| Summary: | 碩士 === 國立交通大學 === 應用化學系 === 83 === One of the most troublesome aspects in the use of plasticating
single-screw extruders , which has long been recognized , is
fluctuations of flow rate in the extruder , commonly referred
to as ''surging''. The cause of ''surging'' has been debated for a
long time. Today , it is widely accepted that the breakup of
solid bed in the melting section of a plasticating extruder is
the primary source of the surging. The reason for breakup of
solid bed is due to the circulation flow of melt pool , which
melting zone of a traditional single screw , would continuously
push the solid bed , thus leading to the solid bed breakup .
Once the solid bed breakup , it would cause the unmelted
particulate solid to suspend in the melt. Consequently , this
would cause the decrease of melting rate and unstable output
rate . The basic idea for barrier screw is to design a
plasticating screw in such a way , that the solid bed can be
separated from the melt pool by a secondary barrier flight.
For the design of a barrier screws , channel width , channel
depth , helical angle and compression ratio etc. would
directly affect the melting rate , pressure distribution and
bulk temperature of the screw . The work aims to develop the
computer simulation with LDPE as the processing material for
the four different types of barrier screws . The solid bed
velocity , melt film thickness , melting rate , pressure
distribution and bulk temperature were investigated under
various processing conditions and geometry of the screw , and
compared the difference for single-flight and double-flights of
the four barrier screws.
|
|---|
