How Ultrasonic Cleaning Works
Ultrasonic cleaning is a high speed, efficient, environmentally friendly cleaning system that uses sound energy passed through a suitable cleaning solution.
Watch our video introduction to Ultrasonic Cleaning.
Ultrasonic Cleaning: A revolution in cleaning technology
Highly efficient and effective cleaning is a requirement in many industries. Manufacturers clean components at various stages in their manufacturing process. Medical professionals need deep penetrating cleaning action that does not damage their precision instruments. Aircraft maintenance crews need to ensure parts are thoroughly scoured without any surface damage to avoid any degradation in flight performance.
In addition, the compaction of geometries has led to the need for deep probing cleansing action to reach tight spaces that may not be easily and effectively reachable otherwise. Plus, the phasing out of environmentally hostile chlorofluorocarbons globally has eliminated the legal (and moral) viability of many cleaning processes. More importantly though, critical factors like performance and warranty requirements lay a greater stress on the need for a high quality, predictable, repeatable, cleaning outcome.
Ultrasonic cleaning is a technology that uses high frequency sound waves (ultrasonic: above the range of human hearing) to agitate an aqueous or organic medium (cleaning chemistry) that in turn acts on contaminants adhering to substrates like metals, plastics, glass, rubber and ceramics. Contaminants can be dust, dirt, oil, pigments, grease, polishing compounds, flux agents, fingerprints, soot wax and mold release agents, biological soil like blood, and so on.
Tovatech’s ultrasonic cleaners cover the entire range of ultrasonic cleaning equipment with suitable models to fit every need. Choosing the right combination of ultrasonic cleaner and cleaning chemistry can be a challenge. There are several gotchas that you need to watch out for. This is where we come in. Our vast experience across industries will help in guiding you towards the most cost effective solution that will match your budget without compromising on your cleaning needs. Call us and we will help you make you the right choice quickly.
Ultrasonic Cavitation: The active cleaning mechanism
A bench top ultrasonic cleaner consists of a generator which provides power to special transducers bonded to the bottom of a liquid-filled stainless steel tank. The vibrating transducers create alternating waves of compression and expansion in the liquid at extremely high speeds, usually between 25 and 130 kHz.
Numerous gas bubbles are formed and expand in the liquid during the expansion phase. This is a low-pressure phase that in essence “cold boils” the water. The water vapor in the bubble condenses rapidly creating a vacuum-filled ‘cavity’.
In the compression phase, the great amount of pressure exerted on the newly expanded bubble leads to a sudden implosion of the bubble. The liquid molecules collide releasing a vast amount of impact energy that rapidly increases the local temperature producing a high-energy liquid stream that collides with the surface of the object being cleaned. This collision agitates contaminants adhering to the surface, effectively and efficiently dislodging them at micron levels.
Cleaning Chemistry: The effective cleaning medium
Depending on the type of cleaning requirement and the substrate that needs cleaning a detergent solution or a similar aqueous medium can dramatically increase the cavitation. Lowering the surface tension of the liquid reduces the energy required to form the form the bubbles, and when combined with the inherent cleaning property of the solution results in superior micro cleansing of the soiled surface.
The choice of the cleaning medium (aka chemistry) is critical. The nature of the substrate and contamination are the key factors in selecting the cleaning chemistry, which is typically aqueous or semi-aqueous.
Temperature: Optimize for maximum efficacy
Temperature also plays a crucial role in the cleaning process. The number of cavitation bubbles increases proportionally to temperature increase. This happens up to about 60°C beyond which cavitation begins to decline and stops completely when the liquid’s boiling point is reached. However as the temperature and vapor pressure increase the cavitation energy decreases. Thus, each cleaning chemistry provides maximum cleaning efficacy at an optimum temperature setting.
Frequency: Control the power of your cleaning action
As with the cleaning chemistry and its properties, the choice of frequency is also critical to your cleaning application.
The size of the cavitation bubble determines the amount of energy released at implosion. This is governed by the frequency of the ultrasonic generator/transducer set. Higher frequencies generate smaller-sized bubbles.
A larger cavitation bubble releases more energy on implosion resulting in a more intense cleansing action. A smaller bubble has a gentler impact. As a general rule of thumb, high frequency is good for fine particles and cleaning of very small features on substrates while the lower frequency is suitable for heavy and coarse contaminants.
Frequency Modulation: Evenly distribute ultrasonic cavitation
Frequency variation, modulation, or sweep prevents formation of standing waves in the tank. A fixed frequency produces areas of high and low cavitation resulting in uneven cleaning. A fixed frequency can also produce harmonic vibrations that damage delicate parts like electronic components. When operating in sweep mode, the ultrasonic frequency is modulated slightly above and below the central frequency, typically ± 1-4 kHz. This modulation results in more uniform cleaning. Till recently sweep ultrasonics were only available in industrial and high end professional cleaning systems. Elma Sweep technology is now available in all its bench top ultrasonic cleaning units.
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