Pheology and Heat Transfer Control of Microscale Instability Phenomena on Injection Molded Polymer Surfaces

现有的流痕生成假说千差万别且仍属推测性质，表明目前尚不清楚流痕的生成机制。基于文献研究的结果。提出了两个主要的研究问题：(1)描述了流痕的产生：波状流痕是在哪里产生的，又是如何产生的？(2)对流痕的产生提出了解释：构建了波状流痕产生机制的假设。进行了实验以获得以下信息：(1)确定流动痕迹的生成点，即熔体与模具之间的接触线之前、之后或处，以及(2)观察实际的生成过程。这是使用注塑机完成的，该注塑机配备了带有观察窗的特殊设计的模具。(3)成型后的微观表面形貌分析在实验研究中也起着重要的作用。重点研究了热边界条件对流痕微观几何形状的影响。采用解析和数值相结合的方法对流动前沿和接触线区的换热进行了数值模拟。建立了解释流痕产生机理的唯象模型和数学模型。这些模型是基于接触线后面紧邻区域的凝固层的假定热变形。对于三种不同的材料，该数学模型可以在广泛的操作条件下与实验数据相关联。主要结论是，接触线后凝固层的非均匀热收缩似乎是波状流痕形成机制的主要因素。

The widely varying and still speculative nature of existing flow mark generation hypotheses indicated that there was no clear understanding of the generating mechanism yet. Based on the results of the literature study. two main research questions were formulated : (1) Provide a description of flow mark generation : Where, and how do wavelike flow marks generate? (2) Provide an explanation for flow mark generation : Construct an hypothesis for the mechanism by which wavelike flow marks are caused. Experiments were done to obtain the following information : (1) determination of the point of generation of flow marks, i.e., before, after, or at the contact line between the melt and the mold, and (2), observation of the actual generation process. This was accomplished using an injection molder equipped with a specially designed mold with an observation window. (3) Microscopic surface profile analysis after molding also played an important part in the experimental investigation. Specific attention was given to the effect of the thermal boundary conditions on the micro-geometry of flow marks. Analytical and numerical methods were used to model the heat transfer in the flow front and contact line areas. Phenomenological and mathematical models for explaining the flow mark generation mechanism were developed. The models are based on presumed thermal deformation of the solidifying layer in the area immediately behind the contact line. The mathematical model could be correlated with experimental data over a wide range of operating conditions and for three different materials. The main conclusion is that non- uniform thermal contraction in the solidifying layer behind the contact line appears to be the dominating factor in the mechanism by which wavelike flow marks generate.