25kHz Ultrasonic Cleaners / Heavy Duty Cleaning for
Simple Part Designs
The very first ultrasonic cleaning systems ever developed utilized very low
ultrasonic frequencies in the 16 to 20 kHz range. This ultrasonic
frequency tends to be most effective when used on parts with little detail,
since 25 kHz ultrasonic systems produce a scrubbing action with many large dead
spots where little ultrasonic activity is found. The problem lies with the
distance between the standing waves produced by these low-frequency
All ultrasonic cleaning systems, regardless of manufacturer or
frequency, produce a scrubbing action which is distributed as a series of an
equidistant bands known as Standing Waves which begin at the transducer
mounting location, typically the bottom of the tank. The frequency of the
ultrasonic cleaner will determine the distance between these bands of activity.
The higher the ultrasonic frequency, the closer these bands will be to one
another, but the less powerful the activity will be at any one location.
High-frequency ultrasonic systems generally produce a very evenly distributed
cleaning effect, but a less powerful one, while low-frequency ultrasonic systems
produce a cleaning effect with large areas of inactivity, but the cleaning
action is more powerful at standing wave locations.
If a customer were
cleaning parts with small threaded blind holes, and these holes happened to rest
in-between the standing waves, there is a good possibility that this area will
not be consistently cleaned. This is primarily the reason why 25 kHz
ultrasonic systems are no longer as common as
40 kHz or higher operational
frequencies. Even if parts are positioned perfectly in a basket, it is
impossible to guarantee an evenly cleaned part in a 25 kHz ultrasonic cleaner.
Although the 25 kHz frequency produces a less evenly distributed cleaning
effect, the scrubbing action that is produced is very powerful, which can be
positive or negative. The power is of benefit when cleaning heavy parts,
such as a plastic injection mold weighing 2000 pounds, or cleaning those parts
with highly-bonded contaminants, such as burned carbon. The power is
destructive when cleaning sensitive components, such as aluminum or soft metals,
or those parts with finely-machined detail.
25kHz system may also remove thicker contaminant layers faster than higher
frequencies. Since 25kHz ultrasonic systems essentially "drill holes" on
the surface of the part with a large amount of power, this frequency tends to
remove thick layers of contaminants in large chunks, while higher frequencies
remove the same contaminants by attempting to gently remove layer by layer.
As such, 25kHz systems may be more effective when removing paint, thick greases
or coatings, or other similar contaminants.
25kHz ultrasonic systems are also very noisy during operation since the
sub-harmonics are within the upper range of human hearing. The sound is a
high-powered squeal which is highly disturbing to many individuals.
Hearing protection will more-than-likely be required when operating a 25kHz
ultrasonic cleaner, unless it is acoustically insulated.
25kHz ultrasonic cleaners are also highly-destructive to the cleaning tank
itself. Cavitational Tank Erosion is the slow deterioration of the
cleaning tank at the transducer mounting locations. From the very first
day of operation, molecules of stainless steel directly above the transducers
are eroded away. Eventually, the tank will become porous, allowing liquid
to enter the transducer area, and destroying the system permanently. The
lower the operational frequency, the faster this erosion will occur.
Acidic cleaning agents will drastically increase the rate of tank erosion.
Some manufacturers of Magnetostrictive Ultrasonic Transducers mount their
transducers to tanks which are over 3/8" thick to increase the life of the tank.
However, there is a problem with this design. The energy being emitted
from the transducer must first pass through 3/8" of material before entering the
cleaning fluid, which significantly reduces the effective power in the tank.
These systems are VERY loud, since the tank is being vibrated rather than the
fluid in the tank, but sound is not an indication of power in an ultrasonic
Today, Zenith includes 25 kHz systems when higher frequencies fail to
successfully clean a part, or when a potential customer must use a machine which
was approved decades ago, before the advent of high frequency ultrasonic
systems. Many large, older firms developed standards which require the use
of low-frequency ultrasonic systems. Changing standards can be a very
large undertaking, and rather than change standards, these firms purchase low
frequency ultrasonic cleaners which have always worked in the past.
However, one must consider that it is very rare that a 25kHz system will clean
an object, and a
40kHz system will not. As such, Zenith will recommend
40kHz even for those applications that are typically the domain of
When to Use 25kHz Ultrasonic Cleaners:
- When Cleaning Large and Heavy Parts with Little Detail.
- When Removing Highly-bonded Contaminants.
- If 25kHz is Required due to Standards Written Long Ago.
- When Higher Frequencies Fail to Clean a Part.
- When Cleaning Thick Contaminants Layers.
For additional information,
Zenith Mfg. & Chemical Corp.
85 Oak St.
Norwood, NJ 07648-0412