（21） Gate area defects Injection Molding Process Defect Handling Manual

1. Light ray
In the design of a point gate perpendicular to the direction of the workpiece, a radiation system consisting of different color depths and gloss, called a ray of light, appears on the surface of the workpiece during injection molding, with the gate as the center. There are generally three manifestations, namely, dark lines on a dark background, dark lines on a dark background, and dense and white dark lines around the gate.
Most of these defects occur during the injection of polystyrene and modified polystyrene mixtures, and are related to the following factors: differences in rheology and colorability between the two materials, and differences in flow rates and heating conditions between the laminar and turbulent layers of the gating system; The formation of charred filaments from plastic due to thermal decomposition; Interference of gaseous substances during injection molding of plastics.
Solution:
(1) When using mixed plastic, it is necessary to mix the plastic well, and the particle size of the plastic should be the same and uniform.
(2) The plastics and colorants should be mixed evenly, and appropriate dispersants should be added if necessary, and mixed mechanically.
(3) The plasticization should be complete, and the plasticization performance of the machine should be good.
(4) Reduce the injection pressure and speed, shorten the injection and pressure holding time, increase the mold temperature, increase the nozzle temperature, and reduce the front furnace temperature.
(5) Molten materials and coking substances that prevent the degradation of plastics and cause increased viscosity: Note that the screw and barrel are
Whether there is wear and tear, or the heating system is out of control, or improper processing operations cause long-term heating and decomposition of plastic. The inner surface of the screw and the front end of the barrel can be polished.
(6) Improve the gate design, such as enlarging the gate diameter, changing the gate position, changing the gate to a fillet transition, attempting to locally heat the gate, and adding a cold well at the runner end.