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雙螺桿擠出機內非牛頓粘性流場計算及其擠出行為研究

本文首先根據相對運動原理對雙螺桿嚙合幾何學進行了全面、系統的研究,得出了螺桿各幾何參數之間的相互關系以及螺桿各截面幾何形狀的解析表達式,推導出了螺桿各特征面積及體積的計算公式,討論了它們同螺桿幾何參數之間的關系,進而從幾何學角度提出了螺桿各段幾何參數的設計準則。本文還比較了理論結果和測繪結果,證明了本文提出的雙螺桿嚙合幾何學理論的可靠性。

   針對雙螺桿擠出機內流動介質的特殊流動特性和流動區域的復雜性,本文在分析指出傳統的壓力——速度有限元法在解這類流場時的不足之后,首次提出用新型的罰函數有限元法及國際上發展不久的邊界元法來求解雙螺桿擠出機內的流場。對非線性問題也提出了自己的處理方法,并證明了上述方法在解復雜流場問題時具有經濟、方便、高效、通用、可靠等優點。

   本文對同向旋轉雙螺桿擠出機計量段及排氣段內的流場建立了迄今為止最接近實際情況的物理模型和數學模型,并利用上述新方法在微機上對計量段及排氣段內非牛頓、不等溫、且含三個方向速度的粘性流場進行了計算。此后,在流場計算結果的基礎上,對計量段、排氣段重要的工作特性參數進行了計算、分析和討論,進而對工藝參數和螺桿幾何參數提出了選擇及設計的原則,對生產中出現的問題(如排氣口冒料及如何改善排氣效果、抑制工作特性參數的波動等)提出了解決途徑。

   本文根據流場相似條件對同向旋轉雙螺桿擠出機計量段的螺桿幾何參數及機器工藝參數提出了相似設計方法。

   本人曾在實驗室及工廠作了大量實驗,文中分析比較了理論計算值及實驗結果,證明了本文提出的模型合理、計算方法先進、結論可靠。因此本文提出的理論均可用于指導生產設計。

Non-Newtonian viscous flow field calculation and extrusion behavior of the twin-screw extruder

In this dissertation, the twin screw intermeshing geometry is systematically analyzed according to the rolative motion principle. The relations among the geometric parameters of screw and the analytic of screw sections are derived, the formulas of calculating the aroa and volume of characteristic screw regions are deduced, and the relations between them and the geometric parameters of screw are discussed. Based on the results above, the principles of designing the geometric parameters of scrow are put forward from the gemotric point of view. To verify the validity of theory, the theoretical and experimontal results of intermeshing geometry are compared.

   Countering the special flow characters of the fluid and the complex of the flow field in twin screw extruder, the penalty finite element method (PFEM) and the boundary element method (BEM) are first adopted in this dissertation to solve the flow field in twin screw extruder after analyzing the defects of the traditional pressure-velocity finite element method in solving the similar flow field and a now method is proposed to handle the nonlinearity. It is proved by practical calculation that new methods above have many advantages (such as economy, convenience, high efficiency, high generality and reliability etc. ) in solving the complicated flow field.

   Based on analyzing the work done by predecssors, the physical and mathomatical models which are most close to practice up to now are established for the flow fields in the metering zone and venting zone of the intermeshing corotating twin screw extruder. By means of PFEM and BEM, the viscous flow fields in the metering zone and venting zone which are nonnewtonian, nonisothermal and include three directional velocities are solved in IBM-PC computer, according to the results of flow field calculation, the operating charaeteristic parameters are colculated, analyzed and discussed. After this, the Principles of selecting the technological parameters and designing the geometric parameters of screw are raised on the basis of the achievement above, in addition, the ways of solving the problems occuring in practice (such as how to restrain melt flooding from vent, improve the venting effect, restrain the fluctuation of operating characteristic parameters and so on) are pointed out.

   In this dissertation, the principles of scaling corotating twin screw extruder up and down are proposed on the basis of analyzing the similar conditions of the flow field in metering zone.

   The experimental results obtained in the laberatory and factories are compared with the theoretical results, it is proved that in this dissertation the models are resonable, the calculating methods are advanced and the conclusions are reliable, therefore, the theory established in this dissortation can be used to direct practice. 
  

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