The material presented in this section features models of ultrasonic cleaners that are unique to this manufacturer. Other sources’ equivalent models’ features should be considered for relevant applications.
Theory of Ultrasonic Cleaning
Everything that makes a sound vibrates, and everything that vibrates makes a sound; however, not all sounds are audible. Ultrasound literally means beyond sound—sound beyond the audible spectrum. Considering 18,000 Hz (cycles per second) as an approximate limit of human hearing, ultrasonics refers to sound above
18,000 Hz.
The ultrasonic power supply (generator) converts 50/60 Hz voltage to high frequency 20 or 40 kHz (20,000/40,000 cycles per second) electrical energy. This electrical energy is transmitted to the piezoelectric transducer within the converter, where it is changed to high-frequency mechanical vibration. The vibrations from the converter are amplified by the probe (horn), creating pressure waves in the liquid. This action forms millions of microscopic bubbles (cavities) that expand during the negative pressure excursion and implode violently during the positive excursion. It is this phenomenon, referred to as cavitation, that produces the powerful shearing action at the probe tip, and causes the molecules in the liquid to become intensely agitated.
What are the differences between an ultrasonic processor and an ultrasonic bath?
The intensity within a bath is fixed, low, location dependent, and inconsistent, due to the fluctuation in the level and temperature of the liquid. With an ultrasonic processor, processing is fast and highly reproducible. The energy at the probe tip is high (at least 50 times that produced in a bath), focused, and adjustable.
With ultrasonic processing, are there any limitations?
Yes, viscosity, temperature, and liquid characteristics. The more viscous the material, the more difficult it is for the vibrations to be transmitted. Typically, the maximum viscosity at which a material can be effectively
processed is 5000 cps. With standard systems the practical upper limit on temperature is approximately 150°C?Solid probes can safely be used with both aqueous solutions and low surface tension liquids (e.g., solvents); however, probes with replaceable tips should never be used with low surface tension liquids.
Which instrument should I use?
The 400, 500, and 600 watt units are the most versatile because they can process both large and small volumes—on a batch basis, as little as 200 mL with a microtip, or as much as 1 L with a 1-in (25-mm) probe; on a flow-through basis, up to 10 L/h. However, since every instrument will perform equally well up to a certain volume, for samples up to 70 mL the 70-watt unit is recommended, and the 130-watt unit for samples up to 130 mL.
