Definition:
Automated
method for producing continuous reinforced plastic shapes by pulling
pre-impregnated reinforcing fibers through a heated die in which the resin is
cured.
Impregnation:
Process
carried out in an impregnator to thoroughly soak the material like wood, paper,
or fabric with synthetic resin so that the resin gets within the body of the
material.
Process:
The
roving strands are drawn through an impregnating tank and a squeeze bushing to
remove the excess resin and air. The extrudate is then cured. There are two
methods of producing Pultrusions based on method of curing the extrudate. They are:
1.
Tunnel
oven process
2.
RF
energy
Tunnel
oven process:
a.
Here
the wet roving bundles are made into rod stock.
b.
It
is passed first through a shaping bushing to impart general desired circular
shape.
c.
It
is then circumferentially and spirally wound with cellophane tape.
d.
The
Pultrusion then passes through the heated curing zones in the long oven for
curing.
e.
The
rod is then pulled by a pulling device and cut to length.
f.
Rectangular
and other simple shapes can also be produced by this technique, especially if
they are finished in a secondary operation.
g.
It
is difficult to produce complex profiles or to retain dimensional tolerances or
high finishes without secondary finishing because there is no shape restraint
during cure.
RF
energy:
a.
The
wet roving bundle is subjected to RF cure when it is drawn into a shaping die.
b.
The
final cure takes place within the short shaping tube because the cure obtained
by this dielectric heating system is very fast.
c.
Any
profile that can be extruded can be produced by this method.
d.
High
surface finish is inherent and do not require secondary finishing.
Application:
It is new in the field of
reinforced plastic structural shapes, but is developing rapidly. Items made are
fishing rods, archery bows, hammer and axe handles, construction I and T beams,
On-site tank construction.
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