What are the elements of pet preform molding?
1. Processing of plastics
Because the PET macromolecules contain lipid groups and have a certain degree of hydrophilicity, the pellets are more sensitive to water at high temperatures. When the moisture content exceeds the limit, the molecular weight of PET decreases during processing, and the products become colored and brittle. Generally, the proportion of recycled PET bottle blanks should not exceed 25%, and the recycled materials should be thoroughly dried.
2. Selection of injection molding machine
Because PET has a short stable time after melting point and high melting point, it is necessary to choose an injection system with more temperature control sections and less self-friction heat generation during plasticization, and the actual weight of the product should not be less than 2/3 of the injection volume of the machine. Powerjet preform injection molding machines can meet your different needs!
3. Residence time
Do not use an excessively long residence time to prevent the molecular weight from decreasing, and try to avoid temperatures above 300°C. If the machine is stopped for less than 15 minutes, it only needs to be air-shot; if it exceeds 15 minutes, it should be cleaned with viscosity PE, and the temperature of the barrel should be lowered to the PE temperature until it is restarted.
4. Design of mold and gate
PET preforms are generally formed by hot runner molds. It is better to have a heat insulation board between the mold and the template of the injection molding machine. Its thickness is about 12mm, and the heat insulation board must be able to withstand high pressure. The exhaust must be sufficient to avoid local overheating or cracking, but the depth of the exhaust port should generally not exceed 0.03mm, otherwise it is easy to generate flash.