EVALUATION OF THE RESTRICTED AIR ENTRY ON THE DISCHARGE RATE FROM SILOS

Abstract

Storage and distribution of solid materials, as well as control under powder discharge, has been fundamental to ore transportation and lately, Additive Manufacturing (AM). AM demands fine powders materials to be fed with high accuracy, by hoppers. It is not only the reliability of flow that becomes important but also to have a trace of repeatability of material discharges and flow characteristics. In this perspective, two types of hopper feeders have been utilized the most: screw feeder and scraper feeder. In the present work, the characteristics of a steady granular flow through an orifice in scraper feeders with a flat and conical bottom have been experimentally investigated under the influence of top ventilation. The discharge rate of granular particles of magnesium, alumina, glass beads and crushed glass have been studied as a function of the outlet diameter and the ventilation configuration. Tests were performed three times under the same configuration, which consisted for both apparatuses, a measurement of discharge time and the mass through outlet orifices of 15, 30 and 50 mm, with different vent area percentage. The results have shown that the discharge rate increases with the increasing outlet diameter and top ventilation in the majority of the materials studied. In both hopper geometries, a rise in mass flow rate was generally observed when ventilation was added to the system, even though the difference when doubled the vent area was not significant.