Discharge Velocity of an Ultrafine Powder on （输送速度的超细粉）.pdf

SILO DISCHARGE OF AN ULTRAFINE COHESIVE POWDER BY VIBRATING HOPPERS G. Kache, D. Pötsch, A. Haack and J. Tomas Otto-von-Guericke-University Magdeburg, Mechanical Process Engineering Magdeburg, GERMANY guido.kache@ovgu.de, phone +49 391 6712590, fax +49 391 6711160 Abstract – The production of ultrafine powders requires reliable powder storage and handling equipment. The powder flow in a silo or bunker – normally driven by the force of gravity – is fre- quently stopped by channelling or bridging. As a solution of this serious problem, the gravity flow can be promoted using an additional energy input by mechanical vibrations. The discharge rate can be controlled by pulsating operation of the vibrating hopper. It is possible to predict necessary oper- ating and idle periods (pulsed operation) by calculation of the discharge velocities at the annular gap of a vibrating hopper and at the outlet. To prove the calculation, experiments on the silo scale are carried out. 1. INTRODUCTION The interparticle adhesion forces of very fine powders which can enormously exceed their weight and cause disturbances in powder flow. This powder flow can be stopped by channelling or bridg- ing during discharging from a silo or bunker. Thus, continuous dosing with a constant powder den- sity is not possible. As a solution of this problem, the powder flow can be improved considerably by applying mechanical vibrations as flow promotion. The tests are carried out with sinusoidal oscilla- tions – this type of mechanical vibration is created by an unbalanced motor of a vibration hopper. To characterise these sinusoidal oscillations, the maximum vibration velocity and vibration fre- quency are used. 2. TEST EQUIPMENT The flow characteristics like effective angle of internal frict