BLOW MOLD TOOLING PREPRESS

Extrusion Blow Molding Pinch-Off & Mold Split DXF Guide

In extrusion blow molding (EBM) of bottles and hollow plastic packaging, the bottom pinch-off land welds the molten tubular parison closed while severing excess flash. Proper pinch knife geometry is critical to achieve high drop-impact weld strength without bottom seam leaks.

1. Pinch-Off Land Hydrodynamics & Seam Weld Integrity

When mold halves clamp shut, the pinch land ($W_p \approx 0.8 \times t_{\text{wall}}$) forces molten polymer molecules to interdiffuse across the parting line while squeezing excess plastic into the flash relief pocket. A $30^\circ - 45^\circ$ relief angle prevents excessive hydraulic backpressure during press closure.

2. Engineering Specifications & Tolerances

3. CNC Blow Mold Cavity DXF Prepress Rules

• Dam & Pinch Steel Inserts: Incorporate hardened Ampco 940 beryllium copper or A2 tool steel pinch-off inserts in the mold bottom for long production life.
• Parting Line Venting: Machine micro-vent grooves 0.025mm deep x 6.0mm wide every 25mm along the parting line to exhaust trapped cavity air.
• Shrinkage Scaling Factor: Scale CAD cavity vectors by +1.8% to +2.5% for HDPE and +1.5% to +1.8% for PP along volumetric shrinkage vectors.