| Electroslag Remelting (ESR) technology is a main method of special metallurgy. ESR ingot has high pure, structure dense and favorable mechanical character and becomes high-grade steel and special steel. It was extensive used in aviation, astronavigation, war industry and energy industry. With the development of modern industry, ESR ingots with larger tonnage and higher quality are badly in need, and large ESR furnace of 100-t level becomes the research emphasis.This paper roots in the China 11th Five-Year National Sponsored Significant Research Project (2009ZX04006-032), undertook by Northeastern University and China First Heavy Industries. Methods of optimal design and remelting speed control of ESR furnace were studied in this paper based on a 120t ESR furnace.According to the contracted technical indexes and product indexes, the research objectives and main technical parameters were specified based on studies of ESR furnace development all over the world. Then the furnace mechanics, full-hydraulic transmission system and constant remelting speed control method were proposed, optimal design and control researched were conducted. Finally, experiment researches were carried out. The follo wings are the main contents and originality innovation results of this paper.The first, based on the design philosophy of energy conservation, high efficiency and high automation, the three-phase double electrode series ESR furnace’s main related research points include mechanisms, full-hydraulic transmission system and computer control system were studied. The furnace mechanisms, including the electrode feeding mechanism, the cross-arm, the split-pillar and so on, were designed. The electrode feeding hydraulic proportional control system was designed, and the full-hydraulic transmission system with three-degree freedom was fulfilled, which enhances the system stiffness and frequency response ability. And the hydraulic system owns excellent energy-saving efficiency. Based on the surplus-ingot length detection method, the electrode auto-replace system was proposed.The second, the ESR technical parameters was designed. The condition parameters, basic control parameters and the aim control parameters were researched, based on the design principle of high product quality, system stability, technical and economy rationality and craft unity. The parameters can adjust automatically according to the real-time working condition.The third, the furnace solid model was established, the finite element analysis and kinematic studies were made. Firstly, the three-dimension solid model of the 120t ESR furnace was established, and provided research basis for FEM analysis and kinematic studies. Then the optimal design of the mechanisms and parts were made, the dynamic process of motion mechanisms were studied under load condition. It was found that, the spring stiffness and system damp have important influence on the cross-arm’s clamping process, and the split-pillar’s oscillation and impact problems can be solved by applying braking torque.The fourth, to achieve high precision speed control of the electrode feeding system, the 120t furnace’s electro-hydraulic proportional system was researched. The system’s DSHplus model was established, and the system parameters were studied and simulated, and thence optimization design was made. The mathematic model of the speed control system was established, and the system’s stability and dynamic characters were studied with MATLAB/Simulink simulator. The system model was corrected by the PID controller designed. It shows that, the corrected control system has the properties of quick response and no overshoot. The system control effect satisfied the need of constant remelting speed control system.The fifth, the electroslag remelting process mathematical model was established based on heat transfer theory and heat balance theory, and then the double-input double-output multi-loop remelting speed control system model was established. The control model was linearized, the system stability and coupling properties were studied. By analyzing the parameters’time-varying characteristics, the fuzzy self-tuning PID controller was designed based on the Smith prodictive control method; the fuzzy rules generator were designed; and the system response simulations were made. It was found that, the control system designed had great response property and fine robustness. The simulation results conforms the manufacturing process.The sixth, the research results were applied to the 120t ESR furnace produced by China First Heavy Industries, and experiments were carried out in the 120t furnace workshop.The experimental ingot was produced, related experimental curves were achieved, anatomy research was made. In the production process, the 120t ESR furnace works stably and controlled, the remelting speed remains stable. The experimental curves showed that, the remelting speed control system designed was correct and effective. It also verified that it’s beneficial to allow more electrodes join the ESR process. The experiment ingot and its dissection results show that, the ingot has excellent surface quality and dense organization. The experimental results verified the research contents studied in this paper. Compared with overseas congeneric products, the 120t ESR furnace researched in this paper enhances production efficiency by 33%,reduces average power consumption by 17%, and leads cost reduction by 67%. The comprehensive economic and technical indicators are better than overseas productions. |
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