Optimizing Your Ultrasonic
How an Ultrasonic Cleaner Works
Factors Affecting the Efficiency of Ultrasonic Cleaners
How to Get Optimal Performance fom Your Ultrasonic Cleaner
Cole-Parmer has been a leading global source of laboratory and
industrial fluid handling products, instrumentation, equipment, and supplies. We
are proven experts in the fields of temperature measurement and control,
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Optimizing Your Ultrasonic Cleaner
cleaners have been workhorses in both laboratories and industry for decades.
This acceptance is based on their ability to remove soils from inaccessible
areas quickly, completely, and consistently without reliance on operator
technique. Tabletop cleaners offer a number of features which allow the operator
to optimize their performance.
How an Ultrasonic Cleaner Works
Ultrasound is sound transmitted at frequencies beyond the range of human
hearing. To understand how ultrasound can perform cleaning, it helps to
understand the underlying principles and how they are applied in cleaning. High
frequency energy is generated by an electrical power supply and applied to heavy
duty, industrial piezoelectric transducers. These transducers convert this
electrical energy to high frequency mechanical energy vibrating at a rate of
40,000 times per second, producing alternating high and low pressure waves
within the cleaning liquid. The liquid is compressed during the high pressure
phase of the wave cycle, then pulled apart during the low pressure phase. As the
pressure in the liquid is reduced during the low pressure phase, cavities grow
from microscopic nuclei to a maximum critical diameter, as shown in the diagram
below. During the subsequent high-pressure phase, these cavities are compressed
and implode. The released energy is powerful, but safe for parts because it is
localized on a microscopic scale. This process is called "cavitation."
Factors Affecting the Efficiency of Ultrasonic
There are many factors affecting the strength of cavitation including
temperature, surface tension, viscosity, and density of the liquid. When
selecting an ultrasonic benchtop cleaner, it is important that it permit as much
control as possible of these factors. If temperature and time can be controlled,
then cleaning consistency can be improved. For example, a microprocessor- based
digital thermostat allows selection and constant digital display of the solution
temperature at the optimum point. The availability of heat can also increases
the chemical activity of cleaning solutions, permitting safer concentrations.
Many solutions operate best at temperatures between 120-150° F. Adding a wetting
agent or surfactant to the bath can reduce surface tension of the liquid.
Reduced surface tension will increase cavitation strength. Higher viscosity
liquids tend not to cavitate well due to their inability to create and collapse
cavities quickly. Higher density liquids create intense cavitation with a
greater implosive force.
Application of these principles can result in faster more effective cleaning.
How to Get Optimal Performance fom Your Ultrasonic
- Never place parts or receptacles directly on the bottom of the unit. It can
cause the unit to fail because the parts will reflect the ultrasonic energy back
into the transducer(s). Always allow at least one inch between the tank bottom
and the beaker or receptacle for adequate cavitation. Keep solution within one
inch of the top of the unit when the beaker or tray is in place.
- If using a tray or basket to lower the parts into the solution, it is better
to use a holder that is of open construction, either an open mesh basket or an
insert tray, that is adequately perforated for drainage. This also permits free
access of the sound waves to the parts.
- Renew cleaning solution often to increase ultrasonic cleaning activity.
Solutions, as with most chemicals, become “spent” over time. Solutions can
become contaminated with suspended soil particles, which can settle to the tank
bottom and inhibit ultrasonic activity.
- Wait 5 to 10 minutes after activating the equipment for fresh solution to
degas. This need not be repeated with subsequent use, as degassing is required
only after the bath is freshly filled.
- Never use solvents in a small benchtop cleaner. It is neither safe nor
environmentally responsible. Solvents vaporize quickly and can collect under the
unit where ignition is possible from electrical components. Mineral acids and
bleach can also damage the unit.
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