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Ultrasonic cleaning is
based on the phenomenon known as cavitation. In an ultrasonic tank,
cavities (or bubbles) are formed by piezoelectric transducers attached to
the bottom or sides of a cleaning tank. The piezoelectric effect
occurs in a certain group of crystalline solid materials, which have no
center of symmetry. When these materials are mechanically stressed,
they produce an electric charge, and when an electric field is applied
across two poles, the dimensions change. By applying high frequency
(20-80Khz) and high voltage, these elements expand and contract rapidly at a
rate proportional to the frequency of the applied voltage. As a result
of the contraction and expansion, the pressure inside the liquid changes
from negative to positive with respect to atmospheric pressure. During
the contraction, the pressure in the liquid is negative, allowing the
cavities inside the liquid to grow in size, subsequently at the next phase
of expansion the pressure in the liquid becomes positive, which causes the
cavities to explode internally. The creation and the implosion of
cavities causes an intense scrubbing action upon a submerged object.
The size of the bubbles are microscopic, and can therefore penetrate the
smallest cracks and holes to loosen the contaminants and remove them. 1. Ultrasonic generator or power supply that converts
electrical energy from the wall (115VAC/60Hz) to high voltage and high
frequency, which is then applied to ultrasonic transducers. 2. Ultrasonic transducers convert high voltage and
frequency to mechanical vibration. 3.
A cleaning tank that receives the mechanical energy and
causes the cleaning media pressure to rise above and bellow the atmospheric
pressure, thereby causing the formation and collapse of bubbles in the
liquid. This process produces an intense scrubbing action that removes
sediments from the submerged parts.
Ultrasonic cleaning equipment ranges from small bench-top
units to larger capacity machines up to several thousand-gallon models.
The smaller units are self-contained with a built-in power supply, and with
the tank, heater and controls all within a single enclosure. The
larger systems require the power supply to be a separate console, and the
very large units may utilize immersible transducers which could then be
mounted on the bottom or the side of the cleaning tank.
Effective application of the ultrasonic cleaning process
requires a number of parameters, such as operating frequency, watts per
gallon of liquid, transducer efficiency, cleaning tank design, and liquid
temperature.
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