Melting Theory Study On Twin Screw Extrusion With Visualization Technology

The study on polymer's melting in twin-screw extrusion has been one of difficulties in theory researches, mainly because we couldn't observe the melting phenomena directly. With the three-dimension successive windowed twin-screw extruder, which is developped by the Institute of Plastics Machinery and Engineering, Beijing University of Chemical Technology, the author carrys on several extrusion experiments. In this thesis the solid conveying and melting phenomena of twin screw extrusion are observed, described and analized. Melting process is studied theoretically,and several new ideas are presented. Main study results are as follows :1. There are several flow patterns at melting section in co-rotating twin screw extrusion. This is caused mainly by the complex geometry and motion relations of the twin screw, and thus feeding rate is independent. Flow patterns in melting section are classified into two types, continuous and uncontinuous. With the idea of manifold flow patterns, we can try to let polymer flowing in planned pattern by means of controlling screw configuration and processing conditions, feeding rate, for instance. When we do theory research, the idea let us understand that we should establish different physical and mathematical models for different flow patterns.2. The phenomena of solid conveying are analized and solid conveying physical model — two region model — is established. In the first region, we call it dispersedsolid region, polymer moves at almost entire positive displacement, and gravity plays an important role here. In the second region polymer pellets adhere to the screw and other pellets slightly, and move round along the " 8 " -shaped channel. This regionis called adhesive solid region.3. We observe that the solid pellets (powder consists of small pellets also) which haven't melted always distribute in melt, because of the intermeshing zone's physical...