In classification one of the methods used to evaluate the effectiveness of classifier’s work is to create the partition curve, which determines the size of the classified particles and characterizes the accuracy of the process. The article presents the results of experiments showing the efficiency of classification in the inertial classifier, designed specifically for the electromagnetic mill. The paper presents the results of tests in order to determine the possibility of controlling the classification by changing the transport air stream flow. In order to verify and assess the classifier work, a series of experiments with different opening level of additional air damper was performed. The results allow thorough assessment of the effectiveness and efficiency of the device and facilitate the optimization of the grinding process by establishing an appropriate control algorithm as well as the air flow in classifier.