Vibration of electrodes in operation strongly affects the efficiency of the electric arc furnace (EAF) fed by ac current during the steel smelting process. Therefore, an effective control of the structural dynamics through an active system is a current goal of the "intelligent manufacturing" approach. A vertical position control applied to each electrode allows keeping the arc length almost constant and reduces the effects of some electromechanical actions due to the mutual magnetic induction among the three electric phases. Nevertheless, control action needs for a detailed model of the whole system dynamic behavior. A new method for modeling the equipment behavior and somehow the process was implemented. A key issue was including into the model all the electromechanical coupling effects occurring in this system and suitably linking to the structural dynamics. Modeling activity was performed by resorting to the multibody dynamics and the finiteelement method, while some analytical formulations were used to describe both the electric arc behavior and the control. A preliminary validation on a real plant was performed as far as the huge size of the system allowed and an assessment of the mechanical design of the EAF was completed.

Shredders are used for comminuting the metallic scrap fed to the electric arc furnace and consist of a set of hammers connected to a main ro-tor, whose rotation converts the kinetic energy into a strong impact. Design of the hammer is still based on some daily practice, but often it looks insufficient to predict the effects of wear and the cracks monitored in service. To reduce costs and improve the product quality manufacturers of shredders urgently need for a design tool suitable to predict the hammer dynamic behavior, the damage of material and to locate the stress concentration. Unfortunately no comprehensive design approach was yet proposed in the literature. This paper investigates the behavior of an industrial prototype of shredder to develop such as design tool. A first rotor-dynamic analysis was combined with a numerical investigation, performed through the Multi

Prediction of structural dynamics of the Electric Arc Furnace (EAF) is rather difficult, because of a number of phenomena occurring during the scrap melting process. Three large electrodes, corresponding to each phase of a AC circuit, are lowered by the main mast towards the scrap to activate the melting process, induced by the electric arc. Electric current fed to each electrode produces a strong magnetic field and applies an electromechanical force on the other electrodes. Arc voltage looks irregular upon time, even because of the scrap motion within the vessel and temperature growth. The vertical position of the mast is controlled by an hydraulic actuator. Nevertheless, a heavy vibration of the structures affects the regularity of the melting process. A fully coupled model of the whole system is herein proposed, through a multi-physics approach. A first analytical approach, describing the electric circuit of the whole system, is implemented into a Multi Body Dynamics (MBD) model of the EAF, while a reduced Finite Element Method (FEM) model of the flexible structures is used for a preliminary optimization of the design parameters. Electromechanical forces due to the mutual induction among the electrodes are computed and the dynamic response of the system is investigated. Proposed model allows a first refinement of the EAF design, although a complete experimental validation on the real machine has to be performed, in spite of problems due the extremely difficult accessibility of structures during the melting process.

Pre-forming and fragmentation of the ferrous scrap used into the electric arc furnace for the melting process is a relevant activity for a steelmaking plant. Shredding machines are applied to suitably reduce the size of scrap. A set of hammers is connected to a main rotor. Rotation converts the high kinetic energy of each hammer into a strong impact against the scrap. Metallic parts are crushed and fed into the electric arc furnace. Damage of the hammer material is due to impact, vibration, wear and temperature. In addition fatigue affects its life. An effective prediction of the damage location as well as of its propagation in the hammer is rather difficult. A resident health monitoring system cannot be easily applied. Therefore a preliminary model was built to predict the dynamic behavior of each hammer in rotation and to compute the applied stress, while the impact is occurring. A rotor-dynamic analysis was performed by means of a Multi Body Dynamics and a Finite Element code, respectively. Magnitude, direction and frequency of the dynamic loads were first computed by the Multi Body Dynamics code. Stress exciting the hammer material was then computed by the Finite Element Method. Nonlinearities are crucial for the design operation. Friction among the materials, clearance between the pin and the hammer and the nonlinear behavior of materials are all relevant for the nonlinear dynamic response of the hammer. Numerical results were compared to some preliminary observations performed on an industrial plant. They allowed motivating the occurrence of cracks and wear effects in some critical points of the hammer. Some design criteria were defined and successfully tested to improve the performance of materials.

Vibration of electrodes in Electric Arc Furnace (EAF) fed by AC current for steel melting is usually fairly large. It might be dangerous for the EAF operation and often reduces the efficiency of melting process. Vibration amplitude depends on the vertical position control operated to keep the arc length constant as much as possible and to the electromechanical actions due to the mutual magnetic induction among the three electric phases. Since designer of the EAF system needs a clear correlation between each design parameter and the dynamics observed a first modeling activity was performed. A mechatronic approach was implemented, by including the electromechanical coupling into the structural analysis performed to predict the system dynamics. A Multi Body Dynamics (MBD) code was used in cooperation with the Finite Element Method (FEM). A preliminary experimental validation on a real plant was tentatively performed.