In addition to the extrusion molding process, Pet Preform are mostly injection molded to produce preforms.
In the whole preform processing equipment, in addition to the injection molding machine, it also includes: hot runner mold, ester particle dehumidifying dryer, mold cooling ice water machine, preform removal robot arm, preform conveyor belt and injection environment control air conditioner dehumidifier, etc. And each machine is to cooperate with the action of the injection machine, so the injection molding machine plays the most important role in the preform molding process.
In general, the main process control parameters of the injection machine are: (1) screw speed; (2) injection pressure; (3) injection speed; (4) tube temperature; (5) nozzle temperature; (6) pressure holding; 7) Pull loose; (8) Switching mode speed; (9) Cooling time; (10) Cycle time. Each parameter is related to the quality of the injected product. Therefore, the control of the parameters is very important. In order to achieve good process parameters, the performance of the injection machine must be designed in accordance with the process requirements.
The general screw is used for the injection of PET, which is of poor quality and is prone to problems. Therefore, the PET injection machine must have its own dedicated screw. Because PET is a heat sensitive material, it is easy to break the molecular chain at high temperature, reduce the molecular weight, produce acetaldehyde, and reduce the quality of the preform. In the material tube, the screw is compressed by the screw to melt heat. If the shear heat generated by the screw compression is too large, PET thermal cracking may occur. Therefore, the PET injection screw must have a low shear design and can melt the crystallized PET ester particles. Too high compression ratio or too short compression length will cause large shear; while too low compression ratio screw will produce insufficient shear heat, which may not completely melt the ester particles, so that the preform crystals are white atomized and cannot be The air inside the tube is completely removed, which makes it easy for the preform to generate air bubbles. The screw design of the PET injection machine is important for the injection molding process of Pet Preforms.