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Precautions for PET preform injection molding
Oct 23, 2017

1. Plastic processing

Because PET macromolecules contain lipid base, with a certain degree of hydrophilicity, the pellets are more sensitive to water at high temperatures. When the moisture content exceeds the limit, the PET molecular weight decreases during processing, and the products are colored and become brittle.


Therefore, before processing, the material must be dried, the drying temperature of 150 ℃, 4 hours or more; generally 170 ℃, 3-4 hours. Air can be used to test whether the material is completely dry. PET preform ratio is generally not more than 25%, and the material should be thoroughly dried.


2. Selection of injection molding machine

PET due to the stability of the melting point after a short time, and the melting point is high, so the need to use more temperature control section, plasticized self-friction less heat when the injection system, and products (water cut material) the actual weight can not be less than the machine The amount of 2/3.


3. Mold and gate design

PET preforms, the general use of hot runner mold molding, mold and injection molding machine template between the best to have insulation board, the thickness of about 12mm, and insulation board can withstand high pressure. Exhaust must be sufficient to avoid local overheating or fragmentation, but the depth of the exhaust port generally do not exceed 0.03mm, or prone to flash.


4. Melt temperature

Can be used to measure air, 270-295 ℃ range, enhanced GF-PET can be set to 290-315 ℃ and so on.


5. Injection speed

General injection speed should be faster, to prevent premature injection when the injection. But too fast, high shear rate, so that the material is fragile. The shot is usually completed in 4 seconds.


6. Back pressure

The lower the better, so as not to wear. Generally not more than 100bar, usually no need to use.


7. Stay time

Do not use too long a residence time to prevent molecular weight degradation, try to avoid temperatures above 300 ℃. If the shutdown is less than 15 minutes, only for air shot treatment; if more than 15 minutes, will use viscosity PE cleaning, and the barrel temperature down to PE temperature until the boot so far.


8. Precautions

(1) recycled material can not be too large, otherwise, easy to produce in the cutting at the "bridge" and affect the plastic;


(2) If the mold temperature control is not good, or improper temperature control, easy to produce "white mist" and opaque; mold temperature is low and uniform, cooling speed, crystal less, then the product transparent.

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