The core components of a plastic container machine vary according to the type of device. The working principle and structure of two typical injection molding machines and blow molding machines machines are introduced in detail below.
Core Parts and Functions of an Injection Molding Machine An The molding machine uses screws to melt plastic and inject molds under high pressure to form precise plastic containers. Its core components include:
Injection Unit
Screws:
Function: To transport plastic granules forward during rotation. Frictional heat melts plastic with external heating elements to form an even melt. During injection molding, the screw moves forward and injects the melt into the mold under high pressure.
Technical characteristics: requirements such as high temperature resistance (up to 500°C), abrasion resistance (service life over 100,000 hours) and corrosion resistance (e.g. PVC materials) must be met. For example, in the production battery pack housing for new energy vehicles, precision screws (tolerances ≤ 0.01mm) can improve the size accuracy of the product.
Gun barrel:
Features: Wrap the studs. External heating elements,such as heating coils, heat plastic buckets to gradually melt the plastic granules.
Technical characteristics: Must be able to withstand high pressure (1500 -2500 bar), inner wall hardness ≥ HRC55, surface roughness ≤ 0.4 μm For example, in the production of medical catheters, mirror polished drums (Ra ≤ 0.2μm) prevent material retention and ensure cleanliness.
Nozzle:
Function: Connect material cylinder and mould, control melt flow, prevent melt backflow.
Mold Closing Device: fixed and Movable Platen:
Role: at the front and rear end of the injection molding machine, a stable frame is formed by tie rods connection. When closing mold, hydraulic cylinder pushes the movable plate forward, closing the mold tightly, preventing melt overflow during injection.
Mold Adjustment Device:
Function: Adjust the distance between fixed plate and movable plate to suit different mold sizes.
Hydraulic System:
Hydraulic Pump:
Function: To convert mechanical energy into hydro energy and provide power for injection cylinder, mold closing cylinder, etc..
Hydraulic Valve:
Function: To control the flow rate, pressure and direction of hydraulic oil Precisely, and to ensure the stability of injection speed, mold closing force and other parameters.
Electrical control systems
PLC (Programmable Logic Controller):
Function: can collect the barrel temperature, screw speed, mold temperature and so on in real time, according to preset programs control each component action. For example, the heating temperature is automatically adjusted according to the characteristics of the plastic material to prevent material from breaking down.
Heating and Cooling System
Heating Elements:
What it does: Distribute the plastic granules around the barrel and heat them to the suitable melting temperature (260-280°C for PET, for example).
Cooling Water Pipeline:
Role: Embedded inside the mold, after injection of cold water circulation heat dissipation, so that the plastic quickly cooling and curing, to prevent deformation.
ii. Core Components and functions of Blow Molding Machines
The blowers inflate the molten plastic using air pressure and attach it to the inside of the mold to form a hollow container. Its core components include:
Extrusion Unit (for extrusion blow molding machines)
Screw and Roller:
Function: Similar to injection molding machines, but screw design emphasizes plasticization uniformity and ensures melt flowability suitable for filling. For example, in the production of multilayer composite membranes, the abrasion resistance of a bimetallic barrel (tungsten carbide alloy layer) can be increased more than threefold.
Mold and pneumatic systems
Mould:
Function: Define container shape, type line design must ensure smooth demolding after filling.
Pneumatic Device:
Function: use high pressure gas (such as compressed air) to inflate the preform to the inner wall of the mold, forming a hollow structure.
Heaters
Infrared Heating Coil:
Function: Uniform heating of the preform (such as the preform) to soften them to inflatable state.
III. Synergistic Effect in Core Components
Take injection molding for mineral water bottle caps:
Injection Stage: The screw rotates, melting PP plastic granules. The injection cylinder pushes the screw forward and injects the melt into the mold cavity under high pressure.
Cooling Stage: Cooling water circulates in the cooling pipe inside the mold, causing the bottle cap to solidify quickly.
Demolition stage: mold closing device is opened and the ejector pins push out the molded bottle cap.
