Research On Key Techniques Of Ultrasonic Monitoring For The State Of Polymer Compounding Extrusion

Real-time monitoring the compounding state of the polymer is very important during extrusion process. It is a good approach to increase production efficiency, shorten the new product development cycle and reduce the product cost. For the issue of monitoring polymer compounding state in screw extruder, a new in-line monitoring proposal using ultrasonic technology was presented. The ultrasonic probes with high SNR suitable for monitoring melt polymer were designed and fabricated. The method using ultrasonic characteristic parameters to represent polymer compounding state and corresponding signal processing technology were studied.The contributions in this paper are described below.(1) In view of the presence of trailing echo during the ultrasonic propagation in a buffer rod, the wave guide theory was used to analyse the wave reflection and mode conversion at the boundary, and the relation between the intervals of the echoes and rod's diameter vs. wave velocity was established. Then the simulation approach based on the system model of ultrasonic propogation in a finite rod was given. The effect of the length and diameter of the rod on the amplitude of ultrasonic signals and trailing echoes was analyzed. The FEM model of ultrasonic propagation in a buffer rod was built, and the ultrasonic echoes through cylindrical rod, clad cylindrical rod, double cone rod and clad double cone rod were analyzed by the FEM. Measures to suppress the trailing signal were studied based on the above results. The results can also be applied for designing and machining buffer rod with high SNR in some related other applications.(2) Aim to design an ultrasonic buffer rod with high SNR, the effects of attenuation, velocity and impedance on ultrasonic signals from rods'end, trailing echoes and characteristic signals were studied based on experiment using different material buffer rods. The results show that the nonmetal buffer rod is more suitable than the metal buffer rod for testing melt polymer. (3) The proposal of ultrasonic probe applying for melt polymer testing was presented to meet the requirement of in-line monitoring polymer compounding state. Based on theoretical and experimental results of ultrasonic propagation in a buffer rod, some ultrasonic probes composed of polyetheretherketone(PEEK) buffer rods with different structure and length were designed. The signal transmission rate in melt polymer of the ultrasonic probes was analyzed. And the probe was tested in the polymer/filler blends at high temperature. The results show that the ultrasonic probe designed in this paper has SNR of above 20dB under the temperature of 150℃.(4) The quasi-periodic between the characteristic signals and the screw was studied in order to gain ultrasonic parameter for characterizing polymer compounding state accurately during monitoring process. The amplitude deviation of ultrasonic signals reflected from the same position in different cycle was used to represent polymer compounding state. Rand filtering technique and low-pass filtering technique were used to correct the amplitude error of signal caused by some outside factors such as temperature. The correlation technique was used to match the signal data from same position in different cycle. The difference-comparative method and ratio-comparative method were studied to represent amplitude deviation of the ultrasonic signal from the same position.(5) The mixtures, which are composed of one polymer and filler, or two polymers, or more than one polymers and fillers, were compounded in single-screw extruder respectively, and the compounding state was monitored at the same time. The scanning electric microscopes of compounding samples were gained and the ultrasonic characteristic parameters representing the compounding state were analyzed. An ultrasonic in-line monitoring prototype system of polymer compounding state in screw extruder has been developed.The work of this paper is of profound theoretical and practical significance on the application in ultrasonic technology in new field and visualization of the preceture of polymer production.