Although commercially practical, hinge quality is only fair for three reasons:
1.Molecular orientation is parallel to the hinge.
2.Extrudate cannot be flexed immediately after molding as it first has to go through the cooling
line, haul-off and other downstream equipment to stabilize its shape.
3.Differential shrinkage due to uneven wall stock between the hinge and adjacent walls, leading
to warpage. Warpage may be minimized if the shoulder thickness does not exceed 2 to 3 times
hinge thickness.