Preparation and application of isostatic pressing graphite

Isostatic pressing graphite production process

Isostatic pressing processing of graphite production through raw material crushing, screening, grinding, melting of adhesive, as well as batching, mixing kneading, molding, baking, impregnation, graphitization and other processes. Professional graphite electrode products for reference.

• 1.Raw materials and crushing

  The raw material of isostatic pressing graphite is needle petroleum coke, which has low sulfur content, low ash and volatile. Graphite products made from needle petroleum coke have the characteristics of high graphitization, low resistance and high surface lubrication.

   

  The particle size of raw petroleum coke is larger and needs to be crushed first. Production of fine particle structure of three high graphite, most of the powder with 0.075mm, part of the powder with 0.042mm or 0.037mm micro powder; Production of ultrafine structure of graphite, powder particle size is less than 0.02mm or smaller. Therefore, the petroleum coke should use the air mill or other grinding equipment for the production of ultra-fine particles. The classification of the fine powder is more difficult than that of the soft powder, and a special technology should be used. In order to obtain petroleum coke powder with suitable particle size, it was pulverized by the commonly used crushing equipment and airflow crushing equipment in metallurgy.

   

• 2.Batching and kneading

  The refined petroleum coke powder with appropriate particle size is mixed with the binder in a certain proportion and fully mixed in the kneading equipment. The commonly used binder is coal tar, asphalt or resin. In the whole production process of isostatic pressing graphite, kneading is a very key process, which is directly related to the subsequent yield of graphite. The organic matter and volatile matter in asphalt have a great influence on the yield of graphite products. In order to achieve high yield, it is necessary to strictly control the temperature rise and fall procedure and kneading time of kneading equipment.

   

  The kneading equipment commonly used in the carbon industry include biaxial kneader, uniaxial kneader and countercurrent high-speed kneader. The countercurrent high-speed kneader is used for the preparation of special graphite. In addition, the kneaded paste needs to be treated by the rolling process. The paste is rolled into 1 ~ 3mm thin sheets (1~2 times rolling) by the rubber mixer, so that the binder and coke powder can be combined more effectively. After rolling, the paste is ground into paste powder by universal mill for isostatic pressing.

   

• 3.Molding

  The production of graphite processed by isostatic pressing adopts cold isostatic pressing. Graphite samples formed by cold isostatic pressing equipment need to be baked and impregnated several times. The purpose of baking is to make the volatile in the binder in graphite escape. Impregnation is to maintain the tightness of graphite. The general impregnating agent is various resins or asphalt. The graphite samples formed by cold isostatic pressing need to be baked and impregnated for many times to meet the requirements of special graphite products.

   

  At present, there are domestic manufacturers of cold isostatic pressing and hot isostatic pressing equipment, which can meet the requirements of special graphite molding.

   

• 4.Baking and impregnation

  For graphite products requiring high bulk density, cracks are easy to occur during baking, so a slow temperature rise curve should be used; For the baking of smaller graphite products, square or circular containers can be made of heat-resistant materials, and then the raw products can be placed in the container and filled with filler for isolation and coverage, and then loaded into the baking furnace for baking. The most important key to impregnation lies in immersion. High density graphite products need to be impregnated for 2 ~ 4 times, and they need to be baked once after each impregnation; For impregnation, the softening point of the impregnant (related to the viscosity of the impregnation agent) should be correctly selected, and the preheating temperature of the baked product before impregnation and the process parameters such as the temperature, pressure, vacuum degree and pressurization time of the impregnation tank should be controlled to achieve the best leaching effect.

   

  The treatment cycle of repeated impregnation baking process is long, generally about 2 ~ 3 months, which puts forward higher requirements for the service life of the equipment, increases the input of manpower and material resources, resulting in poor economic effect.

   

• 5.Graphitization and purification treatment

  Carbon baked products need to undergo high-temperature heat treatment at 2000 ~ 3000 ℃ before they can be transformed into graphitized products. The main difference between carbon products and graphite products is that the carbon atom lattice of the microstructure of carbon products is a disordered layer structure, while the carbon atoms after graphitization are a three-dimensional ordered layer structure. The graphitization treatment of isostatic pressure graphite is carried out in the graphitization furnace. In addition, chlorine and freon gas are introduced in the graphitization process to make the impurity elements form chloride and fluoride volatilize and escape, so as to achieve the purpose of purification.

Application of isostatic pressing graphite

• 1.Solar cells and semiconductor chips field

  In the solar energy and semiconductor industries, isostatic pressure graphite is widely used to make graphite parts for thermal field of single crystal Czochralski furnace, heaters for polycrystalline silicon melting and casting furnace, heaters and crucibles for compound semiconductor manufacturing. In recent years, with the rapid development of solar photovoltaic power generation, the production of monocrystalline silicon and polysilicon in the photovoltaic industry has a great demand for graphite. At present, single crystal and polycrystalline silicon products are developing towards large-scale and high-end, and isostatic pressed graphite also has higher requirements, that is: larger specification, higher strength and higher purity.

   

• 2.Nuclear field

  Isostatic graphite has medium mechanical properties, especially excellent high-temperature mechanical properties, high thermal conductivity and low linear expansion coefficient. In high temperature gas cooled reactor, it is mainly used as reflector, moderator and active zone structural material to form nuclear fuel assembly together with nuclear fuel. Under the temperature of 400~1200℃, by high-energy γ rays and fast neutron radiation for several years, easy to cause irradiation damage, thus changing the structure and properties of graphite, so the requirements of high graphitization, good isotropy, uniform composition and low elastic modulus.

   

• 3.Electrode field

  Graphite has no melting point,good conductors of electricity, good thermal shock resistance, it is an excellent electrode material for EDM. Ordinary graphite material is coarse-grained low-density anisotropic graphite, which can not meet the needs of EDM. However, isostatic pressing graphite electrode has uniform structure, compact structure and high processing precision, which can meet the requirements of this aspect.

   

• 4. Continuous casting of mold and mold graphite
  Mold materials with high temperature and high pressure resistance shall be used for continuous casting mold and superhard material production. Due to its fine particle structure, high mechanical strength and uniform heat conduction, isostatic graphite makes the surface of continuous casting and molding products smooth, high internal quality and long service life. It is the best material for crystallizer. Moreover, for large sintered materials,the thickness of mold wall should be as thin as possible, and high strength of fine structure isotropic graphite must be used.

   

• 5.Other uses

  In the carbon brush, mechanical seal, contact wheel collector plate and other places to use, requiring processing accuracy at the same time, high lubricity and high conductivity is extremely important. Isostatic graphite is also used to make sintering molds of diamond tools and cemented carbide, thermal field components of optical fiber wire drawing machine (heater, insulating cylinder, etc.), thermal field components of vacuum heat treatment furnace (heater, bearing frame, etc.), as well as precision graphite heat exchanger, mechanical seal, piston ring, bearing, rocket nozzle, etc.

Development direction

Isostatic pressing graphite is a new type of graphite material and a fine product of graphite materials. Due to a series of excellent characteristics, it is bound to be closely connected with high and new technology and cutting-edge national defense technology, and become one of the most valuable new materials in the 21st century. With the economic development, the domestic and international market capacity of hydrostatic graphite is increasing day by day, and the development potential is huge. Because of this, the current domestic rise is a hot isostatic pressing graphite production, some in the production of molded graphite carbon production enterprises take a fancy to this "big cake", and successively launch isostatic pressing equipment to squeeze into the ranks of isostatic pressing graphite production. The competition will inevitably enter a white-hot state, competition including the foreign counterparts.

In the fierce market competition,domestic isostatic pressing graphite production enterprise of this foundation and the way out is:the product upgrading, the large size, fine structure (ultra-fine structure), high strength, high purity, multi-function direction, comply with the development trend of photovoltaic industry, machinery manufacturing and nuclear energy utilization, and better serve the development of China's national economy.

China has become a world-class "manufacturing factory", and the development of science and technology has brought a new industrial revolution. The wide application fields of isostatic pressing graphite materials and products have brought vitality to the isostatic pressing graphite industry. At present, due to the outbreak of the economic crisis, the foreign carbon industry has been seriously affected, so they have increased their sales to China. At present, China consumes about 1/4 of the world's isostatic pressed graphite products, and is one of the largest markets of isostatic pressed graphite products in the world. The isostatic pressed graphite industry will embrace a new stage of development, for more technical guidance contact us.