Problems in the production of China steel casting parts

Although China is a large foundry country, it is not yet a powerful foundry country. Compared with industrial developed countries, there is still a large gap in the overall level of quality grade, process level, manufacturing equipment and production environment of steel casting parts in China. It is mainly reflected in:

1. Low level of product design

In terms of casting design, due to the lack of scientific design guidance, low design level and lack of confidence in product performance and casting technology, China pursues absolute safety in product design, the safety factor is too large, and the designed products are thick, large and bulky without considering the production cost. It is difficult for some designers to control deformation based on experience, and the machining allowance is generally 1 ~ 3 times larger than that in foreign countries. It leads to serious energy consumption and raw material consumption of castings, high processing cost, long processing cycle and low production efficiency, which seriously restricts the reduction of casting cost.

2. Backward process level, poor casting quality and low performance

Although the output of China’s steel casting parts ranks first in the world, there is still a big gap in the quality and performance of China’s steel casting parts compared with developed countries, especially high-end steel casting parts. Due to the backward production process, unreasonable casting process design, low level of manufacturing skills and lax production process control, there are macro segregation, coarse grain, shrinkage porosity, inclusions, cracks and other defects in the thick and large section of steel casting parts, low yield and dimensional accuracy of castings and high scrap rate; Unstable casting quality; The development speed of commercial simulation software for predicting the quality of steel casting parts lags behind that of developed countries. Although the existing mature computer simulation software has been applied in some enterprises, the penetration rate is not high. A considerable number of casting enterprises lack professional and technical talents for the development and application of computer simulation software, and the purchased casting simulation software can not play a role. The development and trial production cycle of new steel casting products is long and the trial production cost is high; In terms of quality and performance, due to the backward casting process and unreasonable product material selection, the quality and performance of steel casting parts are not high. About 70% of China’s steel casting parts are still produced by carbon steel with low performance. The output of alloy steel castings is low. The proportion of high-end steel casting parts accounts for only about 25% of the total steel casting parts. The performance of some high-end and key steel casting parts can not meet the special use requirements and still need to be imported from abroad. Foreign developed countries have taken high-performance alloy steel castings as their main products, and the production proportion of high-end steel castings is about 50% higher than that in China, reaching 42% ~ 60%. The casting performance is better than that of domestic similar steel casting parts. This is also one of the reasons that restrict the export of China’s high-end steel casting parts.

3. Low melting level

As we all know, the performance of steel casting parts is closely related to the quality of liquid steel. High quality liquid steel is one of the key factors to obtain high-quality high-performance steel casting parts. Foreign developed countries have generally adopted smelting + out of furnace refining technology and advanced electroslag casting technology to obtain high-quality liquid steel. In addition to the smelting + refining technology adopted by some large enterprises in China, a considerable number of small and medium-sized steel casting enterprises do not have refining equipment. Even if there are refining equipment, the equipment utilization rate is not high, and the traditional steelmaking process is still adopted. The contents of gases such as [H], [O], [n] and harmful elements such as s and P and inclusions in liquid steel are high, which seriously reduces the performance of steel casting parts. As a result, steel casting parts can not meet the use requirements, and some high-end core steel casting parts such as steam turbine cylinder block and main pump in nuclear power equipment still need to be imported from abroad. Therefore, popularizing the application of advanced smelting and refining equipment, improving the level of smelting technology and studying new smelting process are the problems to be solved to improve the quality of molten steel.

4. High energy consumption and raw material consumption

Compared with major industrial countries, the overall level of China’s foundry industry has low product quality, poor economic benefits and more energy and material consumption. The average energy consumption of China’s foundry industry accounts for 25% ~ 30% of the total energy consumption of the machinery industry, the average energy utilization rate is 17%, and the foundry energy consumption is about twice that of developed countries. In China, the energy consumption per ton of qualified steel casting parts is about 800 ~ 1000kg standard coal, while in foreign developed countries, it is 500 ~ 800kg standard coal. According to statistics, the input of materials and energy in the casting production process in China accounts for about 55% ~ 70% of the casting output value, the average weight of casting blank is 10% ~ 20% higher than that in foreign countries, the average process yield of steel casting parts is 55%, and the scrap rate is 5% ~ 15%. The process yield of steel casting parts in developed countries can reach 70%, and the scrap rate is lower than 5%. It can be seen that the utilization rate of materials and energy in the production of steel casting parts in China is low, resulting in serious consumption of materials and energy.

5. Serious environmental pollution and poor working environment

In addition to a few large enterprises with advanced casting technology and basically perfect environmental protection measures, most casting enterprises in China have outdated production equipment, backward technology, excessive consumption of natural resources, weak awareness of environmental protection and serious pollution. Although the government has closed down and professionalized the foundry enterprises with small scale, low technical level and serious pollution, and improved the intensive degree of enterprises, the extensive characteristics of foundry production have not been fundamentally changed. The production site environment of some enterprises is poor, the foundry workshop is filled with pungent smell, high dust and loud noise, especially in the cleaning workshop, the working environment is worse, and the waste is discharged at will; Although some foundry enterprises have installed environmental protection equipment, they rarely use it. According to incomplete statistics, for every 1t of qualified castings produced in China, about 300kg of waste slag, 50kg of dust, 1000 ~ 2000m3 of waste gas and 1.3 ~ 1.5T of waste sand need to be discharged, while the emission of three wastes from 1t of qualified castings produced abroad is less than 1 / 10 of that of China; The investment in environmental protection equipment of Chinese foundry enterprises accounts for about 5% ~ 18% of the equipment investment of the whole foundry, while that of developed countries has reached 20% ~ 30%. In 2016, the output of steel casting parts in China was 5.1 million tons, and the roughly estimated pollutant emission was about 1.53 million tons of waste slag, 255000 tons of dust, 5.1 ~ 10.2 billion cubic meters of waste gas and 6.63 ~ 7.65 million tons of waste sand. In China, about 70% of the casting enterprises that fail to meet the standard in extensive production. It can be seen that the severity of environmental governance in China’s foundry industry.

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