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What Is Plastic Injection-05

Taimi: 2021-09-09 Hits: 3

3. Injection temperature


Injection temperature is an important factor affecting injection pressure. The barrel of the injection molding machine has 5 ~ 6 heating sections, and each raw material has its appropriate processing temperature (for detailed processing temperature, please refer to the data provided by the material supplier). The injection temperature must be controlled within a certain range. If the temperature is too low, the melt plasticization is poor, which affects the quality of formed parts and increases the process difficulty; The temperature is too high and the raw materials are easy to decompose. In the actual injection molding process, the injection temperature is often higher than the barrel temperature. The higher value is related to the injection rate and material properties, up to 30 . This is due to the high heat generated by the shear when the molten material passes through the injection port. There are two ways to compensate for this difference in mold flow analysis: one is to measure the temperature of melt air injection, and the other is to include the nozzle in modeling.


4. Pressure holding pressure and time


At the end of the injection molding process, the screw stops rotating and just moves forward. At this time, the injection molding enters the pressure maintaining stage. During the pressure maintaining process, the nozzle of the injection molding machine continuously replenishes the cavity to fill the empty volume due to the shrinkage of thu oloa. If the pressure is not maintained after the cavity is filled, the mea e gaosi will shrink by about 25%, especially the shrinkage trace will be formed at the rib due to excessive shrinkage. The pressure holding pressure is generally about 85% of the maximum filling pressure. Of course, it should be determined according to the actual situation.


5. Back pressure


Back pressure refers to the pressure to be overcome when the screw reverses and retreats for material storage. The use of high back pressure is conducive to the dispersion of pigment and the melting of plastic, but at the same time, it prolongs the screw retraction time, reduces the length of plastic fiber and increases the pressure of injection molding machine. Therefore, the back pressure should be lower, generally no more than 20% of the injection molding pressure. When injection molded foam, the back pressure should be higher than the pressure formed by the gas, otherwise the screw will be pushed out of the barrel. Some injection molding machines can program back pressure to compensate for the reduction of screw length during melting, which will reduce the input heat and reduce the temperature. However, because the result of this change is difficult to estimate, it is not easy to make corresponding adjustments to the machine.