The cooling system should be checked (especially the cooling lines along the hinge) to make
sure it is properly connected and functional.
2.The part
The part should be filled using medium to high injection rates without any step changes in
velocity profile. Smoothly ramping up or down to suit specific tooling constraints presents no
problem. Filling too slowly will likely cause flow hesitation which may lead to hinge delamination.
Too low a melt temperature will cause similar problems. Excessively high mold temperature in
the hinge area due to poor cooling may also lead to hinge weakness.
3.Mixing and plastication
Polypropylene pellets and pigment concentrates need to be fully melted and blended. If not
properly plasticated, agglomerates may concentrate at the hinge, causing weak areas and
eventual failure.
4.Venting
Because of the fast fill rate requirements, it is of paramount importance that the tool be properly
vented. Clogged, insufficient or poorly placed vents represent additional problems which will
cause flow restrictions and may lead to slow filling, air entrapment, burn marks and cosmetic
defects.