Composite Technology - Introduction to Polymeric Composites with Rice Hulls - page 30

involve the moulding of large parts using thermoset plastic resins in powder form.
Two distinct disadvantages are the need to dry the powder to remove moisture before
moulding and also, being a powder, seepage from the clamped mould and thus the
requirement to de-flash after part removal. Thermoforming resins can also be used, but
they probably will not provide the strength, stiffness and impact resistance required
in parts moulded in this way. Composite resins will provide strength and stiffness
but might need an additional additive to boost impact resistance. If using polymeric
composite resins, the exact amount of resin can be put into a mould, which will not
result in seepage of the melt, thus eliminating the need for de-flashing afterwards.
3.2 Formation of Composites
Composites can be formed in many ways and all methods, whether they are laminated,
extruded, compounded or impregnated, can be classified as composite processing . Over
the years, the importance and need for composites have grown tremendously, especially
in the industrial sector and, due to continuing research, the use of biomasses have
also come to the forefront as reinforcing fibres. At the beginning, only thermosetting
plastics were commercially reinforced in large quantities, but today the demand for
reinforced thermoplastics is increasing rapidly. Because thermoplastics materials can
be processed readily in many ways, various innovative uses have resulted.
Reinforced moulding compounds may be moulded by injection moulding, matched
dies, transfer moulding, extrusion moulding and compression moulding to elicit
products with complex shapes and a broad range of physical properties. Of these,
extrusion moulding and injection moulding are the two most common and effective
methods of processing composite resins. Fibres, short fibres of milled glass, fillers,
tiny glass spherules, and metallic fibres are, in general, used for reinforcing moulding
compounds. The main composite reinforcing processes are:
• Extrusion
• Matcheddie
• Handlayup
• Spray-up
• Rigidvacuumforming
• Vacuumbag
• Pressurebag