【作者】 陈友兴；

【导师】 王召巴；

【作者基本信息】 中北大学 ， 精密仪器及机械， 2010， 博士

【摘要】 在聚合物共混过程中,对聚合物混合状态的实时监测具有重要的意义,它可以有效地提高生产效率,缩短新产品的研发周期,降低生产和研发成本。本文针对聚合物共混过程中混合状态的监测问题,提出了超声在线监测方案,并研制了适用于熔态聚合物监测的高信噪比超声传感器,探讨超声信号特征参数表征聚合物混合状态的方法及其相应的信号处理技术。本文的主要研究内容包括：(1)针对超声波在缓冲杆中传播存在尾随回波的现象,采用波导理论分析了超声波在杆中传播的边界反射、波型转换等情况,给出了尾随信号的间隔与杆直径和声速的确定关系；提出了超声波在有限长中传播的系统仿真方法,剖析了杆长度、直径对回波信号幅值、尾随回波幅值以及信噪比的影响；建立了超声波在缓冲杆中传播的有限元模型,分析了超声波在圆柱杆、包覆圆柱杆、双锥形杆、包覆双锥形杆中传播的回波信号；综合上述的研究结果,探讨了抑制尾随回波的措施。研究成果也可应用于不同监测领域高信噪比缓冲杆的设计和加工(2)为了设计高信噪比的超声缓冲杆,试验分析了声衰减、声速、声阻抗对缓冲杆端面回波信号、尾随信号和检测特征回波信号的影响,结果表明,当使用温度和强度满足要求的情况下,非金属缓冲杆用于检测熔态聚合物时比金属缓冲杆更有优势。(3)针对聚合物混合状态的在线监测要求,提出了适用于熔态聚合物监测的超声传感器设计方案；结合超声波在缓冲杆中传播的理论分析和试验结果,以聚醚醚酮(PEEK)作为缓冲杆材料,设计了多种不同结构、不同长度缓冲杆的超声传感器；测试了所设计传感器在熔态聚合物中的超声传输性能和检测能力,并将其应用于多种聚合物/填充料混合物的高温检测试验,结果表明所研制的传感器在150℃下工作的信噪比达20dB。(4)为了在监测过程中准确获取表征聚合物混合状态的超声参数,探究了特征回波信号与螺杆运转的准周期性,确定了以同一位置不同旋转周期的回波信号的幅值偏差度作为表征聚合物混合状态的参数；利用秩滤波和低通滤波有效地校正了由于温度等外界因素影响所造成的幅度变化趋势,采用相关系数法进行不同旋转周期间同一位置的数据匹配；探讨了获取同一位置幅值偏差度的差值比较法和比值比较法。(5)在单螺杆挤出机上完成了聚合物/填充料混合物、两种聚合物混合物以及多种原料混合物挤出过程的超声在线监测试验,采用扫描电镜观测了试验样品,并分析了各种试验过程的超声特征参数；研制了螺杆挤出机聚合物混合状态超声在线监测系统样机。论文的研究为拓展超声检测技术在新领域的应用和聚合物生产过程的可视化具有重要的理论意义和实用价值。更多还原

【Abstract】 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.更多还原