局部模溫控制應用於射出成形熔合線消除之研究

Abstract

射出成形是廣泛使用的高分子加工技術，其發展時間長，技術趨於成熟，但熔合線問題仍無完備的解決辦法。熔合線乃兩股以上的流動波前交會後停止流動，若處理不當，冷卻後可由肉眼觀察到明顯分界線。又由於熔合線區域的分子配向會趨於平行熔合線方向，使得該處的機械強度會遠低於成形品的其他部分。一般常透過提高模溫來減少熔合線所造成機械強度及外觀的缺陷。 本研究目的為討論以局部模溫控制來改善熔合線處強度的可行性，以期能減少模具升溫所需的能源，因應日益升高的能源成本。本研究使用相同尺寸之工件，分別以整體模溫控制以及熔合線區域的局部模溫控制兩種方式成形。局部的加熱裝置選擇常用的電熱棒，設置於距熔合線生成處的模穴表面3厘米處，電熱棒僅設於模穴之一側。最後則將工件裁切成試片以進行材料拉伸實驗，將整體模溫控制於攝氏30度之成形工件作為對照組，比較其抗拉強度及改善效率。 實驗的結果可知熔合線區域機械強度的確可透過局部模溫控制改善，然可能因局部加熱所用之電熱棒僅設於模穴之一側，在相同溫度下整體模溫控制仍具有較佳的強度。當整體模溫控制加熱至攝氏50度，而局部模溫控制加熱至攝氏60度時，兩者之熔合線區域抗拉強度的改善效率非常接近，分別為15.1%和14.9%，但局部模溫控制所需耗能約僅為整體模溫控制之1/34。 本研究證實以局部模溫控制改善熔合線區域機械強度的可行性，如此在模具設計階段預測熔合線之發生位置並設置局部加熱裝置於該處，透過局部模溫控制可改善熔合線區域機械強度，且相較於整體模溫控制可省去大量能源。

Although injection molding is considered a mature technology, some problems such as the weld line remain unsolved. The weld line results from two or more flows of mold material that stops and connected. Therefore, the welded part of injection-molded products has low mechanical strength since the molecular orientation of the part tends to be parallel to the weld line direction. The typical solution is to increase mold temperature. In this study, partial mold temperature control was used to reduce weld line defects in order to reduce energy costs compared to general mold temperature control. After the products were molded by partial and general mold temperature control, the specimens were subjected to test tensile strength tests. The tensile strength data was used as an indicator of energy-savings efficiency. According to the result, an energy efficiency improvement of 15.1% when the general mold temperature was set to 50 degrees Celsius and an improvement of 14.9% when local mold temperature control heating was set to 60 degrees Celsius. However, local mold temperature control required energy is only 1/34 of the energy required by general control. This study confirms that local mold temperature control is effective for improving the mechanical strength of the weld line area but with substantially lower energy consumption compared to general mold temperature control.