A Novel Theory on the Arching and Doming in Mass Flow Hoppers

摘要

A research scientist made two simplifying approximations in an original theory. He did neither account for the possibility that an arch or a dome across the outlet may slide along the walls, nor for the fact that the arch or the dome will have to sustain a part of the weight of the powder above it in addition to its own weight. Experimental evidence reveals, however, that the original theory yields a substantial overdesign of the critical outlet width for arching. A modified theory is presented here, taking into account the two factors neglected. Furthermore, the new theory includes simplified, purely analytical expressions for the distribution of active and passive stresses in the powder in the converging hopper section of a silo. The theory results in considerably less overdesign of the critical arching/doming width of the hopper outlet than does the original theory. The overdesign still remaining probably stems from shortcomings in the technique of measuring powder properties in the low stress region. Further improvements on the theoretical side are probably impossible until better measurement techniques are available. An alternative principle of measurement, probably capable of producing reliable data in the region of low stresses, is presented.