On the rate of descent of powder in a vibrating tube

Abstract

The flow rate of powder in an open vertical capillary subject to transverse acoustic vibration is predicted using an explicit equation by considering the intermittent arrest and stasis of particles subject to acceleration in a field. The analysis rests solely on physical quantities that are easily measured by experiment. The calculation is supported by measured flow rate and by direct observation using high speed photography. Increasing the horizontal component of acceleration of a particle should not influence rate of descent but the overall time of flight is increased both by re-initiation of descent after collision at the wall and by fixed stationary periods on each cycle. Since flow stops when acoustic vibration stops, the vibrating tube is a valve that provides computer-controlled powder flow metering, mixing and dispensing. The valve is capable of adjusting the flow rate with a ratio of minimum to maximum flow rate of 0.1. It is being used to make three-dimensional functional gradients by solid freeforming operations, notably selective laser sintering.

Acknowledgements

The authors are grateful to the Engineering and Physical Sciences Research Council for supporting this work under Grant No. GR/ N22571 and to Adrian Walker of the Rutherford Appleton Laboratory for help with the EPSRC high-speed camera.