押出吹袋模頭之電腦輔助設計

Abstract

吹袋模頭又稱螺旋軸心模頭，廣為應用於圓管狀產品的製造，例如水管，塑膠袋等。其特徵在於軸心的表面上有數個螺旋溝，此設計最主要目的在於增進流量均勻度和消除縫合線，以增加產品美觀及耐用性。 螺旋軸心模頭共有六個設計參數，分別為軸心直徑、螺旋溝的數目、螺旋溝的最初寬度、螺旋溝的最初深度、螺旋角及間隙，本文以二維流動模式分析模頭內非牛頓流體的流動，並在固定軸心直徑十一公分及四個溝槽下，結合田口法，且以流量均勻度、混合度、總壓力降作為判定模頭優劣的性質，而於等溫假設下，決定其餘四個設計參數之最佳值，從而建立模頭的最佳幾何形狀。 最後檢視這些模頭，於非等溫的真實情況下，其效能如何，並與等溫作比較，結果證實在等溫假設下，已可初步決定模頭的形狀。

The blown film die , which is also called the spiral mandrel die , is widely used in the production of tubular products , such as pipes , plastic bags and so on . In order to produce the beautiful and durable products , helicalgrooves cut on the mandrel surface are designed to increase flow uniformity and eliminate welding lines . They are the main characteristics of the spiral mandrel die . There are six parameters in designing the spiral mandrel die , which are the diameter of the mandrel , the number of the helical groove , the initial width of the helical groove , the initial depth of the helical groove , the helical angle and the gap , respectively . This study analyzed the isothermal-non-Newtonian flow , based on the two-dimensional flow simulation , in a die with a mandrel of 11 cm diameter and four helical grooves . Then , the Taguchi method was used to determine the optimal values of the rest of four parameters by considering the performance of the die . The performance of the die was examined from flow uniformity , degree of mixing and total pressure drop . Finally , the optimal geometry of the die was determined . Sequentially , the performance of the die was examined under the nonisothermal condition and the discrepancy between the isothermal and the nonisothermal condition was compared . The results show that it is enough to determine the elementary shape of the die according to the isothermal assumption .