障壁螺桿接流道式混合元件之電腦輔助設計

Abstract

在傳統單螺桿加入一道障壁梯板可改良因固體床瓦解造成出料不穩的現象，而混鍊效果的提升則是在計量區中加裝混合元件。 本文旨在模擬探討障壁螺桿接混合元件其加工條件及幾何形狀對螺桿接混合元件特性的影響。在障壁螺桿幾何形狀探討部份是改變熔化區起始溝深、液體溝道最終溝寬、障壁梯板螺旋角及液體溝道壓縮比。加工條件方面則是改變轉速及套筒溫度。混合元件幾何形狀則是改變混合元件障壁梯板與套筒之間隙、障壁梯板寬度及障壁梯板傾斜角。在螺桿特性分析包括：固體床速度、熔融薄膜厚度、單位長度熔化率、單位面積熔化率、熔化效率、熔化率、壓力分布及平均溫度，在混合元件特性分析則探討改變流量對混合元件軸向壓力變化的影響。 高分子熔融行為主要根據Tadmor熔融模式，數值方法在障壁螺桿部份採用有限差分法，而混合元件則採用流動分析網路法(FAN)。以電腦模擬LDPE高分子材料的押出程序。

Barrier Flight is introduced in the conventional single screw to improve the phenomena of solid bed break-up and surging. In order to futher increase the mixing effect, the fluted mixing element is also added to the metering section of screw. This study aims to investigate the effect of various processing conditions and geometry of barrier screw with different types of fluted mixing elements on the performance of the entire screw by numerical simulation. For the barrier screw section, various of initial melt channel depth, final channel width of melt channel, helical angle of barrier flight and compression ratio of melt channel were changed to study their effect on the screw performance. In addition, for the fluted mixing element, the clearance between barrier flight and barrel surface, the width of barrier flight and helical angle of barrier flight were also varied to investigate their effect on the screw performance. The performance of the barrier screw was based on the analysis of solid bed velocity, melt film thickness, melting rate per unit length, melting rate per unit contact area, melt efficiency, melting rate, pressure build-up and bulk temperature. For the mixing element section, the relationship between flow rate and pressure drop was evaluated to analyze its performance. For the barrier screw section, finite difference method based on the Tadmor melting model was ultilized. However, flow analysis network was used to simulate the mixing section. Using LDPE as the processing material, the extrusion process was analyzed by computer simulation.