What is "degassing", and why should it be done?
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"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?
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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 ultrasonic cleaner.
Can ultrasonic cleaning damage my parts?
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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, emerald, tanzanite, malachite, turquoise, lapis and coral.
What is "direct" and "indirect" cleaning?
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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?
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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?
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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. Crystal Electronics 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?
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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?
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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 not required.
Why must I keep solution at the tank's level indicator?
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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?
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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?
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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?
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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?
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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?
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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 same degree.
Why must trays or beakers be used?
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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?
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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 50¡C to 65¡C range.
Is rinsing required after cleaning cycles?
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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?
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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 copyright 1999 by Howard Stromberg, Mastersonics