Research On The Measurement Of Polymer Melt Key Parameters Based On Ultrasonic

During the precision injection molding process of polymer, whetherthe weight of polymer melt injected from nozzles can be preciselycontrolled, is the direct factor which affects the weight repeatabilityprecision of accurate injection molding parts.As in the processing of injection, the density of polymer melt varieswith the state variables like pressure and temperature, traditional volumecontrolling method cannot realize consistency control of injection weight.While on the other hand, injection weight controlling method based ononline measurement of melt density is the best solution to solve thisproblem.This paper is going to study a soft measurement method of polymermelt key parameter, namely, the melt bulk modulus; it puts forward a softmeasurement model of melt density based on single value variable ofultrasonic velocity; then, the dependence and quick response to mediumdensity of ultrasonic propagation velocity is used to meet the onlinedensity measurement of polymer melt, which has injection molding cycle and multi-level infection pressure. The paper devotes to the followingtasks:1. Based on the comprehensive analysis of successful applications ofultrasonic technology in online measurement of liquid and solid mediadensity and in polymer processing, the single-valuedness and quickresponse existing in the ultrasonic real-time measurement of polymermelt density based on the transmission mode is studied theoretically andsystematically, Furthermore, online measurement of melt densityachieved by ultrasonic technology during the injection molding processof polymer melt is put forward.2. The response speed of easily-measured variables related to thepolymer melt density variables is studied, and the soft-measurementmodeling method adapted to melt density and volumetric elastic modulusof polymer melt is decided from both mechanism modeling and statisticalmodeling.3. Necessary experimental equipments are researched and developedfor online measurement of melt density based on ultrasonic technology,including the experimental device which could imitate pressure variationin injection process. A study of the measurement methods for the keyphysical parameters of polymer melt, such as active density and bulkmodulus is further performed. Then influences on the measuring accuracyof ultrasonic propagation velocity by the interferences of multiple echoes and environment noises during the ultrasonic transmission propagationare removed by adopting the combined digital filtering method.4. A soft measurement model of the the bulk modulus of polymermelt with the state variables of temperature and pressure as inputvariables is established on the basis of neural network. Meanwhile, themeasurement accuracy of such soft measurement model of bulk modulusof polymer melt is significantly improved through the application ofneural network integration technonology based on the optimal parts of thenetwork.5. The online soft measurement model of melt density based onultrasonic velocity is established by improved least squares binarypolynomial fitting, and used in the injection process. It is certified in theexperiment that the weight control method of injection weight based onthe melt density online measurement is better than the volume controlmethod in the improvement of the weight repeatability precision ofinjection molding parts.