Maillefer,Barr,Dray & Lawrence 及Kim等障壁螺桿之電腦輔助設計

Abstract

傳統單螺桿在熔化區,由於熔融池不斷的洄流運動，會擠壓固體床， 使固 體床有瓦解的可能。一旦固體床瓦解,將會使為熔化的固體顆粒懸浮於膠 料,使得熔化效率下降,且出料不穩。而障壁螺桿即是針對此缺點而設計的 。在障壁螺桿的設計中,溝寬,溝深,螺旋角及壓縮比等,直接影響熔化速率 和膠料在螺桿內的壓 O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四支障壁螺桿,在不同加工 條件下,或不同幾何形狀下,探討整支螺桿在熔化率 ,壓力及平均溫度的表 現情形.由模擬的結果顯示,固定熔化區的長度12D,在一般操作條件下(190 度 ,60rpm),固體傳送區(含 虩１□其長度不會超過4D的距離,即可形成熔 融池.固定幾何形狀及加工條件,熔化率大小順 ヲ□ Kim螺桿最大,Dray & Lawrence,Barr螺桿次之,Maillefer 陰麭怳p.螺桿內最終背壓順序則反 之.四支螺桿在平均溫度部份的表現則差不多. In the melting zone of traditional single screw,the circulationow of melt pool would continuously push th solid bed, thus leading to the solid bed break-up.Once the solid bed break- up, it would cause the unmelted particulate solid to overcome the disadvantage of the traditional single screw. For the design of barrier screw,channel width,channel depth,helical angle and compression ratio etc. direct affect the melting rate, pressure distribution an bulk temperature of the screw.This work aims to develop the computr simulation with LDPE as the processing material for the four different types of barrier screws which rate,pressure distribution and bulk temperature were investigated under various processing conditions and geometry of the screw. The simulation results showed that under the conditions of the melting length twelve turns and normal operation condition barrel temperature 190 degree and screw speed 60 rpm, the length of solid conveying zone includeing delay zone uld not be beyond four turns for the formation of melt pool. Under the condition of fixed processing conditions and geometry of the screw,the melting rate will follow the sequence of Kim,Dray & Lawrence,Barr,Maillefer screws; meanwhile the back pressure follows the reverse order.For the bulk temperature,the four barrier screws showed very little difference.