Carbon fiber is one of the most popular materials chosen to replace metals, wood and plastics. You’ve probably seen videos of liquid iron being poured glowing hot from a furnace into a mold. Or melted plastic pellets being extruded into the mold of its soon to be cooled off shape. It is relatively easy to understand the manufacturing process of these common product building materials as compared to the science required to make carbon fiber.
The Raw Materials of Carbon Fiber:
About 90% of the carbon fiber produced today is made from polyacylonitrile (PAN), an organic polymer characterized by long strings of molecules bonded together by – you guessed it – carbon atoms. During the production process, various gasses & liquids are used to cause a reaction with the fiber. You may also hear the term “precursors” used to describe the raw materials. Many of the exact processes and compositions used to make different grades and types of carbon fiber are considered trade secrets.
The 5 Basic Steps in Manufacturing Carbon Fiber:
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- Spinning – PAN is mixed with a variety of ingredients and spun into fibers which are then washed and stretched to the desired fiber diameter. This provides the basis for the formation of the tightly bonded carbon crystals after carbonization.
- Stabilizing – The fibers undergo chemical alteration to stabilize bonding. The chemical reactions are complex and involve several steps and a variety of equipment.
- Carbonizing – The stabilized fibers are heated at very high temperatures in an oxygen-free oven. Non-carbon atoms are expelled, and the remaining carbon atoms form tightly bonded carbon crystals that align along the axis of the fiber.
- Surface Treating – The surface of the fibers is then oxidized to improve properties for bonding with epoxies. This process must be carefully controlled to avoid the forming of tiny surface defects which could cause fiber failure.
- Sizing – Fibers are coated typically with epoxy or polyester and then wound onto a spool called a bobbin. Then the bobbins are loaded into a spinning machine that twist the fibers into different size yarns.
Prepeg is the name given to composites that have been pre-impregnated with activated epoxy resins which contain a hardening element. Prepreg has become a popular choice for manufacturers because it is easy to manage, handle and mold. It can be easily cut and laid precisely into detailed molds which is ideal for small, complex parts. The ease and accuracy of cutting prepreg also helps to reduce waste and improve efficiency.
Most prepreg carbon fiber is manufactured in rolls which are kept refrigerated to preserve its life. If left in ambient temperature for an extended period, prepreg would become brittle and unusable. The carbon fiber product is molded and bagged, then placed in an autoclave under high pressure and heat to ensure proper curing and bonding.
Summary:
With 5X the strength to weight ratio of steel, the advantages of carbon fiber are numerous and the applications limitless. To see how one innovative product is manufactured using prepreg carbon fiber, give this video a look.
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