Current development status and trend of China's cast iron foundry industry

It is reported that in the early 1980s, the development of cast iron materials entered a peak period. Subsequently, the world's cast iron production showed a sharp decline. However, cast iron is still the most widely used base material in metal materials, and plays an important role in casting alloy materials. .
Due to the influence of energy, labor price and environmental factors, the output of castings in western industrialized countries will gradually decrease, and instead purchase general castings from developing countries, but at the same time export high value-added and high-tech content to developing countries. High quality castings. At present, the acceleration of the globalization of the world economy has provided opportunities for the development of China's foundry industry. The demand for castings in China and the domestic market has continued to grow. At the same time, cast iron, as a traditional metal material, is facing serious challenges in terms of quality, performance and price. Grasping the structural adjustment and technical transformation of China's cast iron foundry industry; striving to improve the quality grade of castings, improve the level of environmental pollution, and realize the high added value of cast iron materials is to cope with the more fierce market competition in the future and meet the diversified needs of users. Countermeasures.
First, the production level and gap of China's cast iron 1. Casting process materials and accessories China's casting process materials such as raw sand, clay, coal powder, binders and coatings in the varieties, performance, quality and other aspects of the gap between industrial and advanced countries, so that China's casting dimensional accuracy and surface The roughness is one to two grades worse than foreign countries, and the scrap rate caused by surface defects of castings is several times higher than that of foreign countries. Standardization, serialization and commercialization of process materials for foundry are still an urgent problem to be solved.
2. Casting process and casting quality inspection and control China's casting process and casting quality detection and control and industrial advanced countries still have a large gap, mainly reflected in the following aspects:
1 Detection of the casting process.
2 Optimization and control of the casting process.
3 casting quality inspection. The improvement of the above detection and control means is a major content to improve the production level of cast iron casting in China.
3. Casting process equipment For the production of casting, a large number of production lines are widely used in foreign countries; high-pressure molding, injection molding, static pressure molding and air-punching molding; core-making all use shell core and cold and hot core box process. In addition to a large number of semi-automatic and automated assembly lines in the domestic automotive industry, most manufacturers still use relatively backward casting technology.
Second, cast iron smelting technology 1. The cupola technology is the first in the cast iron melting equipment of the cupola furnace. It still bears the smelting task of more than 80% of cast iron parts. After the 1970s, the furnace type and smelting technology that conformed to China's characteristics have gradually improved and matured, forming a unique multi-row small air outlet and two rows of large-pitch cupola series. In terms of operation technology, from the pursuit of low coke consumption to the emphasis on the quality of molten iron, and then to improve the comprehensive indicators of technology, economy, labor and environmental protection, and gradually develop and apply from the charge treatment, repair furnace, oven to the feeding And blast. Operating technology for whole process such as furnace condition control and molten iron inspection. In the short course, we are in the theoretical study of cupola, furnace structure, furnace material, air supply system, heat energy utilization, enhanced bottom combustion, furnace atmosphere adjustment control, iron liquid furnace inspection, smoke elimination and dust removal, non- Coke iron, ingredients and computer optimization control of the smelting process have achieved gratifying results.
The development of the furnace is based on improving performance and productivity, reducing consumption, improving operation and reducing pollution. The performance of the cupola is mainly reflected in the combustion of charcoal, the heating of the charge and the metallurgical process. With the expansion of the production volume of cast iron and the increase in casting productivity and casting quality requirements, the capacity of the cupola is also increasing. The large-capacity cupola smelting condition is more stable, which is technically and economically superior to the small furnace. Therefore, in a large-scale production of a single variety, it is reasonable to replace multiple small furnaces with one large-capacity furnace. In the international arena, the latest developments of cupolas are mainly plasma blast furnaces, non-focus cupolas, and new rotary smelting furnaces. Joining the WTO will present a competitive world casting market in front of us. Therefore, the development of cupola smelting will focus on strengthening management, promoting technological transformation, and improving scale efficiency. The development direction of cupola technology in China mainly has the following aspects:
(1) Take specialized production roads and increase the productivity of cupolas to become large-scale and intelligent. Long-term work direction development.
(2) Specialization and scale of charge supply.
(3) Vigorously develop the supporting technology of the cupola, and at the same time strengthen the control and detection of the cupola.
(4) Development of cupola furnace-electric furnace double smelting technology.
(5) High-temperature high-quality molten iron is the fundamental requirement for cupola melting.
2. The electric furnace technology induction electric furnace has a high temperature of molten iron. The advantages of stable composition, less pollution, and easy adjustment of the composition of molten iron began to spread in some industrialized countries in the early 1960s. In recent years, the rapid development of medium frequency induction melting furnaces has injected new vitality into cast iron production.
The development and application of induction furnaces has brought cast iron production to a new stage. Despite some shortcomings of the power frequency induction furnace, it is smelted in metal. Iron composition adjustment. The heating and holding of molten metal, especially as a double furnace for other melting furnaces, is still in common use. The medium frequency induction furnace is particularly suitable for smelting alloy cast iron, ductile iron and compacted graphite iron. Its rapid development and superiority have made it a new trend in cast iron production.
Third, the production status and trend of cast iron parts The production status and trend of cast iron alloy world iron castings is that the proportion of gray iron castings has dropped significantly, but it still dominates. The output of ductile iron castings continues to grow, and compacted graphite iron and special cast iron have also developed considerably.
The global output of gray cast iron has been decreasing year by year, but the proportion of high-strength cast iron in cast iron is increasing. The experimental research on strengthening high-strength gray cast iron is undoubtedly the development direction of China's gray cast iron.
China's total output of malleable cast iron is among the best in the world, but demand will increase. Therefore, in the future, China's malleable cast iron will have a big development. At present, the main gap between the production of malleable cast iron in China and foreign countries is: few varieties, only black heart malleable cast iron; poor quality; galvanizing process is backward; lack of ideal annealing furnace with low energy consumption, good heat preservation and low pollution.
In the case of reduced cast iron production, the proportion of ductile iron in cast iron parts is still increasing. In western developed countries, some gray iron castings and malleable iron castings are usually replaced by ductile iron castings. The output of ductile iron castings in China is relatively low, and the proportion of cast iron parts is much smaller than that of developed countries. In addition, the gap between the quality and production stability of ductile iron castings in China is also large. The outstanding problem of the production of ductile iron in China is that the material has strong toughness and many defects. The reason is that the sulphur content of the molten iron is too loose before the spheroidization treatment, except for the charge, spheroidization treatment method and spheroidizing agent. Therefore, in order to greatly increase the production of ductile iron in China, it is necessary to vigorously implement supporting technologies that can stably provide high quality spheroidal graphite castings with reliable quality.
At home and abroad, the research on the creeping process and the humectant has reached a very high level, and the variety of osmotic agents developed has reached nearly one hundred. At present, the creeping agents used in production are mainly iron-magnesium alloys for rare earths, rare earth silicon-calcium alloys and rare earth magnesium-titanium alloys. The existing creeping treatment processes at home and abroad mainly include the punching method, the flow method, the pneumatic method and the internal method. Vermicular graphite iron has been used in mass production, and a production line (melted by induction furnace) has been built, and the quality is basically stable.
With the development of modern industry, the demand for materials with special properties is increasing. The development speed of special cast iron (anti-wear, corrosion-resistant and heat-resistant cast iron) in China is slow, and the technical level is far from the foreign countries. In order to meet the needs of national economic development under the new situation, the research of special cast iron will become an important direction for the development of cast iron in China.
2. Development of cast iron alloys (1) High-strength and thin-walled is the development direction of China's gray cast iron. The thinning, lightweight and toughening of cast iron is to meet the requirements of the engineering community for energy conservation and reusability of engineering materials. Adapt to the needs of the “Human Sustainable Development Strategy”. The “thin wall high reinforcement” of castings is becoming a trend in the engineering field, and its technical application will be increasingly mature and rapidly expanded. In the foreseeable future, high-strength thin-walled ductile iron castings of 3 to 5 mm will appear in large numbers in general. In mechanical and electrical products.
Low cost and good casting performance are a major advantage of grey cast iron parts compared to aluminum alloy castings. At present, one of the main factors restricting the growth and development of gray iron castings is lightweighting. The lightweight of cast iron will inject new vitality into the cast iron industry. Therefore, the development of production technology for high-strength thin-walled gray iron castings is the key to the problem.
The production technology of thin-walled castings involves the performance and filling process of cast iron. Precision modeling, machining, patterning, process design and marketing. Many studies and practices have shown that the primary task in developing thin-walled cast iron parts is to develop high carbon equivalents. High-strength gray cast iron and its strengthening process. Casting high-strength, thin-walled and complex internal cavity castings must be addressed by comprehensive measures from materials, processes and equipment. Foreign countries have achieved high levels in the casting of diesel engines, engine block cylinder heads and the inoculation of thin-walled high-strength gray cast iron.
The focus of research on high-strength gray cast iron in China is:
1 Improve the temperature of molten iron, improve the metallurgical quality of cast iron, and adopt the synthetic cast iron smelting process.
2 strengthen the inoculation treatment technology. In particular, it strengthens the research and promotion of castings.
3 Research and promote low-alloying cast iron.
4 Adjust the chemical composition and control the Si/C ratio of the cast iron to obtain high-strength low-stress cast iron. Practice has proved that the combined St/C ratio is between 0.5 and 0.9, and then properly inoculated and alloyed to obtain high-strength gray cast iron with good comprehensive mechanical properties. In addition, the Mn and Si contents are adjusted so that the manganese content is 0.2% to 1.3% higher than the silicon content, and a high-strength low-stress cast iron can be obtained. At present, most of the factories in China do not have instruments for rapidly measuring C and Si content before the furnace, so they cannot grasp the fluctuations and changes of carbon and silicon in time, which makes the quality of castings difficult to stabilize. This is a problem that needs to be solved in the future.
(2) Development of new varieties of nodular cast iron, using new technology 1 Strengthening the development and application of thin-walled large-section as-cast ductile iron technology. To ensure that the strength and cutting properties of the casting are not reduced by the reduction of the wall thickness, the basic way is to improve the mechanical properties of the ductile iron. The most important two aspects are: one is the reduction and inhibition of white-skinned tendency, and the other is the improvement of graphite structure. The rational selection of spheroidizing agents and the addition of rare earth (RE) elements are the key to achieving high strength thin-walled ductile iron casting. The core of this technology is to ensure RE / Sk = 2 ~ 2.5 in the casting (melting) process. The spheroidizing agent is selected from Fe-Si-Mg-RE-Ca materials, and the addition of rare earth elements (Ce, La, Pr) and maintaining a certain ratio with sulfur is the key to the spheroidization technology. The experiment confirmed that when RE/S<2, spheroidization occurred; when RE/S>2.5 and Mg/S>5, white mouth appeared easily, while wp<0.04% and wBi=0.003%-0.007% were strictly controlled.
2 Continue to develop and apply Aobei spheroidal graphite cast iron, which is one of the major achievements in cast iron metallurgy research in recent decades. It is the spheroidal graphite cast iron with the best comprehensive performance so far, especially the high bending. Fatigue properties and good wear resistance have gained wide attention and development applications.
3 Development of austenitic ductile iron. This kind of ductile iron has broad application prospects in many fields such as petroleum, chemical, marine and marine, instrumentation and nuclear engineering, and thus has become a new research focus in the field of ductile iron in recent years.
4 Adopt new spheroidal graphite cast iron production process. In terms of smelting, it is best to use induction furnace or cupola-electric furnace double smelting, especially the cupola furnace--furnace desulfurization--electric furnace insulation process can provide high-quality low-sulfur original iron liquid. In terms of spheroidization, there are currently more than 8 methods at home and abroad, and the GF subcontracting method and the covering method are widely used abroad, and China is also promoting its use. In addition, the development of molten iron filtration purification technology in recent years has also been widely used, and it has become a good measure to improve the quality of nodular cast iron.
(3) Development of gestation technology gestation technology promotes the development of high-strength gray cast iron and makes the production of spheroidal graphite cast iron and vermicular graphite cast iron more perfect. Cast iron that has been inoculated has the characteristics of graphite refinement, uniform organization and small wall thickness sensitivity. In the past; the development of gestation technology often hopes to develop new inoculants, which is undoubtedly necessary. However, in recent years, improvements in gestation methods, especially late birth, have received attention. Therefore, in the future, while developing inoculants, research on inoculation techniques may shift to the development of new methods of inoculation.
(4) Development of alloy cast iron alloying is one of the important means to improve the performance of cast iron. With the development of technology, cast iron alloy or microalloying will play an important role. It is necessary to continuously develop new varieties of alloy cast iron in combination with local resources, and use advanced methods to continuously deepen the understanding of the existing alloy cast iron.
(5) Development of surface strengthening technology for cast iron parts For special applications, it is desirable to have special properties on the surface layer of the casting. The laser strengthening treatment of the surface layer of the cast iron part and the alloying technology of the casting surface can form a metallurgical bonded alloy layer on the surface of the ordinary casting, so that the casting has composite properties. The above technology has been gradually applied to the production of wear parts and has achieved remarkable results.
IV. Future Development Direction After China's accession to the WTO, the opportunities in the cast iron foundry industry outweigh the challenges and have greater growth potential in both domestic and foreign markets.
The penetration and integration of advanced technology into traditional industries is gradually having a greater impact on the field of cast iron casting. The application of artificial intelligence and neural network technology can greatly improve the control system, prediction and quality assurance system in casting production, and will play an important role in improving the operating conditions and reducing costs in the foundry industry.
The future cast iron foundry industry will be developed in several ways:
(1) Taking the machine tool industry, energy industry, petrochemical industry and marine engineering as the main objectives, the basic theoretical research on major technical equipment and casting technology is carried out with the characteristics of heavy, high, large and difficult. The development of numerical simulation, physical simulation and expert systems to make cast iron technology from "experience" to "quantitative".
(2) Taking the automotive industry, aerospace and nuclear energy industries as the main objectives, and carrying out the characteristics of strengthening, toughening, precision, and high efficiency, new materials for cast iron are developed. Research on new processes.
(3) In order to improve product quality and productivity, enhance the competitiveness of China's industrial products in the international market, carry out research on automation of casting process, flexible production unit and system and integrated manufacturing technology.
(4) Encourage the research on the basic theory of cast iron technology application with potential application prospects.
(5) Vigorously develop specialized and modernized enterprises that provide cast iron process materials and accessories.
(6) Develop green intensive casting, increase the intensity of environmental pollution caused by the casting process, and strengthen the regeneration and reuse of casting materials.

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