Dry! One article understands the manufacturing process of carbon fiber

In the carefully controlled fiber maze (left), the fiber leaves the surface treatment station of Grafil before transporting into the rolling machine (right, the path is determined by a specific modulus

Although

Many HPC

Readers use carbon fiber, but few people know how it is made. This should not surprise anyone. Carbon fiber manufacturers keep their products as well as bottle. The fiber of each manufacturer is different from the fiber of its competitors, and the processing details of the iconic characteristics of each brand are considered intellectual property. As we all know, the process of carbon fiber manufacturing is also very difficult and expensive. A world -class production line is capital -intensive -at least 25 million US dollars in equipment -and may take up to two years to implement. In fact, the cost may be much higher.

Source | Carbon Fiber 2020 (Nosseville, U.S. Tennesville) meeting, hosted by AJR consulting company Tony Roberts.

Global carbon fiber annual capacity estimates in 2010.

For example, the Mitsubishi Liyang Co., Ltd. (MRC), headquartered in Tokyo, covers an area of ​​9.4 million square feet/874,000 square meters of large bamboo production facility plans for three years. The production line can produce up to 20 million per year Pound/9,072 metric tons of carbon fiber. This explains to a large extent why it is difficult to avoid the plunge and the unbalanced supply and demand of prices and peak. Therefore, it is no wonder that there are currently less than a dozen backbones of global carbon fiber manufacturers.

HPC

With the help of several carbon fiber craft suppliers, behind the confidential veils, it was found to discover the more tolerant (if it is still incomplete).

Clear difference

Different from metal, metal is uniform, and through design, it has the performance that meets the established standards. For example, the P20 steel of each manufacturer can be replaced with the P20 steel of other producers. The composite materials are heterogeneous. Composed of combinations of different materials (fiber and resin), their variability and customization are the core of its attractiveness. Therefore, carbon fiber manufacturers produce similar but incomplete products. The amount of stretching of carbon fiber (or hardness is determined as deformation during strain), as well as stretching, compression and fatigue intensity. PAN base carbon fiber currently has a low mold volume (less than 32 million LBF/IN² or <32 MSI), standard modulus (33 to 36 msi), middle modulus (40 to 50 msi), high modular volume (50 to 70 msi) And ultra -high mode (70 to 140 msi) and so on. The fiber is provided in the form of beam, called drag, with multiple sizes, from 1K to 350K (1K is equal to 1,000 filaments, and the diameter range is from 5 to 10 microns). The type of carbon content and surface treatment/coating of the product is also different.

“The inherent complexity of carbon fiber composite materials is exactly what the carbon fiber structure is added,” said Steven Carmichael, the sales and marketing director of MRC subsidiary Grafil Inc. (Sacraono, California). “Just like brewing wine, appropriate amount of patience, skills and processing professional knowledge can stimulate the delicateness in carbon fiber, thereby increasing value. Of course, this value is very high: as a metal substitute, the strength of the carbon fiber composite material is 10 of the steel 10 of the steel. Be more, the weight is only half of the steel.

In the simplest terms, carbon fiber is produced at a thermal anterior fiber at a temperature that is higher than 982 ° C/ 1800 ° F in the inert atmosphere. However, carbon fiber manufacturing is a complex task. Grafil is located at 60,000 square feet/5,574 square meters of Factory in Sacraono, California. Compared with MRC’s Dazhu factory, it is very small. Even after the capacity of 2 million pounds/544 tons in 2005, it also has a side production line. It laid the foundation for the completion of the primary production stage by HPC. These are polymerization and spinning, oxidation (also known as stability), carbonization (sometimes inaccurate called graphite), surface treatment and glue application. Throughout the process, strict tolerances define the final utility of fiber. GRAFIL’s operating director Gordon Shearer said: “The target mutation coefficient of yield is 1%, and pointed out that the actual change is about 3%for small drags (1K to 24K) for applications such as aircraft such as aircraft (1K to 24K). And the change of large towing (industrial or commercial) may be as high as 15%.

The main steps in the two -stage process used to manufacture PAN -based carbon fiber include process steps for making polypropylene (PAN) “skeleton”.

polymerization

This process starts with a polymer raw material called anterior body (“first in the front body”), and the raw material provides a fiber molecular main chain. Today, about 10%of carbon fiber is made of before artificial silk or asphalt group, but most of them come from polyacrylpylene (PAN), which is made of acrylite, and acrylonitris comes from commodity chemicals acrylic and ammonia.

Therefore, this article describes the production of PAN -based carbon fiber.

Simplified representation of carbonization line

For more than 30 years, PAN has been converted into carbon fiber. Carmichael added that most of the investment in carbon fiber manufacturers is spent on the front -drive body, and the quality of finished fibers directly depends on the quality of the front -drive body. Specifically, shearer pointed out that the attention of the quality of the pre -body can minimize the change in yield or the length of the fiber weight per unit of fiber.

Generally, the front -wheel drive system starts with acrylonitic monomer, which is combined with plasticizing acrylic symbol and catalysts (such as orthopic acid, sulfuric acid, sulfate, or methyl acrylic acid) in the reactor. Continuous mixing and mixed ingredients to ensure consistency and purity, and start the formation of free radicals in the acrylic molecular structure. This change causes aggregation, which is a chemical process that produces long -chain polymers, which can form acrylic fibers.

Details of aggregation, such as temperature, atmosphere, specific co -concentration monomers and catalysts are proprietary. According to Peter Morgan, the author of the book “CRC Press, 2005),” The aggregation should reach at least 85%of the acrylic content and the relative molecular weight of 100,000 grams/Moore. The distribution is evenly distributed to make the Pan white fiber have good mechanical properties. For example, the MRC forether uses the MRC prefabrication of Grafil can reach 94%to 98%of the acrylite content.

After washing and drying, the acrylonine (now the form of powder) is dissolved in organic solvents, such as dizomya (DMSO), dioma acetamide (DMAC), or di metamimamamide (DMF), or water properties Solvent, such as zinc chloride and Rodin salt. Organic solvents help avoid pollution of trace metal ions. Trace metal ions may disturb thermal oxidation stability during processing and reduce the high temperature performance of finished fiber. At this stage, powder and solvent slurry, or the “raw liquid” of the front body is the consistency of maple syrup. The selection of solvents and the degree of control of the original liquid (through extensive filtration) is critical to the success of the formation of fiber formation in the next stage.

Spin

The PAN fiber is formed by the process called wet spinning. Immerse the raw liquid into the liquid solidarity bath and squeeze out the holes in the spray head made of precious metals. Swilish headhole matches the number of PAN fiber long wires (e.g., 12k carbon fiber has 12,000 holes). This wet wet wet fiber is relative to gel -like and fragile. It is washed out of the roller to remove the excess coagulant, and then dry and stretch to continue the PAN polymer. Here, the external shape and internal cross section of the long silk depends on the degree of the selected solvent and the concrete penetration of the front drive fiber. The latter is exclusive to each producer, but JP Morgan asserted that the stretch rate can be up to 12 times that of the initial flexibility of the preliminary fiber.

The replacement method of wet spinning is called a mixed process of dry spray/wet spinning wire, which uses vertical air gap between fiber and solidifying baths. This creates a smooth, round PAN fiber that enhances the fiber/substrate resin interface in the composite material.

The last step of the PAN front body fiber is coated with organic oil to prevent sticky filaments. Then dry the white PAN fiber and wrap it on the line shaft again.

Oxidation

These wiring shafts are loaded into a gauze, and in the most time -consuming production stage, oxidation is delivered through a series of special oven to send PAN fibers. Before entering the first oven, the PAN fiber was flattened into a drag or sheet called the meridian. The temperature range of the oxide furnace is 392 ° F to 572 ° F (200 ° C to 300 ° C). This process combines oxygen molecules from the air with the PAN fiber in the meridian, and the polymer chain began to cross -cross. This increases fiber density from ~ 1.18 g/cc to 1.38 g/cc.

In order to avoid outdooring of outdooring (the total heat -release energy released during the oxidation process is estimated to be 2,000 kj / kg, it will bring a real fire danger). The oven manufacturer uses various airflow design to help heat dissipation and control temperature (see The side bar below). C.A. Litzler Co. Inc. (Ohio Cleveland) President Matt Litzler observed that “each prelude has its own heat control mode. Since a single front -drive chemistry is fixed, the temperature and airflow control in the oxide furnace are suitable Each front -drive body and the stability of the inspiration reaction.

The oxidation time varies from the chemical properties of specific pre -body, but Litzler estimates that on a large production line with multiple oxide furnaces, 24K drag can be oxidized at a speed of about 43 feet/ 13 meters per minute. Randy Strop, the general manager of the oven manufacturer Despatch Industries (Lakeville, Minnesota), said that the typical 60 to 120 minutes are time to pass. There are four or six ovens in each production line. The ovens are stacked and provided two heating areas. Each oven is provided 11 to 12 fiber. Finally, the oxidation (stable) PAN fiber contains about 50%to 65%of carbon molecules, which is balanced to mixture of hydrogen, nitrogen and oxygen.

For a new generation of oven, the kiln is designed to improve efficiency

Air flow and wind speed are the key to controlling the consistency of the heat and temperature during the control of oxidation. The principle diagram of the despatch industry

In the production of carbon fiber, it depends to a large extent on the design of the hot -decomposed fiber oven and furnace.

During the oxidation process, the oven airflow plays a vital role in controlling the temperature of the control process and preventing the heat dissipation reaction. The airflow design can be a single stream (parallel or vertical traction band) or multi -path.

According to Randy Strop, general manager of the oven manufacturer Despatch Industries. Carbon fiber business departments, carbon fiber manufacturers need three important elements in oxide furnaces: throughput, scalability and energy efficiency. In order to determine the best oxide furnace settings specific requirements of carbon fiber manufacturers in customers, Despatch tested the center of the patented patented parallel airflow through 40 different calibration thermocouple measurement temperature gradients on both sides of the oven work area. Strop point out that compared with other oven configurations, this design allows higher air speed -nozzle emissions is as high as 13.1 feet/s (4 meters/s) -and higher air volume. This configuration can also achieve the tight temperature uniformity of ± 1 ° C throughout the traction bandwidth, and the side by side is average. According to customer reports, the oxidation rate of production -scale oven was increased by 25%.

DESPATCH provides a 1 -foot to 11.5 -foot (0.3 -meter to 3.5 meter) oven width, which can maximize the heat loss and reduce the automatic shuttle window window of the setting time, and recycling heating air to reduce total energy consumption. Compared with the design of the traditional oven, on the 6.6 -foot/2 -meter -wide opposite shutter window, the slot opening is reduced to 0.35 inches/9 mm, which is estimated to save 10 kW/h.

C.A. Litzler (Cleveland, Ohio) is a 30-year-old oxide furnace manufacturer. Its products have multiple temperature areas and controlled wrong flow. The speed of 2.7 meters) is transported to the air, thereby evenly handling the front fiber. The patented part -faced seal solves the “simple physical principle of the chimney effect of the chimney effect, which is described by the company’s president Matt Litzler. Among them, the cold air enters a lower product slot, and the hot air is reached from the top slot. This may be generated in the oven. Cold spots are dangerous to operators. Our end sealing parts keep each slot neutral, reduce the required exhaust amount, and effectively extend the useful oven by eliminating cold air penetration.

In addition to the test and production oven with a width of 10 feet/3 meters, C.A. Litzler also designed and manufactured lazy wheel rollers, drive rollers, and tension brackets for fiber stretching.

Since the 1940s, Harper International Corporation (Lanciest, New York) has been a supplier of carbon furnaces. In the 1990s, it began to provide complete carbon fiber production line design and equipment. Travel key installation. Robert Blackmon, vice president of the process system, pointed out that the latest generation of widening furnace system is higher, the energy consumption per pound of fiber is lower, and the carbon fiber output is greater. The furnace width provided by Harper can reach 13 feet/4 meters, and the length is greater than 46 feet/14 meters. It has efficient thermal insulation.

Pay special attention to entering and exiting the sweeping room. Blackmon explained that each oxygen molecule brought into the system will not only degrade the fiber, but also degrade the surface of the graphite refractory material of the furnace. “Our sweeping system significantly reduces the inflow of oxygen, which can improve product output and quality and the service life of equipment. In order to improve energy efficiency and reduce production costs, Harper has designed a kind of heat exchanging heat recovery for heat oxidation and waste heat. System. Blackmun acknowledged that there is cost -oriented environmental control, but he believes that “the energy of recycling usually proves the rationality of cost.

“Harper’s kiln uses inert gases such as nitrogen or salamander to control atmosphere, and can run within the temperature range of 572 ° F to 5,432 ° F [300 ° C to 3,000 ° C] for low To the ultra -high -modular carbon fiber, “marketing and business development manager John Imhoff said. Harper also provides surface treatment and glue application systems to adapt to different electrolytic and matrix resin chemical ingredients.

Carbonization

Carbonization occurs in an inert (anaerobic) atmosphere. In a series of specially designed stoves, these stoves gradually increase the processing temperature. At the entrance and exit of each stove, the sweeping room can prevent oxygen invasion because each oxygen molecule carried through the stove will remove some fibers. Robert Blackmon explained. This can prevent the loss of carbon caused by such high temperatures. In the absence of oxygen, only non -carbon molecules, including hydrogen cyanide and other VOCs (during the stability process of concentration level at 40 to 80 ppm) and particulate matter (such as the local accumulation of fiber fragments) are discharged from the oven from the oven And discharge from the oven to be processed in the incineration furnace of environmental control. In Grafil, carbonization starts from a low-temperature furnace, and places fiber in a low-temperature furnace of 1292-1472 ° F (700-800 ° C), and ends in a high-temperature furnace of 2192-2732 ° F (1200-1500 ° C). Fiber tension must be continued throughout the production process. In the end, the crystallization of carbon molecules can be optimized to produce finished fibers with more than 90%of carbon content. Although the two terms of carbon and graphite can usually be used, the former said that carbonized at about 1315 ° C / 2400 ° F and containing 93%to 95%carbon fiber. The latter is graphized at 1900-2480 ° C (3450-4500 ° F), which contains more than 99%of element carbon.

The amount of kiln is determined by the amount required by the carbon fiber; the relatively high cost of high modular and ultra -high modulus carbon fibers is because the stay time and temperature of the temperature must be achieved in high temperature furnaces. Although the residence time is proper and each level of carbon fiber is different, the oxidation stay is in the hour, but the carbonization time shortens an order of magnitude in minutes. Because the fiber was carbonized, it lost weight and volume, shrinking 5%to 10%in length, and reduced diameter. In fact, the conversion chemistry of PAN front drives and PAN carbon fiber is about 2: 1, which has less than 2%degeneration -that is, the materials exited this process are much less than the materials that enter the process.

Surface treatment and size

Surface treatment and glue increase the total surface area and pore rate of the fiber and change its surface energy to improve the adhesion between the matrix between the fiber and the composite material

The next step is critical to fiber performance. In addition to the front -drive body, it can best distinguish the supplier’s products from the competitors’ products. The adhesion between the substrate resin and the carbon fiber is vital to enhance the composite material; the surface treatment is performed to enhance this adhesion during the carbon fiber manufacturing process. Manufacturers use different treatment methods, but a common method is to pull fiber electrochemical or electrolytic baths containing solutions (such as sodium hypochlorite or nitrate). These materials etch or rough surfaces of each filament to increase the surface area that can be used for interface fiber/matrix bonds, and add reactive chemical groups, such as carboxylic acid.

Next, a high -profile coating is applied, called glue. When the carbon fiber weight is 0.5%to 5%, the gum is protected by the processing and processing (such as woven) to protect the carbon fiber during the intermediate form (such as dry fabric and pre -immersion). The gum also fixes the filament together in a separate wicker to reduce the fluff, improve the processing performance, and improve the interface shear strength between the fiber and the substrate resin. Carbon fiber manufacturers are increasingly using glue suitable for customers’ final uses (see the sidebar below and “the progress of carbon fiber gum and surface treatment”). Carmichael added that in Grafil, “we can process and size according to the resin characteristics of specific customers and the specific performance customization surface processing and size required for composite materials.

Former Hydrosize Technologies, co -founder of Andy Brink (now Michael Michamon (Ohio Cindinnaste), is part of his business development manager. The formed agent provides a stable chemical ingredient, which will produce good coating when drying. Most carbon fiber production lines are allowed to allow quite uniform size applications to minimize the aggregate group blocks or naked spots.

When the gum is dry, the long process is completed. Grafil (like other suppliers) separate a single drag from the yarn and entangle them to the thread shaft to transport customers, including prefabricants and woven workers.

If the history of an industry is the pioneer of its future, then the absolute scale of the mechanical and sharpness required for black carbon fiber to successfully convert the white PAN fiber into the business of the mechanical and sharpness required by the black carbon fiber that the production of this advanced material is not the business of people with timid or lack of experience. Thirty years of processing improvement brings technical maturity, and the ability to transform excellent performance and application through fiber into advanced composite materials. What happened in technology and economy laid the foundation for marking the growth of potential demand in the future.

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