2.1 The pressure of the molten material at the front end of the barrel is too high, the material temperature is high, the viscosity decreases, the counterflow of the molten material in the screw groove and the leakage flow between the barrel and the screw increase, which will reduce the plasticizing efficiency.

2.2 For plastics with poor thermal stability (such as PVC, POM, etc.) or colorants, the temperature of the melt increases and the heating time in the barrel causes thermal decomposition, or the degree of discoloration of the colorant increases, and the surface color and gloss of the product worse.

2.3 If the back pressure is too high, the screw retreats slowly, and the pre-plastic material returns for a long time, which will increase the cycle time and lead to a decrease in production efficiency.

2.4 If the back pressure is high, then the melt pressure will be also high. After the injection, the nozzle is prone to melt salivation. When the glue is injected next time, the cold material in the nozzle flow channel will block the nozzle or cold material spots will appear in the product.

2.5 During the injection molding process, the nozzle often leaks glue due to excessive back pressure, which wastes raw materials and causes the heating ring near the nozzle to burn out.

2.6 The mechanical wear of pre-plastic mechanism and screw barrel increases.