The characteristics of steels during electroplating or induction heating are very complex. Induction heat-treating of steel has become increasingly important as a means of reducing cost and improving the quality of carbon steel components. The use of high frequency (40 to 200kHz) offers many advantages, but tooling and cycle optimization is complex and time consuming. Approximate analytical methods suitable for low-frequency approximations are not sufficient for the low-frequency domain and the fact that important material properties change drastically with temperature makes more exact analysis methods very difficult to implement. Therefore, a powerful computer aided numerical tool (i.e., finite element analysis) is selected to numerically model an induction heating process.
A general-purpose finite element program was employed to simulate and analyze the above problem. The combination of magnetic and thermal routines, within the package, enabled us to complete the task. A coupling method between the two magnetic and thermal routines was also developed and implemented. This was done to incorporate the change in the material properties due to the change in temperature. For the sake of comparison and verification, a high-frequency induction heating experiment was set up and a series of tests was performed.
The finite element results were evaluated and compared with the experimental results. The effect of the time duration size (time step) for coupling between the magnetic and thermal analyses was also studied. Particular attention was given to the coupling procedure after the Curie temperature was reached. The skin effect was studied and demonstrated in the numerical model. A discussion of induced power density profile and transient temperature distribution is also presented. The accuracy and efficiency of the numerical models are demonstrated and appreciated. This tool is therefore proposed to be a powerful alternative prior to the actual induction heating process.
The rolling process of steel sheets changes the strength and properties of the product, so heat treatment is used. High frequency induction heating is a type of heat treatment that uses a high frequency power source to produce rapid heating, allowing the equipment on the production line to be smaller. It also has a multitude of benefits, such as being highly efficient and providing a clean working environment. When the object being heated is a long steel sheet, this process heats it quickly while sending it through a heating coil. For this reason, there are several factors that need to be studied when assigning a heating amount to correspond to the speed at which the sheet passes through the coil. Examples of these are: the arrangement of the heating coil so that it can fulfill the necessary heating amount, and how to adjust the current's frequency and size.
This Application Note presents a simulation of the heating conditions of a sufficiently long steel sheet that passes through a heating coil. The eddy currents produced from the high frequency's varying magnetic fields are uneven on the steel sheet's surface, so its material properties change due to increases in temperature. This is why it is necessary to approximate the amount of heat generated in a numerical analysis based on the finite element method (FEM) in order to handle the detailed phenomena.
This Application Note explains how to create a numerical analysis model when obtaining the optimum coil geometry, current conditions (power supply frequency, current value), and movement speed. It also shows how to evaluate whether the model fulfills the target heating speed by analyzing the elevated temperature process.