How Ultrasonic Cleaning Works & Safety Guidelines

As we know, sound detectable by the human ear consists of sound waves with frequencies ranging from 20 Hz to 20,000 Hz. Waves above 20,000 Hz are defined as ultrasound. Sound travels longitudinally in a sinusoidal pattern, alternating between high-pressure and low-pressure cycles.

When low-pressure sound waves pass through a liquid, they create negative pressure that forms countless tiny vacuum bubbles. As high-pressure waves arrive, they apply positive pressure, causing these micro-bubbles to collapse violently.

Studies confirm that when ultrasound propagates in liquid, the sudden collapse of each bubble releases an extremely powerful shockwave, generating instantaneous high temperatures and pressures of thousands of atmospheres. This phenomenon is known as cavitation. Ultrasonic cleaning relies on these shockwaves produced by collapsing bubbles to scrub and clean both internal and external surfaces of parts.

Sound Wave Classification

Sound waves fall into three categories:

Infrasound: Frequencies below 20 Hz
Audible sound: Frequencies from 20 Hz to 20 kHz
Ultrasound: Frequencies above 20 kHz

Infrasound and ultrasound are generally inaudible to the human ear. Due to its high frequency and short wavelength, ultrasound exhibits excellent directional propagation and strong penetration.

Working Principle of Ultrasonic Cleaners

An ultrasonic cleaner uses transducers to convert acoustic energy from a high-power ultrasonic generator into mechanical vibrations. These vibrations transfer through the walls of the cleaning tank, radiating ultrasound energy into the cleaning solution.

Under ultrasonic irradiation, micro-bubbles in the liquid remain in constant vibration.

When sound pressure or intensity reaches a certain threshold, the bubbles expand rapidly before collapsing abruptly. During this collapse, an intense shockwave is created, producing pressures between 10¹² Pa and 10¹³ Pa around the bubbles.

This powerful force from ultrasonic cavitation breaks down insoluble contaminants and disperses them into the solution.

Ultrasound works in multiple ways to clean effectively:

It breaks the adhesive bond between contaminants and part surfaces.
Fatigues and loosens contaminant layers until they peel away.
Micro-bubbles vibrate and scrub solid surfaces; they penetrate cracks and crevices to dislodge embedded dirt.
Cavitation causes rapid mixing and emulsification of immiscible liquids at interfaces.
Oil layers emulsify, releasing solid particles trapped in grease from part surfaces.

As ultrasound travels through the cleaning fluid, it creates alternating positive and negative pressure waves that form high-speed jets striking the workpiece. Nonlinear effects produce acoustic streaming and micro-streaming, while cavitation at solid–liquid interfaces generates high-velocity micro-jets.

Together, these actions break down contaminants, thin or remove boundary fouling, improve mixing and diffusion, speed the dissolution of soluble residues, and enhance the cleaning performance of chemical detergents.

In short, ultrasonic cleaning acts wherever liquid can reach and sound fields exist — making it ideal for cleaning parts with complex, intricate shapes. Using this technology also reduces reliance on chemical solvents, greatly lowering environmental pollution.

Safety & Operating Instructions for Ultrasonic Cleaners

The main power supply and heater circuit must be properly grounded.
Never operate the unit without cleaning solution — do not turn on the ultrasonic function unless the tank is filled to the required level.
For units with heating, do not activate the heater when the tank is empty.
Avoid striking the bottom of the cleaning tank with heavy or metal objects, as this may damage the transducer crystals.
The ultrasonic generator should be connected to a dedicated 220V/50Hz power supply with a voltage stabilizer rated above 2000W.
Clean the bottom of the tank regularly to prevent excessive buildup of debris or sediment.
When refilling with fresh solution, allow the ultrasonic system to start before inserting parts for cleaning.