How to solve the defects in the product gate area

How to solve the defects in the product gate area

We have defects in the gate area during the injection molding process. What are the reasons for this phenomenon? Is there a good solution?

1. Light line
Cause of formation:
In the design of point gate which is perpendicular to the direction of workpiece, the radiant system composed of different color, depth and luster with gate as the center appears on the surface of workpiece during injection molding, which is called ray line. Generally, there are three kinds of performance, that is, dark bottom dark line, dark bottom dark line and dense and white dark line around the gate.
This kind of defect mostly appears in the injection of polystyrene and modified polystyrene mixture, which is related to the following factors: the two kinds of materials have differences in rheology, colorability and other aspects, the velocity and heating condition of the stratosphere and turbulent layer of the pouring system are different; the scorched wire is formed due to the thermal decomposition of the plastic; the interference of the gaseous substance when the plastic enters the mold.
Solution:
① . when mixed plastic is used, the plastic shall be mixed well, and the particle size of the plastic shall be the same and uniform.
② . plastics and colorants should be mixed evenly. If necessary, appropriate dispersants should be added and mixed mechanically.
③ . the plasticization shall be complete and the plasticization performance of the machine shall be good.
④ Reduce injection pressure and speed, shorten injection and holding time, increase mold temperature, increase nozzle temperature and reduce furnace temperature.
⑤ . to prevent melting materials and coking materials with increased viscosity caused by degradation of Plastics: for example, pay attention to whether there is dead angle due to abrasion of screw and barrel, or heating system is out of control, improper processing operation causes long-term heating and decomposition of plastics. The inner surface of the front end of the screw and the barrel can be polished.
⑥ . improve the gate design, such as enlarging the gate diameter, changing the gate position, changing the gate into a fillet transition, try to heat the gate locally, and add a cold well at the end of the runner.
2. Cold spot
Cause of formation:
Cold spot mainly refers to the spot with fog or light color near the gate or the curved scar like earthworm sticking on it, which is caused by the plastic front entering the cavity or the cold material squeezed into the cavity due to excessive pressure retaining effect;
Because of the cooling effect of the nozzle or flow channel, the front part of the material is cooled and solidified before entering the mold cavity. When it is expanded and injected into the mold cavity through a narrow gate, the melt breaks, and then it is pushed by the later hot melt material, so it becomes a cold spot.
Solution:
① . the cold charging well should be set up well. In addition, the form, size and position of the gate should be considered to prevent the cooling speed of the material from great disparity.
② . the center degree of the nozzle shall be adjusted, and the matching size of the nozzle and the mold feeding shall be designed to prevent leakage of material or cold material being brought into the cavity.
③ . the mold has good exhaust. The interference of gas will make the gate appear turbid stripes.
④ . increase mold temperature. Slow down the injection speed, increase the injection pressure, reduce the pressure maintaining and injection time, and reduce the pressure maintaining.
⑤ . dry the plastic. Use less lubricant to prevent powder from being polluted