【作者】 韩科；

【导师】 李增和；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2011， 硕士

【摘要】 目前国内外对于超声波测量聚合物熔体密度的方法多为离线法,即通过超声波透射声速的波形图,在图上测量出波幅的衰减值,结合相关参数求得熔体的声阻抗值,并利用声阻抗、声速与密度的数学关系,间接得到熔体密度的方法,此法由于其滞后性与低效性,不宜用于聚合物成型加工过程中对熔体的密度进行连续测量。本文介绍了一种利用超声波在线测量聚合物熔体在不同温度及压力状态下熔体密度的方法,该方法分为三个步骤：第一步借助聚合物熔体PVT相互关系原理,将测量微距离的读数百分表安装在改进结构的熔体流动速率试验机上,可以测量出任意熔融温度及压力下的聚合物熔体密度,并对测量结果进行了理论分析,其熔体密度测量值符合聚合物自由体积理论,即聚合物熔体密度随温度增大而减小,随压力的增大而增大。另外,运用该方法还能够测量聚合物熔体的体积弹性模量,通过对测量结果的理论分析,发现熔体的体积模量也随温度的升高而减小,随压力的增大而增大。第二步利用自己设计制作的装置,可以测量出不同温度及压力状态下的聚合物熔体的透射声速,通过对测量结果的分析,发现透射声速与聚合物熔体的动态密度变化规律保持一致。第三步将测量得到的聚合物熔体动态密度与对应条件下的熔体透射声速,采用改进最小二乘多项式拟合曲线法来建立熔体密度软测量的数学模型。通过拟合出的曲线,结合透射声速的数值,直接得到相对应的熔体密度。该方法操作简单,实验装置便于设计制作,所得数据较为准确。后期需要做出相应的配套软件系统,就能够通过透射声速瞬时得到熔体的密度,实现在线测量的目的。更多还原

【Abstract】 At present many domestic and foreign ultrasonic measurement of polymer melt density depend on offline methods. It means through the ultrasonic transmission sound speed oscillogram, measuring the wave amplitude pad value. Use related parameter to obtain the melt acoustic impedance value. Through the acoustic impedance, the sound speed and the density relation, the melt density can be obtained indirectly. Because of its hysteresis and low efficiency, it is not suitable for melt density measurement continuously in the polymer formation process.This article introduced one kind of ultrasonic online measuring polymer melt density under the different temperature and the pressure, and the method divides into three steps:First step, based on the PVT theory of polymer melt, a Melt Flow Rates Tester was modified with a dial indicator for the measurement of the micro distance. With the modified instrument, polymer melt density can be measured under any pressure and melting temperature. By further analyzing the result, the data of the melt density is agreed with the free volume theory, that is, the polymer melt density decreased with the higher temperature and increased with the higher pressure. Moreover, this method also to be able to survey the polymer melt bulk modulus, by analyzing the result, the melt the bulk modulus also elevates along with the temperature reduces and increases along with the pressure increases.Second step, uses the equipment designed and manufactured by ourselves to survey polymer melt transmission sonic speed under different temperature and pressure. With analysis of result, the rule that transmission sonic speed maintains consistent with the polymer melt dynamic density changing was discovered.Third step, depending on polymer melt dynamic density and the corresponding condition melt transmission sonic speed, uses the Least square polynomial method to establish the melt density measurement mathematical model. With the curve the melt density can be obtained directly.This method has a simple operation, and the test equipment is easy to design and manufacture, and the data is more accurate. Later period if the corresponding data software system can be created, the melt density will be obtained through the transmission sonic speed, then the online measurement can be realized.更多还原