Apparatus and method for determining the temperature of a tubular strand

Abstract

The present invention relates to an apparatus for determining the temperature of a tubular strand (12) conveyed from an extrusion device (10), the apparatus comprising a first temperature sensor (30) for measuring a first temperature on the outside of the tubular strand (12) at a first position on the tubular strand (12), and an evaluation mechanism (28) designed to compare the first temperature with a second temperature on the outside of the tubular strand (12) at a second position on the tubular strand (12) spaced from the first position in the conveying direction (14) of the tubular strand (12), and to determine the temperature within and / or inside the tubular strand (12) at a certain position on the tubular strand (12) from a comparison of the first and second temperatures. The present invention also relates to a corresponding method.

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for determining the temperature of a tubular strand conveyed from an extrusion device. [Background technology]

[0002] In the extrusion device, for example, a plastic tube is extruded. After the plastic tube exits the extrusion device, it typically passes through a calibration mechanism having, for example, a metallic calibration sleeve against whose inner surface the plastic tube is pressed, e.g., sucked, to define its outer shape. Following the calibration mechanism, the plastic tube also typically passes through one or more cooling sections in which a cooling liquid, such as chilled water, is sprayed on the outside of the tube to cool it.

[0003] The fundamental objectives of the extrusion process for producing tubular strands are to achieve minimal sagging, i.e., minimal deviation in the wall thickness of the finished strand over its circumference, minimal energy input, and maximum transport speed of the extruded strand. Accurate knowledge of the production process is crucial for optimizing these parameters. For example, the measurement of various geometric parameters, such as the wall thickness of a tubular strand, is known from Patent Document 1. In this case, terahertz waves in the range of 10 GHz to 3 THz are emitted toward the strand to be measured, and the terahertz waves reflected from the strand's boundaries are received again. For example, transit time measurements can be used to reliably determine the distance to the boundaries and, from this, geometric parameters such as diameter and wall thickness. In addition to the geometric parameters measured in this way, the temperature of the tubular strand is also an important process parameter. For non-contact measurement of surface temperatures, pyroelectric sensors (PIR sensors) are known. For example, Patent Document 2 proposes measuring the temperature on the inner circumference of a tubular strand by means of a measuring mechanism guided inside the tubular strand, which directly follows the extrusion device. However, it is not easy to insert a sensor inside a tubular strand, and in addition this is basically only possible following a direct extrusion device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2016 / 139155 [Patent Document 2] International Publication No. 2019 / 166420 Summary of the Invention [Problem to be solved by the invention]

[0005] Starting from the prior art described, the object of the present invention is to provide an apparatus and a method that allows obtaining more accurate information, in particular about the temperature of the tubular strand, and thus optimizing the manufacturing process. In particular, the object of the present invention is also to improve the measurement accuracy during calculation of the diameter and / or wall thickness of the tubular strand at the measurement location, as well as its length, its wall thickness, and its diameter after cooling of the tubular strand. [Means for solving the problem]

[0006] The invention achieves this object by means of independent claims 1 and 17. Advantageous embodiments are disclosed in the dependent claims, the description and the drawings.

[0007] With respect to a device of the type described above, the invention achieves the object in that a first temperature sensor is provided for measuring a first temperature on the outside of the tubular strand at a first position on the tubular strand, and an evaluation mechanism is provided which is designed to compare the first temperature with a second temperature on the outside of the tubular strand at a second position on the tubular strand spaced from the first position in the conveying direction of the tubular strand, and to determine the temperature within the tubular strand and / or inside the tubular strand at the position of the tubular strand from the comparison of the first and second temperatures.

[0008] With respect to a method of the type described above, the invention achieves the object in that a first temperature on the outside of the tubular strand is measured at a first position on the tubular strand, the first temperature is compared with a second temperature on the outside of the tubular strand at a second position on the tubular strand spaced from the first position in the direction of travel of the tubular strand, and from the comparison of the first temperature and the second temperature, the temperature within the tubular strand and / or inside the tubular strand at the position of the tubular strand is determined.

[0009] The device according to the invention can comprise an extrusion device and / or a conveying mechanism for conveying the tubular strand. The device according to the invention can also comprise a tubular strand. The tubular strand can be, for example, a plastic tube. However, the tubular strand can also be, for example, a glass fiber tube or another strand. The device according to the invention can comprise one or more cooling sections through which the extruded tubular strand passes and in which, for example, a cooling liquid is sprayed onto the outside of the strand for cooling. The device according to the invention can also comprise a calibration mechanism, for example, a metallic calibration sleeve into which the tubular strand is pressed, for example, by suction, after leaving the extrusion device. Any cooling section can be located, in particular, downstream of the calibration mechanism.

[0010] According to the present invention, a first temperature on the outside of the tubular strand is measured by a first temperature sensor at a first position on the tubular strand. The measured first temperature is compared with a second temperature on the outside of the tubular strand at a second position on the tubular strand, the second position being spaced apart from the first position in the conveying direction of the tubular strand. The first and second positions are positions along the conveying direction of the strand. These positions are spaced apart from each other in the longitudinal direction of the strand. The second position can be, for example, located upstream of the first position in the conveying direction of the strand. However, the second position can also be located downstream of the first position in the conveying direction. The temperatures at the first and second positions can be measured or determined simultaneously, in particular. However, this is not required. Rather, the first and second temperatures can be measured or determined at different times, whereby the same strand area is measured, for example, taking into account the conveying speed of the strand.

[0011] The second temperature can be measured, estimated, or determined in a known manner. For example, the temperature of the calibration sleeve, against which the strand is pressed to define its outer shape, can be estimated at the exit of the calibration mechanism as the temperature of the outside of the strand at this location. The strand cools after extrusion. The cooling is usually enhanced or controlled by one or more cooling sections through which the strand passes. The cooling sections usually affect the outside of the strand and introduce forced cooling into the material. As a result, especially immediately after passing through the cooling section, the strand initially has a lower temperature on its outside than on its inside, especially its interior, which is not directly affected by the cooling. At the end of the cooling on the outside, i.e., after leaving the cooling section, at the end of the forced cooling, the higher temperature prevailing on the inside of the strand spreads outward again. As a result, the temperature on the outside of the strand initially rises again after cooling. The temperature of the inside, especially its interior, of the strand can be inferred from the level of this temperature increase. To determine the temperature within and / or inside the tubular strand, the strand conveying speed, thermal conductivity and heat capacity of the strand material, as well as the wall thickness of the tubular strand are known from the calculation, in addition to the locations of the first and second temperatures being compared. Based on these parameters, the temperature difference between the outside and the inside of the strand, and therefore the temperature inside and also inside the strand, can be inferred from the temperature comparison. Any energy output of the tubular strand to the surroundings can be ignored here. In this way, the temperature inside the strand can be reliably ascertained by temperature measurement on the outside of the strand, which is simple and flexible to implement, without even placing sensors inside the strand, and thus far downstream in the extrusion device. Furthermore, useful information about the manufacturing process can be obtained from this and used as a control or regulating variable for the process. Therefore, the optimization of the aforementioned parameters of minimum sagging, minimum energy input, and maximum tube conveying speed is more easily possible. If the expansion coefficient is known, the expected dimensions of the tubular strand after its cooling can also be determined more accurately.If the temperature at the wall of the tubular strand is known, its temperature dependent attenuation of the terahertz wave, as well as changes in refractive index, can also be taken into account in analyzing the wall thickness and diameter values.

[0012] The location for determining the temperature in and / or inside the tubular strand may be a third location that is spaced apart from the first and second locations in the conveying direction of the tubular strand. However, it may be simpler for the calculation evaluation if the location for determining the temperature in and / or inside the tubular strand is the same as the first location or the same as the second location. This location may, for example, be the same as one of the first and second locations that is located closer to the extrusion device in the conveying direction of the strand.

[0013] According to one embodiment, a second temperature can also be measured. For this purpose, a second temperature sensor can be provided. By measuring the second temperature in the same way, the inside temperature can be determined particularly reliably.

[0014] According to another embodiment, it is also possible for the first temperature sensor to be designed to measure the second temperature. In this case, in a particularly preferred manner, only one temperature sensor is required. The use of only one temperature sensor can also be advantageous in terms of measurement reliability, since no falsification of the measurement result due to different properties or respective changes in the temperature sensors is to be expected.

[0015] At least the first temperature sensor can be a non-contact temperature sensor, in particular a pyroelectric sensor (PIR sensor). If a second temperature sensor is also provided, it can also be a non-contact temperature sensor, in particular a pyroelectric sensor. Such a sensor provides simple and reliable non-contact measurement, even when the object being measured is very hot. In addition, this sensor technology easily enables temperature measurement at various positions using only one temperature sensor, which in this case detects the thermal radiation of the outer surface of the strand at various angles. This is particularly advantageous if the temperature sensors absorb the thermal radiation of the strand surface at the same angle, i.e., symmetrically. As a result, falsification of the measurement results due to different detection angles is avoided.

[0016] According to another embodiment, at least a first temperature sensor can be arranged so that a first temperature is measured after the tubular strand passes through a cooling section arranged downstream of the extrusion device. If a second temperature sensor is also present, it can be arranged so that a second temperature is similarly measured after the tubular strand passes through a cooling section arranged downstream of the extrusion device. As explained, a cooling liquid, for example, cooling water, is sprayed onto the outside of the strand for cooling in the cooling section. In particular, the first temperature sensor and, if applicable, the second temperature sensor can be arranged so that the first temperature or, respectively, the second temperature is measured after the tubular strand passes through a first cooling section arranged downstream of the extrusion device and before the tubular strand passes through a second cooling section arranged downstream of the first cooling section. Therefore, in this case, a measurement is performed between the two cooling sections. As explained above, the measurement method according to the invention makes it possible to reliably determine the temperature inside the strand, especially after completion of the (first) cooling of the outside of the strand, based on the reheating of the outside of the strand that occurs after completion of the cooling.

[0017] According to a particularly practical embodiment, the evaluation mechanism can be designed to determine the temperature within and / or inside the tubular strand from the comparison of the first and second temperatures, in particular using a finite element iterative method. Such a finite element method, known to those skilled in the art, represents a numerical calculation method in which the body to be calculated, in this case a tubular strand, is divided into a finite number of subregions. Due to their regularly simple geometrical shape, the physical behavior of these so-called finite elements can be well calculated using known test functions. In this way, the physical behavior of the entire body, in this case the spread of a higher internal temperature to the outside of the tubular strand, can be well modeled. In the case of a small wall thickness compared to the diameter of the tubular strand, a linear temperature curve between the inside and outside of the tubular strand can be estimated with good approximation. This simplifies the calculation of the internal temperature. As an iterative calculation method for calculating the internal temperature, the internal temperature can be estimated, for example, in a first step, and whether this internal temperature corresponds to the measured external temperature can be calculated using the finite element method. If this is not the case, the estimated inside temperature is changed and the calculation is checked again, thus allowing the actual inside temperature to be determined iteratively.

[0018] According to another embodiment, it can be provided that the first temperature sensor measures a first temperature at a plurality of positions distributed over the circumference of the tubular strand at a first location, and that the evaluation mechanism is designed to compare the temperatures measured at the plurality of positions distributed over the circumference of the tubular strand with a second temperature at a plurality of positions distributed over the circumference of the tubular strand at a second location, and to determine from this comparison the temperature in and / or inside the tubular strand at the plurality of positions distributed over the circumference of the tubular strand at the tubular strand. The second temperature can also be measured at the plurality of positions distributed over the circumference of the tubular strand at the second location by either the first temperature sensor or an optionally provided second temperature sensor. By measuring and determining the temperature over the circumference, additional important information about the manufacturing process can be obtained, in particular a non-uniform temperature distribution over the circumference, which, on the one hand, gives an indication of the degree of sagging of the tubular strand and, on the other hand, indicates insufficient cooling in individual regions of the circumference of the tube.

[0019] It is also possible to provide that at least the first temperature sensor is rotatable or that each is rotatable at least over a portion of the circumference of the tubular strand. If a second temperature sensor is also provided, the second temperature sensor can be rotatable or can be rotated over the circumference of the tubular strand. However, it is also possible, for example, for one temperature sensor to be designed to be rotatable, while the other temperature sensor is fixed. The rotatability or, respectively, rotation of the first and / or second temperature sensor can naturally be present or occur over the entire circumference. The first and / or second temperature can be measured at discrete positions over the circumference or essentially continuously over the circumference. By determining the temperature over the circumference of the tubular strand, the aforementioned factors of minimum sagging, i.e., minimum undesired wall thickness deviations between the upper and lower wall portions, minimum energy input, and maximum strand conveying speed can be better optimized.

[0020] According to another embodiment, the evaluation mechanism can be designed to determine the temperature of the tubular strand at multiple locations within the tubular strand, at which the temperature within the tubular strand and / or at the location of the tubular strand is determined. Thus, a radial temperature profile of the strand can be determined, from which additional important information about the manufacturing process can be obtained. Determining the temperature inside the tubular strand can be particularly practically calculated numerically by the finite element method, as explained here, since in this method the tubular strand is somehow divided, for example, into multiple radial subzones. The temperature of the tubular strand, and thus the radial temperature profile, can then be determined for each of these individual subzones.

[0021] According to another embodiment, a diameter and / or wall thickness measuring mechanism can be provided for measuring the diameter and / or wall thickness of the tubular strand at a first and / or second position on the tubular strand. In this case, the evaluation mechanism can be designed to take the measured diameter and / or wall thickness into account when determining the temperature within and / or inside the tubular strand. The evaluation mechanism can also be designed to take into account the temperature within and / or inside the tubular strand, as well as, if applicable, the temperature outside the tubular strand at the first and / or second positions, when determining the diameter and / or wall thickness. Thus, the temperature of the strand material is an important value for determining the strand's geometric parameters. For example, the refractive index of the strand material is temperature-dependent. At the same time, the refractive index is an important parameter when determining the wall thickness of the strand, for example, by a terahertz wave measuring mechanism. According to a particularly practical embodiment, the diameter and / or wall thickness measuring mechanism can comprise a terahertz wave measuring mechanism. As explained above, the diameter and wall thickness are important parameters of the manufacturing process. Additionally, accurate knowledge of the diameter or, respectively, the wall thickness can be important for accurately determining the temperature within or at the interior of the tubular strand, since the diameter, and especially the wall thickness, influence the extent to which the higher temperature inside the strand spreads to the outside. The diameter and / or wall thickness can, in principle, be assumed to be known as parameters for the calculation. However, in the case of the above-described embodiment, the actual diameter or, respectively, the actual wall thickness is measured, thus increasing the accuracy of the temperature determination, since any deviation from the expected diameter or, respectively, the expected wall thickness is taken into account. The diameter and / or wall thickness measurement can be performed, for example, as a travel time measurement of terahertz waves reflected from the strand's interfaces, in particular from the outside and the interior of the strand. For this purpose, the terahertz wave measurement mechanism can, for example, comprise a terahertz transceiver, which therefore comprises a terahertz transmitter and a terahertz receiver.The terahertz wave measurement mechanism can be rotated around the strand, thereby determining the diameter or, respectively, the wall thickness at multiple positions distributed over the circumference of the strand. In a particularly simple manner, the first and / or second temperature sensor can be integrated into the terahertz wave measurement mechanism. In this case, if appropriate, the first and / or second temperature sensor can also be rotated together with the terahertz wave measurement mechanism. Thus, the diameter or, respectively, the wall thickness and the temperature can be determined in a particularly simple manner by measuring at the same positions over the circumference of the strand. The diameter and / or wall thickness measurement mechanism can be designed, for example, as described in Patent Document 1.

[0022] According to another embodiment, the evaluation mechanism can also be designed to ascertain the expected shrinkage of the tubular strand, starting from the position of the tubular strand where the temperature in and / or inside the tubular strand is determined, until the tubular strand reaches its final shape, based on the temperature-dependent expansion coefficient of the tubular strand material. The strand material shrinks during its cooling process until it reaches its final shape, for example, when the strand reaches room temperature. If the temperature-dependent expansion coefficient of the strand material is known, the expected shrinkage until the strand reaches its final shape can be determined according to the above-mentioned embodiment, i.e., based on the temperature of the strand in and / or inside the tubular strand ascertained according to the invention, and, if applicable, also taking into account the measured temperature on the outside. This can then be advantageously used to predict certain shape parameters of the strand after it reaches its final shape. Thus, according to another embodiment, the evaluation mechanism can also be designed to ascertain the diameter and / or wall thickness of the tubular strand after it has reached its final shape, taking into account the diameter measured at the first and / or second position of the tubular strand and / or the measured wall thickness of the tubular strand, and taking into account the ascertained expected shrinkage.

[0023] According to another embodiment, the evaluation mechanism can be designed to determine the refractive index of the material of the tubular strand based on the determined temperature. It is known that the refractive index depends on temperature. This means that the refractive index of the strand material at the or each location where the temperature is determined can be inferred from the temperature measurement. This can be taken into account, for example, during wall thickness measurements using the refractive index as a parameter. As a result, wall thickness measurements can be made to a more accurate extent. For example, the refractive index can be determined at multiple locations distributed throughout the wall thickness of the strand. Thus, the refractive index distribution can be ascertained. The refractive index can also be ascertained at multiple locations distributed throughout the circumference of the strand, from which the refractive index distribution can be ascertained. Additional useful information regarding the manufacturing process, such as the composition of the material and its consistency throughout the manufacturing process, can be obtained from these refractive index distributions. In addition, the temperature-dependent absorption of the terahertz waves can be determined, and conversely, a prediction of the expected absorption can be derived by measuring the average tube temperature. If the tube is made of a material whose absorption increases strongly depending on temperature, measuring and limiting the temperature of the material can ensure that reliable wall thickness and diameter measurements can be generated. Knowing the temperature dependent expansion coefficient of the material also allows us to derive the expected degree of its shrinkage from the measurement location at the higher room temperature of the material until its final cooling.

[0024] According to another embodiment, the apparatus may also comprise a control and / or adjustment mechanism for controlling and / or adjusting the extrusion apparatus based on the determined temperature in and / or inside the tubular strand. In this way, improved control or respective adjustment of the process, in particular the extrusion apparatus, is possible based on the information obtained by the present invention.

[0025] The device according to the invention can be designed to carry out the method according to the invention. The method according to the invention can accordingly be carried out by the device according to the invention.

[0026] Exemplary embodiments of the invention are explained in more detail below on the basis of the drawings. [Brief explanation of the drawings]

[0027] [Figure 1] 1 shows a schematic side view of an apparatus according to the invention; DETAILED DESCRIPTION OF THE INVENTION

[0028] The apparatus shown in the drawings comprises an extrusion device 10 with a conveying mechanism. The tubular strand 12, which in this case is a plastic tube 12, exits the extrusion device 10 and is conveyed along its longitudinal axis in a conveying direction 14. The strand 12 passes through a first cooling section 16 and a second cooling section 18, where a cooling liquid is sprayed onto the outside of the strand 12 for cooling. A calibration mechanism (not shown), e.g., a metallic calibration sleeve, can be arranged between the extrusion device 10 and the first cooling section 16, against whose inner wall the strand 12 is pressed, e.g., sucked, for shaping the outer surface. In the region between the first cooling section 16 and the second cooling section 18, the strand 12 is accessible from the outside. This region is provided with a diameter and / or wall thickness measuring mechanism 20, depicted by a dashed line, which comprises a terahertz transceiver 22 that emits terahertz waves towards the tubular strand 12, as seen in the drawing by arrow 24. The terahertz waves penetrate the tubular strand 12 and are reflected at the boundaries of the strand 12, in particular at its outer and inner surfaces. The reflected terahertz waves are then received by the terahertz transceiver 22. The measuring mechanism 20 is connected via a data connection 26 to an evaluation mechanism 28. Based on the reflected terahertz waves, the evaluation mechanism 28 determines at least the wall thickness of the wall of the strand 12 facing the terahertz transceiver 22 and, if applicable, also the diameter as well as the wall thickness of the wall of the strand 12 facing away from the terahertz transceiver 22.

[0029] The measuring mechanism 20 also comprises a first temperature sensor 30, which in this example is a pyroelectric temperature sensor 30. The first temperature sensor 30 measures the thermal radiation emanating from the strand 12 along the directions indicated by arrows 32 and 34, thereby measuring a first temperature on the outside of the strand 12 at a first longitudinal position 36 and a second temperature on the outside of the strand 12 at a second longitudinal position 38. As can be seen in the drawing, the first temperature sensor 30 measures the first and second temperatures symmetrically along the directions 32 and 34 at the same angle relative to the surface of the strand. The measured values ​​of the first and second temperatures are also provided to the evaluation mechanism 28 via the connection 26. From a comparison of the measured first and second temperatures, the evaluation mechanism 28 calculates the temperature within and / or at the interior of the tubular strand 12, e.g., at the second location 38 of the tubular strand 12, taking into account the conveying speed of the strand 12, the heat capacity and thermal conductivity of the strand material, and the measured wall thickness and diameter of the strand 12. This calculation can be based on a finite element iterative method, as described.

[0030] For example, it is possible to determine a radial temperature profile of the tubular strand 12, for example across the wall portion facing the temperature sensor 30. The transceiver 22 and the temperature sensor 30 can also be rotated about the longitudinal axis of the strand 12, thereby making it possible to perform both wall thickness measurements and measurements of the first and second temperatures at a first location or, respectively, at a second location, at multiple locations distributed around the circumference of the strand 12. In this way, the temperature profile of the strand 12 can also be calculated inside or within the strand 12 across its circumference.

[0031] Based on the temperature values ​​ascertained inside or respectively within the strand 12, the refractive index, absorption and shrinkage of the strand material, which are known to be temperature dependent, can be determined more accurately. The better knowledge of the mentioned properties allows to generate significantly more accurate values ​​of wall thickness and diameter, both relating to the high temperature values ​​at the measurement location and also predicted after their cooling, for example to room temperature.

[0032] The wall thickness and temperature values ​​ascertained by the evaluation mechanism 28 are provided in the example shown via a data connection 40 of a control and / or regulation mechanism 42 of the device. Based on this, the control and / or regulation mechanism 42 can control and / or regulate the extrusion device 10 via another data connection 44 and, for example, a mechanism for conveying the strand 12 which the extrusion device 10 comprises. [Explanation of symbols]

[0033] 10 Extrusion equipment 12 tubular strands 14 Conveying direction 16 First cooling section 18 Second Cooling Section 20 Diameter and / or wall thickness measuring mechanism 22 Terahertz transceiver 24 Terahertz waves 26 Data connection 28 Evaluation Organization 30 Temperature Sensor 32 Temperature measurement direction 34 Temperature measurement direction 36 1st position 38 Second Position 40 Data connection 42 Control and / or Regulatory Mechanisms 44 Data Connection

Claims

1. 1. A device for determining the temperature of a tubular strand (12) conveyed from an extrusion device (10), comprising: a first temperature sensor (30) for measuring a first temperature on the outside of the tubular strand (12) at a first position on the tubular strand (12); and an evaluation mechanism (28) designed to determine a difference between the first temperature and a second temperature on the outside of the tubular strand (12) at a second position on the tubular strand (12) spaced from the first position in the conveying direction (14) of the tubular strand (12), and to determine the temperature in and / or inside the tubular strand (12) at a certain position on the tubular strand (12) from the difference between the first temperature and the second temperature; at least the first temperature sensor (30) is positioned to measure the first temperature after the tubular strand (12) has passed through a cooling section (16) located downstream of the extrusion device (10); The evaluation mechanism includes:

10. The apparatus according to claim 9, wherein the apparatus is configured to make a decision based on the second temperature being higher than the first temperature due to heat conduction from inside the tubular strand (12).

2. 2. The device according to claim 1, characterized in that a second temperature sensor (30) is provided for measuring said second temperature.

3. 2. The device according to claim 1, characterized in that the first temperature sensor (30) is also designed to measure the second temperature.

4. Device according to any one of claims 1 to 3, characterized in that at least the first temperature sensor (30) is a contactless temperature sensor.

5. 5. The device according to claim 1, wherein the evaluation mechanism (28) is designed to determine the temperature in and / or inside the tubular strand (12) from a comparison of the first temperature and the second temperature using a finite element method.

6. 6. The device according to claim 1, wherein the first temperature sensor (30) measures the first temperature at a plurality of positions distributed over the circumference of the tubular strand (12) at the first location, and the evaluation mechanism (28) is designed to compare the temperatures measured at a plurality of positions distributed over the circumference of the tubular strand (12) with the second temperatures at a plurality of positions distributed over the circumference of the tubular strand (12) at the second location, and to determine from the comparison the temperatures in and / or inside the tubular strand (12) at a plurality of positions distributed over the circumference of the tubular strand (12) at the location of the tubular strand (12).

7. 7. The device according to claim 6, characterized in that at least the first temperature sensor (30) is rotatable at least in a portion covering the circumference of the tubular strand (12).

8. 8. The device according to claim 1, wherein the evaluation mechanism (28) is also designed to determine the temperature of the tubular strand (12) at a plurality of locations within the tubular strand (12) at which the temperature within the tubular strand (12) and / or the interior of the tubular strand (12) is determined.

9. 9. The device according to any one of claims 1 to 8, characterized in that it is also provided with a diameter and / or wall thickness measuring mechanism (20) for measuring the diameter and / or wall thickness of the tubular strand (12) at the first position and / or the second position of the tubular strand (12).

10. 10. The device according to claim 9, wherein the evaluation mechanism (28) is designed to take into account the measured diameter and / or the measured wall thickness when determining the temperature in and / or inside the tubular strand (12) and / or the evaluation mechanism (28) is designed to take into account the temperature in and / or inside the tubular strand (12) when determining the diameter and / or the wall thickness.

11. 11. Apparatus according to claim 9 or 10, characterized in that the diameter and / or thickness measuring mechanism (20) comprises a terahertz wave measuring mechanism.

12. 12. The device according to claim 1, wherein the evaluation mechanism (28) is also designed to ascertain an expected shrinkage of the tubular strand (12) based on the temperature-dependent expansion coefficient of the material of the tubular strand (12), starting from a position of the tubular strand (12) where the temperature in and / or inside the tubular strand (12) is determined, until the final shape of the tubular strand (12) is reached.

13. 13. The device according to claims 9 and 12, characterized in that the evaluation mechanism (28) is also designed to ascertain the diameter and / or wall thickness of the tubular strand after it has reached its final shape, taking into account the diameter measured at the first and / or the second position of the tubular strand (12) and / or the measured wall thickness of the tubular strand (12), and also taking into account the ascertained expected shrinkage.

14. 14. The device according to any one of claims 1 to 13, characterized in that the evaluation mechanism (28) is also designed to determine the refractive index of the material of the tubular strand (12) based on the determined temperature.

15. 15. The apparatus according to any one of claims 1 to 14, characterized in that a control and / or adjustment mechanism (42) is also provided for controlling and / or adjusting the extrusion device (10) based on the determined temperature in and / or inside the tubular strand (12).

16. A method for determining the temperature of a tubular strand (12) being conveyed from an extrusion device (10), comprising: measuring a first temperature on the outside of the tubular strand (12) at a first location on the tubular strand (12); determining a difference between the first temperature and a second temperature on the outside of the tubular strand (12) at a second location on the tubular strand (12) spaced from the first location in a conveying direction (14) of the tubular strand (12); and determining a temperature within and / or inside the tubular strand (12) at a location on the tubular strand (12) from the difference between the first temperature and the second temperature; measuring at least the first temperature after the tubular strand has passed through a cooling section (16) located downstream of the extrusion device (10); and determining the temperature based on the second temperature, which is higher than the first temperature, due to heat conduction from inside the tubular strand (12).

17. 17. The method of claim 16, further comprising measuring the second temperature.

18. 18. A method according to claim 16 or 17, characterized in that at least the first temperature is measured contactlessly.

19. 19. The method according to any one of claims 16 to 18, characterized in that the temperature in and / or inside the tubular strand (12) is determined from a comparison of the first temperature and the second temperature using a finite element method.

20. 20. The method according to any one of claims 16 to 19, characterized in that the first temperature is measured at a plurality of locations distributed over the circumference of the tubular strand (12) at the first location, and the temperatures measured at a plurality of locations distributed over the circumference of the tubular strand (12) are also compared with the second temperatures at a plurality of locations distributed over the circumference of the tubular strand (12) at the second location, and from the comparison, the temperatures in and / or inside the tubular strand (12) at a plurality of locations distributed over the circumference of the tubular strand (12) at the location of the tubular strand (12) are determined.

21. 21. The method according to any one of claims 16 to 20, characterized in that the temperature of the tubular strand (12) is determined at a plurality of locations within the tubular strand (12) and / or at a location of the tubular strand (12) where the temperature inside the tubular strand (12) is determined.

22. 22. The method according to any one of claims 16 to 21, characterized in that the diameter and / or wall thickness of the tubular strand (12) is also measured at the first and / or second positions on the tubular strand (12).

23. 23. The method according to claim 22, characterized in that the measured diameter and / or the measured wall thickness are taken into account when determining the temperature in and / or inside the tubular strand (12) and / or the temperature in and / or inside the tubular strand (12) is taken into account when determining the diameter and / or the wall thickness.

24. 24. The method according to claim 16, characterized in that the expected shrinkage of the tubular strand (12) is ascertained based on the temperature-dependent expansion coefficient of the material of the tubular strand (12), starting from a position of the tubular strand (12) where the temperature in and / or inside the tubular strand (12) is determined, until the final shape of the tubular strand (12) is reached.

25. 25. The method according to claims 22 and 24, characterized in that the diameter and / or wall thickness of the tubular strand after it has reached its final shape is ascertained taking into account the diameter measured at the first and / or the second position of the tubular strand (12) and / or the measured wall thickness of the tubular strand (12) and taking into account the ascertained expected shrinkage.

26. The method according to any one of claims 16 to 25, characterized in that the refractive index of the material of the tubular strand (12) is determined based on the determined temperature.

27. 27. The method according to any one of claims 16 to 26, characterized in that the extrusion device (10) is controlled and / or adjusted based on the determined temperature in and / or inside the tubular strand (12).

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