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What Are the Precautions for PET Preform Injection Molding Machines?
1. Processing of Plastic
Because PET polymers have hydrophilic, the particles are sensitive to water at high temperatures. When the moisture content exceeds the limit, the molecular weight of PET decreases and the product discolors and becomes brittle. Therefore, the plastic must be dried before processing, and its drying temperature is 150 °C.
2. Selection of Injection Molding Machine
Since the stabilization time after melting point is short and the melting point of PET is high, an injection system with a large temperature control range of the injection section and less self-friction heat during plasticization should be selected.
3. Mold and Gate Design
PET preforms are typically formed by hot runner molds. Preferably, there is a thermal insulation panel between the mold and the injection molding machine template. The thickness of the insulation panel is about 12 mm and the insulation panel must be able to withstand high pressure. The exhaust must be sufficient to avoid local overheating or breakage, but the exhaust outlet depth must not exceed 0.03mm, otherwise flashing is likely to occur.
4. Melt Temperature
Measurements can be made by air irradiation in the range of 270 to 295 degrees Celsius, and the enhanced grade GF-PET can be set to 290 to 315 degrees Celsius.
5. The Speed of Injection
Basically, the injection speed should be fast to prevent premature condensation during the injection. But too fast and high shear rates can make the material brittle.
6. Back Pressure
The lower back pressure is better, so as not to wear.
7. Residence Time
Do not take too long a retention time to prevent molecular weight degradation and try to avoid temperatures above 300 °C. If the shutdown time is less than 15 minutes, only jet treatment is required; if it is more than 15 minutes, use viscous PE cleaning and reduce the barrel temperature to PE temperature until the machine is restarted.
8. Precautions
(1) The recycled material should not be too large; otherwise it is easy to “bridge” at the unloading point and affects plasticization;
(2) If the mold temperature is improperly controlled or the material temperature is improperly controlled, it is easy to produce "white fog" and opacity; if the mold temperature is low and uniform, the cooling rate is fast and the crystallization is small, the product is transparent.
Because PET polymers have hydrophilic, the particles are sensitive to water at high temperatures. When the moisture content exceeds the limit, the molecular weight of PET decreases and the product discolors and becomes brittle. Therefore, the plastic must be dried before processing, and its drying temperature is 150 °C.
2. Selection of Injection Molding Machine
Since the stabilization time after melting point is short and the melting point of PET is high, an injection system with a large temperature control range of the injection section and less self-friction heat during plasticization should be selected.
3. Mold and Gate Design
PET preforms are typically formed by hot runner molds. Preferably, there is a thermal insulation panel between the mold and the injection molding machine template. The thickness of the insulation panel is about 12 mm and the insulation panel must be able to withstand high pressure. The exhaust must be sufficient to avoid local overheating or breakage, but the exhaust outlet depth must not exceed 0.03mm, otherwise flashing is likely to occur.
4. Melt Temperature
Measurements can be made by air irradiation in the range of 270 to 295 degrees Celsius, and the enhanced grade GF-PET can be set to 290 to 315 degrees Celsius.
5. The Speed of Injection
Basically, the injection speed should be fast to prevent premature condensation during the injection. But too fast and high shear rates can make the material brittle.
6. Back Pressure
The lower back pressure is better, so as not to wear.
7. Residence Time
Do not take too long a retention time to prevent molecular weight degradation and try to avoid temperatures above 300 °C. If the shutdown time is less than 15 minutes, only jet treatment is required; if it is more than 15 minutes, use viscous PE cleaning and reduce the barrel temperature to PE temperature until the machine is restarted.
8. Precautions
(1) The recycled material should not be too large; otherwise it is easy to “bridge” at the unloading point and affects plasticization;
(2) If the mold temperature is improperly controlled or the material temperature is improperly controlled, it is easy to produce "white fog" and opacity; if the mold temperature is low and uniform, the cooling rate is fast and the crystallization is small, the product is transparent.
Reference :quora
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