Introduction to Common injection molded plastics in manufacturing Technology:
The injection molding process involve injecting or pressurizes a liquid plastic material into mold operation. it is called injection moulding . it is most common methods for manufacturing of plastics. The common injection molded plastics method is two. there are
- Plunger type injection molding machines
- Reciprocating screw type injection molding machines
Plunger type injection molding machine:
The plastic metal stored in hopper and feed into the barrel part. Then Plunger part move with material along barrel. The metal heated together because of heater is heated the metal. The temperature of the heat chamber is maintain with 150°C to 250°C. The metal pressurized or forced through nozzle into mould cavity. The Plunger or Ram Operated by Hydraulic power. Split up more mass of materials in barrel and increase the heat transfer and torpedo fit in the barrel.
Common injection molded plastics Problems for this Plunger type machining process:
Small amount of mixing in molten plastics
Short size part accuracy will be low
Reciprocating screw injection molding:
The Machine include heating the plastics metal it flow radially in high pressure , inject into mold. The mold closed with solidified from Melton metal and open the mold to allow to remove the part.
The main parts of machine are hopper, Reciprocating Screw, mold Clamp, Heated Extruder barrel, Nozzle . The Hopper part feed the unmelted plastic metal to barrel unit. The hopper have remove the moisture and also remove any iron thinks. The Screw contain which the heater barrel, the thermoplastic is gradually melted in the combination of heating barrel.
The Thermoplastic is moved by rotating screw in front of heater barrel. The Barrel is heated by electrical resistance heater. The Barrel is Remove the Gases from melting parts. The reciprocating screw having three Stages of melting metal.
Three types of Reciprocating screw injection moulding stages:
Feed Stage: Unmelted plastic metal feed to heated barrel from hopper.
Compression Stage: The Gas Removed by along with the material mixing process.
Melting Stage: The shearing heat of metal and mixing the metal.
The check valve or non return valve fitted in end of screw and feed stock melted continuously within sufficient amount of melting point. Now Screw is stopped and thermoplastic is injected into mold cavity through nozzle with high pressure. ( Pressure until 70 to 205 Mpa ). The Screw is rotated by hydraulic power and forced forword direction in the barrel. The high pressure melton metal injected to closed mould and open the mold to allow remove the part after cooling and solidify process completed, Remove the part by using ejection system.
What are the materials used in injection moulding: