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Injection molding
Injection molding. Injection molding (injection molding) is a method to make thermoplastic or thermosetting molding plastic uniformly plasticize in the heating material tube first, then push by plunger or moving screw into the cavity of closed mould.
Injection molding is applicable to almost all thermoplastic plastics. In recent years, injection molding has also been successfully used to form some thermosetting plastics. Injection molding has a short molding cycle (seconds to minutes). The quality of the molded products can range from a few grams to dozens of kilograms. It can be molded into a molding product with complex shape, accurate size and metal or non-metal inserts at one time. Therefore, this method has strong adaptability and high production efficiency.
The injection machines used for injection molding are divided into two categories: plunger injection machine and screw injection machine. The forming method can be divided into:
(1) exhaust injection molding. The exhaust injector used in the exhaust injection molding is provided with an exhaust port in the middle of the material barrel and is also connected with the vacuum system. When plastic is plasticized, the vacuum pump can remove water vapor, monomer, volatile matter and air from the plastic through the exhaust port. Raw materials do not need to be pre-dried to improve production efficiency and product quality. Especially suitable for polycarbonate, nylon, plexiglass, cellulose and other moisture - absorbent materials.
(2) flow injection molding. Flow injection molding can be used for general mobile screw injection machine. That is, the plastic is continuously plasticized and squeezed into the mold cavity with a certain temperature. When the plastic is filled with the mold cavity, the screw stops rotating. The flow injection molding overcomes the equipment limitation of the production of large products, the quality of the parts can exceed the maximum injection amount of the injector. Its characteristic is that the plasticized object is not stored in the material cylinder, but continuously squeezed into the mold, so it is a method of combining extrusion and injection.
(3) co-injection molding. Co-injection molding is a method of injecting different kinds of plastic with two or more injection units into the mold at the same time or successively. This method can produce a variety of color and/or plastic composite products, the typical co-injection molding is two-color injection and multi-color injection.
(4) no flow injection molding. There is no shunt channel in the mould, and the forming method of the melt is directly injected into each cavity by the extending nozzle of the injector. In the process of injection, the plastic in the flow channel remains molten and flowing, and it does not come out with the product when the mould is removed, so there is no runner residue. This forming method can not only save raw materials, reduce costs, but also reduce the process to achieve automatic production.
(5) reaction injection molding. The principle of reaction injection molding is to pump the reaction raw material into the mixing head after being measured by the measuring device, collide and mix in the mixing head, then inject it into the closed mould at high speed, solidify quickly, remove the mould and take out the product. It is suitable for processing polyurethane, epoxy resin, unsaturated polyester resin, organic silicon resin, alkyd resin and other thermosetting plastics and elastomers. At present, it is mainly used in the processing of polyurethane.
(6) injection molding of thermosetting plastic. Granular or bulk thermosetting plastics can be molded into viscosity-plastic state through the action of screw in the material tube with strict temperature control. Under high injection pressure, the material can be cross-linked and solidified within a certain temperature range of mold. In addition to physical changes, thermosetting plastic injection molding also has chemical changes. Therefore, compared with thermoplastic injection molding, there are great differences in forming equipment and processing technology. The following table compares the difference between thermosetting and thermoplastic injection molding.
This is the end of the introduction of Production process of HPLC vials. I hope it can help you.
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