The basic cause of surface depression: From the plastic point of view, when the plastic cools and shrinks, insufficient shrinkage can cause depressions or voids on the outer surface of the article.
   The location of the depression is different, and the cause and solution of the defect will be different.
   1. When the depression occurs at the last cooled position of the thick-walled product, or at a location far from the gate:
   Analysis of the causes: usually the typical thick wall and the surface depression or cavity far from the gate, usually due to the increase of the effective viscosity, the pressure loss is increased, resulting in insufficient cavity pressure, resulting in insufficient feeding pressure.
   Solution: Increase the pressure of feeding and accelerate the rate of feeding
   Second, when there is a surface depression or hole near the gate
   Analysis of the cause: The depression appears near the gate, usually due to the lack of gate freezing.
   There are several reasons that affect the freezing of the gate: it may be caused by a decrease in effective viscosity; in most cases, the gate is not frozen due to an increase in the temperature of the plastic; too high a mold temperature may affect the freezing of the gate.
   Solution: Ensure that the gate is frozen by adjusting the mold temperature, plastic temperature, and increasing the dwell time.
   Third, note: holes and bubbles are easily confused. Holes are sometimes misunderstood as bubbles. The bubbles are trapped inside the gas, and the inside of the cavity is vacuum.