Automated method for producing continuous reinforced plastic shapes by pulling pre-impregnated reinforcing fibers through a heated die in which the resin is cured.
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.
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.
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.