Injection Unit in Plastic Injection Molding Machine
- Posted On: February 5, 2025
- Posted By: admin
The injection unit plays a crucial role in plastic injection molding machine. It melts and injects the plastic raw material into the mold under regulated conditions. The quality and consistency of the molded parts depends on the efficiency, performance and precision of the plastic injection molding machine. The injection unit uses various components to melt the plastic resin and inject it into the mold at high pressure.
Key components of plastic injection molding machine
The Hopper– It serves as a reservoir for holding plastic pellets or granules and moving it down to the barrel for their melting. It is equipped with a dryer for removing moisture from hygroscopic plastic materials like nylon or polycarbonate. It includes additives like masterbatch, liquid colorants and pre-colored resins, phathalates and non-phathalate plasticizers, heat stabilizers, UV stabilizers, antioxidants, halogenated and halogen free flame retardants, glass fibers, carbon fibers and a lot more…
Barrel and Screw Assembly
The screw has three zones
- Feed Zone- For transferring plastic granules alongwith additives from hooper to compression area
- Compression area- It pressurizes and melts the plastic
- Metering Zone- It ensures consistent and uniform melting and prepares injection material
Heating bands
It produces regulated heat for melting the plastic. There are different types of heating bands
- Ceramic heating bands
- Mica heating bands
- Cast Aluminium heating bands
- Mica heating bands
- Induction heating bands
The different types of materials used in heating bands include
- Nichrome (Nickel-Chromium) Wire
- Ceramic Insulation
- Mica Sheets
- Stainless Steel Sheathing
Cooling system
It consists of cooling channels, sensors, hoses, valves, cooling tower and connectors. There are various types of cooling systems
- Conventional Cooling systems
- Baffler and Bubbler cooling
- Conformal cooling
- Spray Cooling
- Chilled water and oil cooling systems
Common cooling problems
| Problem | Reason | Recommendation |
| Inconsistent Cooling | Inefficient channel layout or restricted coolant flow | Redesign cooling channels or enhance flow efficiency |
| Prolonged Cycle Time | Inadequate cooling capability | Increase coolant flow or upgrade to a higher-capacity chiller |
| Warping and Distortion | Uneven heat dissipation | Adjust cooling channel positioning and optimize coolant flow |
| Coolant Leakage | Worn-out hoses or faulty connectors | Conduct regular inspections and replace damaged components |
Check ring/Non-return valve
It is located at the front of the rotating screw and prevents molten plastic from flowing back into the barrel during the injection stage.
Injection Nozzle
It connects the injection unit with the mold and serves as a package of molten plastic. There are two types of nozzles , open ( it is used for less viscous material) and shut off nozzles ( which prevents leakage of material in idle state).
The injection process comprises of two main stages
- Plasticization – Plastic granules are passed through hopper into the barrel. The rotating screw helps in progressing the material forward as the heating band melts it, which then collects infront of the screw fully geared for injection. The geometry of the screw helps in achieving consistent melting.
- Injection- Here the screw moves and forces the molten plastic through the nozzle and inserted at high pressure into the mold cavity. As the mold cavity is filled up, the injection unit ensures enough pressure to prevent material shrinkage during cooling.