The principle of the plastic injection molding machine for plastic mechanical products is to inject molten plastic into the mold and then cool it to become a product. It has a wide range of uses, and different uses depend on different plastics. The injection molding machine is the processing machine with the largest use in the plastic processing industry. Not only can a large number of products be directly produced by the injection molding machine, but also it is the key equipment for forming the injection, drawing and blowing process.

After the 1960s, the plunger type plastic injection molding machine was gradually replaced by the screw type injection molding machine. According to the position of the injection device, it can be divided into horizontal, vertical and angle injection molding machines. The injection capacity (cm3)/clamping force (t) is used internationally to express the specifications of various injection molding machines. For example, SI-190/90 means that the injection capacity of the injection molding machine is 190cm3 and the clamping force is 90t.

Screw injection molding machine is composed of four parts: injection device, mold clamping device, hydraulic transmission and electrical control system.

The injection device is composed of a barrel, a screw, a nozzle, a hopper, a metering device, a screw drive device, an injection pressure cylinder, a movable pressure cylinder of an injection base, etc. Its main function is to make the plastic melt and plasticize evenly, and then inject a certain amount of molten material into the injection mold under a certain pressure and temperature.

Mold closing device, also known as mold locking device. It is composed of mold closing cylinder, movable template, fixed template, mold closing mechanism, pull rod, safety gate of demoulding device, etc. Its main function is to ensure that the mold is opened and closed according to the specified procedure and speed, and that there is enough clamping force to make the mold close. There are three types of clamping devices: hydraulic type, mechanical type and hydraulic/mechanical hybrid type.

The hydraulic transmission and electrical control system ensure that the injection molding machine can work accurately according to the pressure, speed, temperature and time of the procedures specified in the injection molding process. The hydraulic transmission system is composed of power oil pump, directional valve, throttle valve, pressure valve and oil tank. The electrical control system consists of power control, action process control and heating control systems.

In addition to the general-purpose thermoplastic injection molding machines, there are also thermosetting plastic injection molding machines, foaming injection molding machines, exhaust injection molding machines, reaction injection molding machines and other special varieties.

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