The isostatic pressing graphite technology is a kind of super high pressure hydraulic equipment,and its working principle is that products formed under the condition of equal pressure and high pressure in all directions and closed high-pressure container . The working principle of the isostatic pressure is Pascal's Law: "the pressure of the medium (liquid or gas) in the closed vessel can be transferred to all directions equally." Isostatic pressing technology has had 70 years of history, was used in the powder molding of powder metallurgy initially . In the past 20 years, the isostatic pressure technology has been widely used in many fields such as ceramic casting, atomic energy, tool manufacturing, plastics, super high-pressure sterilization of food and graphite, ceramics, permanent magnet, high voltage electricity magnetic insulator, preparation of biological medicine, food preservation, high performance material, military and other fields.

　　The isostatic pressing technology is divided into three kinds of different types such as cold isostatic pressing, temperature isostatic pressing and hot isostatic pressing according to the temperature of the forming and solidification .

　　The cold Isostatic Pressing, CIP for short,it is at room temperature, rubber or plastic are used for package sets of mould material, and a liquid is used for pressure medium,the technology is mainly used in powder material compaction, it provide green body for further sintering, forging or hot isostatic pressing process usually. General application pressure is 100~ 630MPa.

　　The temperature isostatic pressure technology, the pressing temperature is generally in the 80 ~ 120 ℃ ,some are also in 250~450 ℃, it transfer the pressure by special liquid or gas , the application pressure is 300MPa. It’s mainly used in graphite,polyamide rubber and other powder materials which can not be molded in room temperature so that we can obtain a solid body at an elevated temperature.

　　The hot isostatic pressing，HIP for short, it is a technology which make material to go through isostatic pressing under the high temperature and high pressure at the same time, It is not only used for powder consolidation and two step work of traditional powder metallurgy forming and sintering are completed together,but also for diffusion bonding of the workpiece, the elimination of casting defects, and complex shape parts production. In hot isostatic pressure, it generally use argon, ammonia and other inert gas as the pressure transfer medium, the package of materials are usually used in metal or glass. Operating temperature is generally 1000~2200℃, the working pressure is often 100~200MPa.

　The production technology of the isostatic graphite is different from the graphite electrode. The isostatic graphite need the raw material which has an isotropic structure property. It need to grind into finer powder,and use the cold press molding technology(the isostatic press molding is one kind of the the cold press molding) the baking cycle is very long,and for the high density,it need more times’ dipping and baking.and the graphitization cycle is more than normal graphite.

　　The main technology mainly includes:

　　1) raw material grinding

　　the particle size need to processed into 20 μm below. For now,the finest isostatic graphite particle size is 1μm,and it must need the superfine mill.

　　2) the kneading processing

　　make the powder and coal asphalt adhesive into fixed ratio,then put into the heating mixer to make it mixed,the purpose of this is to make the powder surface coated a layer of the pitch. After that get it out and cool it. Compared with the production of graphite electrode,the kneading time need longer,and the temperature need higher,and the QTY of the pitch need more.

　　3) second-grinding

　　The material after crushing,grinding,it will be screened into tens to hundreds of microns and mix it uniformly,then press it and mold it,prepare for the second-grinding.

　　4) molding

　　Defferent from the extrusion molding and molded pressing,the isostatic molding is belong to the cold pressed molding. Press the raw material and make it into the rubber mould, use the high frequency electromagnetic vibration to make the powder pressed,then make it vacuum,put it into the high-pressure container with water or oil,then make the pressure to 100~200Mpa,at last,make it as a cylindrical or rectangular product.

　　5) baking and dipping

　　As the isostatic graphite compact structure,the baking temperature should heating-up slowly,and the temperature inside the furnace should also be controlled well,the heating-up speed should not beyond 1℃ /h,and the temperature difference in the furnace should below 20℃,and during the baking processing, it will take 1~2 month to meet the requistment.

　　After the baking processing, the volatile of the pitch discharged,there are some pores on the surface of the material ,so it need to be dipped,and it usually need many times to bake and dip.

　　6) the most important processing it the graphitization.

　　Heating-up to 3000℃,and it will take 1~1.5 month to make it. After this,the density,electricity conducting,thermal conducting and the erosion resistance will be improved better.

          Isostatic pressing graphite is developed in the 1960 s a new type of graphite materials, has a series of excellent performance. Isostatic pressing graphite heat resistance good, for example, in an inert atmosphere, with its mechanical strength not only the rise of temperature, increase, in the 2500 ℃ maximum when left to the right; Compared with ordinary graphite, fine structure and uniformity; Low thermal expansion coefficient, excellent thermal shock resistance; Isotropic; Thermal conductivity and chemical corrosion resistance is strong, conductive good performance; Excellent machining performance. It is precisely because has a series of excellent performance, such as static pressure graphite in metallurgical, chemical, electrical, aerospace and atomic energy industry and other fields is widely used, and, with the development of science and technology, application field continues to expand.

　　1 the isostatic pressing graphite production process

　　Very apparently, production technology of isostatic pressing graphite and graphite electrodes. Isostatic pressing graphite need the structure of isotropic materials, you need to raw material grinding into a fine powder, need to apply cold isostatic pressing molding technology, roasting cycle is very long, in order to achieve the target density, need many times

　　Dip - roasting cycle, cycle of graphitization is much longer than ordinary graphite.

　　1.1 raw material to produce isostatic pressing graphite materials including aggregate and

　　Adhesives. Aggregate is usually with petroleum coke and pitch coke and pitch coke also have land, such as the POCO AXF series isostatic pressing graphite, pitch coke is land Gilsonitecoke production. In order to according to the different USES to adjust the product performance, also useful carbon black, artificial graphite additives. In general petroleum coke and pitch coke calcined under 1200 ~ 1400 ℃, to use to remove moisture and volatile matter. But in order to improve the mechanical properties and structure of the product density, also has a direct made of raw material to produce the isostatic pressing graphite raw coke. Raw coke is characterized by containing volatile, has since the sintering, and the binder coke synchronous expansion and contraction. Adhesives usually use coal tar, according to the different equipment condition and technical requirements of various enterprises, using the coal asphalt softening point from 50 ℃ to 250 ℃. Isostatic pressing performance of graphite under the influence of raw material is great, the selection of the raw material is needed to produce a key link in the process of the final product. Prior to feeding uniformity of material characteristics and strict inspection.

　　1.2 milling isostatic pressing graphite aggregate size usually require up to 20 microns below. At present, the most elaborate isostatic pressing graphite, maximum particle diameter of 1 mu m, it is very fine. The aggregate coke grinding into fine powder, so need to use superfine mill. Grinding of average particle size of 10 ~ 20 microns powder need to use the vertical roller mill, the grinding powder of average particle size less than 10 microns will need to use the airflow mill.

　　1.3 kneading will manufacture fine powder and coal asphalt binder in proportion into the mix and pinch machine heating type kneading, make coke powder particle surface evenly attached to a layer of asphalt. After kneading, paste, to make it cool. Compared with graphite electrode production, the production of the isostatic pressing graphite kneading asphalt quantity is more, when the temperature is higher, some time longer.

　　1.4 secondary flour paste after crushing, grinding, and the screen is divided into several dozens to hundreds of micron particle size of particles after mixing, used as a molding material, called pressed powder. Secondary grinding equipment is usually use vertical roller mill and ball mill.

　　1.5 molding is different from the ordinary and extrusion molding, such as static pressure is graphite by cold isostatic pressing technology molding (figure 2). Powdered materials will be filled to the rubber mold, high frequency electromagnetic vibration, pressure powder is close-grained, after sealing process of pumping air into vacuum state, discharge the air between powder particles, in the containing water or oil liquid medium, such as high pressure vessel, pressure to 100 ~ 200 mpa, compressed into cylindrical or rectangle products. According to PASCAL's principle, through the liquid medium such as water pressure to the rubber mold, pressure is equal in all directions. In this way, the pressure in the mold powder particles is not according to fill in the direction of orientation, but is compressed by the irregular arrangement, therefore, in spite of graphite on the crystallographic features is anisotropic, but overall, isostatic pressing graphite Is isotropic. After molding products in addition to the cylindrical, rectangular, including the shape of cylinder, crucible, etc. Isostatic pressing molding machine is mainly used in powder metallurgy industry. Due to the aerospace, nuclear industry, hard alloy, high voltage electromagnetic and other high-end industry demand, isostatic pressing technology is developing very fast, already have manufacturing work cylinder inner diameter 3000 mm, 5000 mm, maximum working pressure 600 MPa cold isostatic pressing machine. At present, the isostatic pressing graphite carbon industry used in the production of cold isostatic pressing machine specification is the largest Φ 2150 mm * 4700 mm, and maximum working pressure of 180 mpa.

　　1.6 roasting in the roasting process, complex chemical reaction taking place between aggregate and caking agent, adhesives, release a large number of volatile, at the same time polycondensation reaction. At low temperature preheating stage, raw products, because of the heat in the subsequent heating process, the volume contraction due to condensation reaction. The greater the volume of raw products, the release of volatile, the more difficult, and raw products surface and internal easy to produce temperature difference, thermal expansion, the phenomenon such as uneven contraction, which may lead to crack of raw products. Isostatic pressing graphite because of its fine structure, especially slow roasting process requires you to be, and have to be very uniform furnace temperature, especially in the asphalt volatile discharge temperature stage, sharply to caution, heating process, heating speed cannot be more than 1 ℃ / h, furnace temperature difference requires less than 20 ℃, the process need about 1 ~ 2 months.

　　1.7 dipping in the process of roasting, volatile bituminous coal is expelled. Gas discharge and volume shrinkage when leaving tiny pores in the products, and are almost open porosity. In order to improve the products of the volume density, mechanical strength, electrical conductivity, thermal conductivity, resistance to chemical reaction, can be treated with pressurized impregnation method, namely through opening stomatal coal tar dipping into the products. Products should be preheated, then in the macerate tank vacuum degassing, again good molten coal pitch to join the impregnating tank, pressure make impregnant pitch into the products inside. Usually, the isostatic pressing graphite to after many times of dipping - roasting cycle ring.

　　1.8 graphitization The products are heated to about 3000 ℃ after roasting, carbon atoms in crystal lattice ordered arrangement, completed by carbon to graphite, called graphitization. Graphitization method has acheson method, internal combination method, high frequency induction method, etc. Usually acheson method, products from furnace charging to emerge, needs to yellow four letters about isostatic pressing graphite production technology, main USES and the analysis of the domestic market 5, 34, 1-1.5 months. Each furnace can handle several tons to dozens of tons of calcined product. After graphitization, products of the volume density, conductivity, thermal conductivity and corrosion resistance have been improved greatly, machining performance is also improved. However, graphitization reduces flexural strength of products.

　　1.9 check after graphitization, also need to products of density, hardness, strength, resistivity, ash content, such as index to check, to determine whether meet the requirements of indicators. 1.10 purification isostatic pressing graphite when used in semiconductor, monocrystalline silicon, atomic energy, and other fields, has a high requirement on the purity and must be used a chemical method to remove impurities, can be used in these areas. To remove impurities in the graphite, usually put graphitization products in halogen gas heated to about 2000 ℃, the impurity was halide halide of low boiling point and volatile. Almost all of the products graphitization of the impurity elements can use chlorine gas halide. But exceptions boron element, it can only get rid of fluoride. Used for purification of halogen gas have chlorine, fluorine, or is that under the condition of high temperature decomposition of these halogenated hydrocarbon gas, for example, carbon tetrachloride (CCl4), dichlorodifluoromethane (CCl2F2). The purification method can make full use of the graphite in the heat does not react with halogen, and the unique properties of porous graphite.

　　Electrical discharge machining (EDM) with the advantages of graphite and copper electrode than graphite electrode, the proportion of graphite is 1/5 of the copper, the weight of the same volume of graphite copper relatively light for 5 times. Easy to manufacture large mould; Graphite processing speed, generally 3 ~ 5 times faster than ordinary metals, can reduce the tool wear and the electrode loss; Graphite high melting point and easy not deformation, don't have to worry about because of high processing through deformation and damage of components; Graphite in processing after the completion of the polishing processing generally don't have to. To reduce the error and shorten the production cycle. Graphite electric cremation processing speed and low dissipation factor, as long as well with reasonable processing parameters, the zero loss on the graphite electrode can be theoretical, reduce the number of repeated electrode processing.

　　Because of graphite material is copper material has the advantage, at present, many mold factory are converted into graphite processing, so as to shorten the delivery time of products to enhance competitiveness in the market. Europe's current electricity cremation processing with the ratio of graphite and copper, lo and the Chinese market is 3:7, along with the rise in copper prices and technological progress, the proportion of using graphite will continue to rise, therefore, our country of graphite used for edm great development space. During the period of "15" mold market demand is very prosperous, foreground is very good, Beijing Greatwall Co.,Ltd. will provide better products and services. In the current mould has become a bottleneck of many industry development situation, such as to better meet the needed for the development of national economic sectors, "15" during the mold output each year, about 15% of the growth, upgrading the machinery manufacturing equipment and manufacturing technology level enhancement, to precision mold development, develop in the direction of large, complex, long-life, multi-functional composite die will further development, therefore, request graphite material in "specifications on large-scale, granularity composition, ultrafine particles using on flexural capacity strengthened".

Solar battery and semiconductor wafer with graphite: photovoltaic industrial graphite materials: as a result of the isostatic pressing graphite materials have high strength, density, isotropic, made of graphite parts in use process heating, heating is even, at the same time due to the density of material evenly can effectively reduce material by thermal shock and produce the internal stress of thermal shock resistance (good), so it can greatly prolong the service life of equipment or instruments cycle, so in the semiconductor and solar industries, used the isostatic pressing graphite (isotropic graphite), making Cz type monocrystal pulling of graphite furnace thermal field components (crucible, heater and diversion tube, cover, etc.); Polycrystalline silicon smelting furnace heater,; Compound semiconductor manufacturing with heater, crucible, etc. Belongs to the high-quality goods of graphite materials, such as static pressure graphite with other ordinary graphite have excellent performance, is a hot field in polycrystalline silicon, monocrystalline silicon manufacturing refractory material of choice for basic materials. Fast development of solar photovoltaic power generation, nearly 10 years, the global solar photovoltaic industry average annual growth rate of 41.3% despite the economic crisis of 2009 attacks, too can industry remains more than 30% of global growth, after the Copenhagen climate BBS, will have a bigger development space, is expected to begin in 2010 will have an annual 50% ~ 60% of the global solar market grows.

　　China as the world's largest producer of solar photovoltaic (pv), whose share has reached 70% of the world, the consumption of industry in 2009 reached more than 5000 tons of high-grade graphite materials, are expected annual demand for isostatic pressing of graphite materials to increase at a speed of 25 ~ 30% on average, pv industry a huge demand for graphite monocrystalline silicon and polycrystalline silicon production, CFCCARBON will provide better products and services. The development of clean energy, the demand of the market and policy support, below is the most favorable conditions in the development of industry. Large size, high purity, high density, high strength, such as static pressure (isotropic) graphite materials are electronic and photovoltaic industry development needs, during the \"twelfth five-year\" will be the development of the isostatic pressing graphite manufacturing companies in China the best opportunity.

　　At present, the single crystal size to normalize development, a few years ago the prevailing 18-inch furnace 20-inch furnace quickly replaced in 2010 ~ 2011 years, and the bigger the trend of the development of the specification; Polysilicon is the large-scale development, in addition, polysilicon access rules is still under discussion, is the development direction of high-end products. Photovoltaic industry products of large-scale and high normalized, determines the has higher request to the graphite, i.e., more specifications, higher strength, higher purity.