Today, parts can be manufactured from engineering plastics using a variety of methods, such as computer-aided design, terminal finite element analysis, and in-mold melt flow calculations. Their usefulness is undeniable, but sometimes they do not take into account the importance of the optimal design of the raw material supply system. In this paper, the basic principles of the semi-crystalline plastic feeding system are discussed. However, in practice, these principles need to be combined with the correct placement of gates and the accurate control of processing times. These issues are described in detail in each of the following sections.
Different characteristics of semi-crystalline resins
Semi-crystalline thermoplastics undergo a process of volume shrinkage from a melted to a cured state. Shrinkage can reach 14%, depending on the type of resin, which must be replenished by refilling the mold cavity with additional molten material during the holding time. This feeding operation is only possible if the gate cross-section size is appropriate and the melt in the center of the material is still in a molten state during the holding time.
