- Time – varies depending upon quantity & type of contamination.
- Temperature – most chemistry works best at higher temperature but ultrasonic cavitation reduces above70 C.
- Chemistry – alkalinity/acidity, surfactants, wetting agents, dispersants, emulsifiers, saponifiers, sequestrants, inhibitors, defoamers etc.. are all part of the equation in taking the contaminant off without damaging the part being cleaned. The correct chemistry will depend upon the composition of the contaminant and the part being cleaned.
- Transducers – must be placed at the correct distance on the tank walls and from the parts being cleaned. Badly placed or bonded transducers will affect the power, uniformity and durability of the cleaning action.
- Frequency – Lower frequency for denser harder items with hard dirt, higher frequency for delicate smaller items with smaller particulate contaminant requiring a finer clean. 40KHz is often cited as the “sweet” spot for general cleaning.
- Power – This is usually measured as watts per litre of INPUT power. In tanks of a capacity less than 200 litres 13-25 watts per litre is usually cited as optimal, for tanks greater than 200 litres 5-12 watts per litre. Whilst this is the most frequently quoted measure of ultrasonic capability it must be recognised that:
- This measures input power not effective output as reflected in cavitation;
- Temperature, chemicals in the solution, loading, baskets, transducer placement all affect the effective cavitation produced from any given power input.
- Loading of parts being cleaned affects the ultrasonics and general cleaning effectiveness dramatically. Generally the parts being cleaned should be less than half the weight of the solution in the tank.
The number and variety of parameters determining the effectiveness (or otherwise) of your ultrasonic cleaning does make it difficult to select both the correct machine and chemistry for your needs. The best way of approaching it is to view ultrasonics as just one element in an overall cleaning process that gets your part to the required level of cleanliness.