Numerical simulation and experimental validation of a vibrating screen for the sieving of chamomile (Matricaria chamomilla L.)

Chamomile (Matricaria chamomilla L.) dried flowers contain a large number of interesting biologically active compounds which make it an important medicinal herb. In order to preserve the commodity quality and the biologically active compounds of chamomile, the correct management of the chamomile processing process coming from the field is fundamental. An important phase of the chamomile process is the final sieving of the dried chamomile in which the intact flower heads are separated from the other parts of the flower. In this study a simulation of a vibrating screen machine was carried out in order to find the best kinematical parameters that allow to improve efficiency during the sieving process of chamomile. The study of the movement kinematics provides the acceleration of the vibrating screen depending on its geometric and mechanical characteristics. The frequencies and amplitudes of the vibrations transmitted to the screen were estimated in the main directions, and the optimal parameters were evaluated to guarantee high sieving efficiency and reliable productivity of the machine. To validate the modelling experimental tests were performed by installing three tri-axial accelerometers on the mobile frame of the machine, in order to obtain an accurate measurement on the three reference axes. The comparison of the measured values with the simulated ones demonstrated the suitability of the numerical simulation and its ability to estimate the process performance. Finally, experimental tests demonstrated that by using the optimal sieving frequency a significant reduction of waste was possible, with a consequently increase in the fraction of dried whole and intact flower.