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What should I pay attention to when working with PET preform injection molding machine?

TIME:2020-12-22 Share

PET, also known as polyester, is currently used for preforms. The machine commonly used to produce preforms is an injection molding machine. So what should be paid attention to when the PET preform injection molding machine is working?

1. Plastic treatment:
Because PET macromolecules contain fat base and have certain hydrophilicity, the pellets are more sensitive to water at high temperature. When the moisture content exceeds the limit, the molecular weight of PET decreases during processing, and the product becomes colored and brittle. Because of this, the materials must be dried before processing. The drying temperature is 150°C for more than 4 hours, generally 170°C for 3-4 hours. The air shot method can be used to check whether the material is completely dry. The proportion of recycled materials should generally not exceed 25%, and the recycled materials must be thoroughly dried.

PET preform
2. Selection of PET preform injection molding machine:
Since PET has a short stabilization time after the melting point and high melting point, it is necessary to choose an injection system with more temperature control sections and less self-friction heat during plasticization, and the actual weight of the product (water cut material) cannot be less than the machine injection 2/3 of the amount.

3. Mould and gate design:
PET preforms are generally formed by hot runner molds. It is better to have a heat shield between the mold and the injection molding machine template, the thickness of which is about 12mm, and the heat shield must withstand high pressure. Exhaust must be sufficient to avoid local overheating or chipping, but the depth of the exhaust port should generally not exceed 0.03mm, otherwise it is easy to produce flash.

4. Melting temperature:
It can be measured by air shot method. The temperature ranges from 270-295℃, and the enhanced GF-PET can be set at 290-315℃.

5. Injection speed:
Generally, the injection speed should be fast to prevent premature solidification during injection. But too fast and high shear rate make the material fragile. Injection is usually completed within 4 seconds.

6. Detention time:
Do not use too long a residence time to prevent molecular weight drop. Try to avoid temperatures above 300°C. If the shutdown is less than 15 minutes. Only need to do air injection treatment; if it exceeds 15 minutes, clean with viscosity PE, and reduce the barrel temperature to PE temperature until it is turned on again.
PET preform injection molding machine
⑴Recycled material should not be too large, otherwise it is easy to cause "bridging" at the feeding place and affect plasticization.
⑵If the mold temperature is not well controlled or the material temperature is not properly controlled, it is easy to produce "white fog" and opacity. The mold temperature is low and uniform, the cooling rate is fast, and the product is transparent with less crystallization.

LISONG machine rofessional provide the PET preform injection molding machine. Factory direct sales, quality assurance, and price concessions.email:kevin@lisonginc.com

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