TL;DR

Blow pin air leakage causes parts to blow poorly and increases cycle time. Inspect the blow pin O-ring seals and blow needle seal faces before adjusting blow air pressure.

What you might see

blow air escaping audibly around the blow pin during inflation
parts underfilled or have thin walls
blow pressure cannot reach setpoint
visible wear or scoring on the blow pin body

Likely causes

Tap to mark as ruled out

Worn or pinched O-ring seals on the blow pin body
Scored blow pin body from abrasive resin or foreign material
Blow needle tip worn or damaged not seating correctly
Excessive blow pin side loading from misaligned blow pin guide

Required tools

O-ring replacement set (machine-specific size)
Fine abrasive cloth for pin polishing
Food-grade or resin-compatible grease
Air pressure gauge
LOTO kit

Safety first

Blow air at 6 to 10 bar will cause injury if a fitting is loosened while pressurized. Confirm zero pressure before disassembly.
Blow pin bodies are at elevated temperature near the die area. Allow cooling before handling.

Procedure

7 steps · ~30 min

1
Stop the blow cycle and depressurize the blow air circuit before removing the blow pin assembly.
Warning: Blow air circuits typically operate at 6 to 10 bar. Confirm the pressure is zero at the blow air gauge before disassembling the blow pin.
2
Remove the blow pin assembly from the mold carrier. Disassemble the blow pin body and remove the O-ring seals.
3
Inspect each O-ring for compression set, cuts, or swelling from resin chemical attack. Replace the full O-ring set.[1]
4
Inspect the blow pin body for scoring or wear grooves. A lightly scored pin body can be polished with fine abrasive cloth. Heavily scored bodies require replacement.
5
Re-assemble with new O-rings lubricated with a small amount of food-grade or resin-compatible grease.[1]
6
Re-install the blow pin and run a manual blow cycle. Listen for air leakage and verify the blow pressure reaches the setpoint on the gauge.
7
Run 20 production cycles and inspect parts for consistent wall distribution and part weight.

Sources

Bekum Bekum H-Series Blow Molding Machine general technical documentation, Bekum
Bekum H-Series blow molding machine operator and maintenance manual, blow pin maintenance procedures (general)

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