1. Understanding Ultrasonic Waves
Sound waves are categorized into three types: infrasound, audible sound, and ultrasound. Infrasound has a frequency below 20 Hz; audible sound ranges from 20 Hz to 20 kHz; and ultrasound has a frequency above 20 kHz. Generally, the human ear cannot hear infrasound or ultrasound. Due to their high frequency and short wavelength, ultrasonic waves exhibit excellent directional propagation and strong penetrating power—characteristics that drive the design and manufacture of ultrasonic cleaners.
2. Working Principle
Ultrasonic cleaning achieves its purpose by utilizing the effects of cavitation, acceleration, and acoustic streaming—generated by ultrasonic waves in a liquid—to act directly or indirectly on the liquid and contaminants, thereby dispersing, emulsifying, and stripping away the layer of dirt. Among the ultrasonic cleaners currently in use, cavitation and acoustic streaming are the most widely applied mechanisms.
(1) Cavitation Effect: Cavitation occurs when ultrasonic waves are transmitted into a liquid through high-frequency, alternating cycles of compression and rarefaction (pressure reduction) occurring more than 20,000 times per second. During the rarefaction phase, clusters of vacuum-core bubbles form within the liquid; during the compression phase, these bubbles are crushed by the pressure, generating a powerful shockwave that dislodges dirt from the surface of the object being cleaned, thus achieving precision cleaning.
(2) Acoustic Streaming Effect: The phenomenon where ultrasonic waves induce flow within a liquid along the direction of sound propagation is known as acoustic streaming. When the sound intensity reaches 0.5 W/cm², this flow becomes visible to the naked eye; it moves perpendicular to the vibrating surface at a velocity of approximately 10 cm/s. This direct flow agitates microscopic oil-based contaminants on the surface of the object being cleaned. It creates convection in the cleaning fluid at the contaminant interface, mixing the solution containing dissolved contaminants with fresh fluid; this accelerates the dissolution rate and plays a significant role in transporting the contaminants away.
(3) Acceleration: The acceleration generated by the movement of liquid particles. In high-frequency ultrasonic cleaners, cavitation effects are less significant; cleaning relies primarily on the impact of liquid particles—accelerated by ultrasonic action—against the contaminants to achieve ultra-precision cleaning.
3. Operating Instructions
Operate the ultrasonic cleaner strictly according to the following steps:
(1) Connect the cable between the cleaning tank and the generator;
(2) Pour the cleaning fluid into the tank (the optimal fluid level is approximately three-quarters of the tank's capacity when the object to be cleaned is submerged);
(3) Place the object to be cleaned into the tank;
(4) Connect the power plug;
(5) Set the cleaning time and turn on the machine.
4. Precautions
(1) The power supplies for the ultrasonic cleaner and the heating element must be properly grounded.
(2) Never operate the ultrasonic cleaner without cleaning fluid; do not activate the ultrasonic switch unless the tank contains the required amount of fluid.
(3) For units equipped with heating systems, never turn on the heater without fluid in the tank.
(4) Do not strike the bottom of the cleaning tank with heavy objects (such as iron parts), as this may damage the transducer crystals.
(5) The ultrasonic generator should be connected to a dedicated 220V/50Hz power line equipped with a voltage stabilizer rated above 2000W.
(6) Rinse the bottom of the cleaning tank regularly to prevent the accumulation of excessive debris or dirt.
(7) When changing the cleaning fluid, activate the ultrasonic function before beginning the cleaning process.
5. Methods for Optimal Ultrasonic Cleaning Results
(1) The optimal temperature for the ultrasonic cleaning tank is 30–50°C.
(2) Select the appropriate cleaning agent based on the specific object being cleaned. Cleaning agents are generally categorized into water-based (alkaline) agents, organic solvents, and chemically reactive agents. Water-based cleaning agents are the most commonly used.
(3) Select the cleaning duration based on the degree of contamination and the nature of the soil on the items being cleaned.