At the end of a hot rolling mill a so called power coiler is located, where the finished steel strips are winded round a mandrel to a coil. This mandrel is driven and must be able to change its diameter within certain limits. The aim of this diploma thesis is to identify and optimize the durability of the mandrel and especially of its built-in mechanics. The main loads of the mandrel are the high coiling loads caused by thick strips, the necessary high speeds during coiling thin strips and the thermal loads. The thermal loads are caused by the coil remaining on the mandrel because of a power breakdown and subsequent cooling by water. Since the mandrel loads during coiling cannot be measured on the plant, they have to be determined by using a two dimensional dynamic FEM simulation of the coiling process in Abaqus. In a static FEM analysis, the entire mandrel is modeled as a three dimensional model, whereby the calculated loads of the coiling simulation act as boundary conditions. Based on two more 3D models, both the centrifugal loads caused by high coiling speeds and the thermal stresses are simulated. Because of the size of the models the submodeling technique, which is implemented in Abaqus, is used. This technique is necessary to obtain accurate, detailed stress results in the individual components of the mechanics. The knowledge about critical components and load cases is the basis for the subsequent lifetime calculation. By the use of the lifetime calculation software FEMFAT the safety against fatigue failure and the number of cycles to failure is evaluated for the most highly stressed components. To optimize the durability of the mandrel the part with the lowest number of cycles to failure is modified. The critical area is optimized and the local stresses and the expected lifetime are recalculated. The results of this study show that thermal stresses lead to very different temperature gradients in the mechanics, but the resulting tensions can be classified as uncritical. The other two load cases identify two components, which lie in the fatigue strength range. Through the optimization performed on the component with the lowest number of cycles to failure, both the durability of this part and the entire mandrel mechanics can be increased tenfold.