The manufacturing of carbon fiber is warped by trade secrets, as many companies are unwilling to give up their recipe for carbon fiber composites. Around 40 years ago, carbon fiber was only used in military and NASA centers - that's how exclusive it was. In 1981, the McLaren MP4/1 became the pioneer F1 racing car to have a chassis made entirely of carbon fiber. This led to growing interest in the material, and now nearly every F1 car, as well as the vast majority of luxury sports cars, all utilize carbon fiber in their manufacturing. The world's fastest cars are all composed of carbon fiber. It has the qualities of being lightweight yet incredibly strong, which helps boost the performance of the car considerably.
These days, carbon fiber cars, sports equipment, furniture, and even accessories are sold across the world.
Modern manufacturing methods have made progress in making carbon fiber parts available to the masses. These days, carbon fiber cars, sports equipment, furniture, and even accessories are sold across the world. The cult-like following of carbon fiber parts enthusiasts has created a great market for such products. Despite its popularity, many companies still keep their carbon fiber manufacturing methods a secret. Every company's carbon fiber composite has its own different finish, weave, and properties. In this article, we’ll go over the common carbon fiber manufacturing methods that create the sleek black material which we all know and love.
How It Starts
Carbon fiber is made of raw materials called precursors. The precursors are most commonly polyacrylonitrile (PAN), although occasionally rayon or petroleum pitch are also used. Whatever the precursor, it is always an organic polymer, which means that it is made up of long chains of molecules bound by carbon atoms.
The term “carbon fiber” refers to a long and thin strand of material composed of carbon atoms. Several thousand carbon fibers are generally twisted up to create “tows.” A tow is made up of several thousand fibers, and is often rated according to the number of fibers it contains. Tows can be rated 3k, 6k, 12k, and 15k. The “k” means thousand, so 3k equals three thousand carbon fibers in the tow. The higher the number of carbon fibers, the thicker that the tow of carbon fiber is.
Carbon fiber tows are woven together to create different patterns which have slightly different properties. The most common types of weaves are:
- Plain Weave.
The plain weave is a 1x1 symmetrical pattern that resembles a checkerboard. The plain weave is achieved through an under/over pattern. It results in a very tightly woven fabric which is highly stable. These kinds of weaves are not particularly flexible. High stability in a fabric has to be substituted for low flexibility, as it is difficult to make a fabric stable and flexible at the same time. The plain weave works best for making flat sheets of varying thickness.
- Twill Weave.
The twill weave is a 2x2 or 4x4 pattern. The over/under format is still followed, but one tow passes over and under two tows. This creates a distinctive diagonal pattern. The twill weave is more pliable then a plain weave. It can form contours without compromising its stability. However, it should be noted that 4x4 weaves have less fabric stability compared to 2x2 ones.
- Harness Satin Weave.
Carbon fiber satin weaves were inspired by the satin weaves found in the silk industry. A satin weave is what gives silk its ability to drape across surfaces while looking smooth and seamless. Inspired by this, various methods of satin weaving are used in carbon fiber manufacturing as well. The primary purpose of satin weaving carbon fiber is to create a very pliable end product that can easily be molded into different shapes.
- Other Weaves.
Aside from the ones mentioned above, there are a number of other weaves that can shape carbon fiber in various ways. These include braids, fish weave, spread tow, and custom weaves.
There are many factors to be considered when determining what kind of weave to use for a particular fabric. These may include formability, strength, and fabric stability.
Introduction of composite materials
The use of terminology such as “fabric” to describe a material like carbon fiber may be confusing for some readers. You may be asking yourself: isn't carbon fiber supposed to be tough and stiff? How can a flexible fabric match this kind of stiffness? The answer to the question lies in composites. A composite refers to a mix of two or more materials which has properties separate from its constituents. When carbon fiber is mixed with other materials, it is often referred to as Carbon Fiber Reinforced Polymer (CFRP). CFRP’s contain binding materials such as thermostat resins, the most popular of which is epoxy. The resin impregnation creates a stronger form of carbon fiber. Generally, the fabric is first placed in a mold of any shape or size. Then the resin is poured in to reinforce the carbon fiber and harden it. The resin is an important part of binding the carbon fibers, but a greater ratio of carbon fibers to resin results in a stronger end product.
Properties of carbon fiber composites
Although varying manufacturing methods can result in different properties, the general features of carbon fiber composites are as follows:
- High strength to weight ratio: carbon fiber is as strong as it is light. It has high tensile strength, which is a measure of how well a material holds up to being pulled and stretched. On the other hand, it also has very low weight. It weighs 3 times less than steel. This makes it perfect for applications where the weight of the end product needs to be light in order for it to have maximum performance.
- Resistance to corrosion: carbon fiber is very chemically stable, and it does not rust. It is resistant to most kinds of oxidative damage from the environment. However, certain chemicals like hydrogen peroxide and sulfuric acid will cause damage to carbon fiber parts. While the fibers themselves do not corrode, the materials used to make the composite may cause the structure to wear. Epoxy, in particular, is sensitive to light and UV damage.
- Low thermal expansion: Carbon fiber is very resistant to temperature related changes. It does not expand or contract greatly when exposed to normal environmental temperature changes. Only extreme temperature cycling can wear down carbon fiber parts.
Carbon Fiber Manufacturing Methods
- Resin Infusion: Resin fusion is a method of making carbon fiber composites. During resin infusion, dry fabrics are sprayed with special adhesives to make sure that they fit into the mold and special netting is used to make sure that resin will be properly distributed. A vacuum sealing method is used to make sure that resin is supplied automatically and it easily impregnates the carbon fiber fabrics.
- Prepregs Autoclave Composites: This method is commonly used in the production of F1 racing vehicles. An expensive piece of equipment called an autoclave is used to generate high pressures and temperatures, which are used to create a carbon fiber composite that can be easily molded into complex shapes.
- Hand Lay Up: This is one of the oldest methods of reinforcing carbon fiber. Firstly, dry fibers are placed on a mold and brushes with resin. Hand rollers are used to apply wet composite.
- Hot Press: This is a modern method which involves using a hydraulic press to heated press the carbon fiber and mold it into any shape of choosing.
Overall, the manufacturing of carbon fiber needs to be very sound in order for it to be durable and long lasting. The kind of weave pattern and composite materials all contribute to the final finished product. For this reason, customization is a big thing in the world of carbon fiber. Carbon fiber sheets and panels can be customized for different industrial tasks and uses.