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1. Plastic material
Due to the strong hygroscopicity of PET plastic material, it must be dried at a temperature of 150 ℃ for at least 4 hours before processing; Usually at 170 ° C for 3-4 hours. The air jet method can be used to check whether the material is completely dry. The proportion of recycled PET bottle preforms generally does not exceed 25%, and the recycled material should be thoroughly dried.
2. Selection of Injection Molding Machines
Due to the fact that PET preform molds are generally multi cavity and heavy, attention should be paid to the injection weight when choosing an injection molding machine.
The total weight of the product should be 2/3 of the injection weight.
3. Mold and sprue design
PET preforms are generally formed using hot runner molds. It is best to have a heat insulation board between the preform mold and the injection molding machine template, and the heat insulation board must be able to withstand high pressure. The exhaust must be sufficient to avoid local overheating or fragmentation, but the depth of the exhaust port should generally not exceed 0.03mm, otherwise it is easy to produce burrs.
4. Melting temperature
The air injection method can be used for measurement, with a range of 270-295 ℃, and the enhanced GF-PET can be set to 290-315 ℃.
5. Injection speed
The injection speed should be fast to prevent premature coagulation during injection. But too fast, high shear rate, makes the material fragile, and injection is usually completed within 4 seconds.
6. Back pressure
The lower the better, to avoid wear and tear. Generally not exceeding 100 bar, it is not necessary to use it.
7. Detention period
Do not use too long a residence time to prevent a decrease in molecular weight, and try to avoid temperatures above 300 ° C. If the machine shutdown time is less than 15 minutes, only gas injection is required; If it exceeds 15 minutes, viscosity PE should be used for cleaning, and the barrel temperature should be reduced to PE temperature until it is turned on again.
