Pressure and temperature effects on the flow in a nozzle during injection moulding
yves Bereaux, Jean Balcaen, Jean-Yves Charmeau, Didier Graebling
Ecole superieure de Plasturgie d'oyonnax
FRANCE

Keywords: injection-moulding, pressure dependence, flow simulation

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In the injection moulding process,
the flow of the hot molten polymer
through the nozzle can be viewed as a critical step
for the material in terms of
pressure levels, shear rate, self heating by viscous dissipation
and temperature reached.


For two different Polyamide 6,6
(Zytel 101 and the more viscous Zytel 42),
we have made moulding experiments using
a rheometric nozzle, and an instrumented mould.

During the injection cycle, measurements of the pressure
upstream and downstream the nozzle and at
different locations in
the mould, are performed, together with a record of the screw
displacement with time. The pressure data are then fed as transient
boundary conditions in a numerical simulation
of the non-Newtonian flow of the melt in the nozzle.
Compressibility effects result in a transient flow rate,
different of the prescribed injection speed.
The pressure and temperature
dependence of the viscosity have also to be taken into account for
a complete description of the flow. The heat transfer not only
in the melt but also in the steel nozzle is accounted for.
Simple relations for the compressibility effects on transient flow rate
and for the heat transfer at the interface between the melt
and the steel nozzle are proposed.