CFD Modeling of the Closed Injection Wet-Out Process For Pultrusion

Flow Solver
The mathematical model was solved
by the flow solver ANSYS-CFX 11.0
with additional source terms added to
account for the moving porous
medium.
RESULTS AND DISCUSSION
Flow Patterns in the Injection Box
Streamlines, created by releasing massless
particles from the feed ports, show
how the resin impregnates the fiber
bundle in Figure 5. Resin injected
through the feed ports spreads over the
top of the bundle, then impregnates
into it and finally is pulled through the
injection box, achieving good wet-out.
The streamlines are colored to indicate
the pressure gradient.
Pressure Profiles in the Injection Box
Figure 6 shows the centerline pressure
profiles in the injection box for
different line speeds. As expected the
final pressure rise increases with line
speed. For example, at a line speed of
0.6 m/min, the pressure rise at the die
face is 23 bar, rising to 57 bar at a line
speed of 1.5 m/min. The experimental
results (blue squares in Fig. 6) compare
favorably with the CFD results at ~10
cm from the die face. However, the
injection box pressure measured at
~2.5 cm from the die face is much
higher than predicted. The model
assumes a uniform reinforcement
matrix and does not take into account
factors such as roving twist or
resin/fiber interactions which would
likely be magnified in the constrained
state near the die face. Further
experimental work is in progress to
verify and expand on these results.
Figure 7 shows the influence of the
viscosity of the resin, glass fraction,
box length and box height (i.e., the
effective taper angle of the box) on the
final pressure rise in the injection box.
As expected for a fully wet-out part,
this relationship is linear for viscosity
and box length. While the physics of
the pressure rise are not completely
understood, the model predicts nonlinear
relationships for box height and
glass fraction. The model can also look
at the influence of other geometrical
factors such as injection location(s)
and other operating parameters
including injection pressure on the
pressure profiles in the box.
Fiber Wet-Out in the Injection Box
Figure 8 shows the resin flow-front
development in the injection box. To
achieve good wet-out, both flow fronts
should reach the center of the fiber
bundle but also spread to all regions of
the injection box. In Figure 8, the resin
is colored to indicate residence time in
the box. It can be observed in this case
that the pultruded part is completely
wet-out by the time it enters the die.
The model can be used to illustrate
process conditions under which profile
wet-out becomes an issue. It can also
be used to evaluate the influence of
injection box geometry and operating
parameters such as injection pressure
on wetting efficiency.