Numerical Simulation And Experimental Research For The Induction Heating Process Of Steel Bar Production Line

With the increasing cost of energy resources, raw materials and labors, as well as more and more competitive market, putting forward green manufacturing techniques, improving production efficiency and power conversion efficiency, reducing energy cost have attracted wide attentions and become the major concern of society and the enterprises. The induction heating technique has the unique traits of high efficieny, low energy consumption, no pollution and so on, hereby was used widely in the production of high strength prestressed steel bar. Currently, there are over300sets of induction heating production lines for high intensity prestressed steel bars, the induction heating unit of which are not only the key process flow, but also the high cost and high energy consumming compoents. However, most of the induction heating systems are not broken away from the extensive design and running. The main manifestations are:1) The design of the induction heating system inside china is mainly based on the equivalent circuit model, experiences and the following amendments. The simulation model is too much simplified, and is only suitable for a rough evaluation of the macroscopic electricity parameters, such as power supply, impedance, power factor and so on, and is possible for an accurate analysis of the eddy current, magnetic field, temperature field etc. According to the old design, the hardening component of the induction heating system is usually composed by three heating furnaces. The parameters such as the energy cost, production efficiency and floor space are far behind of the imported production lines.2) Due to the introduction of a lot of empirical correction factors, there is a huge error between the calculated and the practical values. Before the real production of the induction heating system, a lot of experimental test is needed, followed with human and material resources wasting.Based on above issues, this work firstly selected a suitable numerical analysis method suitable for the induction heating process, according to Maxwell Equations and heat transfer differential equations, then succeeded in establishing an electromagnetic-thermal coupling field mathematical model for the induction heating process of high intensity prestressed steel bars. The established model included not only the influence of temperature on materials property, but also the influence of magnetic field intensity on magnetic permeability during the heating process. Contemporary, the study also sets up a platform for exploring the induction heating process and obtaining the related measurements, with which the variation curves of surface temperature, heating frequency, and heating power were achieved. The comparision between the experimental results and the calculated values shows perfect concidence, thus verifying the reliability and accuracy of the selected physical property model.By adopting a non-linear ferromagnetic materials physical property model and a finimite element analysis method, this work secondly constructed one dimensional axis-symmetric model for induction heating process of production lines for high strength prestressed steel bars, and then carried out a numerical analysis of the current induction heating lines. Accordingly, the main technological parameters and mechanism influencing heating efficiency and temperature uniformity were proposed. The analysis results show that the current design with three hardening furnaces exists defect not to be overlooked, and improper techonogical parameters, such as example heating frequency, which usually result in low heating efficiency and high cost. Hence, a new system with two heating furnaces is brought out to optimize the hardening process of the induction system, and the optimized technological parameters were provided. And verification was made with the proposed physical property model. The result reveals that the new design with two furnaces is quite satisfactory for the hardening stage of the induction heating process.Finally, a two-dimensional axis-symmetrical geometric model of the induction heating production line was established. The influnce of the structutral configuration of the heating coil, heating temperature, heating frequency, and electromagnetic intensity on the electrical parameters of induction heating coil and steel rod system were analyzed. According to practical production, the structural parameters of the heating coils for the two hardening furnaces are designed. The electrical parameters for the induction heating system were calculated based on circuit analysis. The result shows that there is a perfect match between the running parameters of the power sources and the designed technological and structural parameters for the induction heating furnaces, namely, the current design can satisfy the needs of high efficency and high stabilty.On the basis of the above researches, a computer aided design method and flow chart was provided, which guided the optimizaion of a real induction heating system for high strength prestressed steel bars. The enegy cost of the new line is reduced by16%with respect to the tradditional one, arriving the goal of increasing heating efficiency, reducing energy consumption, lowering production cost, and achiving a better social benefits and economic benefits.