Injection Molding for Conventional Thermoplastics and Bio-plastics
The component of injection molding machine can be separated into 3 units:
1. The Injection Unit has a function to inject plastic into the mold cavity.
2. Clamping Unit has a function to control the mold.
3. The Control Unit has a function to control all operating parameters of the injection molding machine.
Injection Unit receives the plastic pellets from the hopper feeder and melts them in the barrel and screw zone before injecting the molten plastics into the mold cavity. The main components of Injection Unit are,
Hopper transfers the solid plastic pellets into the barrel and screw zone.
Barrel is the heating zone where the solid plastic pellets are melted. Temperature in the barrel depends on the type and melting temperature of the plastics.
Thermocouple monitors the actual temperature in the barrel.
Screw drives the molten plastic to the nozzle. The screw configuration is designed to match the type of plastics and it can be divided into 3 zones: Feed zone, Compression zone, and Metering zone.
Nozzle is at the end of the barrel and screw zone where the molten plastic is injected into the mold cavity.
Suitable temperature for injection process of thermoplastic materials
Suitable temperature for injection process of bioplastic materials (PLA)
The above tables demonstrate the processing temperatures of conventional plastics and bioplastic. It is noticed that the processing temperature of PLA is lower than conventional plastics because bioplastic is easy to decompose at high temperature, especially if the pellets contain high residual moisture, leading to the deterioration of polymer chains, and changes in melt flowability and actual processing condition.
Clamping Unit relates to the installation of mold, open/close systems of mold lid, and ejection of finishing product from the mold cavity. Technically, the clamping unit has 2 types:
– Direct Clamp controls the open/close system of mold lid by hydraulic cylinder. The advantage of a direct clamp is that it is easy to set-up.
– Toggle Clamp controls the open/close system of mold lid mechanically by servo motor and hydraulic. The advantage of toggle clamps is that the clamping force can be controlled precisely and steadily.
– Control Unit controls all functions of the injection molding machine including barrel temperature, pressure and injection rate, speed of open/close of mold lid, and operating time of each step of the injection process.
“Human has the duty to conserve the environment. Let’s Reduce, Reuse, and Recycle plastics or change to use more eco-friendly bioplastics”