What is Ultrasonic Cleaning?
Ultrasonic cleaning involves use of ultra-sound with the usual frequency range of 20-40 kHz to stimulate a liquid which subsequently cleans a surface through a process known as cavitation. Cavitation occurs when rapid changes in pressure of liquid due to application of Ultrasonic cause formation of small bubbles/voids in liquid. The size of the bubbles depends upon the frequency of ultrasonic waves. When these bubbles or cavities collapse, they send out shockwaves which subsequently produce a ‘scrubbing’ effect and remove contaminants.
The liquid used in Ultrasonic cleaning can be water, but any solvent can be used which is suitable for the surface which is to be cleaned and for the contaminant which needs to be removed. The duration of cleaning process takes on average around five minutes, but it can take much longer as well.
Ultrasonic cleaning might be expensive to manual scrubbing and cleaning but in the long run, the superior cleaning achieved through ultrasonic pays off the investment as it increases the useful life of your object/equipment [1].
What are the Applications of Ultrasonic Cleaning?
Ultrasonic cleaning has very wide applications. It is used to clean jewelry, optical lenses, watches, medical instruments, sports equipment, musical instruments, automobile parts, electronic equipment and many other industrial machinery. Due to its wide use Ultrasonic is being used in automotive, sporting, printing, marine, medical, pharmaceutical, computing, engineering, weapons and many other industries [2].
Material which is non-absorbent and is not affected by chemicals is most appropriate for such cleaning. It should be noted that Ultrasonic cleaning does not kill viruses and spores therefore medical equipment needs to be sterilized separately.
What is the process of Ultrasonic Cleaning?
The object which needs cleaning is placed in a chamber which contains any suitable cleaning solvent. The solvent could be aqueous or organic. If the solvent is aqueous, usually a cleaning detergent is also added in order to remove nonpolar contaminants such as oil and grease. The temperature of the solvent is kept around 130 °F but cleaning of medical equipment requires a temperature below 113 °F in order to avoid coagulation of proteins. A transducer is in place inside the chamber to produce Ultrasonic waves. The frequency of these compression waves can be maintained using electric signal. The strength of these waves is stronger at their source of origin but as they move further away from the transducer their strength reduces.
The waves thus produced make their way into the solvent creating multiple bubbles or vacuum voids along their way. The number of such voids is in millions. These voids collapse releasing energy. Temperature of 5000 K and pressure of 135 MPa are reached on the collapsing of these bubbles which is just enough to remove contaminants and not harm the object itself. At lower frequencies of around 30 kHz, large bubbles/voids are created which explode against surfaces far more violently as compared to small bubbles which are created at higher frequencies of 80 kHz and higher [4].
What are the benefits/advantages of using Ultrasonic Cleaning?
Ultrasonic have the ability to penetrate hidden and microscopic cracks and holes and can clean objects having different shapes and sizes. This ability to reach otherwise difficult surfaces ensures thorough cleaning as well as it allows to clean objects without the need to dissemble them before subjecting them to Ultrasonic waves. The only care which needs to be taken in this regard is to make sure that the object which needs to be cleaned must not be resting on a surface where it is not coming in contact with the cleaning solvent. Contact with the solvent is necessary for cavitation to occur. A solution for this problem is to put the object which needs cleaning in a very fine mesh basket which ensures that liquid reaches the entire surface of the object.
This cleaning process works equally well for multiple objects such as metal, plastic, glass, rubber, ceramic etc. Ultrasonic cleaning has this advantage over other cleaning methods that it has the ability to remove a huge number and multiple types of contaminants such as dirt, oil, grease, pigments, rust, algae, fungus, bacteria, blood, fingerprint, soot, mold etc. Ultrasonic cleaning also does not require harsh solvents for cleaning or at least not in that much quantity as other cleaning processes require because Ultrasonic agitation is more than enough to remove contaminants.
Ultrasonic cleaning is also environment friendly as the use of chlorinated and fluorinated solvents as cleaning solutions is considered outdated and extremely harmful.
What are the precautions taken while using Ultrasonic cleaning?
Equipment such as gyroscopes, accelerometers and microphones are usually not subjected to ultra-sound cleaning because the shockwaves produced during the process can irreversibly damage them. Moreover, high voltage can harm their drive circuits and printed circuit boards (PCBs). This problem can be overcome by using ultrasonic cleaners which are equipped with a sweep mode which helps in avoiding harmonics that could damage the PCBs. Chromium plated objects are also not recommended to be cleaned through this technique.
It is also important not to use any flammable solvent as Ultrasonic waves raise the temperature of the solvent. Human involvement should also be highly regulated as physical contact with the cleaning solution can cause skin irritation and burning [5].
What Precision, Fabricating & Cleaning (PFC) can offer?
PFC is equipped with the best equipment and also has the finest professional team to provide you with tailor made cleaning solutions through the use of Ultrasonic waves. We have years of experience in serving multiple types of industries. We can suggest best cleaning solvents as well as the optimal frequencies for Ultrasonic waves according to the object to be cleaned and contaminant to be removed. We also make sure that cleaning procedure follows the guidelines and recommendations of the relevant professional associations so that our client could maintain the highest standards. Our ultrasonic cleaning units are equipped with heater, timer and sweep modes along with rinsing and drying units to provide complete cleaning solutions. In addition to this PFC also provides a wide range of other industrial services which can be seen here.
Sources
[1] http://www.heatexchanger-fouling.com/papers/papers2011/48_Kieser_F.pdf
[2] http://www.absotecthailand.com/Cavitation.pdf
[3] https://www.nist.gov/sites/default/files/documents/ncnr/UltrasonicCleaner_Branson_1510.pdf
[4] https://www.sonicor.com/the-benefit-of-ultrasonic-cleaners-in-the-automotive-industry/
[5] https://www.tovatech.com/blog/25869/ultrasonic-cleaner/application-ideas-ultrasonic-cleaners