Since the PET macromolecule contains a lipid group and has a certain hydrophilicity, the pellet is sensitive to water at a high temperature. When the moisture content exceeds the limit, the molecular weight of the PET decreases during processing, and the product is colored and brittle.
Therefore, before processing, the material must be dried, the drying temperature is 150 ° C, more than 4 hours; generally 170 ° C, 3-4 hours. Airborne methods can be used to verify that the material is completely dry. The proportion of recycled PET preforms should not exceed 25%, and the recycled materials should be thoroughly dried.
2. Automatic PET Bottle Blow Molding Machine selection
Since PET has a stable time after melting point and a high melting point, it is necessary to use an injection system with more temperature control sections and less self-friction heat during plasticization, and the actual weight of the product (aqueous mouth material) cannot be less than the machine injection. 2/3. 3. mold and gate design
PET preforms are generally formed by hot runner molds. It is best to have a heat shield between the mold and the injection molding machine. The thickness of the preform is about 12 mm, and the heat shield must withstand high pressure. Exhaust gas must be sufficient to avoid local overheating or chipping, but the depth of the exhaust port should not exceed 0.03mm, otherwise it will easily produce flash.
4. Melt temperature
It can be measured by air-to-air method, ranging from 270 to 295 °C, and the enhanced grade GF-PET can be set to 290-315 °C.
5. Injection speed
Generally, the injection speed is fast, which prevents premature coagulation during injection. But too fast, the shear rate is high, making the material brittle. The shot is usually completed in 4 seconds.
6. Back pressure
The lower the better, to avoid wear. Generally no more than 100bar, usually no need to use.
7. Residence time
Do not use excessive residence times to prevent molecular weight degradation and try to avoid temperatures above 300 °C. If the shutdown is less than 15 minutes, only air-to-air treatment is required; if it is more than 15 minutes, it should be cleaned with viscosity PE and the temperature of the barrel should be lowered to PE temperature until it is turned on again.
If you have any question on Plastic Bottle Making Machine. We will give the professional answers to your short questions.