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Trouble Shootings
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Common
Phenolic Injection Molding Defects
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Insufficient
material feeding
Cause:
- Caking at hopper bottom
- Back pressure insufficient
or cylinder temperature too low causing inadequate melting
- Barrel temperature is too low
causing inadequate material melting. Especially when 70% of the capacity
is injected.
- Screw speed in too
fast
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Solutions:
- Have cooling water pass
hopper bottom
- adjust back pressure or
increase barrel temperature
- Reduce screw speed
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Short Shot
Cause:
- Poor melting of material
- Insufficient material flow
- Nozzle diameter, gate runner
too small
- Injection pressure is too
low
- Dwell time too short
- Insufficient charge volume
in the barrel
- Air resistance, no gas
escape
- Product too thin
- Abrasion of screw
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Solution:
- Increase temperature of
barrel and mold
- Use material with better
flow properties
- Repair faulty part
- Increase injection pressure
- Lengthen dwell time
- Increase back pressure,
charge volume
- Increase air vents
- Reconsider mold design
- Replace screw
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Too much flash
Cause:
- Injection pressure too high
- Injection speed too fast
- Material flow too soft
- Clearance of mold surface
- Mold temperature too high
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Solution:
- Lower injection pressure
- Adjust with flow control
bulb
- Use hard flow material
- Make smaller clearance
- Lower mold temperature
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Weld lines
Cause:
- Barrel temperature too low
- Injection pressure too low
- Air pockets
- Insufficient material flow
- Oil on mold surface
- Distance between gate and
weld point too far
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Solution:
- Increase barrel temperature
- Adjust injection pressure;
widen runner, gate
- Increase air vents
- Use soft-flow material
- Remove mold and clean the
oil on the mold
- Study gate position
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Flow Mark
Cause:
- Un-uniform melting of material
causing by low temperature of mould and barrel
- Gate too small
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Solution:
- Increase temperature by step
- Widen the size of the gate
- Decrease the injection speed
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Poor cavity filling
Cause:
- Barrel and mold temperature
are too low
- Injection pressure and/or
speed are too high
- Material flow is too high,
i.e. material is too soft
- Injection starts before
clamping pressure has been applied
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Solution:
- Increase temperature of
Barrel and mold
- Adjust injection pressure and
flow control to fill cavity slowly
- Use harder material
- Delay injection starting
time
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Fragility
Cause:
- Melting temperature is too
high
- Size of runner, sprue, gate are too small
- Material is too hard
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Solution:
- Decrease barrel temperature
- Review the runner, spure and gate design
- Use softer material
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Mold Shrinkage
Cause:
- The shorter the curing time
is, the larger the molding shrinkage
- The shorter the dwell time
is, the larger the shrinkage ratio
- The smaller the gate cross section
area, the larger the shrinkage ratio
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