The Key Technology Of Large Scale Casting Based On Electroslag Remelt

In recent years, equipment manufacturing industry of China has achieved to a higher level. One of its technology tendency is the extreme manufacturing. And the development of large scale is one of its directions. For the equipments become large-scale, complex, the power, petrochemical and metallurgical industries has put forward higher requirement on large-scale casts forging profession. It's a crucial period for industrialization of China in the next 10-15 years, the power, petrochemical, metallurgy, shipbuilding and other industries will continue to develop rapidly, and there are unprecedented demand for large casting and forging. However, in our country, the lack of autonomous technology and shortage of production capacity is serious, and the international demand is significant larger than supply. For the high prices, long delivery cycle, and the critical time, foreign to our technological blockade, and export restrictions when depend on foreign supply. Developing our own technology in high-quality casting and forging has great significance.Because of the characteristics of large scale casting and forging products, requiring a large steel ingot must contain less quality of impurity elements, gas and inclusion content is low; chemical composition is uniformity, which means segregation is small. In fact, the greater the ingot is, the more difficult to achieve these requirements, and there also will be more defects.Electroslag remelting (ESR) process has low equipment requirements, and also has the following advantages:metal pure, dense, homogeneous, smooth surface, with excellent performance, process stability and reproducibility is high, and production is flexibility, also can produce a variety of spindle types. ESR has two important features:the continuity and additivity. Large scale casting of ESR can be produced continously by replacing the consumable electrode, remelt simultaneously via multiple devices. These characteristics makes the ESR process to play an important role in the production of large castings and forgings!However, expand the ESR system simply to product large scal castings, some problems will be faced, such as lower electrical efficiency and lower slag's stability after long working hours, weaker control ability for progressive solidification after the mold size increased, center shrinkage, porosity, fluctuations in process parameters caused by replacement of electrode, etc. This will lead to deterioration of the casting quality and stability. So it is necessary to study the production of large castings using ESR process.Based on above purposes, two new techniques of the production of large scale ingot based on ESR process were proposed in this paper, and a universal automatic control system for the pumping ESR ingot casting equipment was designed, the details are as follows:(1) studied and designed a large scale ingot production program, in which ESR composite technology was applied. And using digital simulation and experimental verification to analyze the feasibility of this program. The numerical simulation results show that, during the ESR process, at the end of the consumable electrode will produce a high temperature area with high current density, which has the capacity of speeding up the melting of the core ingot. That will benefit the core ingot and molten liquid metal compound, to create the conditions for the production of large ingots. Increasing the melting current, voltage, the depth of electrode insertion in the slag, or reducing the distance of electrode-ingot will benefit to the compound of core ingot and molten metal fluid, but in actual production, the feasibility and operation of the device tolerance has to be taken into account.(2) studied and designed a large scale ingot production program using ESR cast. The program using lined electric slag furnace to for the metal melting and purification, obtaining pure liquid metal with higher power factor. This program reached a significant energy-saving effect. Under the control of the slide gate, the liquid metal for large ingot casting stored in the middle of the bag to keep heat. In order to solve the shrinkage in the casting process and osteoporosis and other issues, high-pressure gas and vibration system will be applied in order to makes the appropriate crystallization of castings to the favorable direction.(3) for the common type pumping ESR ingot casting equipment, a universal automatic control system was designed for the control of whole pumping spindle process of, parameter records and quality monitoring and control. In the system, PLC was used as actuators, industrial computer was used as host computer for the parameters setting and ESR remelting process parameters recording, monitoring, and printing. The automatic control system solving the electrode feeding automatically, the detection of liquid metal level and its stability, and the cast ingot's drawing out automatically. This control system can meet the completely automatic control of whole process of a large ingot remelting, the program is important to the stability of the casting quality, increasing productivity, reducing labor intensity, and it also can be used to achieve business's transformation and slag upgrade.