1. Make the mold close under the condition that it can withstand the injection pressure;
2. Take the product out of the injection device and melt the plastic before injecting it into the mold, and then control the pressure and speed to inject the melt into the mold. Injection devices used today come in two designs: screw preplasticizers or two-stage devices, and reciprocating screws. Screw type preplasticizer uses a preplasticized screw (first stage) to inject the molten plastic into a feeding rod (second stage).
The advantages of a screw preplasticizer are constant mass of melt, high pressure and high speed, and precise injection volume control (utilizing mechanical thrusters at both ends of the piston stroke). These advantages are required for transparent, thin-walled products and high production rates. Disadvantages include uneven residence time (resulting in material degradation), higher equipment costs and maintenance costs.
The most commonly used reciprocating screw injection devices do not require a plunger to melt and inject the plastic.
Injection molding machine types are: vertical, horizontal, full electric, but no matter what kind of injection molding machine, its basic functions have two:
(1) Heat the plastic so that it reaches a melting state;
(2) Apply high pressure to the molten plastic so that it is ejected and filled with the mold cavity