Study on the response of a beam in ultrasonic bath operating at the resonant frequency of the beam and the associated effects on cleaning

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Study on the response of a beam in ultrasonic bath operating at the resonant frequency of the beam and the associated effects on cleaning

 

Author: Fok, Kai-fai
Title: Study on the response of a beam in ultrasonic bath operating at the resonant frequency of the beam and the associated effects on cleaning
Degree: M.Sc.
Year: 1994
Subject: Ultrasonic cleaning
Hong Kong Polytechnic -- Dissertations
Department: Multi-disciplinary Studies
Pages: vi, 110 leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1182947
URI: http://theses.lib.polyu.edu.hk/handle/200/4448
Abstract: Ultrasonic aqueous cleaning has been widely used in local industries. Most of the ultrasonic cleaning tanks available in the market are equipped with ultrasonic transducer operating at fixed frequencies. However, the cleaning result is sometimes unsatisfactory. It is the objective of this dissertation to investigate an alternative method of ultrasonic aqueous cleaning that can be operated effectively and efficiently for certain types of articles. Operating the ultrasonic transducers at the resonant frequencies of the workpieces is considered. It is expected that when the workpiece is set to vibrate at resonant mode (excited by incident ultrasound), the surface pressures at the anti-nodes will be much higher than those at the nodal points. At or near these locations the degree of cleaning would be maximum. Changing the operating frequencies the workpiece could be set to vibrate at different mode orders, the surface cleaning pattern could be changed. By tuning and re-tuning the operating frequencies the whole surface of the workpiece can be cleaned. It is also considered that the vibration of the workpiece also helps to peel off the contaminants on surfaces. The experimental work was divided into two parts. First was the modal testing of beam under water to examine the effect of fluid loading. The second part was the excitation of an aluminium beam under water by ultrasound at resonant frequency of the beam. It was observed that resonant vibration of the beam under test was achieved and acoustic cavitation was found to occur on the anti-nodal points. After test, the beam surfaces were examined under microscope and it was found that strong cavitation zones and weak cavitation zones existed alternatively along the beam surfaces. It can be concluded that this cleaning process do produce a distinct pattern of surface cleaning for certain type of workpiece.

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