| Heavy castings and forgings with huge size and weight and high quality are difficult to manufacture. They are key components of important equipments in many trades, for example, metallurgy, power, petrochemical engineering, transportation, mining, and weapon. Heavy casting and forging industry is the base of equipment manufacturing. It significantly affects the economic lifeline and is also important symbols of the industrial level and comprehensive national power of a country.Nowadays, the heavy equipment trade faces downturns in market and economy. It is necessary to make a change in aspects of product transition, reestablishment of manufacture process, and innovations of technology and management for heavy machine manufacture enterprise. In the production of heavy casting and forging industry, nondestructive prediction of through heating is difficult for different materials and types ingots during forging and heat treatment processes. There is lack of defined criterion to establish the holding time. No prediction of through heating system can be used to connect existing heating equipment. These problems lead to low efficiency and high consumption of energy and time. They are all difficulties in heavy casting and forging industries.In this study, the energy consumption speed was measured and analyzed. A new, convenient, accurate, and nondestructive prediction of through heating for heavy casting and forgings was proposed. A typical criterion of holding process after trough heating of heavy castings and forgings was established. This criterion was examined using meters, additional thermal couple, and numerical simulation. Based on these, an intelligent control system was constructed and then practiced in actual production. The main results obtained are as follows:Based on heat transmission science and physical metallurgy theory, the heating process of heavy castings and forgings are analyzed. The heat radiation process of furnace and energy balance criterion were discussed. The migration model for contour of temperature in heavy castings and forgings was proposed. The dependence of energy balance on workpiece size was given. The relationship between heating method and energy input type as well as energy saving and loss reducing was discussed.The heating process of heavy castings and forgings mainly depends on the temperature gradient between furnace and workpiece as well as the heat conductivity. In different furnace and temperature, the main conductive mechanisms are various. In fact, the heating process satisfies energy conservation law. The heat transfer balance will be achieved after through heating and then the energy input speed is certain. No matter how many workpieces are in the furnace, this energy conservation law is available.Based on analysis of energy consumption speed of furnace, a new, accurate, and nondestructive prediction of through heating for heavy casting and forgings was proposed. The through heating time of a backing roller, cake shape forging, and an L shape axis were obtained. The results were examined using further meters, additional thermal couple, and numerical simulation. The empirical formula between gas consumption speed and heating depth for the holding process of the backing roller at 850°C, 950°C, and 1030°C was established. It is found that energy input speed can be used to predict the moment of heating though. Therefore, the nondestructive prediction of through heating for heavy casting and forgings can attain conveniently, accurately. This method is not affected by the material, shape, size and number workpiece. No further thermal couples were used. All of these are very significant for optimization of hot working process of heavy castings and forgings, energy saving and emission reduction, and cutting the cost and increase efficiency.An intelligent control system was constructed and practiced in the heating process of a backing roller and a nuclear power component. The time, temperature, gas consumption speed were examined and analyzed. The nondestructive prediction of through heating was achieved conveniently and accurately through LED lamp and alarm on the control system. The heat treatment data read from the control system and furnace system are almost the same, especially the peak temperature. During the holding process at 930°C, the through heating period of backing roller is about 23 h. For the nuclear power forging, the time, temperature and gas consumption speed are obtained during the reheating process of forging. The time of peak temperature is also similar. The through heating time is about 7.2 h.In the practice of hot working process of huge flange ingot, low carbon steel ingot, and high-low pressure rotor, the through heating time was predicted using the analysis of variation in total gas consumption. Through examination, it is found that the quality of the flange ingot after holding at 1250°C for 5.7 h, 8.5 h, 17.5 h are excellent. The mechanical properties are better than the standard. The grade of grain size of the forging is in the range of 5.5~7.0. The matrix is tempered bainite. After holding at 1250°C for 7.0 h and 26.3 h, the grain size and mechanical properties of low carbon steel ingot are both qualified. The new preheating process without holding period after through heating is available to manufacture qualified product. Therefore, the total gas consumption of the new preheating process is far less than previous process. This further affirms that the prediction of through heating for heavy casting and forgings and holding time criterion are very suitable for actual industry production.Applying on the new approach to non-destructively forecasting temperatureequalization-time, the one-piece forging manufacturing cost of the 100-ton rolling electric products and annual production costs in heavy machine factory can be saved about 2850 RMB and 160 million RMB, respectively. Furthermore, the single forging efficiency in a single heating number and total forging efficiency of the one-piece forging can be increase by 33% and 17.6%, respectively. |
PDF Full Text Request