PET Preform Mould
The chemical name of PET is polyethylene terephthalate. Nowadays, GF-PET is mostly used by customers, mainly for preforms. The rheology of PET in the molten state is better, and the influence of pressure on viscosity is greater than that of temperature. Therefore, the pressure is mainly used to modify the fluidity of the melt.
1. Processing of plastic
Because PET macromolecules contain fat groups and have certain hydrophilicity, the pellets are sensitive to water contrast at high temperatures. When the moisture content exceeds the limit, the molecular weight of PET decreases during processing, and the finished product is colored and brittle. Because of this, it is necessary to dry the materials before processing. The dry temperature is 150℃ for more than 4 hours, generally 170℃ for 3-4 hours. The air-shot method can be used to check whether the data is completely boring. The share of recovered materials should generally not exceed 25%, and the recovered materials should be completely boring.
2. Selection of injection molding machine
Because PET has a stable moment after the melting point and the melting point is higher, it is necessary to use an injection system with more temperature control sections and less self-conflict heat during plasticization, and the practical weight of the finished product (water-containing mouth material) cannot be less than the machine injection 2/3 of the amount.
3. Mould and gate planning
PET preforms are generally formed with warm runner molds. There must be a heat insulation board between the mold and the mold of the injection molding machine. Its thickness is about 12mm, and the heat insulation board must be able to accept high pressure. Exhaust must be sufficient to prevent overheating or chipping, but the depth of the exhaust port should generally not exceed 0.03mm, otherwise flashing may simply occur.
4. Melt temperature
Can be measured by the air shot method. 270-295 ℃ range, enhanced grade GF-PET can be set to 290-315 ℃, etc.
5. Injection speed
Generally, the injection speed should be fast to prevent premature solidification during injection. But too fast, high shear rate makes the material brittle. The shot is usually finished within 4 seconds.
6. Back pressure
The lower the better, to prevent wear. Generally does not exceed 100bar. Generally no need to use.
7. Holding time
Do not use too long a residence time to prevent the molecular weight from decreasing. Try to prevent temperatures above 300°C. If the shutdown is less than 15 minutes. Only need to do air injection treatment; if it exceeds 15 minutes, it should be cleaned with viscosity PE, and reduce the barrel temperature to PE temperature until it is turned on and stopped.
8. Matters attention
A. The recovered material should not be too large, otherwise it will easily happen to “bridge” at the cutting site and affect the plasticization.
B. If the mold temperature is not well controlled or the material temperature is not properly controlled, “white mist” is likely to occur and is unclear. The mold temperature is low and uniform, the cooling speed is fast, and the crystallization is less, the finished product is cle