The crack after the quenching is the biggest defect of graphite mold in the process of heat treatment, it will make the processed graphite mold scrap and the production and economic loss.

　　The causes of the crack: there is serious network carbide segregation in graphite mould material ;there is mechanical or cold plastic deformation stress in the graphite mould; graphite mold heat treatment improper operation (heating or cooling too fast, quenching cooling medium selection improper, cooling temperature is too low, cooling time is too long, etc.) ; the graphite mold has complex shape, uneven thickness, sharp corners and threaded holes, which makes the thermal stress and the tissue stress too large ; graphite mold quenching heating temperature is too high, overheating or over burning ; the graphite mold quenching after tempering is not timely or tempering insulation time is insufficient ; graphite mold repair quenching heating, without intermediate annealing again heating quenching ; graphite mold heat treatment, improper grinding process ; there are high tensile stress and micro cracks in hardened layer after edm.

　　The preventive measures: controlling the internal quality of graphite mold raw material strictly ; improving forging and spheroidizing annealing process, eliminating mesh, ribbon, chain carbide, improving the uniformity of spheroidizing structure ; the graphite mold should be stress annealing after the mechanical processing or cold plastic deformation (>600 degrees) after the heating quenching ; For complex shape graphite mould, asbestos should be used to block thread hole, wrap dangerous section and thin wall, and adopt graded quenching or isothermal quenching ; repair or renovation of graphite mold, it need to be annealed or high temperature tempering ; the graphite mold should be preheated in quenching heating, take pre-cooling measures when cooling, and choose the appropriate quenching medium ; controlling the quenching heating temperature and time strictly to prevent graphite mold overheating and over burning ; the graphite mold should be tempered timely after quenching, holding time should be sufficient, high alloy complex graphite mold should be tempered 2-3 times ; Choosing the correct grinding technology and suitable grinding wheel ; improving the graphite mold EDM process, and stress relief tempering.

　　Mold in the home appliance, automobile, mechanical and electrical, aerospace and other industrial fields are increasingly becoming the main production process of industrial mass production equipment, undertake the processing of these products in the industry 60%-90% production. In recent years, the high speed milling has broken through the limitation of the traditional milling, which is difficult to process the material with high hardness, high strength and high toughness. But the EDM has high machining accuracy and surface quality, machining range, especially in the complex and precise, thin-walled, narrow, mold processing high hard materials in the advantage of high speed milling cannot be compared, so the electric discharge machining will be the main means of mould cavity machining. The graphite electrode (compared with copper) electrode consumption, discharge machining speed, good machining performance, light weight, small thermal expansion coefficient and other advantages.Compared with copper, graphite electrode has the advantages of less consumption, high discharge rate, light weight and low thermal expansion coefficient.

　　Speed: Graphite discharge is 2-3 times faster than copper material, not easy to deformation, obvious advantages in the processing of thin electrodes, copper softening point at about 1000 degrees, easily deformed by heat, graphite sublimation temperature is about 3650 degrees, compared with graphite material thermal expansion coefficient of copper is only 1/30;

　　Light weight: the density of the graphite is only 1/5 of the copper, large electrode discharge processing, can effectively reduce the burden of machine tools (EDM), more suitable for large mold applications;

　　The loss is small: due to the C atom in the spark oil, in the process of discharge, high temperature causes the C atoms in the spark oil to be decomposed, and the protective film is formed on the surface of the graphite electrode

　　Low cost: due to rising copper prices in recent years, today, the price of copper than the isotropic graphite graphite products are lower; the same volume and the price is lower than copper in thirty percent to sixty, the price is relatively stable, short-term price fluctuations are relatively small.

　　Graphite is a covalent semiconductor and metal intermediate half of the metal, inherently good conductivity, thermal conductivity, and most of the molten metal does not react, high temperature state is not deformed (up to 27.. C) and with the temperature increases the electrical conductivity and thermal conductivity, strength is significantly increased (mechanical strength at 1800 C is two times at room temperature), low thermal expansion coefficient than metal, as the ideal material can be widely used in powder sintering industry. The use of graphite mold powder sintering industry began in the early 70s, accompanied by geological exploration, coal exploration and mining, oil exploration and drilling, highway cutting, especially the rapid development of granite and marble mining and cutting industry, demand a substantial amount of diamond alloy material and hard alloy materials increased demand for graphite sintered die with the graphite sintered die matched with the increases. This situation has started since the end of 70s, preliminary statistics, annual domestic need 9000000 sets of graphite mold, the annual amount of 2500 tons. At the same time as a branch of the graphite material, its specifications and materials are gradually standardized and the trend of the series

　　With the exploitation of marble, granite marble cutting, the need for the cutting of the highway and so on. So in the end of 70s there was a square of processing and growth of graphite mold, processing different types of saw blades, that is divided into. 350,. In 400, 450, 600, 1200, in 1400, 1600, 1800 specifications, with the corresponding specification requires alloy, graphite sintered die and different types. On the shape of the graphite sintering mold can be divided into single groove double groove and combination of molds and so on.

　　The purity of the sintered graphite is not as strict as that of the high purity graphite. In simple terms, the material removal characteristics of graphite should have, as their body heat, we must also have some resistance to pressure in heating condition, so it must have certain mechanical strength.

　　Mold in the home appliances, automotive, electrical, aerospace and other industrial areas has increasingly become the main process of industrial production, the main process equipment, and bear the 60%-90% of these industries in the production of parts and components of the processing. In recent years, high speed milling has broken through the limitation of traditional milling hard, high strength and high toughness die materials. But electric discharge machining with high machining accuracy and surface quality, wide processing range, especially in high speed milling can match in the advantage of joints, high hard materials of the mould cavity machining of complex and precise, thin-walled, narrow, so in electrical discharge machining (EDM) will still be the main means of the mold cavity processing. Because the graphite electrode (compared with copper) electrode consumption less, electrical discharge machining speed, good machining performance, light weight, heat expansion coefficient and other advantages, and gradually replace the copper electrode to become the mainstream of the EDM electrode. Compared with copper, graphite electrode has the advantages of less consumption, high discharge speed, light weight and small thermal expansion coefficient. Therefore, it is the main. In contrast, graphite electrode material has the following advantages:

　　1. Fast: Graphite discharge faster than copper 2-3 times, the material is not easy to deform, in the processing of thin reinforced electrode have obvious advantages, copper softening point in 1000, easily due to thermal deformation and graphite sublimation temperature is about 36.5 degrees, compared with, graphite material thermal expansion system only a few copper 1 / 30.

　　2 Light weight: the density of graphite is only copper 1/5, large electrode discharge machining, can effectively reduce the burden of machine tool (EDM), more suitable for large-scale mold application;

　　3 Little loss: because the spark oil contains C atoms, in the discharge machining, high temperature leads to the C atoms in the spark oil is broken down, and the surface of the graphite electrode to form a protective film, the loss of the graphite electrode;

　　4 No burr: copper electrode in the end of the process, it is necessary to manually remove the burr, and graphite processing without burr, which not only saves a lot of cost and manpower, but also easier to achieve automated production;

　　5 Easy polishing: because the cutting resistance of graphite copper is only 1/5, more easily by hand grinding and polishing operation;

　　6. Low cost: as a result of rising copper prices in recent years, now, the price of the isotropic graphite is lower than that of copper; under the same volume of graphite products price than copper low 30 to 60 percent, relatively stable prices, short-term price fluctuations relatively speaking, is relatively small.

　　In recent years, with the development of mold industry, the graphite mold continue to impact the traditional mold market, the graphite itself has the characteristics which can not be replaced by other metal materials, the graphite has been used as the preferred material of mold manufacturing. In the practical application of graphite mold, the oxidation resistance of graphite mold is the focus of the industry. In fact, to do a good job of graphite mold impregnation is the main means to solve the general oxidation resistance, then how to impregnate the graphite mold in the actual operation ?

　　First, paying attention to the material of graphite mold impregnation vessel. The impregnation vessel can select suitable materials for production according to the actual conditions of the plant , but we must pay attention to the material's resistance to acid corrosion resistance, sealing, and hardness, it’s best to use the impregnation vessel which be used in the first application.

　　Second, selecting the appropriate size of graphite mold impregnation vessel, we select the impregnation vessel according to the size of the graphite mold , then we pour antioxidant liquid into the vessel, it should cover the graphite mold of 10cm.

　　Third, the dipping time, at normal room temperature, the general graphite mold soak in the immersion liquid for half an hour or so. the method should be carried out in the special equipment under the reducing pressure situation if we want to further improve the oxidation resistance of graphite mold.

　　Fourth, natural drying , the impregnated graphite mold under good ventilation conditions for natural dry for 3 to 2 days.

　　The graphite mold has a unique advantage in oxidation resistance after impregnated , we will be able to make a good impregnated graphite mold products by fcousing on these four points.

　　We,Beijing Great Wall Co.,Ltd. can provide all kinds of graphite molds for different applications , please don't feel hesitate to contact us in any time , we will have the honour to give you our good products and service.