Different Types of Dry Carbon! Summary of Carbon Manufacturing Methods [includes Wet Carbon]

Everyone loves carbon parts. There are two main types of carbon manufacturing methods: wet carbon and dry carbon. You might say, "I know that! I know that!

However, dry carbon is actually divided into several categories. The manufacturing methods and characteristics can be completely different.

WebiQ provides a little happiness and motorcycle knowledge.

In this issue, we dive into the various methods of dry carbon production!

Carbon products are, in short, plastic products.

The headline is suddenly shocking, but it is true.
To begin with, carbon is described as CFRP, which stands for Carbon Fiber Reinforced Plastics.

In short, it is a technique that does exactly what the name says: reinforcing a resin (plastic) with fibers made of carbon to obtain higher strength and rigidity than the resin used alone.

If you take away the "carbon" at the top, it becomes just FRP, and at once it looks familiar and chalky, doesn't it?
But even FRP is the same in aim and composition as carbon products, just using glass fiber instead of carbon fiber.

The only difference between FRP and CFRP is whether glass fiber or carbon fiber is used for reinforcement of the resin. In either case, the product is essentially plastic, just reinforced with fibers.

There are two main types of carbon

Let's start with a review.

Carbon products can be broadly classified into two types: wet carbon and dry carbon. Wet carbon and dry carbon.
This is well-known nowadays.

A long time ago, there were almost no dry carbon products in the world, and they were super high performance parts that only a very small number of works machines could use.

There were carbon products on the market, but almost all of them were wet carbon. That was the norm.

What is wet carbon?

Wet carbon, as I mentioned at the beginning, is not much different from FRP. FRP has only replaced the part (part of) that was glass fiber with carbon fiber.

Certainly, carbon fiber is stronger, stiffer, and lighter than fiberglass, but not enough to dramatically improve performance on its own. Just a little bit. So wet carbon is basically equivalent to FRP in strength, stiffness, and lightweight.

The manufacturing process is exactly the same as FRP.
While FRP is made by pouring resin over laminated glass fibers and letting it soak in before hardening, wet carbon is made by pouring resin over laminated carbon fibers and letting it soak in before hardening.
The only difference is the material of the fiber used to reinforce the resin.

The resin soaking is done by hand, but if the resin is not fully soaked in, the part is reduced to fibers, and it ends up looking like carbon cloth rather than reinforced plastic.
To prevent this from happening, it is a show of skill to soak the resin firmly so that air bubbles do not form inside.

Wet carbon is more concerned with appearance than absolute performance, so there are many products in which only the front layer is made of expensive carbon fiber and the bottom layer is simply glass fiber.

Or rather, that is the norm.
Carbon fiber is about 10 times more expensive than fiberglass.

However, wet carbon products became very popular because the carbon fiber pattern visible from the surface gives the appearance of a works machine.
Even now, the wet carbon process is usually used when simply talking about carbon.

In the case of cowls, if only one carbon fiber is used on the front side, light leaks through the gaps between the fibers (FRP allows light to pass through the fibers and resin to brighten the product when light is shone from the back), so the back side of the product is coated with light-shielding black paint.

The thick light-shielding paint makes the product heavier, which cancels out the lightweight of carbon fiber, but that is OK because that is not the kind of performance we are looking for.

For example, the NR750, famous for its oval pistons, is also famous for its high price, but its cowl was also made of carbon fiber.

The NR letters on the cowl were clear coated, so the underlying carbon could be seen through it, which made me think "Wow! I was so impressed with the NR logo on the cowl.

But I was disappointed to know that only the NR logo was made of carbon, and the rest of the cowl was just FRP.
At that time, carbon was very expensive, so they probably used carbon only for the visible parts.

Although wet carbon is inferior to dry carbon in terms of performance, it does have its merits. After all, it is basically FRP, so if it cracks, it can be easily repaired at home.

What is dry carbon?

So what is dry carbon as opposed to wet carbon?
If you know a little bit about it, you will answer like this.
Unlike wet carbon, dry carbon is made by baking in a kiln, so it is lighter, stiffer, and has a tremendous difference in strength.

It is not wrong, but it is not quite clear.
I don't understand why kiln-fired carbon is so much better than wet carbon.

So to explain in more detail, dry carbon is carbon that is stronger than wet carbon because it contains far more carbon fibers than wet carbon. To put it another way, for the same thickness, it contains far less resin.

Since a large amount of reinforcing fibers are contained in the same volume, it is only natural that the strength and rigidity would increase.

Conversely, for products that do not require such high strength (i.e., products with the same level of strength as FRP products are sufficient), the thickness of the product can be made much thinner, allowing it to be finished in an overwhelmingly lightweight manner.

However, a new question arises here. How is it possible to use the same carbon fiber whether wet or dry?

The secret lies in the manufacturing process of dry carbon.

How to make dry carbon

I mentioned above that wet carbon is made by soaking carbon fiber laminate with resin and then hardening it.
To be a little more specific.

In the case of dry carbon, which is widely known to the public, it is already different from the "1" stage. The general dry carbon manufacturing process is written in concrete terms.

It is interesting that the resin has already soaked into the fibers and made them moist and wet at the first "1" stage, despite the name "dry.

But that is not important. The key points here are that thermosetting resin is used instead of two-component hardening resin with hardener, and that excess resin is removed by vacuum compression.

The kiln in which this high temperature and pressure is applied to harden the resin is called an "autoclave," and dry carbon products are sometimes referred to as autoclaves.

It is complicated.

It is called "dry" carbon because it has less resin, is lighter, and feels crumbly and dry because it is full of fibers (probably).

Why Dry Carbon is High Performance

The amount of resin contained in the finished product is far less than wet carbon, as explained above. The secret is "because the excess resin is driven out.

For the same thickness, the strength is higher because the carbon fiber content is higher.

For the same strength, it can be made thinner and thus lighter. This is the secret of high performance.

Wet carbon is molded with a resin that hardens naturally and uses carbon fibers as reinforcement, while dry carbon is molded with carbon fibers and baked with a thermosetting resin to prevent the fibers from falling apart. Although they look similar, they are completely different.

However, if you increase the amount of carbon fiber in wet carbon, the same thing will happen, right?

If there is the same amount of carbon fiber as dry carbon, it will have the same performance as dry carbon, right?

This is true, and if it were possible, wet carbon would have the same performance as dry carbon. However, the reality is not so sweet and it is not possible. After soaking the resin into the carbon fiber, the resin cannot be sucked out by vacuum. There is no such convenient resin.

The fact that dry carbon products are baked in a kiln in the manufacturing process does not mean that they are lightweight.

It just happens to be a type of resin that hardens with the heat of the kiln, which has the property that excess resin can be discharged by vacuum compression.

Moreover, this resin cannot be applied or poured afterwards, so it must be soaked into the carbon fiber in advance. When pasting the carbon sheet into the mold, it is slightly sticky and damp, and the resin is not poured in afterward.

Incidentally, the carbon fiber sheet in this resin-damped state is called "prepreg. It is very expensive and has a short shelf life due to severe temperature control.

Dry carbon products are sometimes referred to as "made of carbon prepreg," but it is probably written that way to make it easier for users to understand and differentiate them from other products.

Prepreg refers only to the state of the material, and the finished product after the resin has cured is usually not called prepreg.

The crusty surface of the product is not because it was fired in a kiln.

It is because the excess resin is extruded out and the carbon fiber is almost on the surface because the resin content is low.

However, recently, some products are coated with matte clear to make them look like dry carbon, so it does not mean that they are dry carbon if they are crusty.
Many products are clear coated to protect the surface, and in this case, the surface finish is shiny.

For this reason, it is very difficult to distinguish between wet carbon and dry carbon by surface appearance alone.

In the case of some dry carbon products without clear coating (products that do not care about the glossy surface finish because they focus on performance), carbon fibers appear on the surface in a mesh-like pattern through the gaps between the layers of resin, resulting in a muddy surface finish with no glossy areas in the mesh-like pattern. In this case, only the surface can be judged to be dry carbon.

This can be seen on the unpainted cowl surface of a works machine, but it is not something that is normally seen, and there are very few cases of this being done seriously on production car parts or production parts.

I hope you understand that the word "kiln-fired" does not mean "kiln-fired so it is light due to volatilization of excess materials," "kiln-fired so the surface is crusty," or "kiln-fired so it is hardened and strengthened.

However, there are other methods of production.

I am sorry to have gone on and on about this, but there are actually other manufacturing methods besides those mentioned above.

Rather, other manufacturing methods other than the above are more common for industrial products other than those for motorcycles.

As explained so far, whether dry or wet, it is essential to "stick" the sheets of reinforcing fiber into the mold by hand, which is very inefficient.

It is a time-consuming manual process, and because it is done by hand, the quality of the product inevitably varies.

We wondered if there was any way to stabilize and mass-produce the product. The method developed is called "RTM (Resin Transfer Molding)".

In Japanese, it is called "Resin Transfer Molding".

What is the RTM process?

The process introduced above as a manufacturing method for wet carbon and FRP, in which the fibers are pasted onto the product mold by hand, is called "hand lay-up molding.

Fibers are pasted and laid down, resin is injected later, air bubbles are pushed out with a brush or roller to penetrate the resin to the corners, and then the hardener contained in the resin reacts to harden the resin, resulting in a product.

Dry carbon is a manufacturing method in which resin-soaked fiber (prepreg) is laid in a mold from the beginning, compressed by a vacuum pack to remove excess resin, and then the resin is cured in a kiln (autoclave) at high temperature and high pressure, but it is a type of hand layup in that the fiber is attached by hand.

So what does the RTM process do? 
First, the fibers are laid out in a mold just like wet carbon.

That's hand layup! However, the RTM process is characterized by the fact that there is another male mold that has a gap between the mold and the thickness of the product.

The mold is closed with the fibers sandwiched between the fibers, and the fibers are compressed.

The resin is then pushed into the gap between the compressed fibers at very high pressure. Resin is injected from one side of the mold between the two, and when it comes out the other side of the mold, it's proof that every inch of resin has been injected into the mold!

The fibers are compressed and denser than during a normal hand layup, so it is OK to let it cure as it is.

If it is to be dry carbon, the resin is cured in a high-temperature kiln together with the compressed mold, so the finished product will have almost the same performance as a dry carbon product made by the vacuum-packed method.

Moreover, since this manufacturing method has molds on the front and back, the surface of the finished product will be beautifully flat on both the back and front.

This is a big difference because the vacuum-packed method leaves the back side uneven with wrinkle marks from the shrunken pack.

Perfect! I would like to say that it is, but there are a few drawbacks.

First, you need two sets of very precise molds, one for the male side and one for the female side.

It is not suitable for thin materials, and the initial cost is very high because two high-precision molds must be prepared.

In addition, the resin must be pumped into the compressed fibers, which requires a super-powerful pumping machine, making even an already large dry carbon manufacturing facility even more expensive.
In other words, the same product must be produced in large quantities to make it pay for itself.

To put it bluntly, it is not suitable for manufacturing custom parts for motorcycles.

Other manufacturing methods

The RTM process has many problems, but it can be made a little better with a little ingenuity.

Since it is troublesome to lay reinforcing fibers into a mold, there is a method to cut the fibers into small pieces in advance to make it easier to lay them into the mold.

However, this method is more difficult to work with because the shredded fibers scatter around, so a paste-like sheet (quite hard) is made by soaking the cut fibers with resin in advance, and this is then laid in the mold and compression-molded.

This is called "Sheet Molding Compound (SMC) molding.
As usual, the Japanese word for this method is "sheet molding compound.

The weak point of this method is that the strength of the finished product is low because the reinforcing fibers are cut into small pieces.

Therefore, it is used for parts that do not require relatively high strength, have a certain thickness, have enough demand for mass production, and can replace metal.

For example, engine head covers, tappet covers, and air cleaner boxes for motorcycles and 4-wheeled vehicles.
On the other hand, it is not suitable for parts that require the highest strength, such as carbon wheels, for example.

In the case of SMC, there is a wide range in the degree of fiber cutting depending on the application, from rough cutting where the cut fibers on the surface appear fine to a width of a few millimeters.

If a sheet with fibers cut to almost powder level is used, the finished product will be indistinguishable from ordinary plastic products.

When the sheet is further compressed under high pressure to expel excess resin and harden it by baking, a mysterious object is created that looks like a black plastic product, but when you lift it up, it has the lightness and strength of dry carbon.

As a product I witnessed, the clutch cover of a DUCATI 916 Corsa (race car) was made of dry carbon that was autoclaved and hardened after SMC molding.

Although it looked like a simple black plastic (or black painted aluminum), it was eerily light and had great strength that it would never crack even if you stepped on it or kicked it.

By the way, the most familiar FRP product made by SMC molding is the bathtub in your home.

Apart from luxurious baths made of solid marble or hinoki cypress, most baths are made of FRP, and are quite often mass-produced products made by SMC molding.
It is also very common for the entire unit bath itself to be made of SMC molding.

So if you use carbon fiber instead of glass fiber, press-compress it, and autoclave it to harden it, you can make an ultra-lightweight, racing-spec dry carbon bathtub!
Hmmm! The dreams just keep expanding.

Carbon product construction is the same as reinforced concrete

As you may have somehow noticed, the structure of carbon products is similar to that of reinforced concrete.
The concrete part is resin and the rebar part is carbon fiber.

Wet carbon is made by placing a sheet of woven rebar in a female mold in layers, pouring fresh concrete over the top, and allowing it to dry naturally.

Dry carbon is made by placing a layer of woven rebar in a female mold, removing excess concrete with a vacuum pack, and baking it at a high temperature.

RTM molding is done by placing a sheet of woven rebar in a female mold in layers, compressing it with a male mold from above, and pouring fresh concrete into the gaps.
SMC molding is done by pouring concrete mixed with finely cut rebar into the gap between the male and female molds.

In a nutshell, it is like this.

You can't just say "dry carbon" in one breath.

Did you understand that there are various manufacturing methods such as molding, compression, and resin curing methods other than wet and dry?
Dry carbon is the strongest and lightest! It is not as simple as that.

Moreover, "plastic products using carbon fiber as a reinforcing member" is still in its infancy, and new manufacturing methods are being developed one after another.

Recently, a new manufacturing method called "braiding carbon," in which the reinforcing fibers are not interrupted at all when forming into a tube shape, has been developed.

The fibers are not broken, so a cylindrical structure would be the strongest, but this manufacturing method has been impossible until now.

The cylindrical shape is the best structure if it is used for wheels, and the carbon wheels used for the first time in Porsche 911 were made by this method.

The carbon wheels used on the BMW HP4 are also made using this method.

The carbon wheel used in BMW HP4 is also made by this method. It is completely different from the wheels made of dry carbon up to that time in terms of fiber structure, so it is even wrong to compare them as well as hand layup molding and SMC molding.

The more you know about plastics, the more intriguing they are.

Why don't you get drawn into the magic of such carbon products?

By the way, there is no turning back once you know.
You who have read this article to the end! You can't do it anymore, can you?