Ultrasonic cleaning uses high-frequency, high-intensity sound waves in a liquid to facilitate or enhance the removal of foreign contaminants from surfaces submerged in an ultrasonically activated tank. Ultrasonic cleaning is a technology unique in its ability to remove contaminants that other technologies cannot remove and, in its ability, to effectively clean areas that are not accessible using other methods. Ultrasonic cleaning relies on the jetting action of collapsing cavitation bubbles in contact with a surface to provide a high-pressure jet of fluid against the surface, when used in conjunction with a particular chemical for the specific contaminant the results are outstanding. It is a common misconception that ultrasonics in water alone is enough for cavitation to take place but in fact because of water’s naturally occurring surface tension, only a small amount of the individual water molecule ever come into contact with the item being cleaned. The right chemical to get full contact and maximum cavitation is of fundamental importance. While the basics of ultrasonic cleaning are simple, there are many factors that affect how successful your ultrasonic cleaning process will be.
- 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.
A lot of people ask the question “How clean can the process get these parts ?) However the appropriate question is “How clean do your parts need to be ?”. This is ALWAYS determined by the next process or use of the parts concerned. If a part is being painted/coated/treated/used in the next process to becoming a finished product then that subsequent process will define the level of absence of particles, hydrocarbons or other substances from the part’s surface to enable a satisfactory outcome. To determine a level of cleanliness without considering the requirements of the next process is like setting off on a journey without a destination. You can either not get there or you can go way beyond where you need to be. Both are costly in different ways.
So NEVER start by specifying the level of cleanliness a cleaning process achieves. ALWAYS start by specifying the level of cleanliness required by the next process that part goes through. AND remember that only the next process is important. If another process down the line also requires a specific level of cleanliness, then that must be addressed at the stage prior to entering that process. Each process introduces potential contamination which must be addressed after the process, not before.
Whilst this all sounds complicated in fact it simplifies and reduces the cleanliness specification at each point in the overall process.
There will usually be very clear guidelines as to the level of cleanliness required by a process, defined from amongst the following:
- Maximum size of permissible particulate contaminants
- Maximum volume of permissible particulate contaminants
- Maximum level of permissible organic/hydrocarbon residue
- Maximum level of permissible chlorine, halides or other soluble inorganic residue
You will note that every part of the specification states “maximum level of permissible contaminant”. WHY ? Because you can never guarantee the complete absence of anything, just its absence above a certain level.
Going through the exercise of defining the level of cleanliness you actually require will make the specification of cleaning process, and the systematic control of that process so much easier and more successful.
- When it comes to anilox rollers ultrasonic cleaning is almost universally recognised as the best process out there. The very nature of the small size of cavitation bubbles and the implosion sucking dirt off rather than blasting media on, makes the cleaning more precise and safer for the extraction of contaminant from micron sized cells on the surface of the roller. The chemistry associated with the ultrasonics is equally important though. Contaminants on anilox rollers tend to be 1 of 3 types of ink or coating, water based, solvent based or a UV based. Each type of ink requires a very different chemical agent to be removed.
Filters are usually fine mesh which is exceptionally hard to clean manually. Here again the very nature of the small size of cavitation bubbles and the implosion sucking dirt off rather than blasting media on, makes the cleaning more precise and safer for the removal of contaminant from inside the fine mesh of the filter. Ultrasonic cleaning can really reduce labour, time and costs to keep the filtration essential to the process running as smoothly and effectively as possible. Chemistry is vital and again it is dependent on the contaminant that is on/in the filter such as carbon deposits, grease, organic/ food matter and oils etc. However whatever the contaminant with the appropriate chemistry ultrasonics can restore filters to optimal performance.
Most machined parts are left with oil and swarf residue after manufacture. This residue usually needs removing since subsequent coatings, assembly or use requires the absence of dirts and oils. Ultrasonics with its ability to clean recesses, threads and apertures is perfect for removing these contaminants quickly, safely and effectively leaving the part ready for the next process.
- The difficulties of cleaning a fouled heat exchanger present a significant challenge to the maintenance and operation of chemical, petroleum and food processes. With internal contamination heat exchangers cannot usually be cleaned using normal methods (blasting, brushing, etc). But the combination of chemical, heat, agitation and ultrasonic power has proved an excellent way in removing industrial scale, calcium deposits, rust and carbonised oils from the tubes and other cavities within heat exchangers. Submersion in an ultrasonic cleaner with the appropriate chemical restores heat exchangers to optimal performance with no damage.
Dust and dirt can seriously affect the performance of a circuit board, which are found in a multitude of different devices and machines, such as industrial machines, computers and mobile phones. Being such a delicate part you cannot hope to clean it manually but using a mild detergent these parts can be safely cleaned ultrasonically removing dirts and oils restoring them to a state where they look and perform like brand new.
- One of the most common applications of ultrasonics is to remove high levels of grease on machine parts during production or manufacturing Cleaning grease without the aid of ultrasonics usually requires high levels of labour, strong chemicals and likely large amounts of water. Such parts are also very hard to handle whilst ultrasonic cleaning allows a more hands off approach. Heavy build ups of the grease contaminant can also hide other issues within the industrial parts so having them cleaned is also vital for quality control. We have worked on every type and thickness of grease from industries such as auto, food, gas & oil, and pharmaceutical. Processes vary from simple 1 tank baths to multiple cleaning baths with pre washes and demineralised water rinses. As described above the level of cleanliness required by the NEXT process defines the cleaning method employed. Whenever we get a new enquiry we construct a method statement based upon a trial clean.