A. "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.
A. "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.
A. 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
A. 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.
A. 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.
A. 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.
A. 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. Your Bransonic® representative
can help you to identify either the optimal 'stock' cleaning formula, or
likely candidates to test and evaluate.
A. 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
A. 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.
A. 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.
A. 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.
A. 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
A. 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.
A. 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.
A. 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.
A. 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.
A. 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.
A. 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.
A. 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.
A. Standard Sonifier® products operate
at a nominal frequency of 20 kHz or 20,000 cycles per second. The
auto-tuning feature actually moves the frequency within a small range
during operation to optimize performance.
A. Replaceable tips are generally used in
high-energy applications where tip wear is expected. As energy is
transmitted from the horn tip, traces of metal are eroded. Over time,
this results in light pitting. Tips can be polished with crocus paper or
emery cloth until they are out of dimensional tolerance. When this
happens, the horn will be difficult to tune, may squeal, and eventually
crack. As tips are relatively inexpensive, it is recomended that they be
changed after the second polishing.
A. Microtips are designed to be used in
small containers and are therefore quite thin. This smaller dimensional
cross-section makes them more susceptable to stress cracking at higher
A. The two primary factors for effective
processing of a given sample size are horn diameter and delivered power.
The two must work together for optimal performace. Too little power and
a large horn will stall. Too much power and horn damage may result.
Branson offers a range of horns with each of their Sonifiers® that have
been proven effective with that particular unit.
A. "booster" is a device which
is inserted between the converter and the horn. It mechanically
increases the horn amplitude by some factor. They are typically used in
difficult applications or flow-through applications where exposure time
is very limited.
A. Hazardous materials may be safely
processed with a sealed atmosphere horn. This device isolates the
process sample in a sealed chamber during the entire cycle. It is
available with external cooling and is also used in cases where there is
need for metric evaluation of reaction components.
A. For processing larger volumes or a
continuous flow of material, Branson offers flow-through processing
cells. These specialized chambers permit the continuous flow of material
through a high-density ultrasonic field. Volumes as high as 40 liters
per hour can be reached with a single unit.
A. The greatest difficulty with
processing small samples is providing good horn/sample contact. This can
be improved by using a process container with a conical bottom. This
increases liquid depth for easier horn tip immersion without increasing
liquid volume. The bottom of an Eppendorf cell is often used for this
purpose. A 3/32" or 1/8" microtip should be used and care
should be exercised to not touch the side of the container with the