Large slewing bearings are employed in wind turbines and other energy industry applications where they are subjected to harsh working conditions. In order to bear heavy dynamic loads, slewing ring tracks can be surface hardened by induction heating with a seamless process which allows for a uniform heat treatment without soft zones. In comparison with the traditional furnace carburizing, seamless induction hardening is faster, consumes less energy, and has been developed to achieve the same results utilizing medium carbon steel. The presence of a pre-heating coil, with an independent power source, allows for the adjustment of the heat input rate in order to tune the heating process according to the steel characteristics. The pre-heating operation allows for case depths up to 10 mm to be reached without a reduction in scanning speed or productivity. A mechanical tracking system adjusts the coils to compensate for ring deformation and thus assure a uniform heating pattern. Surface hardness tests and metallography have been performed in different process stages to verify the process consistency. A fine grain microstructure in the end zone has been obtained thanks to the pre-heating coil, which avoids surface overheating.

The inductors design process is the key point in the development of an induction heating machine to fulfil the customer specifications. Some special hardening profiles can be uniquely achieved using the induction heating technology. Different inductors shapes, flux concentrators, power supply frequencies and cooling media can be used to get the optimal thermal profile for the heat treatment. The possibility to study the design robustness of the process using virtual prototyping is the key to speed up the test-trials loop and to give a tool for a better understanding of the process. In the paper, a case study applied to a real industrial problem is presented. A batch of FEM (finite element method) simulations has been done to find the key parameters in the element positioning tolerances, the effect of the misalignment, and the influences of the part geometrical tolerances. Some additional simulation runs have been made to optimize the inductor shape, to stiffen the system and to achieve a more stable process. The method used is based on FEM taking into account the coupling between the electromagnetic and thermal fields, and the nonlinear behavior of the material properties.