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，并为后续的铸造工艺做准备。这包括在挤出过程中使用单螺杆塑化挤出机连续生产管道，型材或薄膜，以及在注塑过程中使用塑化单元不连续生产成型部件。无论操作方式如何，单螺杆机的任务是将通常呈颗粒状的原料喂入，将其作为固体输送，使其塑化并将其转化为均匀的熔体。对于光滑机筒的单螺杆机，通常的做法是在设计螺杆时假定吞吐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，低堆积密度的原料和小螺杆直径，如在注塑机的塑化单元中发现。相反，必须更详细地考虑固体输送发生的螺杆的功能部分。除了吞吐量之外，如果设计不当，固体输送部分也会决定性地降低制造产品的质量，例如，如果进入过程的空气无法再次逸出，并且在产品中发现空气夹杂物。这对于注塑塑化装置尤其如此，因为螺杆在计量阶段的轴向运动阻碍了颗粒的吸入。本研究项目的目的是借助数值DEM模拟，显著提高数学描述的质量和对注射成型塑化装置中固体输送的一般过程的理解。这是通过回答尚未解决的问题来实现的，这些问题是由于注射成型塑化单元与塑化挤出机相比的工艺工程特性。从本质上讲，螺杆的不同运动学以及由此产生的不确定性在进料段颗粒流动过程的描述中应该在这里提到。通过考虑这些运动学特征，通过在DEM模拟中对实验进行统计设计并以此为基础进行建模，系统地改变影响变量，注塑塑化单元中的固体输送可以得到整体描述，并且简化程度比以前大大降低。

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.