LDPE熔体在挤出口模流动时入口区流型的观测

应用毛细管流变仪测量了在接近实际挤出工艺条件下低密度聚乙烯熔体的流变性质，应用流动可视化技术，观测了试样熔体流经突然收缩的轴对称口模时的入口收敛流型，发现，在口模入口前区的两侧存在明显的环流区，环流区长度随着挤出速率和流道收缩比的增加而增大，而随着温度的升高而减小，采用环流区长度的公式估算了实验条件下试样的环流区长度值，结果表明，预测值与实测值之间有较好的一致性。

Observation of flow pattern of LDPE melt in entry region during die extrusion

The rheological properties of low density polyethylene (LDPE) were measured under conditions close to the practical extrusion process by means of a capillary rheometer. The entry convergent flow pattern was observed with flow visualization technique when the resin melt flowed through a die featuring abrupt contraction in cross-section of channel and axial symmetry. It was found that there existed an obvious circular flow zones at both sides of the inlet front region of the die; the length of circular flow zones (Lv) increased with increasing extrusion rate and channel contraction ratio, whereas decreased with raising temperature. The values of Lv were estimated from the experimental conditions of the sample in terms of the Lv equation published in previous paper. The results show that the calculated values are quite consistent with the measured data.