The classification step in grinding circuits presents itself as an appropriate starting point for optimization. Although the biggest part of the energy used for grinding is transferred into the circuit through the mill, the air classification in dry grinding circuits crucially contributes to their efficiency. The thesis at hand puts the focus on cross-flow rotating cage separators. To gain a better understanding for the separation process, an extensive parameter study using a pilot scale plant was conducted and the obtained data intensively evaluated and used for the establishment of a performance map depicting the separator efficiency. To be able to conduct the described research activities, substantial modifications of the pilot plant had to be made. To further characterize the pilot plant, values for the theoretical cut-size were calculated and correlated to characteristic values of the particle size distribution of the fine products of the classification process. This was also done for values obtained on industrial sized separators and the results were compared. Additionally simulations using Computational Fluid Dynamics (CFD) were conducted, whereas calculations characterizing the flow field of the pilot plant marked the starting point. Subsequently particle laden flows were simulated and the results compared with results obtained through test work on the pilot plant. As a conclusion to the test work the influence of the feed point on the classification result was tested.