Herunder we sum several defect that can occur during /after the injection moudling process

There are process or material conditions which may result to some injection molding defects. The following is a summary of what typical defects may occur, usally after injection molding, however the deviations on the defects would depend on specific circumstances.

         Blistering or blisters is a raised zone or  layered zone in the part. It is caused by an over heated tool ( lack of cooling) or material (faulty heater.)

         Short mouldings may be due to an inadequate shot capacity or the materials may freeze off before the mould is completely filled.

         Delamination (Thin mica like layers formed in the wall of the part) may occur if the materials used are incompatible with the moulding or the skin of the material freezes prematurely, there could also be the possibility of a melt fracture.

         Flashing or burrs. (Excess material in thin layer exceeding normal part geometry) could occur if the shut-off faces of the mould are mismatched, the mould opens under the pressure of the materials being injected into it, and it could also be that the melt viscosity may be a bit too low. Other causes are that the Mould is over packed or parting line on the tool is damaged, too much injection speed/material injected, clamping force too low. Can also be caused by dirt and contaminants around tooling surfaces.

         Poor weld lines  ( or Knit lines) may occur if the converging streams of the materials do not weld properly at the interface or the presence of foreign materials at the interface of the converging streams.

         Ejection difficulties may occur if there is insufficient cooling, there is excess pressure within the cavity of the mould, there is insufficient taper, the surface is poorly finished, the positioning or the area of the ejectors itself are not satisfactory, the cores are misaligned or the spruce may be misaligned.

         Sinking and voiding may occur if there is excessive shrinkage of the moulding itself, the cooling time is incorrectly set, the design of the mould or the product itself is not correctly manufactured, and the gate size is not suited for the grade of the material.

         Warping and bowing can occur if there is too much residual stress from the injection pressure, or the cooling temperatures are imbalanced or inadequate, there may also be some variations on the thickness of the walls,  and the ejection system itself needs to reset.

 

 

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