Analysis of pipe vibration in an ultrasonic powder transportation system

Abstract

The transportation of dry fine powders is an emerging technologic task, as in biotechnology, pharmaceutical and coatings industry the particle sizes of processed powders get smaller and smaller. Fine powders are primarily defined by the fact that adhesive and cohesive forces outweigh the weight forces, leading to mostly unwanted agglomeration (clumping) and adhesion to surfaces. Thereby it gets more difficult to use conventional conveyor systems (e.g. pneumatic or vibratory conveyors) for transport. A rather new method for transporting these fine powders is based on ultrasonic vibrations, which are used to reduce friction between powder and substrate. Within this contribution an experimental set-up consisting of a pipe, a solenoid actuator for axial vibration and an annular piezoelectric actuator for the high frequency radial vibration of the pipe is described. Since amplitudes of the radial pipe vibration should be as large as possible to get high effects of friction reduction, the pipe is excited to vibrate in resonance. To determine the optimum excitation frequency and actuator position the vibration modes and resonance frequencies of the pipe are calculated and measured. Results are in good accordance.