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PET Preform Injection Molding

PET PreformsPET Preform Processing:  
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Overview of PET Preform Injection Molding Process Dehumidifier PET Resin / Granule PET Preforms Autoloader Water Chiller PET Preform Injection Mold Hopper Dryer Color Feeder PET Injection Molding Machine

Drying and Dehumidifying of PET
PET is a kind of moisture absorption plastics, usually its water content is about 0.05%. To get perfect PET preform (transparency and physical performance), also to enhance molding efficiency, the water content of PET resin should be <=0.005%. Therefore necessary drying of PET is required.

The common drying methods:

  • By oven:
    A kind of outdated and laborious drying method. Oven is apart from injection machine, dried PET is moved into the hopper of injection machine manually, and un-dried PET is moved into oven manually too.
    As LVPET may get damp and caking while drying, only oven drying method can be used for LVPET so that it can be turned over for 2 to 3 times during drying. The thickness of PET in the trays can be about 50mm. If dried material is not used up, set oven's working temperature to 1100C to keep it warm. PET should not be stayed in oven for more than 8 hours, or it will deteriorate. Cooled material should be dried again.
    For LVPET, luster will appear when it is being dried. And the luster will disappear when drying finished.
     
  • By Hopper Dryer
    Most common and economical method to dry PET. If works together with autoloader, PET will be loaded into hopper dryer and dried continuously and automatically.
     
  • By Dehumidifier
    Efficient but costly drying method, works together with hopper dryer and autoloader. It dries PET in a closed loop system to reach dew-point of at least -320C, thus to exhibit the optimum physical performance and surface finish of PET products.
Drying Temperature

Drying target is to get moisture level <=0.005% (at the same time, AA level should be strictly controlledto avoid peculiar smell in the drink)

The best drying temperature and time are decided by IV value of PET resin. But generally speaking, it should be 150~ 1700C for about 4 hours.

If dried PET contact air with relative humidity 35~40% for 12 minutes, it's moisture content will reach 0.005%. Long-time drying will reduce its IV value. So it is better to shorten drying time. Drying time should not exceed 7~8 hours.

Cooling of Preform Mold
Cooling of preform mold is also very important. It affects preform's quality directly. The temperature of cooling water should be 15~200C, and the pressure of cooling water should be around 5Bar. Water chiller is suggested.
Mold Temperature
For injection machine, temperature of nozzle and front zone should be about 2800C, and middle zone around 2820C, rear zone around 2750C. The temperature of hot runner in preform mold should be around 2700C.

These temperature vary a little bit with IMM, preform's design and weight, mold's structure and cooling, etc.

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