Principle and mode of injection molding machine

Injection molding machine is a kind of plastic machinery, which is called injection machine or injection molding machine for short It is the main molding equipment that makes thermoplastics or thermosetting plastics into various shapes of plastic products by using plastic molding mold Injection molding is realized by injection molding machine and mold Principle and mode of the injection molding machine: the working principle of the injection molding machine is similar to that of the syringe for injection It is the technological process of injecting the plastic in the molten state (i.e viscous flow state) which has been plasticized into the closed mold cavity with the help of the thrust of the screw (or plunger), and obtaining the products after solidification and molding Injection molding is a cycle process, each cycle mainly includes: quantitative feeding, melting and plasticizing, pressure injection, mold filling and cooling, mold opening and taking Take out the plastic part and then close the mold for the next cycle Injection molding machine operation items: injection molding machine operation items include control keyboard operation, electrical control system operation and hydraulic system operation The injection process action, feeding action, injection pressure, injection speed, ejection type selection, temperature monitoring of each section of the barrel, injection pressure and back pressure regulation are carried out respectively
The general molding process of screw injection molding machine is: first, the granular or powdery plastic is added into the barrel, and the plastic is melted by the rotation of the screw and the heating of the outer wall of the barrel, then the machine closes the mould and moves the injection seat forward, so that the nozzle is close to the sprue of the mould, and then the injection cylinder is filled with pressure oil to push the screw forward, so that the high pressure and At a faster speed, melt is injected into a closed mold with lower temperature After a certain period of time and pressure holding (also known as pressure maintaining) and cooling, it can be solidified and shaped, then the mold can be opened to take out the products (the purpose of pressure maintaining is to prevent the reverse flow of melt in the mold cavity, supplement materials to the mold cavity, and ensure that the products have a certain density and dimensional tolerance) The basic requirements of injection molding are plasticization, injection and molding Plasticization is the premise of realizing and ensuring the quality of molded products, and in order to meet the requirements of molding, injection must be guaranteed to have enough pressure and speed At the same time, due to the high injection pressure, the corresponding high pressure is generated in the cavity (the average pressure in the cavity is generally between 20 and 45MPa), so there must be enough mold closing force It can be seen that the injection device and the mold closing device are the key parts of the injection molding machine The evaluation of plastic products mainly includes three aspects: appearance quality, including integrity, color, luster, etc.; the second is the accuracy between size and relative position; the third is the physical, chemical and electrical properties corresponding to the use These quality requirements are different according to the use of products, and the required scale is also different The defects of the products mainly lie in the design, manufacturing accuracy and wear degree of the mould But in fact, the technicians in the plastic processing plant often suffer from the difficult situation of using technological means to make up for the problems caused by mold defects, but the effect is not very good The adjustment of process is the necessary way to improve the quality and output of products Because the injection cycle itself is very short, if the process conditions are not well mastered, the waste products will be endless When adjusting the process, only one condition can be changed at a time Observe more times If the pressure, temperature and time are all adjusted together, it is easy to cause confusion and misunderstanding If something goes wrong, I don't know why There are many measures and means to adjust the process For example, there are more than ten possible solutions to the problem of product dissatisfaction Only by choosing one or two major solutions to solve the problem can we really solve the problem In addition, we should pay attention to the dialectical relationship in the solution For example: when the products have dents, sometimes the material temperature should be increased, sometimes the material temperature should be reduced; sometimes the material quantity should be increased, sometimes the material quantity should be reduced It is necessary to recognize the feasibility of reverse measures to solve the problem