Pinchoff land width is the width of the area on each mold half that nets out against the opposite half. As land width increases, a more substantial seam will be formed, but trimming and finish on the part will be sacrificed. Venting design is crucial to process quality Venting must be incorporated into all blow molds. Venting systems allow for the escape of air between the parison and the cavity. Venting is located on the face of the mold, at the split line, between mold sections and beneath inserted pinchoffs.
Vent depth is dependent upon location and part material.
Poor venting can cause visible air entrapment on the surface of a part and prevent the part from fully contacting the mold. Vents consist of milled paths or slots that are approximately 0.002 in. In applications where evidence of the vent in the finished part is undesirable, small-bore vents are utilized. These vents consist of drilled holes 0.007 in. Several changes in the types of products being blow molded are dictating shifts in blow mold design.