Abstract
A method is disclosed for determining at least one geometric parameter of an object comprising a molten component. The method includes determining a relationship between a refractive index of the object and a shrinkage occurring during a solidification of the object. The refractive index and at least one geometric parameter of the object comprising the molten component is determined using a measuring apparatus. At least one geometric parameter of the solidified object from the refractive index and the at least one geometric parameter of the object comprising the molten component is determined using the measuring apparatus and taking into account the determined relationship between the refractive index of the object and the shrinkage occurring during the solidification of the object.
Claims
1-13. (canceled)
14. A method for determining at least one geometric parameter of an object comprising a molten component, comprising: determining a relationship between a refractive index of the object and a shrinkage occurring during a solidification of the object; determining the refractive index and at least one geometric parameter of the object comprising the molten component using a measuring apparatus; and determining at least one geometric parameter of the solidified object from the refractive index and the at least one geometric parameter of the object comprising the molten component using the measuring apparatus and taking into account the determined relationship between the refractive index of the object and the shrinkage occurring during the solidification of the object.
15. The method according to claim 14, wherein the object comprises a tube.
16. The method according to claim 15, wherein the at least one geometric parameter comprising the molten component is a diameter or a wall thickness of the tube, wherein the relationship between the refractive index of the tube and a shrinkage occurring during the solidification of the tube is determined for at least one of (i) the diameter of the tube and (ii) the wall thickness of the tube.
17. The method according to claim 14, wherein the object comes from an extrusion system and is conveyed along a longitudinal direction during the determination of the at least one geometric parameter comprising the molten component.
18. The method according to claim 14, wherein the determining the relationship between the refractive index of the object and the shrinkage occurring during the solidification of the object is accomplished by determining the refractive index and the at least one geometric parameter of the object comprising the molten component.
19. The method according to claim 18, wherein the refractive index and the at least one geometric parameter of the object comprising the molten component is determined at least one of (i) multiple points in time and (ii) at multiple locations of the object.
20. The method according to claim 14, wherein the determining the relationship between the refractive index of the object and the shrinkage occurring during the solidification of the object is accomplished by allowing the object to solidify at least along a longitudinal portion, wherein the refractive index and the at least one geometric parameter of the object are determined multiple times during the solidification of the object.
21. The method according to claim 14, wherein the determining the relationship between the refractive index of the object and the shrinkage occurring during the solidification of the object is accomplished using at least one characteristic curve in which a degree of shrinkage of the object is plotted over the refractive index.
22. The method according to claim 14, further comprising emitting terahertz radiation towards the object, wherein the refractive index and the at least one geometric parameter are determined from the terahertz radiation reflected by the object comprising the molten component.
23. The method according to claim 22, wherein the terahertz radiation comprises one of (i) a modulated continuous wave terahertz radiation, (ii) a pulse-modulated terahertz radiation, and (iii) a phase-modulated terahertz radiation.
24. The method according to claim 22, further comprising determining the at least one geometric parameter from a propagation time measurement of the emitted terahertz radiation and the terahertz radiation reflected by the object comprising the molten component.
25. The method according to claim 22, further comprising providing at least one transmitter configured to emit the terahertz radiation and at least one detector configured to detect the emitted terahertz radiation and the reflected terahertz radiation by the object, wherein the at least one detector is further configured to move relative to the object during the emission and detection of the terahertz radiation.
26. The method according to claim 25, wherein the emitted terahertz radiation penetrates the object prior to the detection, and wherein the refractive index of the object is determined using a propagation time change of the terahertz radiation emitted and then received after penetrating the object caused by a material comprising the object comprising the molten component.
27. The method according to claim 26, further comprising providing a reflector configured to reflect the terahertz radiation penetrating the object comprising the molten component a first time and, prior to the detection, penetrates object comprising the molten component a second time.
28. The method according to claim 26, wherein the at least one geometric parameter is a wall thickness of a tube, wherein an optical wall thickness of the tube is determined from the detected terahertz radiation, and wherein the refractive index of the tube is determined from a comparison of outside and inside diameters of the tube with the optical wall thickness.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] An exemplary embodiment of the invention is explained in greater detail below with reference to figures, wherein:
[0033] FIG. 1 schematically shows a side view of an embodiment of a device for determining at least one geometric parameter of an object.
[0034] FIG. 2 schematically shows a partial sectional view of the embodiment of the device of FIG. 1.
[0035] FIG. 3 shows a diagram illustrating the temperature dependence of the refractive index.
[0036] FIG. 4A schematically shows a diagram of the cooling behavior relating to measured wall thickness of a first object (tube 1).
[0037] FIG. 4B schematically shows a diagram of the cooling behavior related to the diameter of the first object (tube 1).
[0038] FIG. 4C schematically shows a diagram of the cooling behavior related to the refractive index of the first object (tube 1).
[0039] FIG. 5A schematically shows a diagrams of the cooling behavior related to wall thickness of a second object (tube 2).
[0040] FIG. 5B schematically shows a diagram of the cooling behavior related to the diameter of the second object (tube 2).
[0041] FIG. 5C schematically shows a diagram of the cooling behavior related to the refractive index of the second object (tube 2).
[0042] FIG. 6 schematically shows a characteristic curve of the degree of shrinkage for the wall thickness as a geometric parameter for the first series of measurements (tube 1).
[0043] FIG. 7 schematically shows a characteristic curve of the degree of shrinkage as a geometric parameter for the second series of measurements (tube 2).
[0044] Unless otherwise indicated, the same reference numerals designate the same objects in the figures.
DETAILED DESCRIPTION OF THE INVENTION
[0045] A strand 10, in the present case a plastic tube 10, is depicted in FIGS. 1 and 2, which has a wall 12, a hollow space 14 delimited by the tube 10, an outer surface 16 which is circular in cross-section and an inner surface 18 which is likewise circular in cross-section, which delimits the hollow space 14. The plastic tube 10 is, in the present example, extruded with the aid of an extruder in an extrusion system 20 and conveyed along its longitudinal axis by means of a suitable conveying apparatus, from left to right in FIG. 1. After exiting from the tube head of the extruder of the extrusion system 20, the tube 10 initially passes through a first cooling section 22, in which the tube 10, which exits the extrusion system 20 heated to a great extent and not yet completely solidified, that is to say still having flowable components (molten mass), is cooled down. In its further course, the tube 10 passes through a measuring apparatus 24, in which the refractive index of the tube material and geometric parameters of the tube 10 such as, for example, the diameter and/or wall thickness, are determined in the manner explained in greater detail below. Following the measuring apparatus 24, the tube 10 passes through further cooling sections 26, in which further cooling occurs. After the tube 10 has completely solidified, the latter is cut to predefined lengths, for example in a cutting-to-length device 28.
[0046] The structure and the function of the measuring apparatus 24 are to be explained in greater detail with reference to FIG. 2. In the depicted example, the measuring apparatus 24 comprises a transceiver 30, in which a transmitter and a detector for terahertz radiation are combined. The transmitter emits terahertz radiation 32 toward the tube 10. The terahertz radiation is reflected at different boundary surfaces of the tube 10 and at a reflector 34 arranged opposite the transceiver 30 and travels back to the transceiver 30 where it is detected by the detector. The transceiver 30 is, furthermore, connected to an evaluating apparatus 38 via a line 36. The reflected radiation received by the detector generates corresponding measuring signals which are forwarded to the evaluating apparatus 38 via the line 36. In this way, the evaluating apparatus 38 can determine, for example, the wall thicknesses 40, 42 drawn in in FIG. 2, as well as the diameter 44, for example, using propagation time measurements. The evaluating apparatus 38 can also determine the refractive index of the strand material on the basis of the measuring signals received from the detector, as is described, by way of example, in WO 2016/139155 A1 or DE 10 2018 128 248 A1.
[0047] For example, the diameter 44 and the wall thicknesses 40, 42 of the tube 10 as well as the refractive index are determined with the measuring apparatus 24 at the measuring location shown in FIG. 1, at which the tube 10 has not yet completely solidified, that is to say still has flowable components. It is also possible that the transceiver 30 rotates, by way of example, along a circular path about the tube 10 and, thus, determines the geometric parameters and, optionally, also the refractive index, at different locations over the circumference of the tube 10. The reflector 34 can then either likewise rotate about the tube 10. However, it is also possible for the reflector 34 to be dispensed with.
[0048] FIG. 3 shows the dependency of the refractive index on the temperature or, respectively on the aggregation state in the depicted example for pure polyethylene. On the one hand, it can be seen that the relationship between the refractive index and the temperature or, respectively the aggregation state is non-linear. On the other hand, it can be seen that the refractive index changes particularly significantly in the mixing phase, that is to say, at the transition between the solid and the liquid state. From the course of the refractive index at changing temperatures, it can further be seen that the refractive index remains largely unchanged between room temperature and approximately 100 C. From this, it can be deduced that when the extrusion system is at a standstill and after the tube 10 has cooled, an average refractive index results, which corresponds to the cold value. It is therefore now possible to also calibrate the cold value of the refractive index, which can be ascertained as explained above, from the intensity of the echoes of the outer shell of the tube, for this tube diameter. During subsequent production, the cold value of the refractive index can thus be ascertained in the manner indicated as well and changes in the material can be recognized during production and can be adjusted to the newly recorded refractive index with respect to the shrinkage to be expected.
[0049] As explained, FIG. 3 shows the dependency of the refractive index on the temperature for pure polyethylene. In general, an HDPE (high-density polyethylene) with additives is utilized for tubes. The tubes are preferably colored black by adding carbon black (soot). The viscosity of the molten mass is determined with further additives and, therefore, an optimal flow behavior at high pressure and high temperature in the extruder with viscous flow behavior after leaving the tube head until the molten mass finally cools down in the tube wall in order to keep sagging of the molten mass as low as possible. While the extremely wide range of properties of the material are known for pure PE, these can only be transferred to a typical HDPE with additives to a limited extent. This applies to the melting temperature, the density, the refractive index, the absorption and all of the temperature dependencies thereof for millimeter waves. These problems can be addressed with the method according to the invention.
[0050] The wall thickness, the diameter and the refractive index for a first medium-sized tube (tube 1) extruded, by way of example, in the extrusion system 20 shown in FIG. 1 are plotted in each case over time in FIGS. 4A-C. The wall thickness, the diameter and the refractive index for a second, smaller-sized tube (tube 2) extruded in the extrusion system 20 shown, by way of example, in FIG. 1 are in each case likewise plotted over time in FIGS. 5A-C. The first and second tubes can differ, for example, in terms of their material composition and/or their dimensions. At the zero point in time, the extrusion system 20 was stopped for the measurement carried out and the tubes were accordingly no longer conveyed further along their longitudinal axis. The measured values were then acquired over a longer period of time until the tubes have completely solidified, that is to say when they no longer contained any viscous components. A substantially inverse behavior of the refractive index to the wall thickness or, respectively the diameter can be seen, in each case, for the two series of measured values. While the refractive index increases as the solidification increases, the measured values for the wall thickness and diameter decrease accordingly. Furthermore, it can be seen that considerably different courses are demonstrated with the series of measured values for the two different measured tubes.
[0051] FIGS. 6 and 7 show characteristic curves determined with the method according to the invention, wherein the characteristic curve shown in FIG. 6 was ascertained using the data depicted in FIGS. 4A-C and the characteristic curve shown in FIG. 7 was ascertained using the data shown in FIGS. 5A-C. The relationship between the shrinkage and the refractive index for the wall thickness of the respective tube is shown in each case. In order to create the characteristic curves shown in FIGS. 6 and 7, the wall thickness was normalized to the value following complete solidification. The degrees of shrinkage plotted in each case on the y-axis in FIGS. 6 and 7 in percent as a function of the refractive index plotted on the x-axis for the wall thickness are obtained according to:
[00003]
with the variables explained above.
[0052] These characteristic curves created in the ascertaining step according to the invention can now be used to calculate and, therefore, predict the wall thickness in the completely solidified state using the values for the refractive index and the wall thickness of the tubes which are not yet completely solidified, which are ascertained in the determining step. This can be done for the diameter in a corresponding manner. The refractive index in the completely solidified state can be measured or assumed to be known for the respective material composition. In particular, it is possible to establish the current position on the respective characteristic curve depicted in FIGS. 6 and 7, using the values determined in the determining step, so that the further shrinkage to be expected until the respective tube has completely solidified can accordingly be read off in the characteristic curve.
LIST OF REFERENCE NUMERALS
[0053] 10 Strand, tube [0054] 12 Wall [0055] 14 Hollow space [0056] 16 Outer surface [0057] 18 Inner surface [0058] 20 Extrusion system [0059] 22, 26 Cooling section [0060] 24 Measuring apparatus [0061] 28 Cutting-to-length device [0062] 30 Transceiver [0063] 32 Terahertz radiation [0064] 34 Reflector [0065] 36 Line [0066] 38 Evaluating apparatus [0067] 42 Wall thicknesses [0068] 44 Diameter
