The wash chemical selection is extremely important to the complete success of the ultrasound washing process. The chosen chemicals must be compatible with the base metal to be cleaned and have the capacity to remove the dirt present. They must also form bubbles well. Most cleaning chemicals can be satisfactorily used with ultrasounds. Some are specifically formulated for use with ultrasounds. However, avoid the non-foaming formulas usually used for spray wash applications. Formulas with a high soaking capacity are preferable. Many new petroleum-based cleaning agents, like petroleum and semi-aqueous cleaning agents, are compatible with ultrasound. The use of these formulas may require some special equipment and may need the ultrasound power to be increased in order to be effective.
 

The temperature was mentioned earlier as an important factor in achieving maximum cavitation. Effectiveness is also connected to temperature. While the cavitation effect is maximised in pure water at a temperature of approximately 70°C, an optimum wash can also often be achieved at higher or lower temperatures due to the effect that the temperature has on the washing chemicals. Generally speaking, every chemical will act better at its recommended process temperature, whatever the effect of the temperature on ultrasound. For example, although the maximum ultrasound effect is achieved at 70°C, much more caustic cleaning agents are used at temperatures from 80°C to 90°C because the chemical effect is boosted by the higher temperature. Other cleaning agents may decompose and lose their effectiveness if used at excess temperatures as low as 60°F. The best thing to do is use chemicals at their maximum recommended temperature, whilst not exceeding 90°F.
Degassing cleaning solutions is extremely important in order to achieve satisfactory cleaning results. Fresh or cooled solutions must be degassed before proceeding with cleaning. The degassing procedure is carried out after the chemical has been added thanks to the ultrasound energy present and the increase in the temperature of the solution. The time necessary to degas the liquid varies considerably. It is based on the tank capacity and the solution temperature, and may vary from several minutes for small tanks to an hour or more for large tanks. An unheated tank may take several hours before it is completely degassed.

Degassing is complete when the small gas bubbles no longer rise to the surface of the liquid and rippling can be seen.
The ultrasound power delivered to the washing tank must be sufficient to form bubbles throughout the entire volume of liquid with the washing load in situ. Watts per gallon is the unit of measurement often used to measure the level of ultrasound power in the washing tank. When the tank volume increases, the number of Watts per gallon required to achieve the desired performance is reduced. Large washing parts or those with a large surface area to mass ratio may require additional ultrasound power. Excessive ultrasound power may cause cavitation erosion or “burning” of light metal parts. If a wide variety of parts needs to be cleaned in a single washing system, we recommend checking the ultrasound power in order to make it possible to adjust the power so as to cater for the various washing requirements. Partial exposure to the washing chemical and to the ultrasound energy is important for an effective wash. Make sure that all the areas of the parts to be washed are soaked in the cleaning liquid. Parts, baskets and appliances must be modelled in order to allow the penetration of the ultrasound energy and in order to position the parts, ensuring that they are exposed to the ultrasound energy. It is often necessary to put the parts on a rack individually and face them in a specific direction or rotate them during the washing process in order to clean internal areas and dead end holes.
 

Conclusion. When properly used, ultrasound energy can make a significant contribution to regulating the speed and effectiveness of many immersion and rinsing processes. It is especially beneficial in increasing the effectiveness of today’s most popular semi-aqueous cleaning chemicals and is actually essential to many applications in order to achieve the desired cleaning results. With ultrasound, aqueous chemicals can often provide results that exceed those previously obtained using solvents. Ultrasound is not a futuristic technology – it is actually a technology of our times.