We’ve often been asked ‘what is the best frequency?’ for a customer who is in the market for an ultrasonic cleaner.
Like many things in life, there is no simple black and white answer. It’s like asking a vehicle salesman whether it’s better to buy a truck or a car. Both will get you from A to B, but the best solution depends on the individual’s situation. For instance, a furniture removalist will find a truck more useful, whereas a real estate agent would definitely find a car more appropriate – especially when it comes to parking in busy shopping centres!
Early ultrasonic cleaners tended to be in the low frequency range – roughly 15 – 25 kHz. Their wave patterns meant that they were very good at ‘blasting’ heavy contamination off metallic objects with plane surfaces. But, they were not very good at cleaning items with fine detail (such as apertures, threads and blind holes), nor did they give consistent cleaning results across a surface, unless the object was moved about inside the tank during the cycle. Lower frequencies were also found to have an undesirable impact on softer materials being cleaned.
More modern cleaners tend to deliver frequencies in the upper range – between 40 – 45 kHz. The wave pattern of these cleaners results in a more gentle and more thorough cleaning result, so they usually have no effect, even on softer metals. Often there is no need to adjust an item’s placement in the ultrasonic tank to ensure all surfaces are properly cleaned, which means a faster result with less labour. The higher frequency wave pattern also has a better cleaning effect on parts with fine detail (eg the apertures, threads and blind holes that the lower frequency cleaners do not clean well). However, the trade-off is that higher frequency cleaners will not always have enough ‘grunt’ to remove the heaviest contamination, so it will take longer to properly clean some items, or the machine will need to be more powerful, or some additive will be needed – and in some cases all three!
Cleaning requirements, materials and situations vary. So, operators cannot always get by with a single frequency solution. In summary:
Low Frequencies – ‘blast’ effect, especially for plane surfaces, but can be hit and miss unless object is adjusted inside tank, and poor for fine detail. Not good for softer materials.
High Frequencies – gentle consistent cleaning across a variety of surfaces and good for fine detail. Suitable for even soft metals. Not ideal for heavy contamination.
Option A – Dual Frequency Control
So, how can we overcome the shortfalls of low and high frequency wave patterns in ultrasonic cleaning?
Not every heavily contaminated item has a plane surface. Often these parts are designed with flanges, apertures and threads to connect to other parts. Sometimes these items are weighty, and are awkward to adjust inside the tank. For other items, such as surgical instruments, patient care and infection control policy dictate that instruments need to be perfectly clean, before moving on to the sterilisation procedure.
Dual frequency ultrasonic cleaners combine the advantages of the high and low frequency wave patterns in a single unit. They significantly reduce capital cost and the footprint required to accommodate the equipment. ‘Space’ was the final frontier for Startrek, but the lack of it is equally important in today’s clinic or workshop. The better designs feature options to switch between high and low frequencies and to select a range of power settings. This provides substantially greater control over the cleaning environment than less sophisticated machines, and ultimately leads to a better cleaning outcome.
Dual frequency ultrasonic cleaners allow the operator to clean items in a multi stage process, that minimises cleaning time, staff intervention and the need for additives.
As a general rule, dual frequency ultrasonic cleaning will be conducted as follows:
Stage 1. Use the low frequency ultrasonic cleaner setting to dislodge gross matter and heavy contamination. Unless material is soft or delicate, use full power and complete a 30 minute cycle. Remove basket from tank and examine objects. If heavy contamination remains, repeat process – NB Removal of basket and examination of objects will adjust position of cleaning object – aiding in cleaning consistency.
Stage 2. Use high frequency ultrasonic cleaner setting to address fine detail cleaning and to ensure cleaning result is thorough across all surfaces. Set for additional 30 minutes cleaning cycle and examine object to ensure desired result is achieved.
Option B – Dual Frequency Control
Note: For surgical instruments, refer to practice procedure manual and ensure that at start of day tank is degassed and unit’s working condition confirmed, using the foil test.