吹膜製程之螺旋軸心模頭最佳化設計

Abstract

螺旋軸心模頭廣為應用於圓管狀產品以及高分子薄膜製造，其幾何構造上特徵在於軸心表面上有數個螺旋溝，而高分子熔膠由螺旋溝道漸流入間隙。良好的模頭設計，可增進流量均勻度和避免縫合線產生。 螺旋軸心模頭設計之幾何參數有軸心直徑、螺旋溝數目、起始溝寬、起始溝深、螺旋角、軸心傾斜角、溝道繞行圈數及間隙，其中軸心傾斜角採取兩段式的設計。本文使用二維流動數學模式並假設流體符合冪次定律以分析模頭內非牛頓流體流動，同時配合田口法分別搜尋以流量均勻度及混合度為指標的最佳形狀參數，試圖以較多幾何參數以及不同指標為設計過程中的考量，以求同時達到良好之均勻度以及混合度。 最後檢視在等溫情況下搜尋之最佳形狀參數於非等溫與等溫情況下的性能表現，同時評估加入模唇段對模頭性能的影響。

Spiral mandrel dies are widely used in the production of tubular products and polymeric films. The feature of the die is several helical grooves cut on the mandrel surface, and the melt flow from groove leak to clearance gradually. Proper die design can improve flow uniformity and to avoid occurring the weld line. Geometrical parameters in designing the spiral mandrel die are: diameter of the mandrel, the number of helical groove, initial width and initial depth of the helical groove, the groove helix angle, overlap of helical groove, the initial gap, and the taper angle, which we introduce two-sectional design. In this article we analyze non-Newtonian fluid flow in the die. Two-dimension mathematical model is utilized, and the viscosity of polymer melt is assumed to be Power-Law model. Associated with Taguchi method, several optimal sets of die geometric parameters is searched by assessing the flow uniformity and mixing degree respectively. We consider more geometric parameters and different targets during searching process to attain both good flow uniformity and mixing degree. Finally, performance of dies under nonisothermal condition is compared with those determined on isothermal condition. Die lips is discussed at the same time.