雙梯板障壁螺桿電腦模擬

Abstract

目前使用單螺桿押出機中最煩人的部分是出料不穩，即所謂的 'Surging '。而 障壁螺桿最基本概念就是在固體床與熔融池間加一道障壁，使固體 床與熔融池分離，以解決其缺點而設計的，雙梯板(ch=2)與單梯板(ch=1) 不同在於障壁梯板數(barrier flights)，一為一片，一為兩片障壁梯板 。在障壁螺桿的設計及加工中，不同的幾何形狀，及加工條件，例如：溝 寬、溝深、螺旋角度及壓縮比等及螺桿溫度，轉速等，均會直接影響熔化 速率和膠料在螺桿內的壓力及平均溫度。本論文利用電腦模擬，針對LDPE 高分子材料在Maillefer 、Barr、Dray ＆ Lawrence及Kim 四支雙梯板障 壁螺桿，在不同加工條件下，或不同幾何形狀下，觀察熔化區固體溝道中 ，固體床速度，熔化速率，熔融薄膜厚度，熔化量，及整支螺桿之溫度， 壓力之變化。並就單溝道與雙梯板作一比較。螺桿設計的目的在於押出量 與熔化混合程度的提升，而混合程度與背壓有密切關係。背壓大則物料在 螺桿中有較長的滯留時間，熔化混合效果較佳。經本論文所得結果，我們 知道在障壁螺桿中，雙梯板(ch=2)與單梯板(ch=1)的比較上，雙溝道的押 出量及背壓均較單溝道為理想。 One of the most troublesome aspects in the use of plasticating single-screw extruders , which has long been recognized , is fluctuations of flow rate in the extruder , commonly referred to as 'surging'. The cause of 'surging' has been debated for a long time. Today , it is widely accepted that the breakup of solid bed in the melting section of a plasticating extruder is the primary source of the surging. The reason for breakup of solid bed is due to the circulation flow of melt pool , which melting zone of a traditional single screw , would continuously push the solid bed , thus leading to the solid bed breakup . Once the solid bed breakup , it would cause the unmelted particulate solid to suspend in the melt. Consequently , this would cause the decrease of melting rate and unstable output rate . The basic idea for barrier screw is to design a plasticating screw in such a way , that the solid bed can be separated from the melt pool by a secondary barrier flight. For the design of a barrier screws , channel width , channel depth , helical angle and compression ratio etc. would directly affect the melting rate , pressure distribution and bulk temperature of the screw . The work aims to develop the computer simulation with LDPE as the processing material for the four different types of barrier screws . The solid bed velocity , melt film thickness , melting rate , pressure distribution and bulk temperature were investigated under various processing conditions and geometry of the screw , and compared the difference for single-flight and double-flights of the four barrier screws.