During manufacture, thermosetting plastics indergo a chemical transformation called curing, )rought about by the action of heat or by the addiion of chemicals. Before curing, thermosets are iquid, doughy or solid but capable of being shaped alder pressure and heat. After curing, they are nsoluble and can no longer be shaped even at high emperatures. The reaction time (the time required or curing) is usually several hours in the case of cold curing and a few minutes in the case of hot curng.
The most common thermosetting plastics are the formaldehyde resins, such as Bakelite.
In compression molding a quantity of granular, toughy or even liquid resin, often with a curing agent, a filler and a reinforcing material (such as ;lass fibers) or a glass-fiber mat), is introduced into t compression mold, generally made of steel. The nold is closed and the resin is pressed into the desired shape. The shaped article remains in the nold until curing is complete. If the resin is cured by the action of heat, the mold will incorporate heating equipment. The molded article can be removed from the mold while still hot.
Thermosetting resins can also be processed in njection molding machines. They are heated in the )arrel and injected at high pressure into a hot mold, where curing takes place.
Carbon-fiber reinforced plastics are a new technological development to solve an old problem – how to make something extremely light, yet still retain all the essential strength.
The aviation industry comes across this problem most often; to make aircraft efficient, they have to )e light, but safety standards will not allow for too nuch paring away. With the introduction of carboniber reinforcing, an airplane using extensive car)on-fiber composites can get 25 per cent more per7ormance and 50 per cent less fuel consumption than conventionally built planes.