Main technical status and development trend of China Railway Freight Car Casting Steel Manufacturing Industry

[ Abstract ] In order to make the quality of cast steel products continue to meet the demand of heavy-duty and fast technology of railway wagons in China, and reach the world's leading level as soon as possible, this paper analyzes the main technical status of domestic railway freight car cast steel manufacturing, and looks forward to the railway wagon casting in China. The development direction of steel manufacturing industry and its main tasks in the near future.

At present, China's railway transportation capacity is tight, which seriously restricts the development of the national economy. For this reason, the Ministry of Railways has put forward heavy and fast dual technical requirements for China's trucks. Most of the key components of heavy-duty and fast trucks are cast steel products (such as bolsters, side frames, couplers, etc.). Therefore, China Railway Freight Car Casting Steel Manufacturing Industry is facing tremendous pressure and test, so it is necessary to cast on China Railway Freight Cars. The main technical status of the steel manufacturing industry is analyzed to find out the gap and improve the level to continuously meet the heavy-duty and fast technical demand of railway trucks in China and the world, so as to revitalize the railway steel-making industry in China.

I. Current status and prospects of modeling technology

Most of China's railway wagon cast steel products are sand-cast, widely used in mass production, using mature and reliable technology. Efficient modeling methods such as high pressure molding, injection molding, static pressure molding, air punching molding and production lines are widely used in the production workshop. At present, most of the sand molding processes used in China's railway freight car cast steel manufacturing industry are: CO2 water glass sand, wet sand, furan resin sand and ester hardened water glass sand.

Since the 1950s, CO2 hardened water glass sand has been widely used in China's railway freight car cast steel manufacturing industry due to its simple process, low price and low pollution level. By the mid-1960s, the water-explosion and water bath processes were successively invented to solve the problem of difficulty in clearing sand with water glass. CO2 hardened water glass sand has been widely used, but steel castings are easy to produce under as-cast and chill conditions. Capillary crack defects, while water pollution problems are also increasingly prominent.

In the late 1990s, users demanded the use of dry falling sand and magnetic particle testing for important steel castings of railway wagons. Most railway freight car cast steel mills have undergone technical transformation, and have begun to adopt furan resin sand, wet sand, organic ester modified water glass sand technology, and have successively built a molding production line. Furan resin sand has high dimensional accuracy, good collapsibility and good reproducibility. However, when solving the crack defects of large thin-walled box steel castings, a lot of additional technological measures are needed, and the cost is relatively high, so it has not been widely promoted. . Due to the lack of high-quality bentonite resources in China and the mastery of sand technology, the wet sand process has not been widely used in the production of large-scale steel castings. At present, the process is used in the production of bolster side frames in a railway freight car casting plant in China. . With the breakthrough of organic ester modified water glass sand modeling materials, sand regeneration problems and casting equipment technology at home and abroad, organic ester modified water glass sand technology has been widely used in railway freight car casting mills in recent years.

In the 1980s, the Japan Foundry Association invented the vacuum conversion carbon dioxide hardened water glass sand process, which is a new method for water glass sand hardening. The English name is Vacuum Replacing Hardening – CO2 Process Vacuum Process, referred to as VHR method. At present, some railway freight car casters in China use it for the production of couplers.

In the early 1970s, a special casting method invented and developed by Japan - vacuum seal modeling (also known as negative pressure modeling or decompression modeling), the English name is Vacuum Process, referred to as V method. China has introduced this technology and equipment since the 1980s. At the same time, the scientific and technical personnel in the domestic foundry industry began to develop the equipment of the V-method modeling process, so that the V-method model was applied in many factories in China. V process has been applied in engineering machinery parts, wear-resistant lining parts, auto parts, valve parts and railway turnouts at home and abroad. At present, this process has been applied to the casting of railway wagon bolsters and side frames. It is understood that some countries in the former Soviet Union have introduced 3 to 4 V-process line elements from German companies since 2004, with low gas generation, which can prevent the occurrence of subcutaneous pore defects in steel castings.

(2) The core sand of the process has secondary hardening characteristics and good high temperature thermoplasticity, which can prevent defects such as hot cracking and shrinkage of the steel casting.

(3) If a gas curing agent (methyl formate) is used, the exhaust gas can be directly discharged into the atmosphere without damage to the operator's body. The strength of the core sand of the process is higher, and the crack tendency is greater than that of the water glass sand.

Compared with the traditional water glass sand process, the new ester hardened water glass sand process can fully exert the bonding efficiency of water glass. Under the condition of obtaining the same bond strength, the water glass can be greatly reduced, and the water is greatly improved. The collapsibility of glass sand and the reusability of old sand. The organic ester self-hardening water glass sand process maintains the advantages of the traditional CO2 hardened water glass sand, that is, the production cost is low, the operation is simple, the cracks and pores of the casting are few defects, and since the production process is similar to the self-hardening resin sand process, it has its own The type (core) sand of the hard resin sand process is easy to mix, has good fluidity, is easy to be compact, the mold (core) is self-hardening and high in strength, and the dimensional accuracy of the produced casting is high. Compared with the self-hardening resin sand process, the process is also environmentally friendly (organic ester is a low toxicity, low viscosity, uniform composition of organic liquid), easy to quantify, easy to use and so on. Since the amount of water glass added is reduced to between 2% and 3%, the sand core has good collapsibility, and the dry sand can be completely dried. However, due to the disadvantage of large hygroscopicity, the produced mold (core) is used. It needs to be dried before.

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