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Simulation of the Crystallization Induced by Annealing a Stretch-Blow PET Bottle
|關鍵字:||crystallization;結晶度;PET;maximum crystallization temperatur;stretch-blow;ANSYS;PET;最大結晶溫度;拉伸吹氣成形;ANSYS||出版社:||機械工程學系||摘要:||
本論文針對吹氣拉伸成形PET寶特瓶之退火結晶過程進行電腦模擬。此退火過程為在吹氣拉伸成型過程中，將其外表面與熱模接觸而加熱，待其脫模後直接進行空氣冷卻，故可依此分為兩個結晶時期，分別是加熱結晶時期與脫模後之冷卻結晶時期。本研究中使用商業套裝軟體〝ANSYS〞來求解PET寶特瓶暫態過程之溫度分佈與變化。此外在結晶度方面，利用Malkin等人量測得到之等溫結晶線，回歸分析成Takayangi等人建議之模式，求出相關係數，並利用來評估退火過程之結晶變化，其中發現最大結晶速率發生之溫度為180 。論文中並針對模溫與相對結晶度間之關係，作一研究，研究結果發現，相對結晶度會隨著與熱模接觸時間之增長而增大。對於短貼模時間之操作，最終達平衡時之相對結晶度會隨著模溫之升高而增加;而對於較長貼模時間之操作而言，會有一個最佳之模溫可使最終之相對結晶度達到最大。本研究發現，當模溫高於最大結晶速率之發生溫度(180 )時，冷卻過程對最終之平衡相對結晶度之大小影響甚鉅。
A computer simulation of the crystallization induced by annealing a stretch-blow PET bottle at an elevated temperature was performed. The PET bottle was assumed to be initially heated up by attaching its outer surface to a hot mold during the stretch-blow process. The crystallization can be divided into two stages, namely, a heating stage and a cooling stage. A commercial software, ANSYS, was used to solve the transient temperature distribution of the PET bottle. Takayanagi's model was adopted in evaluating the rate of crystallization during the annealing process. The crystallization isotherms measured by Malkin et al, were used to determine the corresponding coefficients. The maximum rate of crystallization was determined to occur at 453K . The effects of mold temperature on the relative crystallinity were investigated. It was found that the relative crystallinity significantly increases with the attaching time. For a short attaching time, the relative crystallinity increases with the mold temperature. For a long attaching time, an optimum mold temperature was found. This optimum mold temperature corresponds to a maximum relative crystallinity. In this work, it was found that the cooling process play an important role in affecting the final equilibrium crystallinity for operations with mold temperatures higher than the maximum crystallization temperature(453K).
|Appears in Collections:||機械工程學系所|
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