Due to processing materials vary. Thermoplastic injection molding, including feeding, plasticizing, injection, packing, cooling, stripping and other processes. Thermosetting plastics and rubber molding also includes the same process, but the barrel temperature is lower than the thermoplastic, injection pressure is higher, the mold is heated, the material injection is completed in the mold by curing or curing process, and then hot strip . Injection molding refers to a model of a certain shape, which is formed by injecting a colloid in a molten state into a mold cavity by pressure. The process principle is that the solid plastic melts at a certain melting point and is injected into the mold at a certain speed by the pressure of the injection machine Within, the mold is cooled by water to cure the plastic to give the same design as the mold cavity. Injection molding (injection molding) is a process by which a thermoplastic or thermosetting molding compound is first uniformly plasticized in a heating cylinder and then pushed by a plunger or a moving screw into a cavity of a closed mold. Injection molding is suitable for almost all thermoplastics. Injection molding is also successfully used to shape some thermosets. Injection molding of the molding cycle is short (a few seconds to several minutes), the quality of molded products from grams to tens of kilograms, can shape a complex shape, size accuracy, with metal or non-metallic inserts molded products. Therefore, this method is adaptable and has high production efficiency.
The injection molding machine for injection molding is divided into two types: plunger injection molding machine and screw injection molding machine, which are composed of injection system, clamping system and plastic mold. The forming method can be divided into:
(1) Exhaust injection molding. Exhaust injection molding application of the exhaust injection machine, the central cylinder has a vent, but also connected with the vacuum system, when the plastic plastic, the vacuum pump can plastic in the water vapor, monomer, volatile Material and air through the exhaust port pumping away; raw materials do not have to be pre-dried, thereby increasing production efficiency and improve product quality. Particularly suitable for polycarbonate, nylon, plexiglass, cellulose and other materials easily hygroscopic molding.
(2) flow injection molding. Flow injection molding can be used ordinary screw-type injection machine. That is, the plastics are continuously plastified and extruded into the mold cavity with a certain temperature. After the plastic is filled in the cavity, the screw stops rotating, and the material in the mold is kept under pressure for a suitable time by the thrust of the screw, and then cooled and shaped. Flow injection molding overcomes the equipment limitations of producing large products, and the part quality can exceed the maximum injection volume of the injection machine. It is characterized by plasticized objects are not stored in the barrel, but continue to squeeze into the mold, so it is a combination of extrusion and injection method.
(3) co-injection molding. Co-injection molding is the use of injection molding machine with two or more injection units, different types or different colors of plastic, simultaneously or successively into the mold method. In this way it is possible to produce composite products of a wide range of colors and / or types of plastics. Representative co-injection molding is two-color injection and multi-color injection. (4) No runner injection molding. The mold does not set the shunt, but by the injection machine extension nozzle directly to the molten material into each cavity molding method. During the injection process, the plastic in the runner remains in a state of melt-flow and does not come off with the product during demolding, so there is no runner residue in the part. This molding method not only saves raw materials, reduce costs, but also reduce the process, you can achieve fully automatic production.
(5) reaction injection molding. The principle of reaction injection molding is that the reaction raw materials are metered into the mixing head after being metered by the metering device, collided and mixed in the mixing head, and then injected into the closed mold at high speed for rapid curing, demolding and product removal. It is suitable for processing some thermosetting plastics and elastomers such as polyurethane, epoxy resin, unsaturated polyester resin, silicone resin, alkyd resin and so on. Mainly used for polyurethane processing. (6) thermosetting plastic injection molding. Granular or lump thermosetting plastic, in the strict control of the temperature of the barrel, through the role of the screw, plasticized into a plastic state, at a high injection pressure, the material into a certain temperature range of the mold cross-linked curing. Thermosetting plastic injection molding in addition to physical state changes, but also chemical changes. Therefore, compared with the thermoplastic injection molding, molding equipment and processing technology there is a big difference. The following table compares the difference between thermoset and thermoplastic injection molding.