Method for determining at least one geometric parameter of a strand or slab object

Abstract

The invention relates to a method for determining at least one geometric parameter of a strand-like or slab-like object which has not yet completely solidified and which has still flowable portions, comprising the steps of: in a probing step, for the strand-like or slab-like object, ascertaining a relationship between the refractive index of the strand-like or slab-like object and the shrinkage which occurs during the complete solidification thereof; in a determining step, determining the refractive index and at least one geometric parameter of the strand-like or slab-like object which has not yet completely solidified and which has still flowable portions; calculating the at least one geometric parameter of the strand-like or slab-like object in the completely solidified state from the values of the refractive index and the at least one geometric parameter determined in the determining step, taking into account the relationship ascertained in the probing step.

Description

Technical Field

[0001] The present invention relates to a method for determining at least one geometric parameter of a strand or plate-like object that has not yet fully solidified and has a still flowable portion. Background Technology

[0002] For example, a strand of plastic article is manufactured in an extrusion apparatus and conveyed along a conveying direction, for example, through a cooling section, until the plastic article is completely cooled to ambient temperature and accordingly fully hardened or solidified. Immediately after leaving the extrusion apparatus and still in another area of ​​the conveying section, the strand is not yet fully solidified and accordingly still has a flowable portion in molten form.

[0003] Methods and apparatus are known from WO 2016 / 139155 A1 and DE 10 2018 128 248 A1, which allow the determination of the refractive index of a strand or sheet-like plastic object by irradiating it with terahertz radiation and receiving the terahertz radiation reflected by the object. The refractive index is the average refractive index over a cross-section of the object or over the irradiated portion of the object. Based on this, even when the initial refractive index is unknown, the geometric parameters of the object, such as the wall thickness or diameter of a tube, can be reliably determined.

[0004] However, especially when measuring objects shortly after they leave the extrusion equipment, the geometric parameters obtained in this way may deviate from the actual geometric parameters of the object in its fully solidified state. When the object has fully solidified, i.e., no longer has any flowable parts, more reliable results can be obtained by determining the refractive index and geometric parameters later. On the other hand, it is desirable to determine the geometric parameters as soon as possible after leaving, for example, the extrusion equipment, so that the production process can be intervened as quickly as possible if incorrect parameters occur, thereby minimizing the scrap rate.

[0005] Therefore, there is a need to determine the geometric parameters of a fully cured strand or plate even when measuring a strand or plate that is not yet fully cured and still has a flowable portion. Summary of the Invention

[0006] Based on the prior art described, the object of the present invention is to be able to draw reliable conclusions about the geometric parameters of a strand or plate-like object in a fully cured state, even when the object is not yet fully cured.

[0007] The present invention achieves the stated objective by means of claim 1. Advantageous design options are given in the dependent claims, the specification, and the drawings.

[0008] For the methods of the type described above, the present invention achieves the stated objective through the following steps:

[0009] - In the investigation step, for strand-shaped or plate-shaped objects, the relationship between the refractive index of the strand-shaped or plate-shaped object and the shrinkage that occurs during its complete solidification process is determined.

[0010] - In the determination step, the refractive index and at least one geometric parameter of the strand or plate-like object that has not yet fully solidified and still has a flowable portion are determined.

[0011] - Taking into account the relationship identified in the exploration step, the at least one geometric parameter of the strand or plate-shaped object in the fully cured state is calculated from the refractive index determined in the determination step and the value of the at least one geometric parameter.

[0012] The strand-shaped or plate-shaped object studied according to the invention is in a heated state, the object being, for example, from a production device, and has not yet completely cooled to ambient temperature. Accordingly, the object is not yet fully solidified, and the object, particularly its interior, has viscous components in molten form that are not yet fully hardened, these components only hardening during further cooling. During the further cooling and thus solidification of the strand-shaped or plate-shaped object, the material of the object shrinks. The strand-shaped or plate-shaped object can be a strand or a plate, such as a plastic strand or a plastic sheet. The production equipment for producing the strand-shaped or plate-shaped object can be, for example, an extrusion device. The strand-shaped or plate-shaped object can correspondingly be a strand or plate-shaped object extruded in the extrusion device. The strand can be, for example, a tube. Furthermore, during the determination of at least one geometric parameter according to the invention, the object can be conveyed along a conveying direction, for example, along the longitudinal axis of the object.

[0013] This invention is based on the understanding that there is a mathematically well-described relationship between the refractive index of a material and the shrinkage rate that occurs during the complete curing of a strand or plate-like object. Studies have shown that at the curing center of the strand or plate-like object, the refractive index exhibits approximately inverse characteristics to geometric parameters, such as the wall thickness or diameter of a tube. As the refractive index increases with gradual curing, i.e., over time, geometric parameters such as diameter and wall thickness decrease accordingly. This will be explained in detail below with reference to the accompanying drawings. Further research shows that this relationship is specific to the corresponding strand or plate-like object, especially to the specific composition of the material. However, it exhibits good repeatability for a given material.

[0014] Based on this understanding, in the method according to the invention, for the corresponding strand or plate-like object to be determined, in the probing step, the relationship between the refractive index of the strand or plate-like object and the shrinkage process that occurs until it is fully cured is determined. According to the invention, this relationship, which can be obtained, for example, in the form of a characteristic curve, is utilized to determine the expected shrinkage of the material by determining the refractive index of the material in its partially cured state. For this purpose, in the determining step, the refractive index and at least one geometric parameter of the partially cured strand or plate-like object with a still-flowable portion are determined. From the expected shrinkage determined by the previously determined relationship, the corresponding (shrinkage) value of the geometric parameter of the strand or plate-like object in its fully cured state can now be derived from the geometric parameter determined in the partially cured state. According to the invention, taking into account the relationship determined in the probing step, the at least one geometric parameter of the strand or plate-like object in its fully cured state is calculated from the refractive index and the value determined in the determining step of the at least one geometric parameter.

[0015] As will be explained in detail below, the refractive index of plastics, in particular, is strongly nonlinearly related to temperature. The refractive index changes particularly sharply during the transition from a solid to a liquid state. The geometric parameters determined for a partially cured strand or plate-like object continue to change during further curing, especially due to shrinkage, which varies with the proportion of uncured melt within the strand or plate-like object. Here, the shrinkage rate is strongly correlated with the material composition of the strand or plate-like object and also, to a lesser extent, with its size. Accordingly, the assumption of a constant shrinkage rate made in the prior art, and the predictions of the geometric parameters determined in the partially cured state based on this, are not accurate enough for the fully cured state. To achieve better prediction of the cold-state value of at least one geometric parameter, according to the invention, the shrinkage rate is determined more specifically for each strand or plate-like object, i.e., for each product. This takes into account both the material composition and size of the respective object. In addition to material composition and size, shrinkage may also be related to production conditions, such as production speed, to a lesser extent. Thus, for example, the proportion of the melt and consequently the refractive index vary with the production rate. Therefore, the shrinkage rate can also be determined for the corresponding production conditions, i.e., for a given production rate, or the relationship can be identified in the probing step to recognize the effects of different production rates.

[0016] In other words, according to the present invention, in early measurements performed on strands or plates that are not yet fully cured, it is also possible to reliably predict the corresponding geometric parameters to be determined based on their final values ​​in the fully cured state of the strands or plates. Because the relationship is tested for the respective strands or plates to be measured, and preferably also for the respective production conditions, potentially unrecognized variations in material composition or other parameters of the production process will not have a distorting effect on the determination results according to the present invention.

[0017] The prerequisite for determining the shrinkage rate is that the refractive index of the material of the object in its fully solidified state is known. This refractive index can be determined, for example, by one of the methods described below for determining the refractive index, or, if known with sufficient precision, it can be assumed that the refractive index is known for the corresponding current material of the object.

[0018] Using the method according to the invention for predicting the expected shrinkage of geometric parameters, such as the wall thickness and diameter of the tube, the relevant measurements can be detected on the extrusion production line shortly after extrusion, and although there is a certain proportion of melt in, for example, the tube wall, the expected final value can be predicted and indicated for a standard temperature of 22°C, but it can also be used as the actual value to adjust to the nominal size.

[0019] For example, the extrusion of a pipe with a diameter of up to 2.5m is carried out at a creep rate of a few centimeters to about one meter per minute. Traditional measuring equipment can only measure relevant parameters approximately 30 to 50 meters after the end of the extrusion line, i.e., several hours later. Early measurement is economically crucial for adjusting the wall thickness to the desired nominal size and achieving uniformity of wall thickness across the pipe circumference. A typical extruder has a capacity of approximately 400 kg / h; at 5000 h / year, the estimated material consumption is 2 million kg. At a price slightly above 1 Euro / kg, the method according to the present invention can easily save 100,000 to 200,000 Euros annually compared to existing technologies.

[0020] According to a particularly practical design scheme, the geometric parameters can be the diameter and / or wall thickness of the tube. In this case, during the determination step, the relationship between the refractive index of the tube and the shrinkage that occurs with respect to the diameter and / or wall thickness during its complete curing process can be determined. Especially when both wall thickness and diameter are determined as geometric parameters, the relationship between refractive index and shrinkage can be derived separately for both wall thickness and diameter. This design scheme is based on the understanding that the shrinkage rate may differ for different geometric parameters. This has been confirmed by relevant studies. For example, the shrinkage of the diameter during complete curing may be 2 to 3 times less than the shrinkage of the wall thickness. This has been identified as being because the outer side of the tube, especially the defined diameter, cools and solidifies earlier, thus the diameter no longer shrinks significantly, while the inner side of the tube, where a viscous portion still exists, cools and solidifies later than the outer side, resulting in greater shrinkage with respect to the wall thickness. In practice, the relative shrinkage rate of the diameter can be, for example, in the range of 2 to 3%, while the shrinkage rate of the wall thickness can be, for example, in the range of 6 to 8%. Understandably, these values ​​can vary with the material, size, and corresponding production conditions of the strand or plate-like object. For example, for particularly large tubes, significantly larger shrinkage rates of more than 15% may be observed, especially since the surface area increases less with increasing tube diameter compared to volume.

[0021] As already described, the strand or plate-shaped object can originate from the extrusion equipment and can be conveyed along its longitudinal direction during the determination of the at least one geometric parameter.

[0022] According to another design, during the exploration step, the relationship can be determined by measuring the refractive index and the at least one geometric parameter at multiple times and / or at multiple locations on the strand-like or plate-like object. In this way, sampled values ​​(Stützwert) can be recorded, for example, to obtain a characteristic curve that visualizes the relationship. Interpolation can then be performed accordingly between the sampled values, for example. It is understood that the reliability of the values ​​determined to determine the relationship increases with the number of sampled values.

[0023] According to another related design, in the probing step, the relationship can be determined by fully curing the strand or plate-like object at least along one longitudinal segment, during which the refractive index and the at least one geometric parameter are determined multiple times. For example, it is conceivable to stop the strand or plate-like object from the extrusion equipment in the first step, that is, to interrupt production, and then measure the refractive index and the at least one geometric parameter at multiple moments, for example, substantially continuously, until the strand or plate-like object is fully cured.

[0024] As already explained, in the exploration step, the relationship can be expressed as at least one characteristic curve, preferably a curve showing the shrinkage rate of the strand or plate-like object relative to the refractive index. Then, based on the determination of the refractive index of the not-yet-fully-cured strand or plate-like object and the at least one geometric parameter in the determination step, the position on the characteristic curve can be easily determined, thereby determining the expected shrinkage until full curing. For example, the at least one geometric parameter can be normalized for the value after full curing. In this case, the shrinkage rate can be expressed as a percentage, a function of the refractive index.

[0025] For example, if the wall thickness and diameter of the tube are determined as geometric parameters, the shrinkage rate S of the wall thickness can be obtained as a function of the refractive index using the following formula. wt (n):

[0026]

[0027] Where, wt end wt(n) is the final wall thickness after the tube has fully cured, and wt(n) is the wall thickness determined in the determination step before the tube has fully cured.

[0028] Diameter shrinkage rate S, expressed as a percentage d (n) as a function of refractive index is derived as follows:

[0029]

[0030] Where d end d(n) represents the final diameter after the tube is fully cured, while d(n) represents the diameter detected in the determination step before the tube is fully cured.

[0031] According to another design, to determine the refractive index and / or at least one geometric parameter, terahertz radiation is emitted toward a strand or plate-like object; the terahertz radiation reflected by the strand or plate-like object is detected; and the refractive index and / or at least one geometric parameter, such as the diameter or wall thickness of a tube, in a surface region of the strand or plate-like object is determined based on the detected terahertz radiation, especially its intensity. In this design, terahertz radiation is emitted toward the strand or plate-like object. The terahertz radiation may partially enter the strand or plate-like object. The terahertz radiation is reflected at the boundary surfaces (external and possibly internal) of the strand or plate-like object and detected by a suitable detector. The frequency of the terahertz radiation may be, for example, in the range of 10 GHz to 3 THz. This could be so-called millimeter waves. The transmitter emitting the terahertz radiation and the detector receiving the reflected terahertz radiation can be positioned substantially in the same location. For example, the transmitter and detector can be integrated into a single transceiver. Terahertz radiation can be used to reliably determine geometric parameters and refractive indices, especially even in challenging fabrication environments that can pose difficulties for optical systems such as lasers. For example, the determination of refractive indices or geometric parameters using terahertz radiation is described in WO 2016 / 139155 A1 or DE 10 2018 128 248 A1. Refer to these documents accordingly.

[0032] Terahertz radiation can be modulated continuous-wave terahertz radiation, especially frequency-modulated continuous-wave terahertz radiation. Terahertz radiation can also be pulse-modulated or phase-modulated. Frequency modulation can include one or more frequency bursts. In particular, so-called frequency scanning can be performed, in which a predetermined frequency range is traversed one or more times. As pulse- or phase-modulated terahertz radiation, so-called time-domain reflection or frequency-domain reflection methods can be used, for example. It is also conceivable to transmit multiple discrete frequencies instead of the spectrum.

[0033] The at least one geometric parameter can be determined by measuring the propagation time of the emitted terahertz radiation and the radiation reflected by the strand or plate-shaped object, as described, for example, in WO 2016 / 139155 A1.

[0034] According to another design, during the emission and detection of terahertz radiation, at least one transmitter for emitting terahertz radiation and at least one detector for detecting the emitted terahertz radiation and the terahertz radiation reflected by the strand or plate-like object are rotated about the longitudinal axis of the strand-like object, preferably along a circular track, or moved parallel to the surface of the plate-like object. By rotating or moving the pair of transmitters and detectors, such as transceivers, the value of at least one geometric parameter can be detected distributedly along the periphery or width of the strand or plate-like object. In this way, for example, it can be confirmed whether there is so-called sagging, as may occur, for example, during extrusion, that is, the material flowing downwards in a state that is not yet fully solidified. The non-roundness of the strand can also be determined in this way. This is also described in principle in WO 2016 / 139155 A1. Of course, it is also conceivable that multiple pairs of transmitters and receivers are distributedly arranged along the periphery of the strand or plate-like object or parallel to the surface of the strand or plate-like object, and multiple measurements are determined along the periphery or parallel to the surface in this way.

[0035] According to another design scheme, the emitted terahertz radiation can penetrate the strand or plate-like object before detection. In this case, the refractive index of the strand or plate-like object is determined based on the change in propagation time of the emitted and received terahertz radiation after penetration, caused by the material of the strand or plate-like object. This is explained in principle in WO 2016 / 139155 A1. Thus, the material constants of the strand or plate-like object that cause this change, especially the refractive index and / or dielectric constant, can be derived from the change in propagation velocity determined by the presence of the strand or plate-like object in the radiation path relative to the radiation path without it.

[0036] According to another design, the emitted terahertz radiation, after penetrating the strand or plate-like object, can be reflected by a reflector and then penetrate the strand or plate-like object again before detection. In this design, for example, a reflector for the terahertz radiation is positioned behind the strand or plate-like object, along the radiation direction of the terahertz radiation emitted by the transmitter, placed opposite the transmitter. The reflector can be a cylindrical, arched reflector, with its longitudinal axis extending along the longitudinal axis of the strand. The center of curvature of the reflector can coincide with the center of curvature of the strand to be measured. That is, the focal line of the hollow cylindrical reflector coincides with the longitudinal axis of the strand. The reflector amplifies the measurement signal because the signal guided back to the receiver by the reflector can also be used for evaluation. Furthermore, the reflector allows for better differentiation of different measurement signals received by the detectors, especially in the case of multiple reflections. Thus, the reflector allows for separate evaluation of the front and back faces of the strand or plate-like object facing away from the transmitter or detector, thereby avoiding interference caused by multiple reflections. The reflector, particularly along the radiation path from the transmitter to the reflector and the radiation return path from the reflector to the detector, allows for the measurement of reflections occurring at the boundary surfaces of a terahertz or plate-like object. Therefore, for example, the propagation times of signals traveling directly from the transmitter / detector to the reflector and back to the transmitter / detector can be compared with those traveling directly from the transmitter / detector to the reflector, then reflecting off the rear terahertz wall (or on the inner and outer boundary surfaces of the rear terahertz wall), returning to the reflector, and then being reflected back to the transmitter / detector by the reflector. From this propagation time difference, the distance from the rear terahertz wall to the reflector, the wall thickness of the rear terahertz wall facing the reflector, or the diameter of the terahertz can be determined. In this case, the reflector simulates another transmitter. That is, by means of the reflector, even when the original received signal from the rear terahertz wall is interfered with by multiple reflections between the transmitter / detector and the boundary surface of the terahertz facing the transmitter / detector, the side of the terahertz facing the reflector can be reliably measured.

[0037] According to another design, the at least one geometric parameter can be the wall thickness of the tube. In this case, the optical wall thickness of the tube is determined by the detected terahertz radiation, and the refractive index of the tube is determined by comparing the outer and inner diameters of the tube with the determined optical wall thickness. As already explained, the terahertz radiation at least partially enters the strand-like or plate-like object. The terahertz radiation is reflected at least at two boundary surfaces. These boundary surfaces can be, for example, the outer surface of the tube's wall section facing the emitter and the inner surface facing away from the emitter. It is also possible that a large radiation component still exits from the inner side of the wall section facing away from the emitter, and this radiation component is then reflected on the inner side of the opposite wall section facing away from the emitter after passing through the cavity defined by the tube. All radiation components reflected at these boundary surfaces are reflected back and received by the detector. Based on this, the optical wall thickness of each wall section of the tube can be determined without knowing the refractive index of the material. The design scheme described above is based on the understanding that, in its simplest case, that is, if we simply assume that the wall section of the tube that is penetrated towards the emitter and the opposite wall section facing away from the emitter have the same wall thickness, the refractive index can be calculated taking into account the inner and outer diameters of the tube, and especially the difference between the inner and outer diameters. In this regard, when referring to the inner or outer diameter of the tube, we are referring to the geometric inner and outer diameters. The inner and / or outer diameters of the tube can be determined using measurement techniques. For this purpose, different measurement methods can be envisioned, such as those described, for example, in DE 10 2018 128 248 A1. However, it can also be assumed that at least one of these diameters, such as the outer diameter, is known. Furthermore, when the measured radiation undergoes the reflection described above at the boundary surface of the tube, the inner diameter can also be determined based on an evaluation of the reflected measured radiation, since the refractive index of the air in the cavity of the tube is known. Attached Figure Description

[0038] An embodiment of the present invention will now be described in detail with reference to the accompanying drawings. The drawings illustrate, for example:

[0039] Figure 1 An apparatus for implementing the method according to the invention is shown in a schematic side view.

[0040] Figure 2 Show Figure 1 A partial cutaway view of the equipment.

[0041] Figure 3 It is a chart used to illustrate the temperature dependence of refractive index.

[0042] Figure 4 The graph shows the cooling characteristics for different parameters of the first measurement series (“tube 1”).

[0043] Figure 5 The graph shows the cooling characteristics for different parameters of the second measurement series (“pipe 2”).

[0044] Figure 6 For the first measurement series (“tube 1”), a characteristic curve of the shrinkage rate of the wall thickness as a geometric parameter is shown, and

[0045] Figure 7 For the second measurement series (“tube 2”), a characteristic curve of the shrinkage rate of the wall thickness as a geometric parameter is shown. Detailed Implementation

[0046] Unless otherwise stated, the same reference numerals in the figures denote the same objects.

[0047] exist Figure 1 and Figure 2 The diagram shows a strand 10, which in this case is a plastic tube 10, having a wall 12, a cavity 14 defined by the tube 10, an outer surface 16 that is circular in cross-section, and an inner surface 18 that is also circular in cross-section and defines the cavity 14. In the current example, the plastic tube 10 is extruded by means of an extruder in an extrusion device 20 and conveyed along its longitudinal axis by a suitable conveying device. Figure 1 The plastic tube is conveyed from left to right. After exiting the extruder head in the extrusion unit 20, the tube 10 first passes through a first cooling section 22, where the tube 10, which has been intensely heated and is not yet fully solidified (i.e., has a still flowable portion (melt), exits the extrusion unit 20 and is cooled. In a further process, the tube 10 passes through a measuring device 24, in which the refractive index of the tube material and the geometric parameters of the tube 10, such as, for example, diameter and / or wall thickness, are determined in a manner detailed below. After the measuring device 24, the tube 10 passes through another cooling section 26 for further cooling. After the tube 10 has fully solidified, it is cut into predetermined segments, for example, in a cutting device 28.

[0048] according to Figure 2The structure and function of the measuring device 24 should be described in detail. In the example shown, the measuring device 24 includes a transceiver 30, in which a transmitter and a detector for terahertz radiation are combined. The transmitter emits terahertz radiation 32 onto the tube 10. The terahertz radiation is reflected at different boundary surfaces of the tube 10 and at a reflector 34 opposite to the transceiver 30, and returns to the transceiver 30, where it is detected by the detector. Furthermore, the transceiver 30 is 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. The evaluation device 38 can determine, for example, in... Figure 2 The wall thicknesses 40, 42 and diameter 44 are drawn in the diagram, for example, determined based on propagation time measurements. The evaluation device 38 can also determine the refractive index of the strand material based on measurement signals received by the detector, as described, for example, in WO 2016 / 139155 A1 or DE 102018 128 248 A1.

[0049] Using measuring device 24, for example in Figure 1 The measurement location shown determines the diameter 44 and wall thicknesses 40, 42, and refractive index of the tube 10. At this location, the tube 10 is not yet fully solidified, i.e., it still has a flowable portion. The transceiver 30 can also rotate, for example, along a circular track around the tube 10 to determine the geometric parameters and possibly the refractive index at different locations around the periphery of the tube 10. In this case, the reflector 34 can also rotate around the tube 10. However, the reflector 34 can also be omitted.

[0050] Figure 3 The correlation between refractive index and temperature or state of matter is shown in the pure polyethylene example. On the one hand, it can be seen that the relationship between refractive index and temperature or state of matter is non-linear. On the other hand, it can be seen that the refractive index changes particularly strongly in the mixed phase, i.e., in the transition phase between the solid and liquid phases. Further, the curve of refractive index at varying temperatures shows that the refractive index remains essentially constant between room temperature and approximately 100°C. From this, it can be inferred that when the extrusion equipment is shut down, an average refractive index corresponding to the cold-state value will appear after tube 10 has cooled. Therefore, it is possible to now calibrate the cold-state value of the refractive index for this tube diameter using the echo intensity of the tube shell, as described above. Thus, in subsequent production, the cold-state value of the refractive index can also be determined in the manner described, and changes in the material can be identified during production, and the cold-state value can be corrected to the newly detected refractive index for anticipated shrinkage.

[0051] As explained, Figure 3For pure polyethylene, the refractive index is shown to be related to temperature. Generally, HDPE (high-density polyethylene) containing additives is used for pipes. It is preferable to achieve a blackening of the pipe by adding carbon black (Ruβ). Other additives are used to determine the melt viscosity, thereby achieving optimal flow characteristics at high pressure and temperature in the extruder, while maintaining viscous flow characteristics from the end of the pipe head until final cooling in the pipe wall to keep melt sagging as small as possible. For pure PE, various properties of the material are known, but these properties can only be conditionally transferred to common HDPE with additives. This involves melting point, density, refractive index, absorbance, and all temperature-dependent properties for millimeter waves. These problems can be solved using the method according to the invention.

[0052] exist Figure 4 For example, in Figure 1 The wall thickness, diameter, and refractive index, respectively, of a medium-sized first tube (“tube 1”) extruded in the extrusion apparatus 20 shown are indicated with respect to time. Figure 5 The same is also shown, for example, in Figure 1 The wall thickness, diameter, and refractive index of the smaller second tube (“tube 2”) extruded in the extrusion apparatus 20 shown are, respectively, relative to time. The first and second tubes may, for example, differ in their material composition and / or their dimensions.

[0053] At time zero, to perform the measurement, the extrusion equipment 20 is stopped, and the tube is no longer conveyed along its longitudinal axis. Measurements are then recorded over a longer period until the tube is completely cured, i.e., when it no longer contains any viscous portion. For both measurement sequences, it can be seen that the refractive index behaves substantially inversely to the wall thickness or diameter. As the refractive index increases with increasing degree of curing, the measured values ​​for wall thickness and diameter decrease accordingly. Furthermore, it can be seen that the measurement sequences exhibit significantly different curves for the two different tubes measured.

[0054] Figure 6 and Figure 7 The characteristic curve determined by means of the method of the present invention is shown, wherein, Figure 6 The characteristic curve shown is based on Figure 4 The data shown is definite, while Figure 7 The characteristic curve shown is based on Figure 5 The data shown are specific. The relationship between shrinkage and refractive index is shown for each tube's wall thickness. This is to establish... Figure 6 and Figure 7 The characteristic curve shown is normalized to the wall thickness for the fully cured value. For the wall thickness, the following formula is derived as a function of the refractive index plotted on the x-axis: Figure 6 and Figure 7The shrinkage rates are marked as percentages on the y-axis:

[0055]

[0056] The variables in the formula have been explained above.

[0057] These characteristic curves established in the probing step according to the invention can now be used to calculate and thus predict the wall thickness in the fully cured state based on the values ​​of the refractive index and wall thickness of the not-fully-cured tube determined in the determining step. This can also be done in a corresponding manner for the diameter. Here, the refractive index in the fully cured state can be measured, or the refractive index can be determined to be known for the corresponding material composition. In particular, it can be confirmed from the values ​​determined in the determining step that the wall thickness is currently in the corresponding state. Figure 6 and 7 The location of the characteristic curve shown in the figure allows for the reading of the further shrinkage expected to occur until the corresponding tube is fully cured.

[0058] List of reference numerals

[0059] 10 strands, tubes

[0060] 12. Wall section

[0061] 14. Cavity

[0062] 16. Outer surface

[0063] 18 Inner Surface

[0064] 20 Extrusion Equipment

[0065] Cooling sections 22 and 26

[0066] 24 Measuring device

[0067] 28 Cut-off device

[0068] 30 transceivers

[0069] 32 terahertz radiation

[0070] 34 Reflectors

[0071] Route 36

[0072] 38 Evaluation Device

[0073] 40, 42 wall thickness

[0074] 44. Diameter.

Claims

1. A method for determining at least one geometric parameter of a strand or plate-like object (10) that is not yet fully cured and has a still flowable portion, characterized in that, The method comprises the following steps: - In the investigation step, for the strand or plate-like object (10), the relationship between the refractive index of the strand or plate-like object (10) and the shrinkage that occurs during its complete solidification is determined. - In the determination step, the refractive index and at least one geometric parameter of the strand or plate-like object (10) that has not yet fully solidified and has a still flowable portion are determined. - Taking into account the relationship identified in the exploration step, the at least one geometric parameter of the strand or plate-shaped object (10) in the fully cured state is calculated from the refractive index determined in the determination step and the value of the at least one geometric parameter.

2. The method according to claim 1, characterized in that, The at least one geometric parameter is the diameter (44) and / or wall thickness (40, 42) of the tube, and in the determining step, the relationship between the refractive index of the tube and the shrinkage that occurs with respect to the diameter (44) and / or wall thickness (40, 42) of the tube during the complete curing of the tube is determined.

3. The method according to claim 1 or 2, characterized in that, The strand or plate-shaped object (10) originates from the extrusion equipment (20) and is conveyed along its longitudinal direction during the determination of the at least one geometric parameter.

4. The method according to claim 1 or 2, characterized in that, The relationship is determined in the exploration step by determining the refractive index and the at least one geometric parameter at multiple times and / or at multiple locations on the strand or plate-like object (10).

5. The method according to claim 1 or 2, characterized in that, The relationship is determined in the exploration step by completely curing the strand or plate-like object (10) at least along one longitudinal segment, and the refractive index and the at least one geometric parameter are determined multiple times during the complete curing process.

6. The method according to claim 1 or 2, characterized in that, In the exploration step, the relationship is determined in the form of at least one characteristic curve.

7. The method according to claim 1 or 2, characterized in that, In the exploration step, the relationship is determined in the form of at least one characteristic curve, in which the contraction rate of the strand or plate-like object (10) is indicated with respect to the refractive index.

8. The method according to claim 1 or 2, characterized in that, To determine the refractive index and / or the at least one geometric parameter, terahertz radiation (32) is emitted toward the strand or plate-shaped object (10), the terahertz radiation (32) reflected by the strand or plate-shaped object (10) is detected, and the refractive index and / or the at least one geometric parameter is determined based on the detected terahertz radiation (32).

9. The method according to claim 8, characterized in that, The terahertz radiation (32) is modulated continuous wave terahertz radiation.

10. The method according to claim 8, characterized in that, The terahertz radiation (32) is pulse-modulated terahertz radiation or phase-modulated terahertz radiation.

11. The method according to claim 9, characterized in that, The terahertz radiation (32) is frequency-modulated continuous wave terahertz radiation.

12. The method according to claim 8, characterized in that, The at least one geometric parameter is determined by measuring the propagation time of the emitted terahertz radiation (32) and the radiation reflected by the strand or plate-shaped object (10).

13. The method according to claim 8, characterized in that, At least one transmitter for emitting terahertz radiation (32) and at least one detector for detecting the emitted terahertz radiation (32) and reflected by the filamentary or plate-shaped object (10) rotate about the longitudinal axis of the filamentary object (10) or move parallel to the surface of the plate-shaped object during the emission and detection of the terahertz radiation (32).

14. The method according to claim 13, characterized in that, The at least one transmitter and the at least one detector rotate along a circular orbit about the longitudinal axis of the strand-shaped object (10) during the emission and detection of terahertz radiation (32).

15. The method according to claim 8, characterized in that, The emitted terahertz radiation (32) penetrates the strand or plate-like object (10) before detection, and the refractive index of the strand or plate-like object (10) is determined based on the change in the propagation time of the emitted and received terahertz radiation (32) after penetration of the strand or plate-like object (10) caused by the material of the strand or plate-like object (10).

16. The method according to claim 15, characterized in that, The emitted terahertz radiation (32) is reflected by the reflector (34) after penetrating the strand or plate-like object (10), and then penetrates the strand or plate-like object (10) again before being detected.

17. The method according to claim 8, characterized in that, The at least one geometric parameter is the wall thickness of the tube (40, 42), the optical wall thickness of the tube is determined by the detected terahertz radiation (32), and the refractive index of the tube is determined by comparing the outer diameter and inner diameter of the tube with the determined optical wall thickness.

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