Injection Molding Process For Manufacturing Preforms

Injection molding process is one of the popular processes for manufacturing bulk quantities of preforms. It consists of three major steps:

1. Drying: Hopper drying is the most commonly used method of removing humidity from PET. Hopper dryers have autoloaders where PET is conveyed continuously for an even drying. Dehumidifier method uses a closed loop system and brings excellent surface finish and physical properties. It uses a closed loop system to achieve drying of PET in an unvarying way.

2. Melting: When the screw is pushed forward, injection cavity gets filled up completely with molten plastic. There is a temperature difference of around 8 to 10 degree celsius at the front and rear end of injection molding machine. They are typically 270 to 275 degrees and 280 to 285 degrees respectively. Temperature may vary based on the design of the mold and other technical specifications. Molten PET gets entered through the cavities and cooled slowly to solidify it.

3. Cooling and molding: Temperature is maintained in such a way that PET gets solidify in a consistent manner. Cooling water is used to bring down the temperature of the mold. Since the temperature is quite low (around 15 to 20 degree Celsius), internal pressure has to be maintained properly to avoid breakage or deformities. A water chiller is used for cooling preforms under controlled pressure of 5Bar. An automated gripper takes out cooled preforms and deposit to conveyer belts. Preforms get ejected from the mold and send to either packaging or re-heating if they have to be sent for blowing process immediately.