From carbon fibre to the composite material

What does the standard supply chain for a composite material consist of, from the production of the carbon fibre through to the manufacture of the material that will be fitted on an aircraft?

Today, we don't need to look very far to find carbon fibre. Already found on aeroplanes and on some new vehicles, it is destined to be used more and more by companies looking for lighter materials to reduce fuel consumption. For manufacturers, carbon fibre-based composites thus represent a means of achieving their sustainable development objectives and meeting government requirements. 

What is carbon fibre made of?

Carbon fibre is made of filaments mainly composed of carbon atoms. Carbon fibre has some remarkable properties such as rigidity, tensile strength, lightness and thermal stability, all ideal for aeronautical applications.  

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photo: carbon fibre reels

How is carbon fibre made?

The manufacturing procedure takes place in three stages: 

1. polymerization is a chemical procedure that takes place in controlled conditions in a reactor and creates long-chain polymers that can be woven into filaments. 

2. spinning: mixture of polymer and solvent, the weaving solution is woven through spinnerets containing 3000 or 6000 holes in a coagulation bath to form the filaments. The white-coloured woven fibre thus obtained is then washed, dried and stretched to create the desired chemical structure and transversal section (e.g. round, oval or bean-shaped).

3. oxidation and carbonization:  the final process is the oxidation and carbonization of the white fibre, called precursor. In the oxidation oven, the fibre is exposed to a temperature of 300°C. The oxidized fibre is then loaded with carbon in a furnace gradually raised to a temperature of 500ºC. Next, the carbon fibre is given a surface treatment and then glued in order to facilitate the following treatment. At the end of the process, the fibre is wound onto reels for the next stage.

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What happens next to the carbon fibre?

These fine threads are woven in a production unit based in Greenville, Texas, to make a bi-dimensional fabric.  The fabric is then delivered to other Solvay sites. A large part of it undergoes an impregnation process, during which the fabric is immersed in a mixture of resin and solvent, used to reduce the resin's viscosity.

After the impregnation, the product is put into an oven so that the solvent can evaporate, thereby obtaining the definitive form of the preimpregnate. At the end of the process, the preimpregnate is packaged, then shipped in rolls to customers, who mainly use carbon fibre materials to make parts on various  structures of their aircrafts. 

How does carbon fibre become a composite?

The parts' manufacturing process is broken down into several stages at Solvay's facilities. 

Lets take, for example, a fin for Boeing 737, used to reduce the planes' drag and fuel consumption. In the first stage, the preimpregnated material is cut into the different shapes that make up the fin. These shapes are then piled by hand, piece by piece, in order to obtain the desired part configuration, around a honeycomb core that gives it its rigidity (photo). After the piling, the part is placed in a vacuum for the firing process. The part is fired at a specific vacuum pressure and heated in an autoclave. 

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photo: assembly

Once fired, the part is deburred to create the definitive geometric shape, then undergoes non-destructive tests to confirm its quality. Finally, the various pieces of the fin (e.g. stringers and claddings) are assembled and painted before the composite part undergoes a final visual and dimensional inspection.

None of this would be possible without the commitment of Solvay's teams, who carry out the preparatory work and manufacture the carbon fibre used in the parts made by the Group's customers.