Working principle of plastic injection molding:

Similar to the syringe used for injection, it uses the thrust of the screw (or plunger) to inject the plasticized plastic in the molten state (that is, the viscous fluid state) into the closed mold cavity,plastic injection molding,  and the product is obtained after solidification and shaping Process.

Injection molding is a cyclic process, each cycle mainly includes: quantitative feeding-melting plasticization-pressure injection-mold filling and cooling-mold opening and taking parts. After taking out the plastic part, the mold is closed again for the next cycle.

Plastic injection molding method:

1. Exhaust type

The exhaust type injection machine for exhaust type injection molding applications has an exhaust port in the middle of the barrel and is also connected to the vacuum system. When the plastic is plasticized, the vacuum pump can evaporate the water vapor, monomer and volatilization contained in the plastic. Sexual substances and air are drawn away through the exhaust port; the raw materials do not need to be pre-dried, thereby improving production efficiency and product quality. It is especially suitable for the molding of polycarbonate, nylon, plexiglass, cellulose and other materials that are easy to absorb moisture.

2. Flow

Flow injection molding can use ordinary moving screw injection machine. That is, the plastic is continuously plasticized and squeezed into the mold cavity with a certain temperature. After the plastic fills the cavity, the screw stops rotating. The thrust of the screw is used to keep the material in the mold under pressure for a proper time, and then cool and shape. Flow injection molding overcomes the equipment limitations of producing large-scale products, and the quality of the parts can exceed the maximum injection volume of the injection machine. Its characteristic is that the plasticized object is not stored in the barrel, but continuously extruded into the mold, so it is a method of combining extrusion and injection.

3. Co-injection

Co-injection molding is a method that uses an injection machine with two or more injection units to inject different varieties or different colors of plastic into the mold at the same time or one after the other. This method can produce composite products with multiple colors and/or multiple plastics. The typical co-injection molding is two-color injection and multi-color injection.

4. No runner

There is no runner in the mold, but the extended nozzle of the injection machine directly injects the molten material into each cavity. During the injection process, the plastic in the runner is kept in a molten and flowing state, and will not come out with the product during demolding, so there is no runner residue on the part. This molding method not only saves raw materials, reduces costs, but also reduces procedures, which can achieve fully automatic production.

5. Reaction injection

The principle of reaction injection molding is to pump the reaction raw materials into the mixing head after being metered by a metering device, collide and mix in the mixing head, and then inject them into a closed mold at a high speed, quickly solidify, demold, and take out the product. It is suitable for processing some thermosetting plastics and elastomers such as polyurethane, epoxy resin, unsaturated polyester resin, silicone resin, and alkyd resin.

6. Thermosetting plastics

Granular or agglomerated thermosetting plastics are plasticized into a viscous state through the action of a screw in a strictly controlled temperature barrel. Under higher injection pressure, the material enters a mold with a certain temperature range for cross-linking and solidification. In addition to physical state changes, thermosetting plastic injection molding also has chemical changes. Therefore, compared with thermoplastic injection molding, there is a big difference in molding equipment and processing technology.

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