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The working principle of the injection molding machine

Update:03-12-2020
Summary:

The working principle of the injection molding machine […]

The working principle of the injection molding machine is 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. The process of obtaining products after curing and shaping.

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.
Injection molding machine operation items: injection molding machine operation items include three aspects: control keyboard operation, electrical control system operation and hydraulic system operation. The selection of injection process action, feeding action, injection pressure, injection speed, ejection type, temperature monitoring of each section of the barrel, and adjustment of injection pressure and back pressure are performed respectively.

The molding process of a general screw injection molding machine is as follows: first add granular or powdered plastic into the barrel, and turn the screw and heat the outer wall of the barrel to make the plastic into a molten state, and then the machine closes the mold and moves the injection seat forward. Make the nozzle close to the gate of the mold, and then pass pressure oil into the injection cylinder to push the screw forward, thereby injecting the melt into the closed mold with a lower temperature at a high pressure and a faster speed. Time and pressure hold (also known as holding pressure), cooling to make it solidify and form, then the mold can be opened to take out the product (the purpose of holding pressure is to prevent the backflow of the melt in the mold cavity, replenish materials into the mold cavity, and ensure the product Has a certain density and dimensional tolerance).

The basic requirements of injection molding are plasticization, injection and molding. Plasticization is a prerequisite for realizing and ensuring the quality of molded products, and in order to meet the requirements of molding, injection must ensure sufficient pressure and speed. At the same time, due to the high injection pressure, a correspondingly high pressure is generated in the cavity (the average pressure in the cavity is generally between 20 and 45 MPa), so there must be a sufficient clamping force. It can be seen that the injection device and the clamping device are the key components of the injection molding machine.

There are three main aspects to the evaluation of plastic products. The first is the appearance quality, including completeness, color, gloss, etc.; the second is the accuracy of the size and relative position; the third is the physical properties, chemical properties, and Electrical performance, etc. These quality requirements are different depending on the use occasion of the product, and the required scale is also different. The defects of the product mainly lie in the design, manufacturing accuracy and degree of wear of the mold. But in fact, the technicians of plastic processing plants often suffer from the difficult situation of using technological means to compensate for the problems caused by mold defects without great results.

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