Apparatus and method for verifying the settings of an extrusion apparatus.

Abstract

Summary The present invention relates to a device for verifying the settings of an extruder that manufactures tubular objects conveyed in a conveying direction, wherein the extruder is set up so that extruded material of different outlet widths comes out from the upper and lower parts of the extruder's extrusion nozzle. The present invention also relates to a corresponding method.

Description

【Technical Field】 【0001】 The present invention relates to an apparatus and a method for checking the settings of an extrusion device for manufacturing tubular objects conveyed in a conveying direction. 【0002】 For example, plastic tubes for supplying gas and water to residential and industrial areas, and further plastic tubes for drainage, are mainly manufactured from materials such as high-density polyethylene (HDPE), polypropylene (PP), and polyvinyl chloride (PVC). The diameter of a general tube is up to 3 m, and the wall thickness is up to 250 mm. Usually, it is manufactured by an extrusion device. In the extrusion device, the plastic material is melted and generally discharged through an annular extrusion nozzle. The tube thus extruded is conveyed after being pulled out in the front-rear direction from the extrusion device. The diameter of the pulled-out tube is formed into a desired outer diameter in a downstream, for example, sleeve-shaped calibration device. During the conveying process, the tube usually passes through several cooling sections, where the tube is cooled and the initially still-fluid plastic melt is gradually solidified. In the first cooling section, the formed tube is prevented from collapsing, for example, by vacuum. The tube is often cooled in the cooling section by a coolant such as water. The cooling water flows around the tube and rapidly solidifies its outer region. After leaving the first cooling section, the outer surface of the tube is usually hardened, so that the outer shape of the tube then changes only slightly. However, inside the tube wall, there is usually a flowable component of the tube material even after leaving the first cooling section. As the tubular object continues to be conveyed, especially as it passes through further cooling sections, the inside of the tube is also gradually cooled and hardened up to the inner surface of the tube. The tube is then cut to a desired length using a flying saw. 【0003】 The shaping of the tube during the process of complete hardening after it leaves the extruder is essentially influenced by two effects that must be taken into consideration, for example, in order to achieve the most uniform wall thickness of the tube. One of these effects is the shrinkage of the tube material that occurs during cooling. The other effect is sagging, that is, the sinking of the flowable viscous mass component due to gravity during hardening. 【0004】 To address these effects that affect the final shape of the tubular object, it is known to set the outlet width of the extruded material in the upper region of the extrusion nozzle of the extruder to be greater than in the lower region. To set the outlet width, it is possible to set the outlet spacing of the extrusion nozzle to be wider in the upper region than in the lower region. Alternatively, or additionally, the extrusion nozzle can be heated more strongly in the upper region than in the lower region, which will result in a larger outlet width of the extruded material in the upper region than in the lower region of the extrusion nozzle. Thus, both measures result in more material being discharged in the upper region of the extrusion nozzle than in the lower region. This intentional asymmetrical discharge of material is intended to compensate for sagging so that the wall thickness of the hardened tube is as uniform as possible around its entire circumference. 【0005】 Important geometric values ​​such as tube wall thickness and diameter can only be finally measured after the tube has fully hardened, that is, when shrinkage and sagging have completely finished at all cooling ends of the tube. The typical production rate of an extruder for medium-sized tube cross-sections is approximately 1,000 kg / h. Depending on the material, the temperature of the molten material when it exits the extrusion nozzle is approximately 200°C to 240°C. For example, for a tube with an outer diameter of 330 mm, a wall thickness of 30 mm, and a typical tube cooling section of 60 m, initial measurements of wall thickness and diameter are often only obtained several hours after the start of production. Only then can geometric deviations from the target values ​​be detected, potentially affecting the extruder's production parameters, but any changes made at this stage can only be re-verified several hours later. After the start of the process, several corrections often required to achieve an optimal process, such as ensuring uniform wall thickness across the circumference and setting it to its nominal value, can take several days. 【0006】 To compensate for sagging, as explained, when setting up the extrusion nozzle, the outlet width of the upper region of the extruded material, or more precisely, the wall thickness of the upper region, is set to be larger than that of the lower region. To ensure that the wall thickness does not fall below the minimum even if sagging occurs, sagging is usually overcompensated using empirical values. Ultimately, this leads to the discharge of unnecessary amounts of material. 【0007】 Therefore, it is desirable to obtain information as early as possible about the expected shrinkage and sagging of the tubes produced by the extruder. For example, measurements of the tube wall thickness and diameter after the first cooling section cannot correspond to the desired final values ​​that will exist after the tube has completely cooled, because at this point, the solidified material is only in the external region of the tube wall, while recrystallized components and molten material remain inside. As a result, the diameter and wall thickness values ​​recorded at the measurement position after the first cooling section are those that will still be subject to shrinkage and sagging. Predicting the expected shrinkage and sagging values ​​as early as possible is economically crucial for accelerating the start-up process and ensuring consistent nominal values. 【0008】 German Patent Publication No. 40 18 051 discloses an apparatus for closed-loop control of the outer diameter of a strand in a cable, wherein a first diameter measuring device is located downstream of an extruder, and a second diameter measuring device is located at a distance from the extruder, preferably downstream of the strand's cooling section. The diameter measurement signal from the first diameter measuring device is applied to a first comparator and a delay stage, the delay time of which corresponds to the time it takes for the strand to move between the first and second diameter measuring devices. The second comparator compares the diameter measurement signal from the second diameter measuring device with the delayed first diameter measurement signal. The difference signal in the second comparison direction is applied to the first comparator in addition to the target cooling value of the diameter. When a deviation from the target cooling value is detected by the first comparator, the deviation is sent to a controller to control the outer diameter of the strand in a closed-loop manner. The apparatus described in German Patent Publication No. 40 18 051 can be used to measure the shrinkage of a strand between the measuring positions of a first diameter measuring device and a second diameter measuring device, and a delay ensures that the actual shrinkage of the strand is measured. 【0009】 International Patent Publication No. 2022 / 058081 proposes a method for determining the geometric parameters of a strand-like or plate-like object, by which shrinkage can be predicted. For this purpose, the relationship between the refractive index of the object and the shrinkage that occurs during its solidification is confirmed in a confirmation step. In the determination step, the refractive index and at least one geometric parameter of the object, which has not yet completely solidified, are determined, particularly after the first cooling portion of the object, and the geometric parameters of the fully solidified object are calculated from the determined values, taking into account the relationship confirmed in the confirmation step. Thus, the shrinkage of the material of the object is predicted during its solidification process, and based on this, the geometric parameters of the fully solidified object, such as the wall thickness, are calculated. 【0010】 According to the method described, shrinkage can be reliably predicted and can be considered as one of two decisive influences on the final shape. Advantageously, measurements are available immediately after the material leaves the extruder, and therefore the final geometric parameters can be calculated early to avoid waste. However, sag, the second decisive influence on the final shape of the object, cannot be predicted by known methods for reasons explained in detail below. 【0011】 A method for detecting sagging in tubes extruded by an extruder is known from International Patent Publication 2022 / 106180. The wall thickness of the tube is measured along its circumference, and a wall thickness profile is created using the measured wall thickness. Sagging of the molten material is identified from the frequency and / or amplitude of the wall thickness profile. While this method allows for reliable detection of sagging, it does not allow for prediction of sagging. 【0012】 European Patent No. 2 086 744 B1 also discloses a method for operating a production system for manufacturing strands, in which an extrusion model of an extruder is stored in a computer. When strand manufacturing begins, the extrusion model is used to calculate the diameter and / or wall thickness of the strands that will be produced as predicted by the extruder, based on speed-dependent data values ​​for the extruder's bore diameter, linear speed, screw speed, and extruder's power output. The calculated values ​​of the diameter and / or wall thickness are displayed, and these calculated and displayed values ​​are adjusted to target values ​​of the diameter and / or wall thickness by changing the extruder's screw speed and / or linear speed using manual operation or closed-loop control. At a distance from the extruder, at a measurement position where the strand has completely passed through the cooling section and cooled, the diameter and / or wall thickness of the strand are measured at a measuring head. The extrusion model ensures that the actual values ​​of the diameter and / or wall thickness measured at the measuring head are very close to their respective target values. Any remaining deviations can be eliminated by properly controlling the extruder. The method described in European Patent No. 2 086 744 B1 functions such that a (virtual) measuring head is placed between the extruder and the cooling unit, already displaying the cold values ​​of the strand's diameter and / or wall thickness at this early stage in manufacturing. Using the described method, the production system can be set to values ​​that avoid waste at a very early stage, especially before the strand reaches the measuring head. However, creating the extrusion model requires some effort, it needs to be adapted when changes are made to the components of the production system, and often requires extensive validation testing. 【0013】 Based on the prior art described above, the present invention aims to provide the type of apparatus and method described at the beginning that allows for reliable verification and modification of the settings of an extruder, particularly taking into account the sagging of tubular objects produced by the extruder. 【0014】 The present invention achieves this objective by independent claims 1 and 16. Advantageous embodiments are shown in the dependent claims, specification, and drawings. 【0015】 Regarding the type of device described at the beginning, the present invention achieves this objective using the following: A first wall thickness measuring device for measuring the wall thickness of at least one wall of a tubular object at a first measuring position located in the transport direction upstream of at least one cooling section for the tubular object. A second wall thickness measuring device for measuring the wall thickness of at least one wall portion of a tubular object at a second measuring position located in the transport direction downstream of a first measuring position. An evaluation device to which wall thickness measurements from a first wall thickness measuring device and wall thickness measurements from a second wall thickness measuring device are applied, wherein the wall thickness measurement from the first wall thickness measuring device is delayed compared to the wall thickness measurement from the second wall thickness measuring device by a delay stage of the device, and the delay time corresponds to the transport time of the object between the first measurement position and the second measurement position. The evaluation device is designed to verify the ratio of the outlet width at the top to the outlet width at the bottom of the extrusion nozzle for the extruded material set in the extruder by comparing the wall thickness measurement from a first wall thickness measuring device with the wall thickness measurement from a second wall thickness measuring device, and the wall thickness measurement from the first wall thickness measuring device is delayed by a delay stage. 【0016】 The present invention also achieves this objective by using the apparatus according to the present invention and by the type of method described at the beginning. 【0017】 According to the present invention, the settings of the extruder used to manufacture the tubular object can be checked and modified as necessary, as described below. In particular, the expected sagging after the first measurement position, i.e., the sagging of the tubular object as it exits the extruder during solidification due to the effect of gravity on the still-fluid viscous mass component, is also taken into consideration. 【0018】 As is known, an extruder has an extrusion nozzle, for example, in the shape of a circular ring, from which molten plastic material exits. Also, as is known, after leaving the extruder, the tubular object passes regularly through several cooling sections, in which the material of the object is continuously cooled by a coolant, such as water, until it is cooled and completely hardened. For example, after leaving the first cooling section immediately downstream of the extruder, the outer surface of the tubular object may already be hardened, and thus the shaping of the outer surface of the tubular object is complete. On the other hand, inside the tube wall, the material of the tubular object still contains recrystallized regions and soluble components, and is therefore at least partially still flowable, and it is known that sagging occurs in addition to shrinkage when the object cools. In order to finally shape the tubular object in the first cooling section, it is possible to press the material of the object against the inner surface of a calibration sleeve, for example, by applying a vacuum. 【0019】 In principle, not only shrinkage but also expected sag can be modeled in detail using the Navier-Stokes equations based on precisely known framework conditions and material properties of the tubular object. However, this is numerically extremely complex and therefore not practical for the rapid prediction of sag desired here. According to the present invention, a reliable prediction of expected sag, and thus the final shape of the object, is intended to be available as soon as possible after it leaves the extruder to avoid waste, so that intervention in the manufacturing process can be made at an early stage if necessary, for example, by adjusting the settings of the extruder. Prediction of sag should preferably be made in real time. Both of these factors prevent the use of the Navier-Stokes equations, which are themselves reliable, in this application. 【0020】 Unlike shrinkage, as already mentioned, sagging is unpredictable in the manner described in International Patent Publication 2022 / 058081. Shrinkage from the extrusion temperature to complete cooling does not depend on the time progression of curing, particularly the cooling rate. Furthermore, changing parameters such as the extruder or cooling parameters does not substantially affect shrinkage. This is an inherently immutable process characteristic, yet it is relatively easy to predict. 【0021】 Sagging is a different situation and involves a far more complex process than shrinkage. In sagging, the temperature-dependent flow behavior of the material, its temperature, and the cooling rate play a crucial role. Generally, the higher the initial temperature of the molten material and the longer the time it takes for the molten material to cool and harden completely, the more pronounced the sagging of the molten material will be during tube manufacturing. Changes in operating conditions such as extrusion temperature, extruder feed rate, discharge rate, and cooling intensity and duration affect the degree of sagging. For example, predicting shrinkage using refractive index can be achieved by stopping a system that records the change in refractive index along with the shrinking wall thickness and diameter over several hours. However, this reliable method cannot be used to accurately predict sagging because the sagging of wall thickness becomes significantly more pronounced with longer cooling periods, or less pronounced with shorter cooling periods. Unlike shrinkage, sagging can be decisively influenced by changing the parameters of the extruder and the cooling parameters of the tubular object. 【0022】 A tubular object manufactured in an extruder is transported along the longitudinal axis in the transport direction during measurement. The tubular object is in particular a tube, for example, a plastic tube. This may be a multilayer tube. The tubular object may also be a cable, in which a tubularly formed hollow space extends in the front-to-back direction and is filled with one or more electrical conductors. According to the present invention, a first wall thickness measuring device is used to measure at least one wall portion of a tubular object at a first measuring position located in the transport direction upstream of at least one cooling section for the tubular object. As is known, an object manufactured in an extruder passes through one or more cooling sections, where the object is continuously cooled, for example by spraying a coolant. At the first measuring position, the tubular object coming out of the extruder at a high temperature is still hot, so the object still has a particularly fluid component, i.e., a molten component. 【0023】 According to the present invention, a second wall thickness measuring device is used to measure the wall thickness of at least one wall portion of a tubular object at a second measuring position located downstream of the first measuring position in the transport direction. At the second measuring position, which may be located downstream of at least one cooling section located between the first and second measuring positions, the temperature of the object has already cooled so that at least the still fluid components are reduced, or preferably it has reached an essentially cooled state, i.e., a completely hardened state. Therefore, the first wall thickness measuring device measures the wall thickness value at high temperature, but this value changes regularly as it cools further, and the second wall thickness measuring device can measure the cold value and final wall thickness of the tubular object. 【0024】 The wall thickness measurement from the first wall thickness measuring device is transmitted to the evaluation device via a delay stage, and this delay time corresponds to the transport time of the object between the first and second measurement positions. The evaluation device then receives the wall thickness measurement from the second wall thickness measuring device without any delay caused by the delay stage. The evaluation device compares the wall thickness measurement from the first wall thickness measuring device, which has been delayed by the delay stage, with the wall thickness measurement from the second wall thickness measuring device. Thus, the evaluation device compares the wall thickness measurements from the first and second wall thickness measuring devices, obtained at the same position in the transport direction of the tubular object, with each other due to the relative time difference caused by the delay stage. This means that the wall thickness measurements are compared at the same position, making it possible to accurately confirm the actual change in the wall thickness value between the first and second measurement positions. Naturally, it is also possible to introduce further delays to the wall thickness measurements from the first and second wall thickness measuring devices, and since the delay is the same for both wall thickness measuring devices, the wall thickness measurements continue to be compared at the same position. 【0025】 Based on the comparison performed by the evaluation device, the device confirms the ratio of the outlet widths, more precisely the ratio of the wall thicknesses, of the extruded material set at the top and bottom of the extrusion nozzle. As explained, sagging has a particularly significant effect on changing the wall thicknesses of the top and bottom of a tubular object because, during sagging, the fluid components of the object sag downwards due to gravity. By using the wall thickness measurement according to the present invention and the comparison of the wall thickness measurements obtained at the same location between the first and second measurement positions, the actual sagging that has occurred can be reliably determined. This can then be used as a basis for setting the outlet widths of the top and bottom of the extruded nozzle, particularly the extruded material produced by the extruded nozzle, thereby obtaining the desired final shape of the tubular object. If the final cold value of the wall thickness has already been measured at the second measurement position, the extrusion nozzle can be controlled, for example, so that the wall thicknesses of the top and bottom of the tubular object are the same at this point. If further sagging is expected at the second measurement position, the extrusion nozzle can be set accordingly so that the wall thickness of the top of the tubular object is still considerably larger than the wall thickness of the bottom at the second measurement position. 【0026】 According to the present invention, this enables a simplified method of thermal-cooling closed-loop control of an extruder based on actual measurements at first and second measurement positions, particularly taking sagging into consideration. By comparing wall thickness measurements at the same position via a delay stage, resulting distortion due to changes along the longitudinal direction of a tubular object is eliminated, for example, as part of the startup of a production system including an extruder. The delay stage may be integrated into, for example, an evaluation device. The delay stage can be implemented in software or hardware, for example, in the form of runtime memory or a shift register. 【0027】 To measure the wall thickness at the first and second measurement positions, the first and second wall thickness measuring devices may in particular comprise a transmitter that emits measurement radiation that at least partially passes through the object. This may be, for example, electromagnetic radiation through which the object is at least partially transparent. The radiation is reflected at the boundary surface of the object, in particular at the boundary surface of the wall of the object. Thereby, each wall thickness can be determined, for example, using runtime evaluation. 【0028】 According to an embodiment, the first measurement position may be arranged downstream of the first cooling section for the tubular object and upstream of at least one further cooling section, and the second measurement position may be arranged downstream of all the cooling sections for the tubular object. The first measurement position may in particular be arranged downstream of only one cooling section and upstream of a plurality of further cooling sections. At the first measurement position, the tubular object already has a partially defined shape. At the same time, the object still has a fluid component that is affected by dripping during further cooling. However, at the second measurement position, the object is essentially completely cured in the aforementioned embodiment. 【0029】 According to a further embodiment, the first wall thickness measuring device at the first measurement position can measure the wall thickness at at least one measurement position at the upper part and at least one measurement position at the lower part of the tubular object, and the second wall thickness measuring device at the second measurement position can measure the wall thickness at at least one measurement position at the upper part and at least one measurement position at the lower part of the tubular object. The measurement of the wall thickness at the upper part of the tubular object can be carried out, for example, at the highest point of the object. Accordingly, the lower measurement can be carried out at the lowest point of the object. Measuring and comparing the upper and lower wall thicknesses between the first and second measurement positions of the tubular object is particularly important when considering dripping as described above, because dripping appears particularly prominently in the change of the upper and lower wall thicknesses. 【0030】 The evaluation device can also be designed to take into account the sag coefficient when comparing wall thickness measurement values, and this sag coefficient indicates the expected sag of the tubular object between the first measurement position and the second measurement position. In particular, the evaluation device can be designed to confirm the sag coefficient and adapt it as necessary by comparing the wall thickness measurement values. Furthermore, the evaluation device can be designed to compare the actual sag of the tubular object between the first measurement position and the second measurement position with the sag expected particularly according to the sag coefficient between the first measurement position and the second measurement position based on the comparison of the wall thickness measurement values. 【0031】 The sag coefficient indicates the expected degree of sag. A larger sag coefficient indicates a greater expected degree of sag. The volumetric or mass flow rate of the still-flowable viscous material of the object is approximately proportional to the sag coefficient. In this way, the sag coefficient represents an index at each measurement position, from which it is possible to estimate the extent to which the regularly and intentionally set difference between the wall thicknesses exiting the extrusion nozzle in the upper and lower regions will still change as the extrusion line progresses. Based on the sag coefficient, by setting the annular spacing of the extrusion nozzles and / or appropriately setting the temperature of the extrusion nozzles of the extruder, it is possible to achieve the desired, generally uniform wall thickness of the object around its entire circumference, while retaining some sag. As will be described in more detail below, according to the present invention, it is also possible for the first and / or second wall thickness measuring devices to measure the refractive index of the object at the first and / or second measurement positions, respectively. The sag coefficient can also be described as the product of the refractive index difference between the refractive index measured at the first measurement position and the cold value of the refractive index, and a constant coefficient. The cold value of the refractive index may be present, in particular, at the second measurement position. The refractive index is known to be temperature-dependent and changes periodically between the first and second measurement positions. The sag coefficient can be determined, for example, initially empirically. If the measurement according to the present invention reveals that the determined sag coefficient does not apply to the respective manufacturing process or production system, it can be adapted accordingly. The evaluation apparatus may also be designed to compare the ratio of the upper and lower wall thicknesses of the tubular object at the first measurement position with the ratio of the upper and lower wall thicknesses of the tubular object at the second measurement position in order to compare the actual sag with the expected sag. 【0032】 Furthermore, the evaluation device may be designed to adapt a sag coefficient when a deviation between the actual sag and the expected sag is detected, and / or to display a target ratio of the outlet width of the extruded material at the top and bottom of the extrusion nozzle, which results from a desired wall thickness shape of the tubular object, and / or to set this ratio by controlling the extruder. 【0033】 The outlet width or wall thickness of the extruded material at the top and bottom of the extrusion nozzle can be adjusted by mechanically setting the outlet spacing at the top or bottom of the extrusion nozzle, as described above. Alternatively or additionally, the outlet width can also be affected by controlling the temperature of the extrusion nozzle, particularly by controlling different temperatures at the top and bottom of the extrusion nozzle. 【0034】 In particularly practical configurations, the first and / or second wall thickness measuring device may include a terahertz measuring device or an X-ray measuring device. Using a terahertz measuring device, terahertz radiation in a wavelength range of, for example, 1 GHz to 6 THz is irradiated onto the tubular object. Similar to X-rays, this radiation can penetrate the object, especially if the tubular object or cable contains common plastic materials. The aforementioned measuring devices are particularly suitable for challenging manufacturing conditions in the context of extrusion lines, where vapor formation and contamination that can interfere with optical measurements often occur, as they do not use optical radiation such as laser radiation. In the case of an X-ray measuring device, it should be noted that X-rays must be irradiated horizontally onto the object, for example, to measure the upper and lower wall thicknesses. 【0035】 In a further embodiment, the first and / or second wall thickness measuring device may be a portable, handheld measuring device. Therefore, it is a measuring device that can be carried by an operator and can be flexibly used as needed at the first and / or second measurement locations. In particular, when using a portable wall thickness measuring device, according to a further configuration, the first and second wall thickness measuring devices can be formed by the same wall thickness measuring device. In this case, the wall thickness may be measured, for example, first at the first measurement location and then at the second measurement location. The wall thickness measurements obtained in each case can then be compared with each other at the same location by delaying the wall thickness measurement obtained at the first measurement location via a delay stage according to the transport speed of the tubular object. Advantageously, in this embodiment, only one wall thickness measuring device is required. 【0036】 In order to ensure a defined measurement alignment at the first and / or second measurement positions, according to further embodiments, the holders for the first and / or second wall thickness measuring devices may be positioned at the first and / or second measurement positions. The first and / or second wall thickness measuring devices may be detachably held in the holder. This is particularly advantageous in relation to portable wall thickness measuring devices. 【0037】 In a further embodiment, the evaluation apparatus may be further designed to determine the refractive index of the material of the tubular object at a first measurement position and a second measurement position from the wall thickness measurement values ​​obtained from a first wall thickness measuring device and a wall thickness measurement value obtained from a second wall thickness measuring device. 【0038】 As already explained, the refractive index is temperature-dependent and therefore changes regularly between the first and second measurement positions. In particular, in the case of the wall thickness measuring device illustrated above, the wall thickness is first measured optically and then converted to the geometric wall thickness using the refractive index. Knowledge of the refractive index of the material is very important in determining the geometric wall thickness. The refractive index is not only temperature-dependent but also changes, for example, due to changes in the proportion of additives that are usually added to plastics that are extruded, and the exact proportion of the additives is often not precisely known, and the proportion of the additives may also change. The refractive index determined by the present invention can be appropriately taken into consideration when determining the wall thickness at the first and / or second measurement positions. The sag coefficient can also be determined based on this, in particular due to the aforementioned relationship between the sag coefficient and the difference in refractive index between the cold values ​​of the refractive index at the first measurement position and especially at the second measurement position. 【0039】 Furthermore, to determine the refractive index, the first and / or second wall thickness measuring device may have, for example, a reflector that reflects terahertz measuring radiation. The terahertz wall thickness measuring device may include a terahertz transceiver that integrates a terahertz transmitter and a terahertz receiver. For example, the refractive index can be determined by comparing the propagation time of measuring radiation emitted from a measuring device in which the tubular object is not positioned in the beam path of the measuring radiation with the transit time of measuring radiation in which the tubular object is positioned in the beam path of the measuring radiation. This procedure for measuring the unknown refractive index of an object is described, for example, in European Patent No. 3 265 748 B1. The measurement of the refractive index can be carried out in the corresponding manner in the present invention. However, it is also possible to determine the refractive index by optically determining the wall thickness of the tubular object using the measuring device, further determining the outer and inner diameters of the tubular object using the measuring device, and then determining the refractive index of the tubular object by comparing the determined outer and inner diameters with the optically determined wall thickness. This alternative method for measuring an unknown refractive index is described, for example, in German Patent Publication No. 10 2018 128 248 A1. Again, this procedure is applicable in the present invention as well. 【0040】 In further embodiments, the evaluation apparatus may be designed to take into account, when verifying the settings of the extruder, material parameters of the tubular object, in particular thermal conductivity and / or heat capacity, and / or manufacturing parameters, in particular the temperature of the extruder nozzle and / or the discharge speed of the extruder and / or the cooling parameters of the tubular object being manufactured. In particular, changes to the aforementioned material and / or manufacturing parameters may be taken into consideration. The material or manufacturing parameters described above particularly affect sag and sag coefficient. 【0041】 The apparatus according to the present invention may further include an extrusion apparatus and / or at least one cooling unit and / or a conveying apparatus for conveying a tubular object along the conveying direction and / or a tubular object. 【0042】 The apparatus according to the present invention is suitable for carrying out the method according to the present invention. Therefore, the method can be carried out by the apparatus according to the present invention. [Brief explanation of the drawing] 【0043】 Exemplary embodiments of the present invention will be described in more detail below with reference to the drawings. 【0044】 [Figure 1] A schematic side view of the apparatus according to the present invention. [Figure 2] Partial cross-sectional view of the apparatus shown in Figure 1. [Modes for carrying out the invention] 【0045】 Unless otherwise specified, the same reference numeral indicates the same object in the figure. 【0046】 In Figures 1 and 2, a tubular object 10, in this example a tube 10, specifically a plastic tube 10, is shown, having a wall portion 12, a hollow space 14 partitioned by the tube 10, an outer surface 16 with a circular cross-section, and an inner surface 18, also with a circular cross-section, that partitions the hollow space 14. In this embodiment, the tube 10 is extruded by an extruder in an extruder 20 and transported along its longitudinal axis from left to right in Figure 1 using a suitable transport device. After exiting the extruder 20, for example, an annular extrusion nozzle, the tube 10 first passes through a first cooling section 22. The tube 10, having exited the extrusion nozzle, is strongly heated and not yet completely solidified, i.e., still containing recrystallized components and fluid components (molten material), and is cooled in this first cooling section 22. The first cooling section 22 may include a calibration device, particularly a calibration sleeve, against which the tube 10 is pressed, for example, by vacuum and atmospheric pressure inside the tube 10. This determines the final outer diameter of the tube 10 preformed by the extrusion nozzle. As the process progresses, the tube 10 passes through a first wall thickness measuring device 24, in this invention a terahertz measuring device 24, where the refractive index and wall thickness are determined in a manner that will be described in more detail below. Following the first terahertz measuring device 24, the tube 10 passes through at least one further cooling section 26, where it is further cooled. The dashed line on the tube 10 indicates that further cooling sections 26 may be provided. After the tube 10 has completely solidified, it is cut to a predetermined length, for example, with a length cutting device 28 having a flying saw. 【0047】 The structure and function of the first terahertz measuring device 24 will be described in more detail with reference to Figure 2. In the illustrated example, the first terahertz measuring device 24 comprises a transceiver 30 that combines a transmitter and a detector for terahertz radiation. The transmitter irradiates the tube 10 with terahertz radiation 32. The terahertz radiation is reflected by different interfaces of the tube 10 and by a reflector 34 positioned opposite the transceiver 30, and returns to the transceiver 30, where it is detected by the detector. The transceiver 30 is further connected to an evaluation device 38 via line 36. The reflected radiation received by the detector generates a corresponding measurement signal, which is transmitted to the evaluation device 38 via line 36. In this way, the evaluation device 38 can determine, for example, the wall thicknesses 40, 42 shown in Figure 2, using, for example, measurements of propagation time. The evaluation device 38 can also determine the refractive index of the tube material based on the measurement signal received by the detector, as described, for example, in International Patent Publication WO 2016 / 139155 A1 or German Patent Publication 10 2018 128 248 A1. 【0048】 For example, at the measurement position shown in Figure 1, the wall thickness 40, 42 and refractive index of the tube 10 are determined using the first terahertz measuring device 24, where the tube 10 is not yet completely solidified, meaning that it still contains a fluid component. The transceiver 30 rotates, for example, along a circular path around the tube 10, and thus the wall thickness and refractive index can be determined at various positions on the circumference of the tube 10. The reflector 34 is similarly rotatable around the tube 10. However, the reflector 34 can be omitted. 【0049】 The second wall thickness measuring device 25, in the present invention the terahertz measuring device 25, is positioned between at least one further cooling unit 26, particularly the last cooling unit 26, and the length cutting device 28. The second terahertz measuring device 25 also includes a transceiver 27 that combines an transmitter and a detector for terahertz radiation. On the opposite side of the tube 10 is another reflector 29 for terahertz radiation. This reflector receives the terahertz radiation 31 emitted from the transmitter, which is emitted through the tube 10, reflected at the interface of the tube 10, and then reflected back to the detector. 【0050】 At a second measurement location where the tube 10 is substantially completely hardened, the second terahertz measuring device 25 measures the refractive index of the tube 10 and the wall thickness at least at the top and bottom of the tube 10. The second terahertz measuring device can operate in the same manner as the first terahertz measuring device described above. For example, the second terahertz measuring device 25 may be a portable, handheld measuring device. In this case, a holder for the second terahertz measuring device 25 may be provided at the second measurement location, and the device may be detachably inserted into the holder. The wall thickness, refractive index, etc., can be measured by the method described above. The measurement results from the second terahertz measuring device 25 are also available to the evaluation device 38. 【0051】 The evaluation device 38 further includes a delay stage, the delay time of which corresponds to the transport time between the first and second measurement positions of the tube 10. The measurement from the first terahertz measuring device 24 is delayed by the delay stage compared with the measurement from the second terahertz measuring device 25. The evaluation device 38 compares the measurement from the first terahertz measuring device 24, delayed by the delay stage, with the measurement from the second terahertz measuring device 25, thereby comparing the measurements obtained at the same position on the object 10 with each other. By comparing the measurement, in particular the wall thickness measurements obtained at the top and bottom of the tube 10 at the first and second measurement positions, a sag coefficient indicating the expected sag between the first and second measurement positions can be confirmed, for example, empirically. For this purpose, the evaluation device 38 can compare the ratio of the wall thicknesses at the top and bottom of the tube 10 at the first measurement position with the ratio of the wall thicknesses at the top and bottom of the tube 10 at the second measurement position. If a deviation from the expected sag is detected by the sag coefficient, this can be presented to the operator, for example, by the evaluation device 38, and / or the sag coefficient can be corrected accordingly. The evaluation device 38 can also control the extruder 20 to adapt the outlet width of the extruded material at the top and bottom of the extruder nozzle, more precisely, the wall thickness of the extruded material, so that a desired ratio of the upper and lower wall thicknesses of the tube 10 is obtained at the second measurement position. To set the outlet width, for example, the annular gap of the extruder nozzle can be mechanically adjusted and / or the temperature of the extruder nozzle of the extruder 20 can be adapted. The sag coefficient can also be verified using the refractive index measured at the first and second measurement positions. Furthermore, the geometric wall thickness at the first and second measurement positions can be determined based on the refractive index measurements. [Explanation of Symbols] 【0052】 10 tubular object 12 Wall 14 Hollow space 16 Exterior 18. Inner self 20 Extruder 22 Cooling section 24. First terahertz measuring device (first wall thickness measuring device) 25. Second terahertz measuring device (second wall thickness measuring device) 26 Cooling section 27 Transceivers 28 Length cutting device 29 Reflector 30 transceivers 31 Terahertz radiation 32 Terahertz radiation 34 Reflector 36 lines 38 Evaluation device 40,42 wall thickness

Claims

[Claim 1] A device for checking the settings of an extrusion device (20) that manufactures a tubular object (10) that is conveyed in the conveying direction, wherein the extrusion device (20) is set up so that extrusion materials of different outlet widths come out from the upper and lower parts of the extrusion nozzle of the extrusion device (20), - A first wall thickness measuring device (24) for measuring the wall thickness (40, 42) of at least one wall portion of the tubular object (10) at a first measuring position located upstream of at least one cooling unit (26) for the tubular object (10) in the transport direction, - A second wall thickness measuring device (25) for measuring the wall thickness (40, 42) of at least one wall portion of the tubular object (10) at a second measuring position located downstream of the first measuring position in the transport direction, - An evaluation device (38) to which the wall thickness measurement values ​​from the first wall thickness measuring device (24) and the wall thickness measurement values ​​from the second wall thickness measuring device (25) are applied, wherein the wall thickness measurement value from the first wall thickness measuring device (24) is delayed compared to the wall thickness measurement value from the second wall thickness measuring device (25) by a delay stage of the device, and the delay time corresponds to the transport time of the object (10) between the first measurement position and the second measurement position. - The evaluation device (38) is designed to check the ratio of the outlet width at the top and the outlet width at the bottom of the extrusion nozzle of the extrusion material set in the extrusion device (20) by comparing the wall thickness measurement value from the first wall thickness measuring device (24) with the wall thickness measurement value from the second wall thickness measuring device (25), and the wall thickness measurement value from the first wall thickness measuring device is delayed by the delay stage. [Claim 2] The apparatus according to claim 1, characterized in that the first measurement position is located downstream of the first cooling unit (22) for the tubular object (10) and upstream of at least one further cooling unit (26), and the second measurement position is located downstream of all the cooling units (22, 26) for the tubular object (10). [Claim 3] The apparatus according to one of claims 1 and 2, characterized in that a first wall thickness measuring device (24) located at the first measurement position measures the wall thickness (40, 42) at at least one measurement position on the upper part of the tubular object (10) and at least one measurement position on the lower part of the tubular object, and a second wall thickness measuring device (25) located at the second measurement position measures the wall thickness (40, 42) at at least one measurement position on the upper part of the tubular object and at least one measurement position on the lower part of the tubular object (10). [Claim 4] The apparatus according to claim 3, characterized in that the evaluation device (38) is designed to take into account a sag coefficient when comparing the wall thickness measurements, wherein the sag coefficient indicates the expected sag of the tubular object (10) between the first measurement position and the second measurement position. [Claim 5] The apparatus according to claim 4, characterized in that the evaluation device (38) is designed to confirm the sagging coefficient based on the wall thickness measurement value and to adapt it as necessary. [Claim 6] The apparatus according to claim 5, characterized in that the evaluation device (38) is designed to compare the actual sagging of the tubular object (10) between the first measurement position and the second measurement position with the sagging between the first measurement position and the second measurement position, based on a comparison of the wall thickness measurements. [Claim 7] The apparatus according to claim 6, characterized in that the evaluation apparatus (38) is designed to compare the ratio of the upper and lower wall thicknesses of the tubular object (10) at the first measurement position with the ratio of the upper and lower wall thicknesses of the tubular object (10) at the second measurement position in order to compare the actual sagging with the expected sagging. [Claim 8] The apparatus according to claim 6 or 7, characterized in that the evaluation device (38) is designed to adapt the sag coefficient when a deviation between the actual sag and the expected sag is detected, and / or to display a target ratio of the outlet width of the extruded material at the upper and lower parts of the extrusion nozzle, which results from a desired wall thickness shape of the tubular object (10), and / or to set this ratio by controlling the extruder (20). [Claim 9] The apparatus according to one of the above claims, characterized in that the first and / or second wall thickness measuring devices (24, 25) comprises a terahertz measuring device (24, 25) or an X-ray measuring device. [Claim 10] The apparatus according to one of the above claims, characterized in that the first and / or second wall thickness measuring devices (24, 25) are portable, handheld measuring devices. [Claim 11] The apparatus according to claim 10, characterized in that the first and second wall thickness measuring devices (24, 25) are formed by the same wall thickness measuring device. [Claim 12] The apparatus according to claim 10 or 11, characterized in that the holders of the first and / or second wall thickness measuring devices (24, 25) are arranged at the first measurement position and / or the second measurement position. [Claim 13] The apparatus according to one of the above claims, characterized in that the evaluation device (38) is further designed to determine the refractive index of the material of the tubular object (10) at the first measurement position and the second measurement position from the wall thickness measurement value obtained from the first wall thickness measuring device (24) and the wall thickness measurement value obtained from the second wall thickness measuring device (25). [Claim 14] The apparatus according to one of the above claims, characterized in that the evaluation device (38) is designed to take into consideration the material parameters of the tubular object (10), particularly thermal conductivity and / or heat capacity, and / or manufacturing parameters, particularly the temperature of the extrusion nozzle and / or the discharge speed of the extrusion device (20), and / or the cooling parameters of the tubular object (10) being manufactured, when checking the settings of the extrusion device (20). [Claim 15] The apparatus according to one of the above claims, further comprising the extrusion apparatus (20), and / or the at least one cooling unit (22, 26), and / or a conveying apparatus for conveying the tubular object (10) along the conveying direction, and / or the tubular object (10). [Claim 16] A method for confirming the settings of an extruder (20) for manufacturing a tubular object (10) that is conveyed in a conveying direction, wherein the extruder (20) is set up using an apparatus according to one of the above claims so that extruded material of different outlet widths comes out from the upper and lower parts of the extruder nozzle of the extruder (20).

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