Ultrasonic cleaning employs high frequency sound waves into a solution or solvent. These sound waves cause microscopic gas bubbles to expand to their limit which when collapse or implode cause a pressure wave.
This process is called cavitation and together with a solution or solvent force contamination from parts and instruments.
The operating frequency is an integral part of the cleaning process.
The lower frequencies generate a larger gaseous bubble which when collapses produces a much stronger shock wave.
At the higher frequency the microscopic bubbles will grow to a collapsible size at a more rapid rate causing many more times the number of implosions per unit time.
temperature of a cleaning liquid also has significant impact on performance levels. Maximum cavitation intensity occurs at a temperature range of between 50degC - 60degC in aqueous solutions with a decline in efficiency evident above this to boiling. Heating helps to degas as well as increase the chemical action of the liquid. A proper combination of temperature and the gaseous condition of the liquid helps to achieve the best cavitation and overall cleaning results.
Liquids also play a significant role with two broad classifications being aqueous and solvent. The type of soil to be removed determines the type of liquid. Aqueous systems are best for inorganic soils, however by adding a detergent to the liquid many light greases and oils can be removed. Solvents best serve heavy organic grease, oil or waxy soils.
The following includes the 10 major factors that influence cleaning efficiency.
- Size and shape of tank
- Depth of the liquid in the tank
- Amount of dissolved soil in the liquid
- Trays or basket used to contain parts
- Number, size and shape of parts
- The density + composition of the cleaning fluid
- Type of liquid
- The temperature of the liquid
- The position of larger parts
- The operating frequency