Transient Solids Conveying in Single-Screw Machines

今天生产的大量塑料产品在其制造周期中在单螺杆机器上进行加工，并为随后的铸造工艺做好准备。这包括在挤出工艺中使用单螺杆塑化挤出机连续生产管材、型材或薄膜，以及在注塑工艺中使用塑化单元不连续生产模塑部件。无论采用哪种操作模式，单螺杆机的任务都是将通常为颗粒状的原料进料，以固体形式输送，并将其粉碎和转化为均匀的熔体。对于具有光滑机筒的单螺杆机，通常的做法是在设计螺杆时假设产量由熔体输送部分决定。然而，这种假设不再适用于高螺杆速度、低原料堆积密度和小螺杆直径，如在注塑机中的塑化单元中所发现的。相反，必须更详细地考虑发生固体输送的螺杆的功能部分。除了生产率之外，如果设计不当，固体输送段也会显著降低产品的质量，例如，如果送入工艺的空气不能再次逸出，并作为空气夹杂物出现在产品中。这对于注塑塑化单元尤其如此，由于螺杆的轴向运动在计量阶段阻碍了颗粒的摄入。本研究项目的目的是显着提高质量的数学描述和一般工艺的理解固体输送在注塑塑化单元的帮助下，数值离散元模拟。这是要实现的，通过回答未解决的这些问题是由于注塑塑化单元与塑化挤出机相比的工艺工程特性造成的。本质上，这里应该提到螺杆的不同运动学以及由此导致的进料部分中颗粒流动过程描述的不确定性。通过考虑这些运动学特征，通过在DEM模拟中通过实验的统计设计系统地改变影响变量，并通过基于此的建模，可以整体地描述注塑塑化单元中的固体输送，并且比以前简化得更少。

A large amount of plastic products produced today are processed in the course of their manufacturing cycle on a single-screw machine and prepared for a subsequent casting process. This includes both the continuous production of pipes, profiles or films using a single-screw plasticizing extruder in the extrusion process and the discontinuous production of moulded parts using a plasticizing unit in the injection moulding process. Regardless of the mode of operation, the task of the single-screw machine is to feed the raw material, which is usually in granular form, to convey it as a solid, to plasticize it and to convert it into a homogeneous melt.In case of single-screw machines with smooth barrels, it is common practice when designing the screws to assume that the throughput is determined by the melt conveying sections. However, this assumption no longer applies at high screw speeds, low bulk densities of the feedstock and small screw diameters, as found in plasticizing units in an injection moulding machine. Instead, the functional sections of the screw where solids conveying takes place must be considered in more detail. In addition to the throughput rate, the solids conveying section can also decisively reduce the quality of the manufactured products if it is incorrectly designed, for example if air that is fed into the process cannot escape again and is found in the product as air inclusion. This is particularly true for injection moulding plasticizing units, since the axial movement of the screw during the metering phase impedes the intake of the granules.The aim of this research project is to significantly increase the quality of the mathematical description and the general process understanding of solids conveying in injection moulding plasticizing units with the aid of numerical DEM simulations.This is to be achieved by answering unresolved questions, which are due to the process engineering characteristics of the injection moulding plasticizing unit in comparison to a plasticizing extruder. Essentially, the different kinematics of the screw and the resulting uncertainties in the description of the flow processes of the pellets in the feed section should be mentioned here. By taking these kinematic characteristics into account, by systematically varying influencing variables by means of statistical design of experiments in the DEM simulations and by modelling based on this, solids conveying in injection moulding plasticizing units can be described holistically and with significantly fewer simplifications than before.