system in the area of ​​a fourth embodiment of a post-temperature control unit, Figure 5 is a plan view of the post-temperature control unit according to Figure 1,

[0065] Figure 6 is a side view of the post-temperature control unit according to Figure 5, viewed radially outwards from the longitudinal axis and

[0066] Figure 7 is an enlarged plan view of the post-temperature control unit according to Figure 5 in a further embodiment.

[0067] Figure 1 shows a side view, partially in longitudinal section along a longitudinal axis L, of a film blowing system for producing a film tube 1. An extruder 3, on which two feed hoppers 4, 5 for thermoplastic material can be seen, stands on a machine base 2. A thermoplastic material fed in granulate form via the feed hoppers 4, 5 is plasticized and homogenized by pressure and additional heating medium in a screw of the extruder 3 and pressed into a blow head 6 connected to the extruder 3 with a vertical axis along the longitudinal axis L of the film blowing system. The blow head 6 has a schematically shown annular nozzle 7 on its upper side, from which the expanding, axis-symmetrical film tube 1, made of initially still plasticized film material, emerges. After the film material has solidified, the film tube 1 essentially retains its diameter.The film tube 1 is flattened in a flattening unit 8 and pulled upwards via a pull-off unit 9. The flattened film tube 1 is then wound onto coils or rolls (not shown here). In the direction from the blow head 6 to the pull-off unit 9, the functional terms "upstream" and "downstream" are used in such a way that they spatially mean "below" and "above."

[0068] Directly above the blow head 6, a cooling gas ring 10 is shown with a partially schematically illustrated gas supply line 11. The gas supply line 11 is connected on the inlet side to a blower 12, via which cooling gas, usually air, is conveyed to the cooling gas ring 10. For this purpose, ambient air is sucked in by the blower 12. Other cooling gases or cooling gas mixtures can also be used. The cooling gas ring 10 has internal outlet nozzles 13, from which the cooling gas flows out and flows in a ring-shaped manner, essentially parallel to the wall, onto the film tube 1, which is under increased internal pressure and is passed through a central opening 19 of the cooling gas ring 10. The cooling gas flow from the blower 12 to the film tube 1 is symbolized by arrows. The film tube 1 plasticized in this area initially expands in diameter under the aforementioned overpressure inside until it hardens under the effect of the cooling gas and assumes a constant diameter.The transition point from the plasticized material to the hardened material is called the "freezing point" and is designated 14. The freezing point 14 does not have to be a clear line, but can extend over a limited area along the longitudinal axis L. To generate an internal overpressure, an internal cooling tower 15 is mounted centrally on the die head 6, through which cooling gas is introduced into the interior of the film tube 1. The introduced cooling gas is discharged via a gas exhaust pipe 16 in such a way that a defined internal pressure prevails.

[0069] Above, i.e. in the withdrawal direction along the longitudinal axis L downstream of the freezing limit 14, there is a calibration basket 17 which contains calibration elements 18 with superimposed roller arrangements which are arranged essentially in a ring around the film tube 1. In order to enable adaptation to film tubes 1 of different diameters, the roller arrangements are generally located on pivoting segments forming individual partial circumferences, by means of which the diameter of a calibration opening of the calibration basket 17, through which the film tube 1 is guided along the longitudinal axis L, can be changed. In cross-section, these segments form a polygonal calibration opening. In the example shown, the calibration opening has a diameter K.

[0070] The still relatively warm film tube 1 is stabilized and guided in cross-section by the calibration basket 17. The calibration basket 17 can be arranged so that it can be adjusted in height relative to the blowing head 6 in order to always be able to assume an optimal height position relative to the freezing limit 14.

[0071] Downstream of the calibration basket 17 is a post-temperature control unit 20, which serves to post-temperature the film tube 1. The post-temperature control unit 20 has a plurality of guide elements 21 with roller arrangements, whereby other guide elements can also be provided instead of the roller arrangements. The guide elements 21 enclose the film tube 1 and form a guide opening with a diameter F. In the present exemplary embodiment, the diameter F of the guide opening is identical to the diameter K of the calibration opening. The guide elements 21 serve, among other things, to guide the film tube 1 centrally to the longitudinal axis L, so that the film tube 1 is guided centrally into the flattening unit 8 in order to avoid wrinkles or edge misalignment. As will be explained in more detail below, the guide elements 21 are adjustably hinged to a frame of the post-temperature control unit 20 in order to be able to vary the diameter F of the guide opening.

[0072] In addition, the post-temperature control unit 20 has a plurality of blowing elements 22 that enclose the film tube 1 and form a through-opening for the film tube 1 with a diameter D. The blowing elements 22 are also adjustably hinged to the frame of the post-temperature control unit 20, as explained in more detail below, for adjusting the diameter D of the through-opening. The blowing elements 22 blow the tempering gas diagonally upwards in the withdrawal direction onto the film tube 1. In principle, however, it is also conceivable for the tempering gas to be blown out horizontally, i.e. in a plane perpendicular to the longitudinal axis L, against the film tube 1.

[0073] The diameters K, F and D are each defined as the largest possible diameter of an imaginary circle within the adjustable elements, i.e. the calibration elements 18 of the calibration basket 17 as well as the guide elements 21 and the blowing elements 22 of the post-temperature control unit 20.

[0074] Downstream of the blowing elements 22, a suction unit 23 is arranged, through which the film tube 1 is guided centrally. The suction unit 23 comprises one or more suction elements 24 for sucking away tempering gas. In order to extract as much tempering gas as possible before it escapes into the environment, a guide plate arrangement with several guide plates 25 is provided downstream of the at least one suction element 24. The guide plates are circular in shape and arranged transversely to the longitudinal axis L and have a relatively small distance from the film tube 1 compared to the distance of the at least one suction element 24. The individual guide plates 25 are each fastened to one of the blowing elements 22, but can also be arranged on a support 47 to which the blowing elements 22 are fastened. The suction element 24 can be designed as a rigid circumferential ring.Alternatively, it is also possible for several suction elements 24 to be arranged distributed over the circumference, wherein these are arranged pivotably similar to the blowing elements 22 in order to be able to vary an inner diameter of the suction unit 23 and to adapt it to different film tube diameters.

[0075] The blower elements 22 are supplied with tempering gas by a blower 26. The blower 26 draws in ambient air and directs it to the blower elements 22. This is done by a supply line 27 that connects the blower 26 to an air distribution ring 28 of the post-tempering unit 20. The air distribution ring 28 is arranged in a ring around the film tube 1 and, in the illustrated embodiment, around the guide elements 21, and serves to evenly distribute the tempering gas around the circumference. The air distribution ring 28 is fluidly connected to the individual blower elements 22 via supply lines 29.

[0076] A cooling unit in the form of an air cooler 30 and a heating unit in the form of an air heater 31 are arranged in the supply line 27, whereby external cooling or heating sources can also be used. Thus, the tempering gas can be optionally cooled or heated before being directed to the blowing element 22. Alternatively, it is also possible to provide only one air cooler 30 or only one air heater 31. The arrangement sequence of the blower 26, the air cooler 30, and the air heater 31 can be selected as desired.

[0077] It should be noted that the blower 26, the air cooler 30, and the air heater 31 are shown at the level of the post-temperature control unit 20. For this purpose, these components can be arranged in a tower frame of the film blowing system. However, they can also be located on the machine foundation. The at least one extraction element 24 is fluidly connected to the blower 26 via an extraction line 32. Thus, for energy recovery, the temperature control gas can be fed via the blower 26 upstream of the air cooler 30 and the air heater 31 to reduce the required heating or cooling power.

[0078] The film blowing system further includes a control unit 33, which is connected to the blower 26, the air cooler 30, and the air heater 31 for controlling them. Furthermore, the control unit 33 is connected to a control valve 34 in the exhaust line 32 for controlling the volume flow of the recirculated tempering gas in the exhaust line 32. The signals from several sensors are processed for the control.The control unit 33 is connected to a temperature sensor 35 in the supply line 27 for detecting the temperature of the tempering gas, to a pressure sensor 36 on the air distribution ring 28 for detecting the pressure in the air distribution ring 28, to a temperature sensor 37 upstream of the post-tempering unit 20 for detecting the temperature of the film tube 1 before entering the post-tempering unit 20 and to a temperature sensor 38 downstream of the post-tempering unit 20 for detecting the temperature of the film tube 1 after leaving the post-tempering unit 20.

[0079] Figure 2 shows an enlarged view of a film blowing system in the area of ​​a second embodiment of a post-temperature control unit 20. Components that correspond to components of the film blowing system according to Figure 1 are provided with the same reference numerals and are described there.

[0080] In contrast to the post-temperature control unit 20 according to the first embodiment, the post-temperature control unit 20 of the second embodiment does not have an extraction unit or a baffle arrangement. In order to allow the tempering gas flowing out of the blowing elements 22 to flow as laminarly as possible along the surface of the film tube 1, one or more air curtains can be blown out. For example, an inner air curtain 39 flowing in the withdrawal direction can be blown out. This inner air curtain flows out through openings (not shown in detail) in the blowing elements 22 and thus encloses the tempering gas between itself and the film tube 1. Alternatively or additionally, an outer air curtain 40 flowing in the withdrawal direction can be blown out and flows out through openings (not shown in detail) in the air distribution ring 28.

[0081] Alternatively or additionally, an inner air curtain 41 flowing against the discharge direction may be provided, which is blown out of openings (not shown in detail) of the blowing elements 22. Furthermore, alternatively or additionally, an outer air curtain 42 flowing against the discharge direction may be provided, which is blown out of openings (not shown in detail) of the air distribution ring 28.

[0082] In addition, or alternatively, a radially flowing lower air curtain 43 can be blown out of openings of the air distribution ring 28 (not shown in detail).

[0083] Figure 3 shows an enlarged view of a film blowing system in the area of ​​a third embodiment of a post-temperature control unit 20. Components that correspond to components of the film blowing system according to Figures 1 and 2 are provided with the same reference numerals and are described there.

[0084] In contrast to the post-temperature control unit 20 according to the second embodiment, no air curtains are provided. Instead, the post-temperature control unit 20 has a baffle arrangement consisting of several baffles 25 arranged downstream of the blowing elements 22. The individual baffles 25 are each attached to one of the blowing elements 22, but can also be arranged on a support 47 to which the blowing elements 22 are attached. In the illustrated embodiment, the baffles 25 form a frustoconical baffle arrangement and a narrow annular slot between the individual baffles 25 and the film tube 1 for passing the tempering gas.

[0085] Figure 4 shows an enlarged view of a film blowing system in the area of ​​a fourth embodiment of a post-temperature control unit 20. Components that correspond to components of the film blowing system according to Figures 1 to 3 are provided with the same reference numerals and are described therein. In contrast to the post-temperature control unit 20 according to the first three embodiments, in the fourth embodiment, the blowing elements 22 are arranged upstream of the guide elements 21. Furthermore, the blowing elements 22 do not blow obliquely upward in the withdrawal direction, but obliquely downward, opposite to the withdrawal direction.

[0086] Figure 5 shows a plan view of the post-temperature control unit 20 according to Figure 1, wherein components that correspond to components of the film blowing system according to Figure 1 are provided with the same reference numerals and are described there.

[0087] The post-temperature control unit 20 has a frame 44 to which the movable elements described below are attached and which, if necessary, is arranged so as to be height-adjustable relative to the blow head. The air distribution ring 28 is also attached to the frame 44.

[0088] The frame 44 forms a central passage through which the film tube 1 is guided parallel to the longitudinal axis L according to Figure 1. Six adjustment units 45 are distributed around the circumference. The adjustment units 45 serve to adjust the guide elements 21 in a direction radial to the longitudinal axis L.

[0089] The adjustment units 45 each have a pivot arm 46 pivotally mounted on the frame 44. The pivot arm 46 is pivotable about a pivot axis arranged parallel to the longitudinal axis L.

[0090] Furthermore, the adjustment units 45 each have a support 47, which in the illustrated embodiment carries two guide elements 21 in the form of rollers, which are spaced apart from one another in the direction of the longitudinal axis L and arranged in a V-shape overlapping manner when viewed in the direction of the longitudinal axis L. The support 47 is pivotally connected to the pivot arm 46. The support 47 is pivotally connected to the pivot arm 46 about a pivot axis arranged parallel to the longitudinal axis L.

[0091] Furthermore, the adjustment units 45 each have a coupling rod 48 pivotally connected to the support 47. Finally, the adjustment units 45 each have an adjustment mechanism by means of which the coupling rod 48 is pivotally connected to the frame 44.

[0092] To illustrate the adjustment mechanism, the coupling rods 48 of the adjustment units 45 are each pivotally and slidably connected to the frame 44 via a coupling element (not shown). The coupling element is rotatably connected to the frame 44. The coupling rod 48 is slidably coupled to the coupling element. In addition, a driver 49 is fastened to each coupling rod 48 and is guided so as to be translationally movable along a guide 50 on the frame 44. In the exemplary embodiment shown, the guide 50 is a groove in a plate 51 which is firmly fastened to the frame 44. However, other guide systems are also conceivable. The guide 50 is curved and adapted such that the carrier 47 is always aligned centrally to the longitudinal axis L, regardless of the distance from the longitudinal axis L or to the film tube 1.This ensures a precise centric alignment of the guide elements 21 in the form of the two rollers relative to the film tube 1, so that both rollers are always held in contact with the film tube 1.

[0093] In principle, other adjustment mechanisms, such as parallelogram arrangements, are also conceivable, whereby it should be ensured that the supports 47 are at least largely adjustable radially to the longitudinal axis L.

[0094] The blowing elements 22 are also attached to the support 47, whereby they are slightly radially offset from the guide elements 21. In the illustrated embodiment, the blowing elements 22 are each arranged in axial overlap with one of the guide elements 21.

[0095] In the illustration shown in Figure 5, the guide elements 21 have not yet been fully brought up to the film tube 1 in order to guide it. For the sake of clarity, the guide elements 21 are shown at a slight distance from the film tube 1. Figure 6 shows a side view of the post-temperature control unit according to Figure 5, viewed radially outwards from the longitudinal axis. Four guide elements 21 and two blowing elements 22 are permanently mounted on the support 47. The guide elements 21, in the form of rollers, are arranged in pairs overlapping one above the other in a V-shape. The two pairs of guide elements 21 are arranged one above the other in a matching arrangement.

[0096] The two blowing elements 22 are arranged above the guide elements 21, i.e. downstream of the guide elements 21. The blowing elements 22 are arranged one above the other in a V-shape, similar to the guide elements 21, and overlap one another. The blowing elements 22 have blowing openings 52 facing inwards, i.e. in the direction towards the film tube. The tempering gas exits through the blowing openings 52 and flows against the surface of the film tube. In the exemplary embodiment shown, the blowing openings 52 are arranged such that the tempering gas, in contrast to the embodiments according to Figures 1 to 4, is not blown out obliquely to the longitudinal axis in or against the withdrawal direction, but horizontally, i.e. in a plane perpendicular to the longitudinal axis L, against the film tube.

[0097] Figure 7 shows an enlarged plan view of the post-temperature control unit according to Figure 5 in a further embodiment. The embodiment of the post-temperature control unit shown is largely identical to that according to Figure 5, with corresponding components being provided with the same reference numerals. In contrast to the embodiment according to Figure 5, the blowing elements 22 have outlet nozzles 53 which are aligned parallel to the longitudinal axis L. The outlet nozzles 53 blow out temperature control gas upwards, parallel to the longitudinal axis L, and thus form an air curtain encircling the longitudinal axis L. However, they can also be arranged additionally or alternatively on an underside of the blowing elements 22 and blow out an air curtain downwards.

[0098] Furthermore, in the embodiment shown, outlet nozzles 54 are also provided on the air distribution ring 28, which are aligned parallel to the longitudinal axis L. The outlet nozzles 54 blow out tempering gas upwards, parallel to the longitudinal axis L, and thus form a further air curtain circulating around the longitudinal axis L. They can also be arranged additionally or alternatively on an underside of the air distribution ring 28 and blow out an air curtain downwards.

[0099] It is also conceivable that outlet nozzles 53, 54 are arranged only on the blowing elements 22 or only on the air distribution ring 28. Furthermore, it is also possible to additionally or alternatively provide a separate distribution ring equipped with outlet nozzles for generating one or more air curtains. Furthermore, radially aligned outlet nozzles may also be provided. Furthermore, a separate gas supply from the tempering gas could be provided for the formation of one or more air curtains.

[0100] The blowing nozzles 52 and the outlet nozzles 53, 54 can have any desired shape, such as holes or slots. For example, the blowing elements 22 can each have a single blowing nozzle 52 and / or a single outlet nozzle 53 in each direction, which extends at least approximately over the entire length of the blowing element 22. Several slot-shaped blowing nozzles 52 or outlet nozzles 53 can also be provided, which are arranged overlapping and / or obliquely to a plane perpendicular to the longitudinal axis L.

[0101] List of reference symbols

[0102] 1 film tube

[0103] 2 Machine foundation

[0104] 3 extruders

[0105] 4 feed hoppers

[0106] 5 feed hoppers

[0107] 6 Blow head

[0108] 7 Ring nozzle

[0109] 8 Flat-laying unit

[0110] 9 Puller

[0111] 10 Cooling gas ring

[0112] 11 Gas supply line

[0113] 12 fans

[0114] 13 Outlet nozzle

[0115] 14 Freezing limit

[0116] 15 Internal cooling tower

[0117] 16 Gas extraction pipe

[0118] 17 Calibration basket

[0119] 18 Calibration element

[0120] 19 central opening of the cooling gas ring

[0121] 20 night temperature control unit

[0122] 21 Guide element

[0123] 22 Blowing element

[0124] 23 Suction unit

[0125] 24 Extraction element

[0126] 25 baffle

[0127] 26 blowers

[0128] 27 Supply line 28 Air distribution ring

[0129] 29 Supply line

[0130] 30 air coolers

[0131] 31 air heaters

[0132] 32 Suction line

[0133] 33 Control unit

[0134] 34 Control flap

[0135] 35 Temperature sensor in the supply line

[0136] 36 Pressure sensor in the air distribution ring

[0137] 37 Temperature sensor in front of the night temperature control unit

[0138] 38 Temperature sensor after the night temperature control unit

[0139] 39 inner air curtain flowing in the direction of extraction

[0140] 40 Outer air curtain flowing in the direction of extraction

[0141] 41 inner air curtain flowing against the direction of extraction

[0142] 42 outer air curtain flowing against the extraction direction

[0143] 43 radial flow lower air curtain

[0144] 44 frames

[0145] 45 adjustment unit

[0146] 46 Swivel arm

[0147] 47 carriers

[0148] 48 coupling rod

[0149] 49 drivers

[0150] 50 leadership

[0151] 51 plate

[0152] 52 Blowing nozzle

[0153] 53 Outlet nozzle

[0154] 54 Outlet nozzle

[0155] D Diameter of the through hole F Diameter of the guide hole

[0156] K Diameter of the calibration opening

[0157] L Longitudinal axis

Claims

Claims 1. Process for the subsequent tempering of a film tube extruded by means of a film blowing system, comprising the following process steps: - ejecting a film tube (1) made of plasticized thermoplastic material in a withdrawal direction along a longitudinal axis (L) of the film blowing system by means of a blowing head (6), - flowing cooling gas onto the film tube (1) in the withdrawal direction downstream of the blow head (6) by means of at least one cooling gas ring (10), so that the film tube (1) hardens at a freezing point (14) under the effect of the cooling gas, - post-tempering the film tube (1) by means of a post-tempering unit (20) downstream of the freezing limit (14), wherein the post-tempering unit (20) has several adjustable blowing elements (22) for blowing the film tube (1) with tempering gas, which form a through-opening for the film tube (1), - adapting a diameter (D) of the through-opening formed by the blowing elements (22) to a diameter of the film tube (1) by adjusting the blowing elements (22), - measuring the actual temperature of the film tube (1) downstream of at least one of the blowing elements (22), and - Regulating the temperature of the film tube (1) downstream of the at least one blowing element (22) to a desired temperature by blowing the film tube (1) with tempering gas by means of the post-tempering unit (20).

2. Method according to claim 1, characterized in that the post-temperature control unit (20) has a plurality of guide elements (21) which are adjustably hinged to the frame (44) for guiding the film tube (1), which form a guide opening for guiding the film tube (1), wherein a diameter (F) of the guide opening is adapted to a diameter of the film tube (1) by adjusting the guide elements (21).

3. Method according to claim 1 or 2, characterized in that the actual temperature of the film tube (1) is measured at least over at least one circumferential region of the film tube (1) and that temperatures and / or volume flows of the tempering gas of at least one blowing element (22) arranged in the at least one circumferential region are each set as a function of the difference between the actual temperature in the respective circumferential region of the film tube (1) of the respective blowing element (22) and the target temperature in the respective circumferential region of the film tube (1).

4. Method according to one of claims 1 to 3, characterized in that the film tube (1) downstream of the freezing limit (14) is cooled or heated at least in regions over the circumference by means of the tempering gas.

5. Method according to one of claims 1 to 4, characterized in that the actual temperature of the film tube (1) is measured in a region of an outlet of the post-temperature control unit (20), from which the film tube (1) emerges from the post-temperature control unit (20).

6. Method according to one of claims 1 to 5, characterized in that a temperature and / or a volume flow of the tempering gas is set as a function of the difference between the measured actual temperature of the film tube (1) and the target temperature of the film tube (1).

7. Method according to one of claims 1 to 6, characterized in that an annular air curtain is blown out substantially parallel to the longitudinal axis and around the flow of the tempering gas.

8. Method according to one of claims 1 to 7, characterized in that the film tube (1) is guided downstream of the at least one cooling gas ring (10) and upstream of the freezing limit (14) by means of a calibration basket (17) with a plurality of calibration elements (18) which are designed to enclose the film tube (1) and to form a calibration opening, wherein the calibration elements (18) are adjusted to set a diameter (K) of the calibration opening.

9. Film blowing system comprising: a blowing head (6) for ejecting a film tube (1) made of plasticized thermoplastic material in a withdrawal direction along a longitudinal axis (L) of the film blowing system, at least one cooling gas ring (10) in the withdrawal direction downstream of the blowing head (6) for flowing cooling gas onto the film tube (1) in order to allow the film tube (1) to harden under the effect of the cooling gas at a freezing point (14), and a post-temperature control unit (20) for post-temperature control of the film tube (1), which is designed and intended to be arranged downstream of the freezing point, characterized in that the post-temperature control unit (20) has a plurality of blowing elements (22) for Blowing the film tube (1) with tempering gas, which are designed to enclose the film tube (1) and to form a through-opening for the film tube (1), wherein the blowing elements (22) are adjustable to set a diameter (D) of the through-opening, that downstream of at least one of the blowing elements (22) a temperature sensor (38) for detecting the temperature of the film tube (1) is arranged and that the film blowing system has a control unit (33) which is designed to regulate the temperature of the film tube (1) downstream of the at least one blowing element (22) by blowing the film tube (1) with tempering gas by means of the post-tempering unit (20) to a desired temperature.

10. Film blowing system according to claim 9, characterized in that the post-temperature control unit (20) has a plurality of guide elements (21) which are designed to enclose the film tube (1) and to form a guide opening in order to guide the film tube (1), wherein the post-temperature control unit (20) has a frame (44) to which the guide elements (21) are adjustably articulated in order to set a diameter (F) of the guide opening.

11. Film blowing system according to claim 10, characterized in that the blowing elements (22) are arranged downstream of the guide elements (21).

12. Film blowing system according to claim 10 or 11, characterized in that the blowing elements (22) and the guide elements (21) are adjustable synchronously.

13. Film blowing system according to one of claims 10 to 12, characterized in that the diameter (F) of the guide opening of the post-temperature control unit (20) is smaller than the diameter (D) of the through-opening of the post-temperature control unit (20).

14. Film blowing system according to one of claims 9 to 13, characterized in that the post-tempering unit (20) has a cooling unit (30) for cooling the tempering gas and / or a heating unit (31) for heating the tempering gas.

15. Film blowing system according to one of claims 9 to 14, characterized in that the blowing elements (22) each have at least one inwardly facing blowing nozzle (52) for blowing the film tube (1) with tempering gas.

16. Film blowing system according to claim 15, characterized in that the blowing elements (22) or an air distribution ring (28) which is arranged radially outside the blowing elements (22) and supplies them with tempering gas, each have at least one outlet nozzle (53, 54) pointing radially outside the at least one blowing nozzle (52) at least substantially parallel to the longitudinal axis in order to produce an air curtain flowing out in a ring-shaped manner around the longitudinal axis (L) and parallel to the axis.

17. Film blowing system according to claim 16, characterized in that the post-temperature control unit (20) has a plurality of supports (47) distributed over the circumference, which are adjustably hinged to the frame (44) and that at least one of the blowing elements (22) and at least one of the guide elements (21) is fastened to the supports (47).

18. Film blowing system according to one of claims 9 to 17, characterized in that the film blowing system comprises a flattening unit (8) for folding the film tube (1) downstream of the post-tempering unit (20) and that an area between the post-tempering unit (20) and the flattening unit (8) is free of elements influencing the film tube (1).

19. Film blowing system according to one of claims 9 to 18, characterized in that downstream of the post-temperature control unit (20) there is arranged an annular guide plate arrangement (25) through which the film tube (1) can be passed.

20. Film blowing system according to one of claims 9 to 19, characterized in that the post-tempering unit (20) has a suction unit (23) for at least partially sucking off the tempering gas and that the suction unit (23) is fluidly connected to a supply for tempering gas of the blowing elements (22).

21. Film blowing system according to one of claims 9 to 20, characterized in that at least one temperature sensor (37) for detecting the temperature of the film tube (1) is arranged upstream of the blowing elements (22) over the circumference around the longitudinal axis (L).

22. Film blowing system according to one of claims 9 to 21, characterized in that the film blowing system comprises a temperature sensor (35) for detecting the temperature of the tempering gas.

23. Film blowing system according to one of claims 9 to 22, characterized in that the film blowing system comprises a pressure sensor (36) for detecting the pressure and / or a volume flow sensor for detecting the volume flow of the tempering gas for supplying the blowing elements (22) with tempering gas.

24. Film blowing system according to one of claims 9 to 23, characterized in that a calibration basket (17) is arranged downstream of the at least one cooling gas ring (10), with a plurality of calibration elements (18) which are designed to enclose the film tube (1) and to form a calibration opening in order to guide the film tube (1), wherein the calibration elements (18) are adjustable for setting a diameter (K) of the calibration opening.

Images