Device and method for non-invasive measurement of melt temperature in extrusion processes

Abstract

The invention relates to a device (1) for measuring the melt temperature in extrusion processes in which heated and plastic substances are processed by means of extrusion screws (2), wherein at least one temperature sensor (5) is arranged on or in the shaft (3) of at least one extrusion screw (2) and detects the local temperature of the melt, wherein the at least one temperature sensor (5) is connected via a transmission device (6, 7) also arranged on or in the shaft (3) to an evaluation unit which evaluates the measurement signals. The temperature sensor (5) can be in electrically conductive contact with a stationary counter-slip ring (7) via measuring lines (6) arranged on or in the shaft (3) and at least one slip ring (7) arranged at the end of the shaft (3), which couples the measurement signals from the at least one temperature sensor (5) and forwards them to the evaluation unit.

Description

[0001] The invention relates to a device for non-invasive measurement of the melt temperature in extrusion processes according to the preamble of claim 1 and a method according to the preamble of claim 15.

[0002] The processing of substances in chemical or chemical engineering processes, and especially of polymers, using extrusion equipment is of great importance, especially for the processing of chemical substances in processes with high throughput. Accordingly, process control and monitoring of the extrusion process are of great technical and economic importance. Even minor, unacceptable deviations from the target extrusion process can lead to damage to the processed substances, even to their complete unusability. In addition to pressure, an important influencing factor in the processing of chemical substances using extrusion processes is the temperature of the melt during extrusion.

[0003] Precise temperature measurement of the melt in extrusion processes is very important in many technical applications. Firstly, such extrusion processes often involve temperature-sensitive materials in the pharmaceutical, food, and life science sectors, which may only be processed under specific processing conditions, particularly with regard to temperature control, if the quality and properties of the temperature-sensitive materials are not to suffer. Furthermore, in chemical processes, the reaction rate is exponentially related to temperature, so that even small, unacceptable temperature deviations can quickly lead to significant, unacceptable changes in the properties of the processed substances. Furthermore, reducing the temperature during processing enables energy savings during extrusion, which in turn directly impacts the economic efficiency of the processing.

[0004] Extruders with one or more extruder screws are often used to extrude such substances. The extruder screws are usually mounted as replaceable elements on rotating shafts. Various approaches have been used to measure the temperature inside an extruder during operation. For example, thermocouples for temperature measurements are screwed into the barrel wall of the extruder with and without insulation and can measure the temperature of the processed substance close to the barrel walls of the extruder with or without a blade reaching into the melt. However, a blade reaching into the melt complicates the design and operation of the extruder. Another option is to screw IR temperature sensors into the barrel, which optically measure the temperature of the processed substance using windows leading to the interior of the extruder.It must always be ensured that the window for the IR temperature sensor is always transparent and not covered by the melt.

[0005] An overview of the state-of-the-art measurement methods and devices can be found in the publication by Chamil Abeykoon: "Sensing technologies for process monitoring in polymer extrusion: A comprehensive review on past, present and future aspects" in Measurement: Sensors 22 (April) (2022) 100381. The state-of-the-art measurement methods all have the disadvantage of measuring the temperature of the processed substance only inadequately or with excessive construction and process engineering effort.

[0006] The object of the present invention is therefore to enable a technically simplified and more accurate recording of the temperature conditions within extrusion processes.

[0007] The solution to the problem of the invention arises with regard to the device from the characterizing features of claim 1 and with regard to the method from the features of claim 15, each in conjunction with the features of the corresponding preamble. Further advantageous embodiments of the invention emerge from the dependent claims.

[0008] The invention is based on a device for measuring the melt temperature in extrusion processes in which heated and plastic substances are processed by means of extrusion screws. Such a generic device is further developed according to the invention in that at least one temperature sensor is arranged on or in the shaft of at least one extrusion screw and detects the local temperature of the melt. The at least one temperature sensor is connected to an evaluation unit via a transmission device for the measurement signals, which is also arranged on or in the shaft.The arrangement of the temperature sensor on or in the shaft of at least one extrusion screw enables very process-oriented measurement of the melt temperature, as the shaft of the extrusion screw extends directly into the area of ​​the screw elements themselves, which in turn interact directly with the melt within the extrusion device. Thus, the temperature is measured by the temperature sensor precisely where the melt temperature is most relevant for monitoring the melt temperature. Furthermore, in contrast to measurement in the area of ​​the cylinder wall of the extruder, the measurement of the melt temperature is not or only slightly influenced by the temperature of the cylinder wall itself, by temperature gradients, and other distorting effects that cannot be avoided due to the relatively high mass of the cylinder wall.The arrangement of the temperature sensor on or in the shaft of the extrusion screw generally does not interfere with the use of conventional screw elements, as these can be mounted on the modified shaft over the temperature sensor arrangement and operated in the conventional manner. This means that normal operation of the extrusion system is not affected, and all screw elements can continue to be used at any position along the shaft. Furthermore, the measuring points can be freely positioned in the axial direction of the screw shaft at precisely those locations where melt temperatures are of particular importance.

[0009] The research project leading to this patent application has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 820716.

[0010] In order to solve the problem of temperature detection on the shaft of the extrusion screw, which rotates during operation, and of forwarding the signal to a generally stationary evaluation unit, in a first embodiment the at least one temperature sensor can be in electrically conductive connection with a stationary counter-slip ring via measuring lines arranged on or in the shaft with at least one slip ring arranged on the end area side of the shaft, which counter-slip ring decouples the measuring signals of the at least one temperature sensor and forwards them to the evaluation unit.In a conventional manner, the electrical signals recorded by the temperature sensor are transmitted via measuring lines that are also concealed in or on the shaft to a slip ring that is located at the end of the shaft and also rotates with the shaft. This slip ring is in electrical contact with a stationary counter-slip ring in a conventional manner and transmits the temperature sensor signals via the slip connection and forwards them to an evaluation unit. Such a slip ring connection has been tested and can be operated safely. Furthermore, the slip rings can be arranged in an area of ​​the extrusion device that is not subject to such high thermal and mechanical stress thanks to the transmission of the temperature sensor signals via the measuring lines. A separate transmission can be implemented for each temperature sensor using an associated slip ring.

[0011] In another embodiment, however, it is also conceivable for the at least one temperature sensor to be connected to the evaluation unit via wireless transmission technology. Radio links or other commercially available transmission methods can be used here, for example.

[0012] It is particularly advantageous if the at least one temperature sensor is arranged on or in the shaft below the removable screw elements. For example, the temperature sensor can be arranged in recesses that lie within the shaft cross-section unobstructed by the shaft teeth. As a result, the temperature sensor is arranged in a virtually concealed manner and does not affect the attachment of the screw elements to the shaft teeth. This allows conventional screw elements to be used and the screw elements do not require complex modification. For example, the at least one temperature sensor can be arranged radially below the shaft teeth, below the screw elements, in a corresponding recess in the shaft.

[0013] To ensure the best possible heat conduction from the melt to the temperature sensor, it is advantageous if the at least one temperature sensor and the shaft are connected to each other via heat-conducting substances, particularly thermal paste. This allows the temperature sensor to measure the temperature of the melt almost directly.

[0014] Furthermore, it is conceivable for more than one temperature sensor to be arranged at different locations along the shaft axis, measuring the temperature of the melt prevailing at those locations. Thus, the temperature at various stages of the material being processed through the extrusion device can be of interest. This can be measured separately by temperature sensors arranged according to the invention at specific points along the extrusion device and transmitted to the evaluation device. For example, each temperature sensor can be connected via separate measuring lines to associated slip rings, which in turn transmit the measured values ​​to separate counter-slip rings.

[0015] It is particularly advantageous if thermocouples, especially PT100 thermocouples or PT100 resistance temperature sensors, are arranged on or in the shaft as temperature sensors. Such thermocouples are widely used in technology and are reliable in operation. However, it is also conceivable to use other commercially available temperature sensors.

[0016] It is particularly advantageous if the measuring lines also run on or in the shaft below the removable screw elements. This way, for example, the measuring lines are also concealed and protected within the cross-sectional area of ​​the shaft within the screw gearing and do not interfere with the attachment of the screw elements.

[0017] It is conceivable for the measuring lines to run from the temperature sensor to the gear mount of the extruder screw shaft. The gear mount area is located at one end of the shaft and relatively far away from the effective zone of the extrusion device, and thus in an area less subject to mechanical and thermal stress. For this purpose, in a further development, the measuring lines in an end region of the extruder screw shaft can be in conductive connection with a slip ring that rotates with the shaft and interacts with a stationary counter-slip ring, preferably arranged in the area of ​​the extruder's lantern, e.g., between the first block and the gear, which couples out the measurement signals from the at least one temperature sensor.

[0018] Furthermore, it is conceivable that the evaluation unit receives and evaluates the measurement signals of at least one temperature sensor via a measuring sensor.

[0019] It is particularly advantageous if the evaluation unit corrects the measured values ​​with regard to the effect of heat conduction between the shaft of the extruder and the temperature sensor.

[0020] The invention further relates to a method for measuring the melt temperature in extrusion processes in which heated and plastic substances are processed by means of extrusion screws, in particular using the device according to claim 1. Such a generic method is further developed in accordance with the invention in that at least one temperature sensor on or in the shaft of at least one extrusion screw detects the local temperature of the melt, and a transmission device for the measurement signals, also arranged on or in the shaft, forwards the measurement signals to an evaluation unit, which then evaluates the measurement signals. The essential properties and advantages of such a method have already been explained in connection with the properties of the device; therefore, express reference is made thereto.

[0021] It is particularly advantageous if the evaluation unit corrects the values ​​measured by the at least one temperature sensor with regard to the effect of heat conduction between the extruder shaft and the temperature sensor. Since the heat transfer from the melt to the temperature sensor is not entirely unaffected by heat conduction through the shaft and the screw elements, it can be advantageous for these effects of heat conduction to be corrected by the evaluation unit, for example by the evaluation unit correcting the measurement signals by mathematically correcting the deviation between the temperature of the melt and the shaft, in particular by taking into account the stationary heat conduction in the shaft. For this purpose, the known laws of heat conduction can be used and calculated with the measured values ​​of the temperature sensor, whereby more precise temperatures and temperature profiles can be determined.

[0022] A particularly preferred embodiment of the device according to the invention and the corresponding device is shown in the drawing.

[0023] They show: Fig. 1 - a schematic side view of the device according to the invention on a shaft of an extrusion device provided with attachable screw elements, Fig. 2 - a cross-section through the shaft and screw elements according to Fig. 1 and temperature sensors and measuring lines arranged in the shaft, Fig. 3 - a sectioned individual part view of the shaft according to Fig. 1 without screw elements, Fig. 4 - a sectioned individual part view of the shaft according to Fig. 1 with suggested snail elements.

[0024] In the Fig. 1 and in the Fig. 3 and Fig. Figure 4 shows a schematic side view of the device according to the invention on a shaft 3 of an extrusion device 1 provided with attachable screw elements 2. The basic structure of such extrusion devices 1 with two intermeshing screw elements 2 is generally known and will only be explained here to the extent that it is important for understanding the invention. Not shown are the components of the extrusion device 1 surrounding the shaft 3, such as the cylinder walls, bearings, etc. Only the bearing 9 of the shaft 3 is indicated schematically.

[0025] The shaft 3 has, as shown in the cross-sectional view according to Fig.2, on its outer circumference, but still radially within the toothing 4 between the screw elements 2 and the shaft 3, there are recesses 10, 11 for the measuring lines 6 and the temperature sensors 5. These recesses 10, 11 are machined or otherwise introduced into the shaft 3, wherein the recess 11 for the temperature sensors 5 is only provided locally at the insertion point of each temperature sensor 5, while the recesses 10 extend between each temperature sensor 5 and a slip ring arrangement 7, with which the signals on the measuring lines 6 are tapped and fed to an evaluation device (not shown in detail). The respective recesses 10 also have openings leading to the associated recess 11 of the associated temperature sensor 5.

[0026] This arrangement of the recesses 10, 11 and the temperature sensors 5 and measuring lines 6 arranged therein has the advantage that, on the one hand, the temperature sensors 5 can be arranged in such a way that they can be attached close to the actual effective zone of the extrusion of the material to be processed and can therefore record the process temperature very well and largely accurately. On the other hand, the temperature sensors 5 and the measuring lines 6 are attached in such a way that they are protected beneath the screw elements 2, which can usually be pushed onto the shaft, and are covered by them from the melt. However, the temperature sensors 5 and the measuring lines 6 do not interfere with the pushing of the screw elements 2 onto the shaft 3, since they lie within the circumferential cross-section of the shaft 3 and are therefore set back from the circumference of the shaft 3.Therefore, conventional screw elements 2 can also be used with the modified shaft 3, which is particularly economical.

[0027] To ensure good heat transfer between the temperature sensors 5 arranged at different locations along the length of the shaft 3 and the melt or the screw elements 2 that come into direct contact with the melt, the temperature sensors 5 are coated with highly heat-conducting substances or cast with them within the recesses 11. Thus, the temperature formed at the temperature sensors 5 is largely identical to the temperature of the melt.

[0028] Thermocouples such as PT 100 thermocouples or PT100 resistance temperature sensors can be used as temperature sensors 5, but it is of course also conceivable to use other conventional sensors.

[0029] The electrical voltages or resistances generated by the temperature sensors 5, which correlate with the temperature of the melt, are conducted by means of measuring lines 6 from the temperature sensors 5 to the bearing-side end 8 of the shaft 3. There, via a known arrangement of slip rings 7, they are transmitted from the shaft 3, which also rotates with the rotation of the screw elements 2, to a stationary and stationary sensor (not shown here). Such slip ring arrangements 7 are known per se.

[0030] The measured values ​​are then transmitted from the transducer to the evaluation unit (not shown), which then calculates temperatures at the temperature sensors 5 from the electrical voltages or resistances. In this case, it is also possible for the evaluation unit to correct the values ​​measured by the temperature sensors 5 with regard to the effect of heat conduction between the shaft 3 of the extruder and the temperature sensor 5. Since the heat transfer from the melt to the temperature sensor 5 is not entirely unaffected by heat conduction through the shaft 3 and the screw elements 2, it can be advantageous for these effects of heat conduction to be corrected by the evaluation unit, for example by the evaluation unit correcting the measurement signals by mathematically correcting the deviation between the temperature of the melt and the shaft 3, in particular by taking into account the stationary heat conduction in the shaft 3.For this purpose, the known laws of heat conduction can be applied and calculated with the measured values ​​of the temperature sensor 5, allowing more precise temperatures and temperature profiles to be determined. This also makes it possible to measure the melt temperature even if the section between adjacent screw elements 2 is not completely filled with melt.

[0031] The inventive arrangement of the temperature sensors 5 also makes it easy to increase the number of measuring points and achieve a variable spatial distribution of the measuring points by adjusting the desired position of the temperature sensors 5. Furthermore, the temperature sensors 5 can be easily calibrated. Furthermore, the temperature measurement is more accurate, since the temperature measurement is not influenced by the temperature of the extruder barrel. Furthermore, wear and tear or the problem of deposits, as is the case with optical measurement methods, are avoided.

[0032] The method and the device according to the invention can be used in extrusion processes with one or two screws, for example for compounding, reactive extrusion, product formulation (chemicals & pharmaceuticals) as well as for process development and process optimization of extrusion processes and allows a significantly improved process control. Part number list 1 extrusion device 2 screw elements 3 shaft 4 Gearing shaft / worm elements 5 Temperature sensor 6 measuring line 7 slip ring transformers 8 bearing-side end shaft 9 Shaft bearing 10 Deepening measuring line 11 Temperature sensor recess

Claims

[1] Device (1) for measuring the melt temperature in extrusion processes in which heated and plastic substances are processed by means of extrusion screws (2), characterized by in that at least one temperature sensor (5) is arranged on or in the shaft (3) of at least one extrusion screw (2) and detects the local temperature of the melt, wherein the at least one temperature sensor (5) is connected to an evaluation unit via a transmission device (6, 7) for the measurement signals, which is also arranged on or in the shaft (3), which evaluation unit evaluates the measurement signals. [2] Device (1) according to claim 1, characterized bythat the at least one temperature sensor (5) is in electrically conductive connection with a stationary counter-slip ring (7) via measuring lines (6) arranged on or in the shaft (3) with at least one slip ring (7) arranged on the end region side of the shaft (3), which counter-slip ring decouples the measuring signals of the at least one temperature sensor (5) and forwards them to the evaluation unit. [3] Device (1) according to claim 1, characterized by that the at least one temperature sensor (5) is connected to the evaluation unit via wireless transmission techniques. [4] Device (1) according to one of claims 1 to 3, characterized by that the at least one temperature sensor (5) is arranged on or in the shaft (3) below the removable screw elements (2). [5] Device (1) according to claim 4, characterized bythat the at least one temperature sensor (5) is arranged radially below the toothing (4) of the shaft (3) below the screw elements (2). [6] Device (1) according to one of the preceding claims, characterized by that the screw elements (2) can be pushed over the shaft (3) with the at least one temperature sensor (5). [7] Device (1) according to one of the preceding claims, characterized by that the at least one temperature sensor (5) and the shaft (3) are in good thermal connection with one another via thermally conductive substances, in particular thermal paste. [8] Device (1) according to one of the preceding claims, characterized by that more than one temperature sensor (5) is arranged at different points along the axis of the shaft (3) and records the temperature of the melt prevailing there. [9] Device (1) according to one of the preceding claims, characterized bythat thermocouples, in particular PT100 thermocouples or PT100 resistance temperature sensors, are arranged on or in the shaft (3) as temperature sensors (5). [10] Device (1) according to one of the preceding claims, characterized by that the measuring lines (6) run on or in the shaft (3) below the removable screw elements (2). [11] Device (1) according to one of the preceding claims, characterized by that the measuring lines (6) run from the temperature sensor (5) to the gear holder (8) of the extruder screw shaft (3). [12] Device (1) according to one of the preceding claims, characterized byin that the measuring lines (6) in an end region of the extruder screw shaft (3) are in conductive connection with a slip ring (7) which is rotatable with the shaft (3) and which interacts with a stationary counter-slip ring (7), preferably arranged in the region of the lantern of the extruder, which decouples the measuring signals of the at least one temperature sensor (5). [13] Device (1) according to one of the preceding claims, characterized by that the evaluation unit receives and evaluates the measurement signals of the at least one temperature sensor (5) via a measuring sensor. [14] Device (1) according to claim 13, characterized by that the evaluation unit corrects the measured values with regard to the effect of heat conduction between the shaft (3) of the extruder and the temperature sensor (5). [15] Method for measuring the melt temperature in extrusion processes in which heated and plastic substances are processed by means of extrusion screws (2), in particular using the device according to claim 1, characterized by that at least one temperature sensor (5) on or in the shaft (3) of at least one extrusion screw (2) detects the local temperature of the melt and a transmission device (6, 7) for the measuring signals, also arranged on or in the shaft (3), forwards the measuring signals to an evaluation unit and the evaluation unit evaluates the measuring signals. [16] Method according to claim 15, characterized by that the evaluation unit corrects the values measured by the at least one temperature sensor (5) with regard to the effect of heat conduction between the shaft (3) of the extruder and the temperature sensor (5). [17] Method according to claim 16, characterized bythat the evaluation unit corrects the measurement signals by mathematically correcting the deviation between the temperature of the melt and the shaft (3), in particular by taking into account the stationary heat conduction in the shaft (3).

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