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The Ultrasonic FAQ
Just starting out with ultrasonic cleaning? Read this first.
What is cavitation?
"Cavitation" is the rapid formation and collapse of millions of tiny bubbles (or cavities) in a liquid.
Cavitation is produced by the alternating high and low pressure waves generated by high frequency
(ultrasonic) sound. During the low pressure phase, these bubbles grow from microscopic size until,
during the high pressure phase, they are compressed and implode.
What is "degassing' and why should I do it?
"Degassing" is the initial removal of gases present in the solution. Useful cavitation occurs after gasses
have been removed from the cleaning solution, leaving a vacuum in the formed bubble. When the high
pressure wave hits the bubble wall, the bubble collapses; it is the energy released by this collapse that
will assist a detergent in breaking the bonds between parts and their soils.
How do I get the best ultrasonic cleaning?
There are many considerations important to ultrasonic cleaning. Optimizing these variables will produce
the best cleaning. The most important decisions to be made are choosing the proper cleaning solution,
cleaning at the right temperature for the correct amount of time, and choosing the right size and type of
Can ultrasonic cleaning damage my parts?
With certain cautions, ultrasonic cleaning is considered safe for most parts. While the effects of
thousands of implosions per second is very powerful, the cleaning process is safe since the energy is
localized at the microscopic level. The most important cautionary consideration is the choice of cleaning
solution. Potentially adverse effects of the detergent on the material being cleaned will be enhanced by
the ultrasonics. Ultrasonic cleaning is not recommended for the following gemstones: opal, pearl,
tanzanite, malachite, turquoise, lapis and coral.
What is "direct" and "indirect" cleaning?
Direct cleaning occurs when the parts are cleaned in a cleaning solution which fills the cleaner, usually
inside a perforated tray or mesh basket. The limitation of direct cleaning is that a solution must be
chosen that will not damage the ultrasonic cleaner. Indirect cleaning involves placing the parts to be
cleaned in an inner non-perforated tray or beaker that often contains a solution that the user may not
want directly filling the ultrasonic tank. When choosing indirect cleaning, make sure that the water level
inside the tank itself is maintained to the fill line (about 1" from the tank top) at all times.
Why is a special solution required for cleaning?
Soils adhere to the parts... if they didn't, the soil would just fall off the parts! The purpose of the solution
is to break the bonds between parts and their soils. Water alone has no cleaning properties. The
primary purpose of the ultrasonic activity (cavitation) is to assist the solution in doing its job. An
ultrasonic cleaning solution contains various ingredients designed to optimize the ultrasonic cleaning
process. For example, increased cavitation levels result from reduced fluid surface tension. An
ultrasonic solution will contain a good wetting agent or surfactant.
What cleaning solution should I use?
Modern ultrasonic cleaning solutions are compounded from a variety of detergents, wetting agents and
other reactive components. A large variety of excellent formulations are available, designed for specific
applications. Proper selection is crucial for acceptable cleaning activity and to preclude undesirable
reactivity with the part being cleaned. We can help you to identify either the optimal 'stock' cleaning
formula, or likely candidates to test and evaluate.
What cleaning solution shouldn't I use?
Flammables or solutions with low flash points should never be used. The energy released by cavitation
is converted to heat and kinetic energy, generating high temperature gradients in the solution, and can
create hazardous conditions with flammable liquids. Acids, bleach and bleach by-products should
generally be avoided, but may be used with indirect cleaning in a proper indirect cleaning container,
such as a glass beaker, and appropriate care. Acid and bleach will damage stainless steel tanks,
and/or create hazardous conditions.
When should solutions be changed?
Cleaning solutions should be replenished when a noticeable decrease in cleaning action occurs, or
when the solution is visibly dirty or spent. A fresh batch of solution at each cleaning session is usually
Why must I keep solution at the tank's level indicator?
The solution level should always be maintained at the level indicator in the tank, with trays or beakers
installed. The ultrasonic cleaning system is a 'tuned' system. Improper solution levels will change the
characteristics of the environment, can affect the system frequency, decrease effectiveness, and
potentially damage the cleaner. Maintaining the proper solution level provides optimum circulation of
solution around parts, and protects heaters and transducers from overheating or stress.
What is the length of cleaning time?
Cleaning time will vary, depending on such things as soil, solution, temperature and the degree of
cleanliness desired. Highly visible removal of soils should start almost immediately after the ultrasonic
cleaning action begins. Cleaning time adjustment is the easiest (and most often misapplied) factor
used to compensate for process variables. Although new application cycle duration can be
approximated by an experienced operator, it usually must be validated by actual use with the chosen
solution and the actual soiled parts.
What is the purpose of the unit heater?
The primary purpose of the unit heater is to maintain a solution temperature between cleaning cycles.
The tremendous energy released by cavitation will generate the heat for cleaning.
How do I know if the unit is cavitating properly?
Most poor cleaning usually results from improper control of one or more process variable(s); such as
choosing the wrong detergent solution, insufficient heat, or not allowing enough time for the particular
soil to be removed. If you suspect that your ultrasonic cleaner is not cavitating properly, there are two
simple tests you can perform: the "glass slide" test and the "foil" test.
How do I perform the "glass slide" test?
Wet the frosted portion of a glass slide with tap water and draw an "X" with a No. 2 pencil from corner to
corner of the frosted area. Making sure that the tank is filled to the fill line, immerse the frosted end of the
slide into fresh cleaning solution. Turn on the ultrasonics. The lead "X" will begin to be removed almost
immediately, and all lead should be removed within ten seconds.
How do I perform the "foil" test?
Cut three small pieces of aluminum foil about 4" x 8" each. Fold each piece over a rod that you will use
to suspend the foil in the tank. A clothes hanger works well. Your cleaner should be filled with an
ultrasonic cleaning solution, degassed, and brought up to normal operating temperature. Suspend the
first "square" in the center of the tank and the other two a couple of inches from each end of the tank.
Make sure that the tank is filled to the fill line, and turn on the ultrasonics for about ten minutes. Remove
the foil and inspect: All three pieces of aluminum foil should be perforated and wrinkled to about the
Why must trays or beakers be used?
Items being cleaned should never be placed directly on the tank bottom. Transducers (which produce
the ultrasound) are bonded to the bottom of the tank. Items resting directly on the tank bottom can
damage the transducers and/or reduce cavitation. Additionally, a tray or beaker will position the item
within the optimal cleaning zone of the tank. The tray or beaker will also hold the load together and allow
for easy, no-touch removal, draining and transport of the items to the next step in the cleaning process.
What is the optimum cleaning temperature?
Heat usually enhances and speeds up the cleaning process, and most detergent solutions are
designed to work best at an elevated temperature. The best way to find the optimum temperature, which
will give you the fastest, cleanest and safest results, is to run tests. Usually, the best results are within
the 50C to 65C range.
Is rinsing required after cleaning cycles?
Rinsing is recommended to remove any chemical residue, which could be harmful to the part. Parts can
be rinsed right in your ultrasonic cleaner, using a clean water bath, or in a separate tub containing tap,
distilled or deionized water.
Why shouldn't I leave my cleaner on constantly?
Low solution levels can seriously damage your cleaner. Running your unit continuously runs the strong
risk of lowered levels as the solution evaporates, especially when heated. Getting into the habit of
shutting off the ultrasonics when not in use, and monitoring the solution level when in use, will yield
many years of trouble free service from your ultrasonic cleaner.
Ultrasonic FAQ courtesy of Howard Stromberg - Thanks Howie!