Use of graphite

I. Graphite and Graphite Industry

Graphite is formed at high temperature. The most widely distributed metamorphic deposit is graphite, which is formed by regional metamorphism of sedimentary rocks rich in organic matter or carbon. Graphite or graphite products is widely used in industry, which is used to make high-temperature crucibles in smelting, lubricants in machinery industry, electrodes and pencil lead. Graphite or graphite products is widely used in advanced refractories and coatings in metallurgical industry, pyrotechnic stabilizers in military industry, pencil lead in light industry, carbon brushes in electrical industry, electrodes in battery industry and catalysts in fertilizer industry. After deep processing, flake graphite can also produce high-tech graphite products such as graphite emulsion, graphite sealing materials and composite materials, graphite products and graphite anti-wear additives. Graphite or graphite products has become an important nonmetallic mineral raw material in various industrial sectors.

Most of the world's consumption of graphite or graphite products is concentrated in industrialized countries such as Japan, the United States, Germany and Britain, and the annual consumption of graphite or graphite products in these countries accounts for about 30% of the world's total consumption. In the past few years, the consumption of graphite or graphite products in the world has remained relatively stable. The main consumption areas of graphite or graphite products are: refractories account for 26% of the total consumption, castings 15%, lubricants 14%, brake pads 13%, pencils 7%, others (carbon brushes, batteries, expanded graphite, etc. ) 25%. Judging from the current situation, it is difficult for graphite or graphite products to have a big and new application field in the near future. Therefore, the demand for graphite or graphite products in the international market will not increase too much.

China is the largest producer of natural graphite in the world. In 2008, the graphite output reached 65,438+650,000 tons. China's output accounts for about 55% of the world's total graphite or graphite production. In addition to natural graphite, many countries in the world also produce artificial graphite. The output of graphite in 2008 increased by 654.38+200,000 tons compared with 654.38+500,000 tons in 2007, with an increase of about 8%. This is a great development of graphite industry.

Scaly graphite ore crystallizes well, and the grain size is greater than 1mm, generally 0.05- 1.5mm, and the maximum is 5- 10mm, mostly aggregates. The grade of graphite ore is low, generally 3- 13.5%. Associated minerals include mica, feldspar, quartz, tremolite, diopside, garnet and a small amount of pyrite and calcite. Sometimes it is accompanied by useful components, such as rutile and vanadium-bearing mica. According to the rock lithology of flake graphite ore, it can be divided into seven types: gneiss, schist, diabase, granulite, migmatite, marble and granite. The first six types of ores occur in regional metamorphic deposits, while the latter one occurs in magmatic hydrothermal deposits. Since 2000, due to the further development of flotation technology and mechanical equipment, the output of flake graphite has been increasing.

Since 2009, the export volume of domestic flake graphite has declined, and the sharp decline in the export volume of flake graphite has further accumulated domestic flake graphite stocks. However, due to the impact of the economic crisis, domestic steel, downstream products, refractories and other industries have been affected to varying degrees, and the demand for flake graphite will also drop by about 5% in 2009. In 20 10-20 12 years, the inventory of flake graphite in China will remain at a high level, and the supply of flake graphite will remain surplus in one to three years.

Under the guidance of the direction of graphite deep processing proposed in the Tenth Five-Year Plan, the graphite deep processing products to be developed in China in the next five years include special-shaped carbon, graphite fluoride, graphite silicide, graphite emulsion for kinescope, lithium-ion battery, carbon material and carbon material for fuel cell.

Second, the new use of graphite

With the continuous development of science and technology, people have also developed many new uses of graphite. Flexible graphite products.

Flexible graphite, also known as expanded graphite, is a new graphite product developed in 1970s. 197 1 year, the United States successfully researched flexible graphite sealing materials, which solved the leakage problem of atomic energy valves, and then Germany, Japan and France began to develop and produce graphite sealing materials. This product not only has the characteristics of natural graphite, but also has special flexibility and elasticity. Therefore, it is an ideal sealing material. Widely used in petrochemical, atomic energy and other industrial fields. The international market demand is increasing year by year.

Manufacturing semi-metallic friction materials. Since 1970s, semi-metallic friction materials have been widely used in clutches and automatic linings. Semi-metallic friction material is made of graphite bonded with metal powder, steel fiber and clay powder by synthetic resin. These automatic linings can be mainly used for high-speed equipment, such as braking devices and clutch plates of airplanes, trucks and off-road vehicles. In recent years, asbestos has been gradually replaced by graphite, and the graphite content in some semi-metal linings has increased from 1%-2% to 5%. The consumption of graphite in this field depends on the development of automobile industry.

Third, graphite materials have characteristics.

Graphite is mainly composed of polycrystalline graphite, which belongs to inorganic non-metallic materials, but it is called semi-metal because of its good thermal and electrical conductivity. Graphite has higher thermal conductivity and electrical conductivity than some metals, and at the same time, it has much lower thermal expansion coefficient, high melting point and chemical stability, which makes it of great value in engineering applications. Graphite has good corrosion resistance and does not react with any organic compounds.

Graphite is also a kind of high temperature resistant material, which will not melt at high temperature. Graphite also has good thermal shock resistance and good self-lubricating performance.

The disadvantage of graphite is poor impact resistance, and the oxidation rate increases with the increase of temperature.

Fourth, the performance parameters

1. Average particle size of material

The average particle size of materials directly affects the discharging status of materials. The smaller the average particle size of the material, the more uniform the material discharge, the more stable the discharge conditions and the better the surface quality.

For forging and die-casting dies with low surface and precision requirements, coarse-grained materials, such as ISEM-3, are usually recommended. For electronic dies with high surface and precision requirements, it is recommended to use materials with average particle size below 4μm to ensure the precision and surface smoothness of the processing dies. The smaller the average particle size of the material, the smaller the loss of the material and the greater the force between ion groups. For example, it is generally recommended that ISEM-7 is sufficient for precision die casting and forging dies; However, when customers have particularly high requirements for accuracy, TTK-50 or ISO-63 materials are recommended to ensure less material loss, thus ensuring the accuracy and surface roughness of the mold.

At the same time, the larger the particles, the faster the discharging speed and the smaller the rough machining loss. The main reason is that the discharge energy is different due to the different current intensity during the discharge process. However, the surface smoothness after discharge also changes with the change of particles.

2. Bending strength of materials

The bending strength of the material directly reflects the strength of the material and shows the tightness of the internal structure of the material. The material with high strength has good discharge wear resistance. For high-precision electrodes, try to choose materials with good strength. For example, TTK-4 can meet the requirements of general electronic connector molds, but some electronic connector molds with special precision requirements can be made of TTK-5 material, with the same particle size but slightly higher strength.

3. Shore hardness of materials

In the subconscious understanding of graphite, graphite is generally considered as a relatively soft material. However, the actual test data and application show that the hardness of graphite is higher than that of metal materials. In the special graphite industry, the general hardness test standard is Shore hardness measurement, and its test principle is different from that of metals. Because of the layered structure of graphite, it has excellent cutting performance in the cutting process, and the cutting force is only about 1/3 of that of copper, so the machined surface is easy to handle. However, due to its high hardness, the loss of cutting tools will be slightly greater than that of cutting metal tools. At the same time, the high hardness material has a good control over the discharge loss. In our EDM material system, there are two materials to choose from, one with slightly higher hardness and the other with slightly lower hardness, so as to meet the needs of customers with different requirements. For example, materials with an average particle size of 5μm include ISO-63 and TTK-50；; ; The materials with an average particle size of 4μm are TTK-4 and TTK-5. Materials with an average particle size of 2μm include TTK-8 and TTK-9. Mainly consider the bias direction of various customers for discharge and machining.

4. Intrinsic resistivity of materials

According to our statistics of material characteristics, if the average particles of materials are the same, the discharge rate with high resistivity will be slower than that with low resistivity. For materials with the same average particle size, the strength and hardness of materials with low resistivity will be slightly lower than those with high resistivity. That is, the speed and loss of discharge will be different. Therefore, it is very important to choose materials according to the needs of practical application. Due to the particularity of powder metallurgy, each parameter of each batch of materials has its representative value and has a certain fluctuation range. However, the discharge effect of graphite materials of the same grade is very close, and the application effect caused by various parameters is very different. The choice of electrode material is directly related to the effect of discharge, and to a great extent, the choice of material determines the final situation of discharge speed, machining accuracy and surface roughness.

V. Process and technical features:

1. High temperature resistance

Graphite is one of the most high temperature resistant materials known at present. In 2000? Above c, the general substance has become a gas or is in a molten state, that is, some refractory metals are at 2500? C or so will also lose strength. Tungsten, for example, has the highest melting point among known metals, reaching 3600? C, but graphite won't melt at this temperature. Its melting point is 3850? C 50？ C, the boiling point should be 4250? C put all kinds of heat-resistant materials at 7000? C Under the ultra-high temperature arc of 10s, the loss of graphite is the smallest, which is 0.8% by weight, the loss of nylon fiber reinforced phenolic plastics is 1.2%, the loss of silicon carbide is 1.7%, the loss of high-alumina steel jade is 8.2%, and the loss of the most heat-resistant metal oxide zirconia is/kloc-. It can be seen that the high temperature performance of graphite is outstanding.

The strength of general materials gradually decreases at high temperature, while graphite is heated to 2000? C, its strength is doubled than that at room temperature. The oxidation resistance of graphite is poor, and the oxidation rate increases with the increase of temperature.

2. Special thermal shock resistance

Graphite has good thermal shock resistance. When the temperature changes rapidly, the thermal expansion coefficient is small, so it has good thermal stability and will not produce cracks when the temperature changes rapidly.

3. Thermal and electrical conductivity

Graphite has good thermal conductivity. Although the conductivity of graphite is not as good as that of copper, aluminum and other technologies, it is still quite high compared with ordinary materials, such as 4 times higher than stainless steel, 2 times higher than carbon steel and 0/00 times higher than ordinary nonmetals.

The thermal conductivity of graphite not only exceeds that of steel, iron, aluminum and other metal materials, but also decreases with the increase of temperature, which is different from ordinary metal materials. The thermal conductivity of general technology increases with the increase of temperature. At extremely high temperatures, graphite even tends to be adiabatic. Therefore, under the condition of ultra-high temperature, graphite has thermal insulation.

Step 4 be cunning

The lubrication performance of graphite is similar to that of molybdenum disulfide, and the friction coefficient is less than 0. 1. Its lubricity varies with the scale size. The larger the scale, the smaller the friction coefficient and the better the lubricity.

5. Plasticity

Graphite has plasticity, which can be developed into breathable and light-transmitting flakes. However, high-strength graphite has great hardness and is difficult to be machined with diamond tools.

6. Chemical stability

Graphite has good culture stability at room temperature, and can resist the corrosion of acid, alkali and organic solvents, but it is easy to oxidize at high temperature.