High-intensity sound can be used for sonic cleaning to remove powders from surfaces, or for sonic fluidisation to promote the flow of powdered material; both of which can increase efficiency for industry.

Research into the removal of electrostatically deposited powders using high-intensity low-frequency sound has been carried out to experimentally investigate deposition and removal of powders [1] as well as to quantify adhesive and cohesive forces using vibration [2]. An important industrial application is the cleaning of electrostatic precipitator filters in coal-fired power stations. Initial work quantified the sound pressure level and frequency content required to overcome adhesive and cohesive bonding forces formed when powder is electrostatically deposited onto a metal surface. A repeatable method was designed to electrostatically deposit powder layers on to a metal surface. Measurements in a high intensity wave tube capable of generating 155dB at a single frequency without distortion were used to compare the sound pressure level required for removal with predicted levels. Further work aimed to quantify the adhesive and cohesive bonding forces formed when powder is electrostatically deposited on to a metal surface by removing deposited layers using vibration. It is these forces that sound must overcome in order to remove deposited layers. The aim was to establish a link between the layer de-bonding acceleration and de-bonding sound pressure level. Powder layers were electrostatically deposited onto one surface of an aluminium cube. The deposited layers then were removed using a calibrated vibration table in order to estimate powder bonding forces. 

Orthopedic components, such as the acetabular cup in total hip joint replacement, can be fabricated using porous metals, such as titanium, and a number of processes, such as selective laser melting. The issue of how to effectively remove loose powder from the pores (residual powder) of such components has not been addressed in the literature. In this work [3], we investigated the feasibility of two processes, acoustic cleaning using high-intensity sound inside acoustic horns and mechanical vibration, to remove residual titanium powder from selective laser melting-fabricated cylinders. With acoustic cleaning, the amount of residual powder removed was not influenced by either the fundamental frequency of the horn used (75 vs. 230 Hz) or, for a given horn, the number of soundings (between 1 and 20). With mechanical vibration, the amount of residual powder removed was not influenced by the application time (10 vs. 20 s). Acoustic cleaning was found to be more reliable and effective in removal of residual powder than cleaning with mechanical vibration. It is concluded that acoustic cleaning using high-intensity sound has significant potential for use in the final preparation stages of porous metal orthopedic components.

Selected publications

[1] Seiffert G and Gibbs B M (2010) Removal of electrostatically deposited powders using high intensity low frequency sound. Part 1: Experimental deposition and removal. Journal of Low Frequency Noise, Vibration and Active Control vol 29 issue 3 pp 171-187.

[2] Seiffert G and Gibbs B M (2010) Removal of electrostatically deposited powders using high intensity low frequency sound. Part 2: Quantification of adhesive and cohesive forces using vibration. Journal of Low Frequency Noise, Vibration and Active Control vol 29 issue 4 pp 267-279.

[3] Seiffert G, Hopkins C and Sutcliffe C (2017) Comparison of high-intensity sound and mechanical vibration for cleaning porous titanium cylinders fabricated using selective laser melting. Journal of Biomedical Materials Research - Part B Applied Biomaterials vol 105(1) pp 117-123