Device and method for producing a film tube

Abstract

The invention describes a device for producing a film tube with - an outlet nozzle of a blow head, from which a plastic melt can be led out in a transport direction and can be formed into a film tube, - a cooling device, which is arranged downstream of the outlet nozzle in the transport direction, - at least one detection device for observing the film tube in an observation area. The observation area is located between the outlet nozzle and the cooling device.

Description

[0001] Windmöller & Hölscher KG

[0002] Münsterstraße 50

[0003] 49525 Lengerich / Westphalia

[0004] February 16, 2023

[0005] Our reference: 9525 WO - SCHN

[0006] Device and method for producing a film tube

[0007] The invention describes a device for producing a film tube according to claim 1 and a corresponding method according to claim 8.

[0008] In a blown film line, which embodies a device for producing a film tube, one or more plastic melts are produced from plastic granules in one or more extruders. Within a blow head, the plastic melt or melts are distributed in a ring shape and discharged from the blow head through an outlet nozzle, thereby forming a film tube. The film tube thus produced can be drawn off via a take-off device comprising a pair of rollers with at least one driven roller. Downstream of the outlet nozzle as seen in the transport direction of the film tube, the blown film is usually cooled internally and / or externally by means of cooling devices so that the plastic melt solidifies. In particular, the external cooling device can extend annularly around the film tube.Furthermore, detection devices are known with which the area in which the plastic melt solidifies can be determined, so that conclusions can be drawn about the cooling behavior of the film tube.

[0009] In some generic devices, the outlet nozzle and the cooling device, especially the external cooling device, are spaced apart from each other. This distance can often be adjusted variably. In this area between the outlet nozzle and the cooling device, the still very hot melt is guided freely without any guidance. This can quickly lead to deformation of the melt, which often leads to melt breakage. A melt or film tube breakage results in downtimes of the blown film line, as the film tube must first be manually transported from the outlet nozzle to the take-off point. Stable production must then be achieved again.

[0010] The task is therefore to propose a device and a method with which melt breakages can be avoided.

[0011] The above object is achieved by a device having the features of claim 1 and by a method having the features of claim 8. Further features and details of the invention emerge from the subclaims, the description, and the drawings. Features and details described in connection with the method according to the invention naturally also apply in connection with the blown film line according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is always made to each other.

[0012] The invention relates to a device for producing a film tube, comprising an outlet nozzle of a blow head, from which a plastic melt can be discharged and formed into a film tube, and a cooling device arranged downstream of the outlet nozzle in the transport direction. The film tube can be cooled using this cooling device. This is preferably achieved by subjecting the outer wall and / or the inner wall of the film tube to a fluid, which in particular emerges from openings in the cooling device, wherein the openings are directed towards the wall of the film tube so that the fluid is directed onto the wall of the film tube. The fluid preferably has a temperature that is lower than the temperature of the film bubble when the latter is located in the region of the cooling device. The fluid can, for example, be at room temperature.Air is preferably used as the fluid, but a liquid, such as water, can also be provided. Furthermore, the device comprises at least one detection device for observing the film tube in an observation area. The invention is characterized in that the observation area is arranged between the outlet nozzle and the cooling device. The entire area between the outlet nozzle and the cooling device is the maximum observation area. The observation area, seen in the transport direction of the film tube, can, however, also be smaller than the maximum observation area. The cooling device refers to the first cooling device that the film tube passes through after leaving the outlet nozzle. This first cooling device can in particular consist of several individual elements and can be arranged outside and / or inside the film tube and can be annular or circular.An external cooling ring thus encloses the film tube. The film tube and the external cooling ring are preferably arranged concentrically with each other. In particular, an external cooling ring can also comprise several individual rings arranged one behind the other in the transport direction.

[0013] The detection device comprises at least one detector with which the electromagnetic radiation emitted by the blown film can be detected. This electromagnetic radiation can be in the so-called infrared range, with a wavelength between 780 nm and 1 mm, but also in the human-visible range (wavelength between 380 nm and 780 nm) or in the high-energy range (UV radiation, wavelength below 380 nm).

[0014] Infrared radiation is generally generated within the blown film itself and is attributable to thermal radiation. Visible, high-energy radiation is typically generated by a dedicated light source, which is either reflected or transmitted by the film bubble. Using radiation of different wavelengths, various properties of the film bubble can be examined. Visible radiation can be used, for example, to visualize defects in the film bubble, such as streaks or specks. Radiation in the infrared range originates, at least in part, from thermal radiation from the film bubble. The wavelengths and / or intensity of this radiation are therefore a measure of the temperature of the film bubble.

[0015] For example, at least one of the following camera types can be provided as the detection device: color camera, laser scanner camera, LIDAR (three-dimensional laser scanning), 3D camera (e.g., stereo cameras, triangulation system, interferometric measuring system, time-of-flight measuring system, light field camera). Of course, multiple detection devices can also be provided, with all detection devices comprising the same camera type or two or more different camera types being provided. With the detection device, the film tube can now be observed at a high frequency or even continuously. In particular, the lateral outer edges of the film tube can be detected.If the shape of the film tube deviates from the normal shape during operation, an evaluation and control device that compares the observed shape of the film tube with the normal shape or the target shape stored in memory can issue a warning signal to the operator and / or return the actual shape of the film tube to the normal or target shape by influencing production parameters. The normal shape refers to the shape that the film tube has during stationary operation. If a camera or a system is even provided with which the film tube can be viewed in three dimensions, the shape of the film tube can change not only perpendicular to the line of sight of the detection device, but also in or against the line of sight. This allows shape deviations to be detected even more effectively.

[0016] Alternatively or additionally, the temperature of the film tube can be detected using the detection device. The temperature results from the intensity of the radiation absorbed by the film tube in the wavelength range or wavelength ranges that can be detected by the detection device. One or more calibration elements can be provided, each of which can be brought to a specific temperature, particularly to different temperatures if there are multiple calibration elements. If the detection device only detects one calibration element, the temperature value measured by the detection device can be adjusted to the actual temperature of the respective calibration element. This modified measured value can then be retained for subsequent measurements of the film tube. The calibration element can be the film bubble itself if its absolute temperature is known.

[0017] In this way, it is possible to detect any deviation in the tube shape and react to it before such a deviation leads to a melt or film tube break. A timely reaction therefore ensures that such a break is avoided and the film tube can be kept stable over a long time and production can continue uninterrupted. A change in the shape of the film tube can, for example, be caused by a change in the ambient temperature. It is also possible to detect changes in the temperature of the film bubble. The ambient temperature can also have an influence here. Changes in the temperature and / or the tube shape can occur in particular during a product changeover from one current product order to a subsequent product order, whereby the film tube or film bubble continues to exist even during a product changeover.Detection of the tube shape is particularly important here, as it ensures the stability of the film bubble, especially during product changeover.

[0018] The tube shape can be observed across the entire observation range of the detection device. However, it is also advantageous to determine the tube shape, in particular the diameter of the film tube, directly after it leaves the outlet nozzle. Furthermore, it is advantageous to determine the tube shape, in particular the diameter of the film tube, directly before it passes through the cooling device. In a further embodiment, the diameter of the film tube can be compared with the inner diameter of the cooling ring, i.e. the diameter of the free space within the cooling ring, using the evaluation and control device. If this results in a difference above a threshold value, i.e. a distance between the outer wall of the film tube and the inner diameter of the cooling ring above the threshold value, the diameter of the film tube can be controlled so that the difference lies below the threshold value.This results in improved cooling of the film tube.

[0019] In a further embodiment of the invention, at least one cooling ring can be provided, which comprises a suction device for sucking the film tube towards the inner wall of the cooling ring. The detection device can then measure the diameter of the film tube and compare it with the area of ​​influence of the suction device on the film tube. If, in this case too, the diameter suggests that the distance between the film tube and the suction device is too great, the evaluation and control device can be used to adjust the diameter of the film tube so that it enters the area of ​​influence of the suction device and is sucked in. In this case, improved cooling of the film tube is achieved.

[0020] In particular, as described, an evaluation and control device is provided with which the actual and desired shape of the film tube can be detected. Furthermore, the evaluation and control device is preferably designed to compare the actual shape of the film tube, in particular its outer diameter, with geometric data of the cooling device, in particular with the inner diameter of a cooling ring surrounding the film tube. Thus, in particular, it is provided that the diameter of the film tube is smaller than or equal to the passage diameter of a cooling ring.

[0021] A comparison of successively detected shapes of the film bubble by the evaluation and control device is also advantageous, as the temporal development of this shape can be analyzed and changes detected. A comparison with a nominal shape of the film bubble is not necessary in this case. For example, strong pumping of the film, i.e. a periodic enlargement and / or reduction of the shape of the film tube, in particular its diameter, can be detected. Suitable countermeasures can be implemented by the evaluation and control device, such as the material throughput or the pull-off speed. Fluttering of the film tube, i.e. small, but frequently occurring diameter changes and / or periodically occurring, local shifts of the center of the film tube relative to the nominal line of symmetry, can also be detected. Countermeasures can be taken in this case, too.The line of symmetry can be formed by the imaginary connection between the center of the circular outlet nozzle and the center of another circular or annular element, such as the annular cooling element. Of course, a deviation of the film tube's axis of symmetry from the line of symmetry can also be detected. Appropriate countermeasures are also conceivable.

[0022] A comparison of the desired and actual shapes, or a comparison of successively detected shapes of the film bubble, can also lead to the detection of a subsidence of a widened portion of the film bubble, i.e., a movement of the widened portion opposite to the transport direction of the film bubble. In this case, the computing and control system can also initiate countermeasures.

[0023] Furthermore, monitoring the film tube makes it possible to detect bubble breakage and / or holes or other openings in the film tube wall. Here, too, the control and regulation system can initiate measures. In addition to immediately issuing an alarm, this can include, especially in the case of bubble breakage, the immediate interruption of further melt flow from the outlet nozzle.

[0024] In an advantageous embodiment of the invention, a displacement device is provided with which the cooling device can be displaced relative to the outlet nozzle in or against the transport direction of the film tube. This displacement device can, for example, comprise threaded rods that engage with screws attached to the cooling device. Rotation of the threaded rods leads to a linear movement of the cooling device. The threaded rods can be supported on the die head. Such a displacement device can be used to enlarge the observation area in order to more easily detect deviations in the shape of the film tube.

[0025] Furthermore, it is advantageous if the detection device can be displaced relative to the outlet nozzle in or against the transport direction using a positioning device. The positioning device can be designed similarly to the displacement device of the cooling device. With this positioning device, the detection device can be positioned at a level of the film tube where the greatest effect is expected if deviations in the shape of the film tube occur. This allows for very early response to such deviations.

[0026] In an advantageous embodiment of the invention, the detection device is arranged on the cooling device, in particular on the underside of the cooling device. Preferably, the cooling device is a cooling ring surrounding the film tube. Such an arrangement on the cooling device eliminates the need for a separate installation of the detection device, for example, using a tripod or other support elements. Particularly when the cooling device is arranged to be movable, the described arrangement of the detection device on the cooling device also makes a device for positioning the detection device superfluous in many cases.

[0027] It is also advantageous if the detection device, particularly one mounted on the cooling device, is adjustable in angle, inclination, and / or height relative to the cooling device using an adjustment device. Height adjustability refers to adjustment in or against the transport direction of the film tube. The purpose of this measure is to be able to change the observation area.

[0028] It is also preferable for the observation area to be located in the second half of the path between the outlet nozzle and the cooling device, as seen in the transport direction of the film tube. The greatest effect of the expected deviations can generally be observed in this area, so the deviations can be more easily detected here.

[0029] Furthermore, it is advantageous if the observation area, viewed transversely to the transport direction of the film tube, extends essentially across the entire width of the film tube. The term "across the entire width" implies that, due to the viewing angle of the detection device, the film tube cannot be detected across its entire diameter, but rather appears to have a reduced width. However, since the described deviations often occur rotationally symmetrically, this does not lead to any relevant limitations.

[0030] In a further embodiment of the invention, at least one second detection device is provided, which is arranged downstream of the cooling device. This second detection device can also be used to observe the film tube, but downstream of the cooling device. This second detection device can also be designed in the same way as the first detection device with regard to the detectable wavelengths of electromagnetic radiation, the structure, the determination of the shape of the film bubble, and other properties already described. This second detection device can also be connected to the already described evaluation and control device, with which the detection results of the second detection device can be evaluated. It is advantageous that the calibration of the first and second detection devices are coordinated with one another.If, for example, the first detection device is calibrated, in particular with regard to temperature determination, the second detection device can be calibrated to the first detection device.

[0031] The shape of the film bubble determined by the second detection device can be correlated with the shape determined by the first detection device. For example, it is possible to determine the diameter or shape of the film bubble within the cooling device by interpolating the shapes. At this location, the film bubble cannot be directly determined by any of the detection devices.

[0032] The data obtained by the first and second detection devices can be combined for various purposes using the evaluation and control device. For example, parameters such as the flutter value (i.e., the periodic temporal change in shape), shape parameters, and temperatures can be combined to form common key figures, such as the total flutter value, a composite shape and temperature key figures. Stability key figures can also be exchanged and / or compared between the detection systems. The evaluation and control device can fulfill this purpose. For example, the probability of bubble breakage can be determined. Calculations can also be made based on the flutter value, temperature homogeneity, temporal shape constancy, possible asymmetry of the film tube, and / or the diameter of the film bubble near or within the cooling ring.These calculations can form a basis for calculating the probability of bubble rupture. This probability calculation can, in turn, serve as a basis for controlling the machine parameters to reduce the probability of bubble rupture. The probability of bubble rupture can also be displayed to a machine operator via a display device. This can, for example, be in the form of a traffic light that can display a green, a yellow, and a red light to clearly indicate the probability. A further aspect of the invention, which also solves the problem, relates to a method for producing a film tube, in which:

[0033] . from an outlet nozzle of a blow head

[0034] . a plastic melt is fed out in one transport direction and formed into a film tube,

[0035] . the film tube is cooled by a cooling device arranged downstream of the outlet nozzle in the transport direction,

[0036] . the film tube is observed in an observation area using a detection device.

[0037] The method according to the invention is characterized in that the observation area is arranged between the outlet nozzle and the cooling device.

[0038] This makes it possible to achieve the same advantages that have already been described above in connection with the monitoring method according to the invention.

[0039] Further advantages, features, and details of the invention will become apparent from the following description, in which various exemplary embodiments are explained in detail with reference to the figures. The features mentioned in the claims and in the description may be essential to the invention individually or in any combination of mentioned features. Within the scope of the entire disclosure, features and details described in connection with the device according to the invention naturally also apply in connection with the method according to the invention, and vice versa, so that with regard to the disclosure, reference is always made to the individual aspects of the invention. The individual figures show:

[0040] Fig. 1 : Side view of a blown film line according to the invention

[0041] Fig. 2: Detail of Fig. 1 Figure 1 shows a device 1 for producing a film tube, namely a blown film system 1, which initially comprises at least one extruder 2, with which plastic present, for example, in granulate form can be plasticized. The plastic melt thus produced is fed via a line 3 to a nozzle head 4, from which this melt is transferred into a film bubble 6, so that this melt stream can be pulled out of an annular nozzle 5 (not visible in this figure) in the transport or withdrawal direction z. A film bubble 6 which has not yet solidified is now present. This is inflated from the inside in the tube formation zone by a slight overpressure so that it has a larger diameter within the calibration device 7. For this purpose, an air supply device 13 is provided, which is located inside the annular nozzle 5 and extends partially in the transport direction.This air supply device is supplied with air through the extrusion tool.

[0042] Solidification of the film bubble occurs by cooling, whereby part of the heat of the film bubble is released to the environment, in particular by a cooling device 8, which is often also referred to as a cooling ring due to its ring-like design enclosing the film tube.

[0043] After passing the calibration device 7, the film bubble 6 enters the effective area of ​​a flattening device 9, in which the circular film tube is converted into an elliptical cross-section with an increasing eccentricity, until it finally forms a double-layered plastic film in the area of ​​influence of the take-off device comprising in particular two take-off rollers 10, which are connected to one another at their sides.

[0044] The flattening device is arranged so that it can rotate, with the axis of rotation essentially aligned with the hose or symmetry axis 11, which is indicated by a dot-dash line in Figure 1. The rotatability of the flattening device is indicated by arrow 12.

[0045] Figure 1 also shows a reversing device 15, which is designed to guide the flattened film tube from the flattening device to the stationary roller 16 without causing damage. Arrow 17 indicates that this film tube, after passing through the reversing device 15, is guided to further processing, which is not specified in detail here.

[0046] Viewed in the transport direction z, between the annular nozzle 5 and the cooling device 8, at least one detection device 20 is arranged, with which at least partial surface areas of the surface of the film bubble 6 can be detected. The detection device 20 is preferably arranged outside the film bubble 6, but directed towards it. The detection device 20 can be attached directly or indirectly to any component of the blown film line 1. However, it is also conceivable to install the detection device 20 independently of the blown film line 1 on a separate frame, for example a tripod, within the production facility.

[0047] Figure 2 now shows a section of Figure 1, wherein essentially the film bubble 6 in the tube formation zone as well as the ring nozzle 5, the cooling device 8, the calibration device 7 and the detection device 20 are shown.

[0048] The detection device 20 comprises in particular at least 32 detection elements so that a sufficient number of points on the circumference of the film tube can be detected simultaneously. However, the detector preferably has at least a so-called HD resolution, i.e. at least 720 detection elements per lateral direction. A detector preferably has a repetition rate of at least 3 Hz, preferably at least 9 Hz, i.e. at least three and preferably at least nine detections can be carried out per second with each detection element. Each of the detection elements is capable of measuring the associated intensity in one or more wavelength ranges. In particular in the infrared radiation range, the radiation intensity in a specific wavelength can be assigned to a temperature of the film tube.

[0049] As shown, a detection device 20 can be provided. However, in order to be able to scan a larger circumferential area, it is advantageous to design the detection device 20 so that it can be moved in the circumferential direction of the film bubble. Alternatively or additionally, at least one second detection device can be provided, with which areas of the surface of the film bubble 6 can be scanned that are at least partially not scannable by the first detection device 20.

[0050] Figure 2 shows an enlarged detail of the area between the annular nozzle 5 and the cooling device 8. It is shown that the detection device is preferably, but not necessarily, arranged on the cooling device by means of a holder 21. It is possible for the detection device to be rotatable about a vertical axis in the direction of the double arrow 22 and / or about a horizontal axis 21 via the holder in order to vary the observation area.

[0051] The double arrow 24 illustrates that the cooling device 8 can be moved in or against the transport direction z of the film tube.

[0052] Figure 2 also shows, by way of example, that the shape of the film bubble 6 deviates from the ideal cylindrical shape shown in the example (represented by dashed lines) in a barrel shape. Such a deviation can be detected by an evaluation and control device (not shown). The evaluation and control device can, for example, derive and / or implement measures to correct the deviation.

[0053]

Claims

Device and method for producing a foil tube Patent claims Device for producing a foil tube with • an outlet nozzle of a blow head, from which a plastic melt can be conveyed in one transport direction and formed into a foil tube, • a cooling device arranged downstream of the outlet nozzle in the direction of transport, • at least one detection device for observing the film tube in an observation area, characterized in that the observation area is arranged between the outlet nozzle and the cooling device. Device according to claim 1, characterized in that at least one displacement device is provided with which the cooling device can be displaced relative to the outlet nozzle in or against the transport direction. Device according to claim 1, characterized in that a positioning device is provided with which the detection device- The device is displaceable in or against the direction of transport relative to the outlet nozzle. A device according to one of the preceding claims, characterized in that the detection device is arranged on the cooling device, in particular on the underside of the cooling device. A device according to one of the preceding claims, characterized in that the detection device is adjustable relative to the cooling device by means of an adjustment device in terms of angle and / or inclination in order to change the observation area. A device according to one of the preceding claims, characterized in that, viewed in the direction of transport, the observation area is located in the second half of the distance between the outlet nozzle and the cooling device. A device according to one of the preceding claims, characterized in that, viewed transversely to the direction of transport, the observation area extends substantially over the entire width of the film tube.Method for producing a foil tube, in which. • from an outlet nozzle of a blow head • a plastic melt is conveyed out in one transport direction and formed into a foil tube, • the film tube is cooled by a cooling device arranged downstream of the outlet nozzle in the direction of transport, • is observed with a detection device of the foil tube in an observation area, characterized in that The observation area is located between the outlet nozzle and the cooling device.

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