The HDPE bottle lip surface and “I” opening play a critical role in sealing the bottle contents. When a smooth clean surface is produced and the critical bottle tolerances are in specification, a plug style closure will have a positive sealing application. Over time however, blow mold tooling wears out and creates problems in the bottle lip and “I” dimension. The bottle lip will show signs of jagged edges, flash and other issues. Sometimes when checking the bottle lip finish, it may appear to be concentric and may look clean, but the “I” opening in fact may be damaged. The lip may have slight distortion due to worn shear steels. This issue can be seen by using a bottle ID Gauge or measuring the lip with calipers.

The jagged edges on the bottle lip occur when the shear steels are chipped. This may occur when the blow pins are not lined up. Over time, after repeatedly hitting, the shear steels may, also, crack causing the deformation on the lip. When this occurs, the cap plug cannot seal this area due to the imperfection. A new shear steel and blow pin will be needed in order to resolve this problem.

Another issue occurs when the angle wings do not trim cleanly creating a triangle at the parting line. This may happen if the bottle gram weight is too light. Trimming the angle wings is very difficult which will result in snagging the bottle finish at the parting line creating this problem. Another possible cause for this issue can be the mold is not clamping up, creating a thicker pinch off area restricting the angel wings from trimming. The picture at the bottom right shows the triangle resulting from the snagged angel wings.