The fantastic fiber: Useful facts about carbon fiber production

Whether in aerospace, the automotive industry or medical technology, there is one material that cannot be missed. We are talking about carbon or CFRP. Its triumphal march through industry began more than 40 years ago, when it was used in military research centers and by NASA. And today? We encounter carbon in almost all areas of life, for example as prostheses, on the road in the form of bicycle frames, or even in the BMW i3, the first production car with a passenger cell made of carbon. Let's begin our journey through the impressive development of this material.

Carbon, carbon fibers and CFRP – which is which?

Carbon – this term can denote so many things. First of all, it refers to the chemical element carbon. Carbon can be arranged in a graphite-like manner. In this case, carbon fibers or carbon fibers are obtained. This is done by chemical reactions in which heat plays an important role. You can read more about the production of carbon fibers and how kiln systems from ONEJOON come into play in this process further down in the article.

Now it's one more step to prostheses, bicycle frames or skis: when we speak of "carbon" here, we mean CFRP, carbon-fiber-reinforced plastic. The name already suggests that this is a composite material. This material is characterized by the fact that carbon fibers are embedded in a plastic matrix. Why is this done? The matrix binds the fibers together and at the same time fills the spaces between them. CFRP can now be used to form a wide variety of components and products – and these have impressive properties.

Lightweight and tensile

Carbon is particularly light and harder than steel. Let's take a closer look at carbon fiber: It has seven times the tensile strength at a quarter of the weight of steel. This is very practical when rapid acceleration and high speeds are required. It is therefore hardly surprising that the beginnings of carbon as a material go back to military aircraft and spacecraft construction. Heavy components made of metal could be replaced by lightweight CFRP elements. Research began in the 1960s, and carbon fiber technology was initially extremely expensive.

Production: Step by step to the finished carbon fiber

How exactly is carbon fiber produced? The starting material is polyacrylonitrile, or PAN for short. PAN serves as the precursor of the carbon fiber. About 90% of the carbon fibers produced consist of PAN, the remaining 10% of petroleum pitch or artificial silk. Here is an overview of the most important manufacturing steps:

1. The PAN fibers are lined up evenly next to each other and run over rollers into the furnace system.
2. First they are oxidized and stabilized by pyrolysis. In the process, the fibers become darker and darker, leaving behind almost exclusively carbon, which is arranged in a hexagonal lattice of atoms.
3. The fibers are then carbonized at extremely high temperature to refine the molecular structure.
4. The fibers are rolled up.
5. The final product is further processed in various ways, such as woven into a mat or laid side by side and sewn. The fabric or scrim can be provided with a composite material, for example epoxy resin. This produces so-called prepregs that can be used directly for CFRP components.

As you can see, several production steps are necessary to produce carbon fibers. We at ONEJOON have specialized in integrating customer-specific production lines in a carbon fiber line – and we are the world market leader in this area. Very important: depending on the line and the desired properties of the fiber, different temperature and carbonization stages are installed. This explains the number of furnaces in the diagram below. Strength, stiffness and also elongation at break can thus be precisely influenced.

The largest growth markets

Currently, aircraft construction, wind turbines and the manufacture of pressure vessels for storing hydrogen (H2) can be identified as the largest growth markets in the carbon fiber sector.

In aircraft construction, the use of CFRP instead of aluminum brings significant weight and thus fuel savings, as mentioned above. Wind turbine blades have traditionally been made of glass fibers. The switch to carbon fibers also results in weight savings here. In addition, the excellent properties in terms of tensile and compressive strength are an advantage, because state-of-the-art wind turbines with outputs of 6 to 9 MW require blade lengths of 70 to 90 meters. At this length, they are subject to high requirements in terms of deflection and stiffness – requirements that carbon fibers can meet. Last but not least, CF technology is developing its potential in the field of fuel cells: pressure vessels for storing hydrogen are made of carbon fibers. For example, the weight of trucks or buses can be reduced by around 450 kg.

Carbon and the climate: a double-edged sword

The equation could be as simple as this: lightweight components = lower fuel consumption = better climate balance. To some extent this is true, because CFRP can save quite a bit of weight, especially in aircraft, vehicle and mechanical engineering. Just imagine an electric car with the conventional, rather heavy components – its range would be severely impaired. But on the other hand, CFRP production requires a lot of energy. In addition, there are large material losses during production.

The environmental institute bifa was commissioned by Fraunhofer IGCV to analyze the environmental balance sheet for CFRP production and came to the conclusion that compared to fuel savings in vehicle use, CFRP production offers greater potential for improving the climate and resource balance. Above all, the use of renewable energy sources plays an important role.

As an industrial furnace manufacturer, we are therefore constantly optimizing our plants with regard to these criteria in order to be able to reduce our CO2 footprint in the future and make our technology as climate-friendly as possible.

Conclusion and outlook

Carbon or CFRP and its production is an important future technology that needs to be improved against the background of its climate footprint. One option on the way to greener carbon: algae. At the Technical University of Munich, a project is being funded that is dedicated to the production of carbon fibers from algae. The team is developing PAN fibers from these algae, which are then carbonized into carbon fibers in a CO2-neutral process.

The advantages of CFRP are crucial for future mobility concepts: carbon is lighter, harder and more tensile than steel. Aircraft construction, wind turbines and fuel cell technology in particular are proving to be strong growth markets. However, the production of CFRP is particularly complex, which is illustrated by the individual production steps. This is also associated with correspondingly high costs. Innovations made of carbon, however, are already indispensable today – and will probably be even more so in the future.