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TROUBLESHOOTING
BLOW MOULDING TROUBLESHOOTING
Problems Possible Causes Suggested Solutions
Rough crystalline 1. Overheating of 1. a. Lower extruder temperature and increase
surface copolymer barrel cooling if possible. Try to reduce
melt temperature to below 400°F
(204°C).
b. Slow down extruder.
1. The suggested solution is same as above.
2. Reduce heat buildup in grinder.
Great number oflarge 1. Overheating of 1. a. The best plan is to disassemble head and
gels copolymer in blow screw thoroughly clean.
moulder or grinder b. If purging is the selected method of clean-
out, purge for full time needed to complete
clean-out.
Contamination from 1. Resin will not purge out 2. Inspect bags, hopper loader and grinder if
highly incompatible some polymers easily used. Take indicated steps to eliminate
resins and other 2. Contamination by foreign material.
sources foreign material 3. a. Clean die and extruder of any degraded
3. Contamination by material.
decomposed particles b. Cool extruder before shutdown.
Pock marks, bubbles 1. Moisture 1. Dry resin at 140°F (60°C) for
or streaks in part approximately one hour.

Cloudy or hazy part 1. Contamination 1. Same as contamination problem above.
2. Melt temperature too 2. Correct melt temp. to 360- 390°F (182-
high or too low 199°C).
3. Mould temperature too 3. Adjust mould temperature to approximately
cool 75°F (24°C).

Part dull in 1. Mould finish not 1. Polish mould.
appearance polished (i.e., grit- 2. Clean and polish with Simichrome polish.
blasted) 3. Adjust mould temperature to 75°F (24°C).
2. Mould finish dirty
3. Improper mould temp.
Poor wall thickness 1. a. Program parison.
distribution, top to 1. Parison necking down b. Increase extrusion rate.
bottom 2. Larger part periphery at c. Lower melt temp.
top 2. Invert mould, if possible.
Poor wall thickness 1. a. Shape die to increase parison thickness
circumferentially 1. Non-symmetrical part in thin area.
shape b. Preblow parison.
c. Use larger parison diameter.
Parison rupture or 1. Too large a blowup 1. Use larger die tooling.
part “blowout” ratio 2. Increase clamp pressure or decrease blow
2. Mould separation pressure.
3. Pinch-off too sharp 3. Provide wider pinch-off land.

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