Elimination of foreign bodies from seed mixtures or their calibration for use as seed material, but also the fractional classification of granular materials requires separating surfaces with vibrating motion. The paper presents some aspects regarding the working process of a perforated sheet metal screen with external conical surface having an oscillating (alternative) circular movement on the horizontal. The results of some experimental researches on the movement of the material on the sieve for various kinematic parameters of the sieve (amplitude and frequency of oscillation) are presented. The conical sieve, suspended at the top and bottom at three points, was tested for sieving rapeseed in order to estimate the influence of the oscillation frequency on the separation process. The separation intensity curves were plotted on the sieve generator, and by regression analysis with the normal distribution law the coefficients of the equation and the correlation with the experimental data were determined. The movement of the material on the sieve and its working process, in general, was appreciated by the position of the maximum distribution curve depending on the oscillation frequency of the sieve, considering that the normal distribution law correlates very well the data obtained from experiments.