Who determines whether something is clean? Or in other words "How much contamination may be left on an object to be cleaned"?
Ultrasound is the science of sound waves that goes above the boundaries of human audibility. The frequency of a sound wave determines the tone or pitch. Ultrasound is a sound with a pitch that is so high that it cannot be determined by the human ear. Frequencies above 18 kilohertz are usually considered to be called Ultrasound. The frequencies used for ultrasonic cleaning vary from 20 kilohertz (kHz) to more than 500 kHz and even 1 MHz. The most frequently used frequencies for industrial cleaning are those between 25 kHz and 120 kHz. Frequencies above 40 kHz are often used for parts with a high-precision demand; removal of small particles and delicate parts.
Ultrasound used for cleaning applications consists of an electrical and a mechanical component. Generating the desired frequency is done in a so-called oscillator. This oscillator is called a Generator. A Generator whit a frequency of 20,000 Hz. is in fact a "switch" that is switched on/off 20000 times per second. By giving power to this electrical switch and connecting it to a sort of loudspeaker, we can cause a vibration. This vibration is transferred to a medium. For cleaning we use a liquid.
The so called speaker is a metal cone which is mounted on the bottom or in a side of a tank. On this cone there are ceramic discs bolted on. These discs are connected to the generator. By putting on a certain voltage (pressure) on a ceramic disk it will expand. When the voltage is put off, these disc shrinks again. This goes on for example at 20000 times per second. This movement is transferred to a tank. This "loudspeaker" is called a transducer or vibrating element and is constructed with piezo-ceramic PZT elements. (Plubum Zircon Titan)
In principle, for example the bottom of a tank, as a whole will be brought in vibration. With compressible media such as air and most solids, there is a continuous propagation of the sound wave (vibration). With non-compressible media such as water and most liquids, there is a sound propagation as long as the amplitude (strength of the vibration) is relatively low. When increasing the amplitude the medium, liquid, will cause a negative pressure. This pressure increases so vacuum bubbles arise. These bubbles grow and become unstable until they implodes (breaks) due to external pressure of the liquid. This effect is called cavitation. Countless vacuum bubbles develop by the continuous supply of energy to the vibrating elements.This creates a chaos of unstable bubbles and implosions. These implosions are used for ultrasonic cleaning. The cavitating vacuum bubbles acts like a smooth brush along the surface of the part to be cleaned.
Who determines whether something is clean? Or in other words "How much contamination may remain on an object to be cleaned"?
This question is increasingly difficult to answer and is strongly dependent on the type of industry in which you work. For the high-tech industry such as suppliers of semi-conductor parts other cleaning standards are demanded as for companies in the chemical or in the surface treatment sector. It is also important to know from what kind off material the object to be cleaned is, and its shape? Do the items have to be cleaned individually or per batch? Where can I hold the objects? May they rotate? What is the pollution etc.
Please contact B&M Service B.V. for the right advice.
For a good Ultrasonic sound propagation, the cleaning fluid must be as thin as possible.
Viscous liquids phase out the Ultrasonic cavitation effect.
For an optimum Ultrasonic operation, the cleaning fluid must be free of gas (oxygen).
The ultrasonic power and intensity are directly linked to the volume of the bath and the geometry of the parts to be cleaned.
Low frequencies are usually used to remove of “big” particles. (25 kHz.)
The higher frequencies are usually used to remove small particles. (40 kHz. and higher up to 1 Mhz.)
For a right cleaning method it is important to collect relevant information.
B&M Service B.V. can advise you which cleaning process best fits your product and production method. Please contact us.
Ultrasonic is used in various ways in the industry. The most common applications are ultrasonic cleaning and ultrasonic welding of thermoplastics. Less known are: Ultrasonic nebulizing; Drilling; Sieving; Crushing; Non Destructive Detection; Medical ultrasound; Homogenization; Sonochemistry; Degassing; Leak detection; Disinfection etc.