What is an ultrasonic cleaner?
An ultrasonic cleaner is a cleaner that generates and cleans ultrasonic waves.
Originally widely used industrially, nowadays it has become a major measure that can be easily purchased by individuals for cleaning eyeglass cleaning machines and precious metal and wristwatch belts, thanks to ultrasound. Dirt that could not be removed by conventional cleaning methods can now be cleaned.
Ultrasonic cleaning enhances the cleaning effect by combining the physical action of ultrasound and the chemical action of the cleaning liquid.
What was not removed only by the chemical effect of the cleaning solution can be removed, dispersed and emulsified by physical action by cavitation and vibration acceleration, and fine dirt can be cleaned.
Ultrasonic cleaning can also be expected to achieve uniform cleaning quality and shorten cleaning time.
Why can ultrasound be cleaned?
1. Ultrasonic cavitation
Cavitation is a physical phenomenon in which a pressure difference is generated by the flow that occurs in a liquid and bubbles are generated and disappeared in a short time.
Also known as “cavity phenomenon”.
When powerful ultrasonic waves are irradiated into a liquid, countless microcavities (= cavitation) close to vacuum are generated.
A powerful shock wave is generated at the moment when the cavitation is crushed, and it is a mechanism that can destroy dirt directly from the workpiece and disperse it in the liquid for cleaning. This shock wave is actually quite powerful, and depending on the conditions, if a cavitation shock wave is applied to aluminum foil placed in water, a hole will open in tens of seconds.
Cleaning by cavitation is said to be effective against oil stains, and will remove dirt as shown below.
The degree of cavitation generation depends on the depth of the liquid, the type of liquid, and the frequency of the ultrasonic wave, and is adjusted according to the object to be cleaned.
The lower the frequency, the greater the cavitation, and the greater the shock wave when crushed.
The higher the frequency, the smaller the cavitation and the smaller the shock wave, so it can be used for cleaning precision parts.
2. Ultrasonic vibration
When the liquid is irradiated with ultrasonic waves, the liquid molecules vibrate.
The acceleration of this vibration is
1000 times in the case of 28kHz and
100000 times in the case of 950kHz
than the state where it is left still without applying ultrasonic waves.
The dirt is peeled off from the workpiece surface at this tremendous vibration speed.
950kHz ultrasonic waves are so fine that cavitation does not occur, so oil stains cannot be cleaned, but submicron stains can be cleaned.
We wrote that oil dirt cannot be washed at a frequency of 950kHz, but the field of dirt that can be removed depends on the frequency.
By selecting an appropriate frequency, the cleaning effect can be maximized, so a prior check is required.
Let’s look at the compatibility between frequency and dirt in descending order of damage.
The cleaning energy is strong, and it is ideal for removing oil and cleaning visible trash. This can wash metal parts and resin parts.
As it is less damaging than 28kHz, ideal for washing precision parts and glass. Specifically, it plays an active role in cleaning glasses and accessories. Suitable for removing dust.
This is a frequency that has recently attracted attention. Used when damage occurs even at 40kHz. Suitable for cleaning electronic precision parts such as hard disks and CSP boards.
There is little damage to the workpiece, and fine dirt can be removed. Ideal for cleaning compound wafers and hard disks.
0.2-5μm dirt can be cleaned.
Used to remove invisible stains. There is little damage to the workpiece, and it is attracting attention with wafer cleaning.
Ideal for 0.2μm cleaning. Acceleration is stronger than 1MHz, yet finer dirt than 1MHz can be removed.
Kind of Ultrasonic cleaner
The ultrasonic cleaning machine mainly consists of an ultrasonic vibrator that generates ultrasonic waves, an ultrasonic oscillator that moves the ultrasonic vibrator, and a tank that contains liquid.
There are two types of existing tanks, one with a vibrator and an oscillator, and the other with a tank and a vibrator / oscillator.
The advantage of another type of tank is that it can be handled with a special cleaning object even if the shape of the tank is unique, and it is relatively easy to move and move.
One-body type is easy to place even in a narrow space and is characterized by a relatively compact point.
In addition, there are many types that are soaked, and there are also types that wash by placing ultrasonic waves on the water flow. (See the figure below)
Some ultrasonic cleaners not only apply ultrasonic waves, but also have other functions.
For example, it is a function that can enhance the cleaning effect by combining it with ultrasonic waves, such as those with a heater that raises the liquid temperature and those with a decompression function.
There are many other useful functions such as an explosion-proof specification that can be used with various cleaning solutions, and a function that can change the frequency to handle various types of dirt. Let’s check well.
How to select an ultrasonic cleaner
Up to this point, you can see that there are various types of ultrasonic cleaners.
In addition to frequency and shape, the cleaning solution must also be compatible with the cleaning machine.
It is important to maximize the cleaning effect by combining the physical action of ultrasound and the chemical action of the cleaning solution.
1. Clarify the purpose of cleaning
Before selecting a washing machine, clarify what you want to wash once again.
Example) Degreasing, cleaning of abrasive powder and chips, removal of particles, etc.
2. Understand the type of workpiece
Make sure you know what is being cleaned.
Example) What is the size of the workpiece, what components are made of, etc ….
After carefully recognizing the situation, look at the washing machine. The following are important at that time.
3. Select the cleaning solution
here are lots of different types of cleaning liquids.
This selection is very important because if you select the wrong cleaning solution, you may not be able to clean at all.
In addition to water-based and solvent-based systems, “quasi-water-based” cleaning agents have recently attracted particular attention in ultrasonic cleaning.
Originally, ultrasonic cleaners were often cleaned using chlorofluorocarbon or chlorinated solvents, but alternatives are being investigated due to their adverse effects on health and the environment.
4. Select the frequency
As already introduced, the effect obtained by the frequency is different.
Therefore, you must select the frequency according to your purpose.
Also note that the tabletop type ultrasonic cleaner has few ultrasonic output points, and the cleaning performance will be different even at the same frequency.
5. Consider the cleaning position
In an ultrasonic cleaning machine, it is necessary to consider which part the pressure reaches most.
You may have grasped the size in (2), but even if a workpiece enters the washing machine, it is often the case that the workpiece is too large, which causes uneven cleaning, and in that state the cleaning effect cannot be 100%.
Generally, it is possible to eliminate unevenness by shaking or swing.
6. Select the insert tray
If a workpiece is placed directly in the cleaning tank, the workpiece may come into contact with the vibrator and normal ultrasonic waves will not be emitted, leading to defective cleaning and failure.
As countermeasures, it is common to use a container called an insert tray or a washing basket.
However, depending on the type of tray and the fineness of the mesh of the cleaning bowl, the ultrasonic wave may be greatly attenuated, and the cleaning effect may be reduced.
7. Liquid temperature setting
Generally, when the temperature of the liquid rises, bubbles are generated in the liquid and the ultrasonic wave becomes weaker.
However, when viewed with a single cleaning solution, the higher the temperature, the better the cleaning power. (However, do not raise the temperature above the limit temperature!)
Therefore, it must search for the point where the effects of the ultrasonic wave and cleaning solution are maximized, but this depends on the cleaning solution.
For example, in the case of water, 50-60 ° C is said to be optimal.
There are many points that must be taken into account, it will be difficult for people to use. However, if a suitable washing machine and solution are found, the workability will change greatly.
We are also accepting consultations on cleaning solutions, so please feel free to contact us!