Pet Bottle Preform Processing Method Introduction

The main injection molding conditions for Pet Bottle Preform:
1. The temperature of the barrel. The molding temperature range of PET is very narrow, and the temperature will directly affect the performance of the product. If the temperature is too low, it is not good to manufacture plastic parts, dents, and lack of material defects; on the contrary, if the temperature is too high, it will cause overflow, the nozzles will flow, the color changes deeply, the mechanical strength decreases, and even the degradation occurs. Typically, the barrel temperature is controlled at 240 ~ 280 ° C, and the glass fiber reinforced PET barrel temperature is 250 ~ 290 ° C. The temperature of the nozzle should not exceed 300 ° C, and the temperature of the nozzle is usually lower than the temperature of the barrel.
2, mold temperature. The mold temperature directly affects the cooling rate and crystallinity of the melt, the crystallinity is different, and the properties of the plastic parts are also different. Usually, the mold temperature is controlled at 100 ~ 140 °C. Small values ​​are desirable when forming thin-walled plastic parts; when thick-walled plastic parts are formed, it is preferable to have a large value.
3. Injection pressure. PET melt has good fluidity and is easy to form. Medium pressure is usually used, the pressure is 80 ~ 140 MPa, and the injection pressure of glass fiber reinforced PET is 90 ~ 150 MPa. The injection pressure should be determined by considering the viscosity of the PET, the type and amount of the filler, the location and size of the gate, the shape and size of the plastic part, the mold temperature, the type of injection molding machine, and the like.
How much do you know about the processing of PET plastics?
1, plastic processing
Since PET macromolecules contain a lipid group and have a certain hydrophilicity, the particles are sensitive to water at high temperatures. When the moisture content exceeds the limit, the molecular weight of the PET will decrease and the product will become color and crisp. In this case, the material must be dried before processing. The drying temperature is 150.4 hours, usually 170.3 – 4 hours. The air jet method is used to test whether the material is completely dry.
2. Selection of injection molding machine
PET has a short time after melting point and a high melting point. When plasticizing, it is necessary to select an injection system with a large temperature control section and less self-heating. The actual weight of the product cannot be less than 2 / 3 of the injection volume of the machine. Based on these requirements, in recent years, Ramada has developed a series of small and medium-sized PET special plasticizing systems. The clamping force is chosen to be greater than 6300 tons / square meter.
3. Mold and gate design
PET preforms are typically molded from hot runner molds. The heat shield between the mold and the injection molding machine is preferably 12 mm thick, and the heat shield can withstand high pressure. The exhaust must be sufficient to avoid local overheating or chipping, but the depth of the vent is typically no more than 0.03 mm, otherwise flashing is likely to occur.
4. Melting temperature
It can be measured by air jet method. At 270 – 295 ° C, the enhanced level GF – PET can be set to 290 – 315 ° C.
5. Spray speed
Generally, the injection speed is fast, which prevents early coagulation of the injection. But the speed is too fast and the high shear rate makes the material brittle. The spray is usually completed in 4 seconds.
6, back pressure
The lower the better, to avoid wear. Generally no more than 100 bar. Usually not used.
7. Staying time
Do not use too long residence times to prevent molecular weight degradation. Try to avoid temperatures above 300 °C. If the shutdown time is less than 15 minutes. It only needs to be air-burned; if it is more than 15 minutes, the viscosity PE should be cleaned and the barrel temperature lowered to PE temperature until the machine is turned back on.
8. Preventive measures
If the Pet Bottle Mould temperature is not well controlled or the material temperature is not properly controlled, it is easy to produce “white and opaque”. The mold temperature is low and uniform, the cooling rate is fast, the crystallization is small, and the product is transparent.


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