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The principle of plastic injection mould. |
Injection molding is made by injecting plastic melt into a closed mold cavity at high pressure. After cooling, the plastic products are completely consistent with the shape of the mold cavity.
The injection molding must meet two necessary conditions: first, the plastic must be injected into the mold cavity with molten state; Second, the injected plastic melt must have enough pressure and flow rate to fully fill mold cavity. Therefore, the injection molding must have the basic function of plastic plasticizing, melt injection and pressure forming.
(1) plasticizing process in the process of injection molding of plasticizing, solid plastic through the rotation of the screw conveyor, constantly move forward along the spiral groove direction, after heating, the compaction, the screw thread of shear mixing effect and heat up into a uniform density, viscosity and composition and temperature distribution in homogeneous plastic fluid viscous flow. The heat required for plasticization of solid plastics is mainly from the external cylinder's heating of plastic and the friction and shear heat of the injection screw to plastic. In plasticizing process, the temperature of the plastic melt whether meet the requirements of injection as well as the temperature distribution is uniform and so on is the important measure of injection molding machine plasticizing function is good or bad, and plasticizing function refers to the injection moulding machine in a unit time can provide the size of the amount of molten plastic.
After solid plastic molded into the melt have been rotating screw to screw's head, and stored in the barrel of the front-end material stock area, save the plastic melt has a certain pressure, the melt pressure effect on the screw driven screw to overcome all kinds of resistance and back. After the screw has retreated to a certain distance, the plastic melt volume in the storage area (known as injection quantity) is determined, and the plasticization process is completed and the injection process is entered. (2) the injection process has good plasticizing good plasticification plastic melt material stock area, stored in a barrel, injection screw axial movement, under the action of screw injection pressure, the plastic melt at a certain rate through the installation in the barrel of the front spray nozzle, mould pouring system and injection mold cavity.
(3) after heating process into the plastic melt in the mold cavity to overcome all kinds of flow resistance and full of cavity, cavity of plastic melt by cavity pressure, the pressure has driven the plastic melt flow back to the barrel of the drive; And, due to the effect of cooling of the mold cavity to make plastic melt cooling contraction, the injection screw continues to provide pressure, maintain full of plastic melt ininjection mould cavity and do not return, and appropriate to supplement the plastic melt in cavity to fill the cavity of the contraction space, until the plastic melt cooling solidification for products.
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Down：How do injection molds prevent streak defects?
Up：There are some reasons for the crack defects in injection molding. |
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