Polymer Melt Temperature Distribution Measuring Mechanism And Experiment Based On Electrical Capacitance Tomography

Polymer melt temperature is one of the most important process variables to measure duringthe manufacture of polymer products, because polymer rheology and stability are directlyrelated to polymer melt temperature. However, there is no effective means so far to measurethe internal melt temperature distribution，which has direct influence on final product qualityand properties, then so much raw material and energy goes to waste. This paper proposes anovel method to measure polymer melt temperature distribution. It is based on electricalcapacitance tomography (ECT) technology. This method will promote test technologydevelopment and improve mechanical and electrical equipment automation level, which hasan important academic value and practical significance for the promotion of development andapplication of the precise measuring technology. The research work is funded by the Programof National Nature Science Foundation of China (NO.60801034).The thesis firstly analyzes the domestic and international research status of electricalcapacitance tomography technology and different kind of polymer melt temperaturemeasurement methods, secondly puts forward a novel method to measure polymer melttemperature distribution based on ECT, and then researchs the mechanism of this newmeasurement method, finaly builds the experiment device to prove it works. Main researchworks in this paper are as follows:(1)Present a novel method and system to measure polymer melt temperature distributionbased on ECT, and describe the work mechanism of the new measurement method and systemin detail. The system consists of capacitive polymer melt temperature distribution sensor,polymer melt temperature distribution data acquisition system and polymer melt temperaturedistribution imaging system and so on three function modules. The mathematical descriptionof polymer melt temperature distribution gray vector is deduced and get the melt temperaturedistribution of the polymer acquisition method, which is based on the capacitance tomographypolymer melt temperature distribution measurement method, and the basic principle of theinverter, transformation and change maxwell equation. This method has some characteristics,such as non-intrusive and response speed, simple structure and easy to implement and so on.(2) Establish polymer melt permittivity and the temperature relation model on the basis of experiment, study the polymer permittivity and influence factors, discover one of thestrongest influence factors is polymer polarity, polymer permittivity increase with itsmolecular polarity; The polymer temperature impact permittivity and varies with thepolarization types, how polymer temperature to impact permittivity is not clear, so choose avariety of polarity polymer materials from weak to strong, and are extensive using, namelythe low density polyethylene, polycarbonate, nylon66. Do the dielectric performance testinganalysis using dielectric analyzer, broadband dielectric spectrometer. The results show thatpolycarbonate permittivity and temperature are into one-to-one relationship at the measuringtemperature range; the experiment results of low density polyethylene comply with expectedin test frequency, so can get its temperature by measuring the permittivity; in frequency2Hzand20kHz the experiment of nylon66is not in conformity with the expected results, and therest of the test frequency comply with the expected. Then, establish polymer melt permittivityand temperature relation model. Use of general global optimization method, the BP neuralnetwork two kinds of methods to build low density polyethylene and nylon66related datamodeling. Low density polyethylene data fitting, best fitting effect f=1000Hz, maximumabsolute residual is0.12℃; For nylon66data fitting, f=2kHz/2MHz, best fitting effect,maximum absolute residual of0.52/0.37℃. Use MISO, SISO model and the BP neuralnetwork model of low density polyethylene, f=1000Hz that was set model optimal, and SISOmodel of the BP neural network model is better than the general global optimization model,the largest absolute residual is0.08℃; Modeling nylon66, MISO model of the BP neuralnetwork model each index all the best, maximum absolute residual is0.29℃.(3)Present ideas about designing melt temperature distribution measurement experimentdevice, which simulates high temperature polymer melt station in the extrusion processing,measures polymer melt temperature distribution based on ECT technology and thermocoupletemperature measurement way, and then can provides the groundwork experiment platformfor measuring the melt temperature distribution in extrusion molding process. Then, designmelt temperature distribution measurement experiment device, which include capacitivepolymer melt temperature sensor, polymer heating, cooling module, polymer temperaturecontrol module three parts. First design the overall structure of capacitive polymer melttemperature sensor, then respectively design sensor electrode, signal lines, insulation pipe, solve the insulation pipe resistance to high temperature high pressure sensor, electrodes withinsulation pipe arrangement and the connection, high temperature signal lines connectedelectrode and problem and so on. When designing polymer heating, cooling module, firstchoice heating, cooling way, then the heating power, the final determination cooling devicestructure; Polymer temperature control module temperature control instrument and relateddevices including, design temperature control circuit. Finally, build the polymer melttemperature distribution measurement system, which includs thermocouple melt temperaturemeasurement system and polymer melt temperature distribution measurement system twoparts. The polymer melt temperature distribution ECT measurement system includes:thermocouple type selection, thermocouple positioning module, temperature acquisitionmodule, hardware and software of polymer melt temperature distribution ECT measurementsystem.(4)Design polymer melt temperature distribution measurement experiment device, whichis used to measure nylon66, so get the permittivity distribution of nylon66at melting andcooling process, and get the relationship between temperature and average value ofcapacitance when temperature from24℃to300℃and300℃to24℃. The experimentalresults show that inserting thermocouple will lead to measuring area permittivity becomesmaller, influence area more than90%, and close to the thermocouple influence in degree. Allover, the experimental results show that, using the ECT technology can measure polymer melttemperature distribution.