How to choose a best ultrasonic cleaning frequency?
How to choose a best ultrasonic cleaner frequency?
1. What is the ultrasonic frequency?
The inherent vibration frequency is produced by the ultrasonic transducer under the cleaning machine and the frequency selection is general in the range 20-130KHZ.Choosing the best frequency is very important and you need to do some experiments if you want your working frequency is very exactly.
We can wash the different parts according to the different frequency but in addition to the ultrasonic frequency ,the ultrasonic sound pressure strength and physical properties of the cleaning medium is also significant such as temperature, vapor pressure, surface tension, density, viscosity, etc.
In addition cleaning medium containing gas and dissolved oxygen has significant influence.
2.what is cavitation effict?
we need to know what is cavitation before we discuss relationship between cavitation and ultrasonic frequency
Ultrasonic vibration propagation of sound waves in the liquid reaches an atmospheric pressure, its power density is 0.35w/C㎡, when the ultrasonic sound waves can reach the peak pressure vacuum or negative pressure, but in fact there is no negative pressure, so the liquid generate a great force, pulling the liquid molecules split into cavities of an empty core. This cavity is very close to a vacuum, it reaches the maximum reverse pressure ultrasonic rupture rupture arising due to the strong impact of the impact surface of the dirt off. This composed of numerous tiny cavitation bubbles rupture and resulting shockwave phenomenon known as “cavitation” phenomenon.
3.Cavitation and Frequency
There is a close relationship between Ultrasonic cavitation threshold and ultrasonic frequency.
The higher the frequency, the higher the cavitation valve, the needed pressure strength which is generated cavitation is more high.
The lower the frequency, the lower cavitation valve,the needed pressure strength which is generated cavitation is more low.
The generated cavitation is large and few but strong when the ultrasonic frequency is low.——For cleaning of large components.
The generated cavitation is small and more,weak but widely when the ultrasonic frequency is high.—For cleaning of tiny parts.
However, if the frequency is increased when the UHF near 1000KHZ no cavitation effect, the cleaning energy is mainly by the acceleration , to reach 105 times the acceleration of gravity, for the removal of sub-micron particulate contamination.
4.Summary——How to choose an ultrasonic cleaning machine frequency?
(1) Low-frequency ultrasonic cleaning (20-30 KHZ)
It will used to clean the big parts,the large pieces of grease on the surface or the component without considering surface damage.such as 28khz–it used to clean Hardware, machinery, automobile and motorcycle, compressor.but when the frequency is too low it will corrode the parts,so it is not Suitable for cleaning workpiece with high surface finish and the noise is very large.when the frequency is below 20khz,it may be beyond relevant safety regulations prescribed noise limits.
(2) 40KHZ Around——For our cleaning equipment
At the same intensity, the resulting number of cavitation bubbles is more than the frequency of 20KHZ,Strong penetration, the surface should be cleaned with blind holes or complex shape of the workpiece, cavitation noise is small, but the low cavitation intensity, suitable for cleaning dirt and the surface to be cleaned with a weak items. Such as optical photonics cleaning, circuit board cleaning, precious metals
(3) High-frequency ultrasonic cleaning (68KHZ,80KHZ,120KHZ Customizable)
It is usually used for cleaning smaller, more sophisticated components, or remove small particles. Such as computers, microelectronic components fine cleaning; The high-frequency is also used by the application of surface damage is not allowed.Using high frequency can improve cleaning performance from several aspects. As the frequency increases, the number of the cavitation bubbles increases linearly, thereby generating a shock wave for more intense so that it can enter into the gap smaller. If the power is kept constant, small cavitation bubbles, a corresponding reduction in the release of energy, which effectively reduces the damage to the surface of the workpiece. Another advantage of high frequency reduces the viscous boundary layer (poise Nuri effect), making ultrasound can” find” very small particles. This situation is similar to the creek you can see the water level is lowered riverbed pebbles.
(4)MHz ultrasonic cleaning
For integrated circuit chips, wafers and thin films Wave washing, to remove micron and submicron dirt there is no damage of the cleaning parts.