20/02/2022
Post id:02 Preform defects.
1. Bubbles:
causes Solutions
1.Gas or air entrapped in the melt 1.Increse screw back
during plasticizing process pressure.
2. check resin supply for
degradation.
3. reduce feed zone
temperature.
2. Air drawn in due to excessive 1. reduce decompression
decompression by reducing pullback
stroke or pullback
dwell time.
3. Premature melting of the resin due 1. reduce feed zone
to excessive feed zone temperature. temperature.
4.Moisture in the resin due to insufficient 1. check resin dryer
drying. operation. make sure
temperature, dew point,
airflow, hopper resin
level, and residence
time are within
specifications.
5. Excess IV drop. 1.check IV of resin
before and after
drying.
2.reduce barrel
temperature.
3.reduce melt residence
time by reducing
the overall cycle time.
6.Improper feeding of screws due to 1.check and clean barrel
excessive fines, powders, and strings, feed hose if necessary.
in the extruder feed throat. 2.check incoming resin
quality for excessive
fines, powder and
strings.
3.check and clean resin
conveying and
filtration system if
necessary.
7. Inconsistent screw recovery due to 1. check and adjust
excess or irregular infeed of regrind regrind/colorant
and /or colorants. mixing and dosing
devices for proper
operation.
8. formation of gases in the melt caused 1.increase barrel
by resin pellets melting temperature.
downstream of the extruder 2.increase shear heat
by increasing back
pressure.
3. increase shear heat by
increasing screw
speed.
