Why Do Injection Molded Parts Produce Dents and Sink Marks?

Injection Core Tube Supplier to share with you the reasons for the depressions and sink marks in the injection molded parts.

(1) Improper molding conditions.

If the injection pressure is too low, the injection and holding time is too short, the injection rate is too slow, the material temperature and mold temperature are too high, the plastic parts are insufficiently cooled, the temperature is too high during demolding, the temperature at the insert is too low, or the supply is insufficient. It will cause the surface of the plastic part to have a concave or orange peel. In this regard, the injection pressure and injection speed should be appropriately increased, the compression density of the melt should be increased, the injection and holding time should be prolonged, the melt shrinkage compensated, and the injection backlash amount increased. However, the pressure should not be too high, otherwise, it will cause embossing.

(2) Mold defects.

If the flow path and gate section of the mold is too small, the filling resistance is too large, the gate setting is asymmetrical, the filling speed is not balanced, the inlet position is unreasonably set, and the die exhaust is adversely affected by the feeding, feeding, and Cooling, or pressure loss caused by mold wear, will cause depressions and sink marks on the surface of plastic tape plastic core. For this reason, the gate and runner cross-section should be appropriately enlarged according to the specific conditions. The gate position should be set at the symmetry as much as possible. The mouth should be placed on the thick part of the plastic part.

(3) Raw materials do not meet molding requirements.

If the shrinkage of the molding material is too large or the flowability is too poor, and the lubricant in the raw material is insufficient or the raw material is wet, it will cause dents and sink marks on the surface of the Pvc Pipe Core. Therefore, for plastic parts with higher surface requirements, resin grades with low shrinkage should be used as much as possible.

(4) The design of the shape of the plastic part is unreasonable.

If the wall thicknesses of the plastic parts vary greatly, the thick-walled parts are prone to depressions and sink marks due to insufficient pressure. Therefore, when designing the shape of the plastic part, the wall thickness should be as uniform as possible. For special cases, if the wall thickness of the plastic part is different, it can be solved by adjusting the structural parameters of the casting system.