Barr及Dray & Lawrence障壁螺桿之電腦輔助設計

Abstract

單螺桿於熔化區內，會聚集熔融液體於固體床側，因熔融池中迴流運動不 斷地對固體床擠壓，使固體床有瓦解之可能。一旦固體床瓦解，將使未熔 化之顆粒懸浮於膠料中，使得熔化效率下降而且不穩。而障壁螺桿即是針 對單螺桿此缺點設計的。對螺桿各部份之功能區分上和單螺桿相同，皆分 為固體傳送區、遲滯區、熔化區、融熔物傳送區。本論文乃利用電腦模擬 方式，分別對 Barr和Dray & Lawrence這二支障壁螺桿於各部份因操作條 件的改變，觀察其表現情形，以期對此二支障壁螺桿有一完整性的認識。 操作條件的變化方面，我們分別於各部份改變了螺桿轉速、套筒溫度、並 在固體傳送區中加入了梯度和非等壓性等因素的影響。結果顯示，由於幾 形狀的不同，在相同的操作條件下，Dray & Lawrence螺桿的熔化率比 Barr螺桿好一些，最後的物料平均溫度兩者大致相同，但在背壓方面， Bar螺桿則高出Dray & Lawrence螺桿甚多。 In the melt zone of single screw, the melt would accumulate beside the solid bed, leading to the formation of melt pool. The solid bed was continuously compressed by the circulating flow of melt pool. This would cause the possible occurrence of solid bed break-up. Once the solid bed breaked up, the unmelted resin particles would suspend in the melt, causing the melting efficiency to decrease and become unstable. The barrier screws were designed based on the disadvantages of single screw. The barrier screw has same function zones as those of the single screw. Those function zones can be classified as solid conveying zone, delay zone, melting zone and metering zone. In this paper, the computer simulation was made to investigate the performance of each function zone under various operation conditions. By doing this, we expect to have more clear under- standing for two barrier screws. With respect to the operation conditions, we varied the screw speed and barrel temperature respectively and took into consideration the influence of taper and nonuniform pressure distribution in solid conveying zone. The results demonstrated that Dray & Lawrence screw has better melting rate than that of Barr screw under the same operation conditions. This is attributed to the facts that both of the screws have different geometry. The simulation results also illustrated that the bulk temperature of melt was approxi- mately the same, meanwhile, for back pressure, Barr screw will generate higher pressure than Dray & Lawrence.