Dalian injection molding has large shrinkage and stable size, but the product has large internal stress and is easy to crack. Therefore, it is appropriate to improve the fluidity by increasing the temperature rather than the pressure, and reduce the possibility of cracking by increasing the mold temperature, improving the mold structure and post-treatment. When the injection speed is low, the gate is prone to ripple and other defects. The radiation nozzle temperature should be controlled separately, the mold temperature should be high, and the resistance of runner and gate should be small.

The working process is: heat the material to the flowing (plasticizing) state in the barrel, then inject it into the mold with high pressure to cool, solidify or harden it, and then open the mold to take out the molded product. The specific operation steps of this method are: mold closing, material injection, pressure maintaining, cooling (heating, plasticizing and metering of the next injection material in the barrel during this period), mold opening, taking out the molded products and carrying out the next injection molding operation.

The screw barrel temperature is set according to the properties of different plastic materials. The barrel temperature is generally 10 ℃ - 30 ℃ higher than the plastic melting point. It must be noted that the melting point and allowable residence time in the barrel of materials provided by different manufacturers will also be different due to different synthesis methods or types of additives.

Due to the different geometry of sprue system and mold parts, in order to meet the product quality requirements, there are different requirements for the flow state of mold filling melt (mainly refers to the pressure and speed during flow) in different parts. In an injection process, when the screw pushes the melt to the mold, it is required to achieve different pressure and speed at different positions, which is called multi-stage injection molding.

The speed of fire is closely related to gate design. When using direct gate or edge gate, a slower speed of fire should be used to prevent wave flow marks. In addition, if the thickness of the finished product is more than 5.0mm, slow injection will help to avoid bubbles or depressions. Generally speaking, the principle of fire speed is that the thin is fast and the thick is slow.