Carbon fibre is an exciting material with many variations and applications. Carbon fibre can normally be purchased in one of three forms: continuous, woven, and chopped. Continuous filament carbon fibre is the type of carbon fibre that SageZander can supply. Essentially, continuous filament carbon fibre is the carbon fibre yarn that can be processed in many ways. Continuous filament carbon fibre is often woven into a fabric, which can be purchased already woven, or you can weave it yourself.
Woven carbon fibre fabrics can be impregnated with polymer resins in order to produce a very stiff and lightweight material.Carbon fibre can also be “chopped”, which is a form of carbon fibre made from short and broken fibres that can be placed in a random pattern, meaning that when it is impregnated with resin, the strength of the composite material is in all directions, as opposed to woven carbon fibre composite, whose fibres are normally only laid in two directions. When processed, this is sometimes called forged carbon.
In order for carbon fibres to be of much use, they need to be able held together. For this reason, carbon fibres use polymer resins to encapsulate the fibres, producing a material called a carbon composite, or a carbon fibre reinforced polymer. The final use for the carbon fibre product dictates much of what happens upstream in the production process, including how the carbon fibre is prepared. There are various methods for impregnating the carbon fibre with the polymer resin. Some common types are prepreg, injection, towpreg, and pultrusion.
Prepreg carbon fibre comes pre-impregnated with the resin needed to secure the carbon fibres. The resin is highly sensitive to heat, so is normally stored at cold temperatures to prevent it curing before it is ready to use. The prepreg carbon fibre comes as a fabric already and remains flexible, so it can be shaped in a mould and then simply heated to produce the carbon composite product. This heating is be done at high or low pressure, with low pressure ovens and autoclaves, or high-pressure presses.
Two types of resins are used in carbon fibre composite manufacturing. By far the most common resin type is a thermoset resin, which once cured cannot be re-heated and re-shaped. This is the industry standard type. The second type, thermoplastic resin, is garnering more interest as it can be reheated and remoulded. This means that thermoplastic carbon fibre composites can be more easily recycled, resulting in a more environmentally friendly product.
Carbon Fibre Sizing
The sizing on a carbon fibre filament is a coating placed onto the individual fibres that allows the fibres to be processed in different ways. Carbon fibre sizings generally prevent the individual carbon fibre filaments from fraying during handling and allows the specific resin material to fully impregnate the carbon fibre. Different sizings can, for example, produce wildly different amounts of dust when the filaments are being processed. Each sizing is specific to the manufacturer, so the properties of the sizing and carbon fibre differ with each carbon fibre brand sold.
Pressure vessels are pressurised tanks designed to hold a liquid or gas with a pressure different to the exterior. Steel pressure vessels can range in size from a can of squirty cream to a nuclear submarine. Carbon fibre pressure vessels are used to hold liquids and gases at very high pressures when low weight is a priority. As a result of their weight savings, carbon fibre pressure vessels are used in industries like aerospace. For example, SpaceX uses carbon fibre pressure vessels with an interior aluminium liner to hold high pressure helium.
There are 5 types of pressure vessel of which three use carbon fibre. Type III pressure vessels have a metal liner, with carbon fibre wrapped around to hold the pressure, while relying on the metal liner to keep the seal. The SpaceX helium tank is an example of a type III pressure vessel. Type IV pressure vessels use a plastic liner to form the seal, while similarly relying on the carbon fibre to withstand the high pressures.
Type V pressure vessels are not commercially available yet, but they rely on the carbon fibres and the resin to fully seal the tank and use no liner. Carbon fibre composite pressure vessels are one of several pressure vessel solutions in consideration for high pressure hydrogen storage particularly in vehicles where the weight saving from carbon fibre compared to steel or other composites is considerable.