Blow Molding Troubleshooting

Possible Causes

Suggested Solutions

1. Overheating of copolymer

1. a. Lower extruder temperature and increase barrel cooling if possible. Try to reduce melt temperature to below 400°F (204°C).
   b. Slow down extruder.

1. Overheating of copolymer in blow molder or grinder

1. The suggested
   solution is the same as above.
2. Reduce heat buildup in grinder.

1. Resin will not purge out some polymers
   easily
2. Contamination by foreign material
3. Contamination by decomposed
   particles

1. a. The best
   plan is to disassemble head and screw thoroughly clean.
   b. If purging is the selected method of clean-out, purge for full time needed to complete clean-out.
2. Inspect bags, hopper loader and grinder if used. Take indicated steps to eliminate foreign material.
3. a. Clean die and extruder of any degraded material.
   b. Cool extruder before shutdown.

1. Moisture

1. Dry resin at 140°F (60°C) for
   approximately one hour.

1. Contamination
2. Melt temperature too high or too low
3. Mold temperature too cool

1.  Same as contamination problem above.
2. Correct melt temperature to 360- 390°F (182-199°C).
3. Adjust mold temperature to approximately 75°F (24°C).

1. Mold finish not polished (i.e., grit-blasted)
2. Mold finish dirty
3. Improper mold temperature

1. Polish mold.
2. Clean and polish with Simichrome
   polish.
3. Adjust mold temperature to 75°F (24°C).

1. Parison necking down
2. Larger part periphery at top

1. a. Program parison.
   b. Increase extrusion rate.
   c. Lower melt temperature.
2. Invert mold, if possible.

1. Non-symmetrical part shape

1. a. Shape die to increase parison thickness in thin area.
   b. Preblow parison.
   c. Use larger parison diameter.

1. Too large a blowup ratio
2. Mold separation
3. Pinch-off too sharp

1. Use larger die tooling.
2. Increase clamp pressure or decrease blow pressure.
3. Provide wider pinch-off land.

1. Dirty or damaged die

1. a. Clean die land surfaces.
   b. Nicks or scratches in die or mandrel may need to be removed.
   c. Check for foreign material.
   d. Streamline flow to eliminate holdup in die.

1. Mandrel not up to temperature
2. Mandrel too high
3. Die face dirty

1. Allow mandrel to reach equilibrium with rest of system.
2. Lower mandrel slightly.
3. Clean die.

1. Cooling to extruder feed zone not turned on
2. Insufficient back pressure
3. Extruder operating erratically
4. Extruder slipping

1. Turn on air/water cooling to feed section.
2. Increase back pressure.
3. Repair extruder.
4. Repair extruder.

1. Wall thickness of parison too thin

1. a. Increase
   annular opening to make wall thicker.
   b. Make parison faster.

1. Wall thickness of parison too
   heavy

1. Decrease annular opening to make wall thinner.

1. Blow air pressure inadequate

1. a. Increase blow air pressure.
   b. Check for blocked air lines.

1. Insertion rate too slow
2. Needle stroke too short
3. Needle is blunt

1. Increase pressure to needle cylinder.
2. a. Lengthen stroke if possible.
   b. Install cylinder with longer stroke.
3. Sharpen needle to ensure good puncture.

1. Blow air incorrectly timed

1. Start blow air earlier in cycle.

1. Low blow pressure
2. Air entrapment

1. Increase blow pressure.
2. Improve mold venting.

1. Mold temperature too high
2. Mold closing speed too fast
3. Pinch-off land too sharp

1. Reduce mold temperature to 75°F (24°C).
2. Increase mold "cushion" or decrease mold closing speed.
3. a. Widen pinch land.
   b. Dam up pinch-off relief to thicken pinch weld.

1. Insufficient cooling
2. Non-uniform cooling due to air entrapment
3. Cooling differential in thick and thin areas

1. a. Provide good water flow in molded
   channels.
   b. Increase cooling time.
2. 2. Increase good venting.
3. 3. Improve wall distribution.