What is ultrasonic cleaning and how does it work?

 

Ultrasonic cleaning is a process that uses non-audible sound waves (usually from 20 to 400 kHz) and a suitable cleaning solvent (occasionally ordinary tap water) to rapidly clean objects. The objects are placed in a tank with liquid flooded with high-frequency ultrasound energy that gently removes any contaminants from the surface of the item.

Simply put, ultrasonic cleaners work similarly to automatic dishwashers, although obviously the process is slightly more refined. While automatic dishwashers are used for pans and bowls, ultrasonic cleaners are utilized for items difficult or impossible to clean using other methods.

Cavitation or how does ultrasonic cleaning work?

The secret of ultrasonic cleaning is a process called cavitation. Cavitation is a result of ultrasonic energy which is produced by converting high-frequency electrical energy with the help of a transducer placed at the bottom of the tank.

The high-frequency sound waves (or ultrasonic energy) enter the fluid in the tank, and that causes the rapid formation and collapse of small bubbles – a process known as cavitation. These small bubbles move at high velocity inside the tank which makes them implode (not explode) on the surface of any item immersed, releasing a reasonable amount of energy.

As the bubbles continue imploding and cavitation occurs, the cleaning solvent moves into the gap left behind by bubbles, mildly removing any dirt, tarnishing, and contaminants from both the surface and the most intricately shaped parts of the object.

 

The transducer

There are more than enough variables to take into account when cleaning items using ultrasonic cleaners: heat, frequency, power, cleaning solvent type, and time – all of these affect the process, but we are safe to assume that the core of the device is the transducer.

The ultrasonic equipment’s ability to clean even the most persistent contaminants from objects is determined by the transducer. Therefore, the cleaning power of the ultrasonic cleaner derives from the transducer’s performance, making this component a key part of the entire process.  

There are two main types of transducers: the piezoelectric (or electrostrictive) transducer and the magnetostrictive one.

Both types are sensitive to the current provided by the unit’s generator and start vibrating at ultrasonic frequencies which then cause the bottom and the sides of the tank to vibrate. This process makes the tank serve as a membrane, and the vibration forms the bubbles that implode on contact with items immersed in the ultrasonic cleaner.

Ultrasonic frequency

Another important part of the ultrasonic cleaning process is the ultrasonic frequency as this is what determines the size of the bubbles.

Lower frequencies like 25 kHz (or 25,000 cycles per second) produce significantly larger bubbles that implode more vigorously than the bubbles created at higher frequencies such as 80 or 130 kHz that are at the root of a more gentle cleaning movement.

To remove contaminants from items made of cast iron or metal, one should use lower frequency cleaners whereas softer metals or objects made of plastic and items with polished surfaces should be cleaned at higher frequencies. That’s because smaller bubbles manage to penetrate difficult areas such as crevices and small holes and protect polished surfaces.

 

Where do the contaminants go?

To continue with our automatic dishwasher analogy – in the case of the dishwasher, the dirt goes down the drain. However, in the case of the ultrasonic cleaner, the contaminants remain in the cleaning solution – they either sink to the bottom or float to the surface or simply remain in suspension in the liquid, depending on what kind of cleaning solution is used.

Because of this, the efficiency of the ultrasonic equipment will eventually decline, and when that happens, the solvent must be drained and disposed of along with the contaminants, according to the manufacturer’s instructions and local regulations.

Ultrasonic cleaning applications

Ultrasonic cleaning is extensively used across many industries, from jewelry and watchmakers workshops to electronic repair shops. They can also be used in hospitals, factories, and other similar businesses.

Ultrasonic cleaners are generally customized to suit a certain type of items. For example, tabletop and benchtop cleaners are excellent for cleaning small or delicate objects like laboratory glass and plasticware, surgical instruments, optical parts (like telescope mirrors), or carburetor components.

On the other hand, precision cleaning is mostly used for fragile items that have been damaged by other cleaning methods (like coins, gramophone records or jewelry).

 

 

 

Benefits of using ultrasonic cleaning

Ultrasonic cleaning is a cleaning method widely used in a multitude of industries, from the pharmaceutical industry to weapons manufacturing. This method is  so popular because it has a high number of advantages and we will focus on a few of the said advantages in this short article.

Environmentally friendly

Before the environment became a major concern, many industries mostly used chemical cleaners. It was often the case that these cleaners contained harmful substances, such as esters and chlorinated hydrocarbons, which can seriously pollute underground water supplies.

These chemicals also emanated highly toxic vapors and the workers were often required to wear masks to protect them from the dangerous fumes. In contrast, ultrasonic cleaners use detergents soluble in water to remove contaminants instead of harsh chemicals.

 

Thorough and gentle cleaning

More delicate objects, such as jewelry or certain instruments, could be damaged by harsh chemicals or hand cleaning. These items require both a thorough and gentle cleaning.

The cavitation process which occurs during ultrasonic cleaning allows the solvent to reach into narrow crevices and remove unwanted contaminants, while keeping the piece safe from damage. That’s one of the reasons many jewelry workshops are equipped with some of the best ultrasonic jewelry cleaners out there.

 

Wide range of applications

Ultrasonic cleaners can be customized to suit specific cleaning needs. These systems can be used by nearly anyone, from passionate collectors to government agencies and private companies.

At home, ultrasonic cleaners can be utilized to clean jewelry and collectible coins in order to remove rust, skin oils or dust. Automotive workshops clean their tools with an ultrasonic unit to remove lubricants or other residue that can keep a car from working well. Police and federal agents clean their weapons or handcuffs and other pieces of equipment with ultrasonic cleaners.

Wide range of sizes

Due to its many applications, ultrasonic cleaners come in different sizes, made to fit specific cleaning needs. They can vary from tabletop units to big, industrial-sized units.

That means the perfect-sized machine can be purchased for each service needed, and there is no need to waste energy or solvents on a “one size fits all” cleaning mechanism. Nor space to store the unit is wasted either, for that matter. Some units use specific solvents to remove certain contaminants, while other ultrasonic cleaners will only require water and a small amount of detergent or degreaser.

 

Low electricity consumption

When comparing ultrasonic cleaners to other types of cleaning systems that use different motors to pump, agitate, circulate, spray, and capture the cleaning chemicals and their vapors, ultrasonic cleaners are clearly in advantage as they only require one small motor to filter the solution in the tank.

The entire cleaning process is done with electrical energy and transducers, keeping electricity consumption to a minimum. Using less electricity is another reason ultrasonic cleaners are more environmentally friendly than other cleaning equipment.

 

Remove an extensive array of contaminants

Ultrasonic cleaners can remove a variety of residues from an item’s surface, including grease, wax, sand, rust, dirt, dust, or clay down to a microscopic particle size. There is no other cleaning machine that offers this level of flexibility in one system.

In addition, ultrasonic cleaners can also remove mold and bacteria from surfaces. This makes them perfect for cleaning equipment used in food industry for preparation and processing of food, as well as for cleaning instruments and devices used in the medical and pharmaceutical industry.

Work safety

Because it does not use dangerous chemicals during the cleaning process, an ultrasonic cleaner prevents those that handle it from inhaling harmful chemical fumes. Moreover, it also prevents technicians from handling sharp instruments that could contain biological residue.

Previously, workers had to handle medical instruments, such as scalpels and drill parts, which could puncture the skin and expose them to a potentially dangerous contaminant. With an ultrasonic cleaner, the technician only needs to place the item in the tank, add water and cleaning solution, and turn on the unit.

 

Efficiency

One of the biggest advantages of relying on ultrasonic cleaners is their long-term cost efficiency. The ability to clean multiple items quickly, thoroughly and gently is paramount for many industries, ranging from medical facilities to manufacturing plants and automotive workshops.

These systems are automated and they are so efficient that a technician can clean up to 20 items at a time using ultrasonic cleaning technology.

 

 

 

How to select the right ultrasonic solution

 

Ultrasonic cleaning is favored among all the other cleaning methods because of its versatility, efficiency and thoroughness. In addition, an ultrasonic cleaner is very easy to use as long as you follow a few basic rules, the most important being the one concerning the type of cleaning solution utilized.

Failing to use the right type of solvent might lead to damaged items and to a damaged ultrasonic cleaner tank.

Some basic questions

Before deciding on a specific solution formulation and a supplier, it is best to take some time and analyze a few basic aspects.

First of all, you need to take into account what sort of residue you are trying to remove. There is a difference between removing blood or tissue from medical instruments, clearing of contaminants the best lenses for telescopes and eliminating chips or dust from a machined part.

Secondly, pay attention to the composition of the item you are trying to scrub and how it will interact with the solution. In theory, any object that can be immersed is suitable for ultrasonic cleaning, but a cleaning solvent with the wrong chemical composition may cause damage. For example, a solution formulated with 70% sulfuric acid removes scale, but damages carbon steel.

Finally, are there any more steps after the cleaning process is complete? When it comes to machined parts, maybe they will be subjected to painting or to adding another coating once the parts are cleaned. Surgical instruments have to be sterilized because ultrasonic cleaning does not remove viruses or spores. This aspect must be taken in consideration as well when choosing what type of detergent to use.

 

Alkaline solutions

These solvents have a pH of 10 or higher – the higher pH the solution has, the more aggressive it is. Depending on how powerful the ultrasonic cleaner is, this type of solution may or may not contain caustic soda (sodium hydroxide).

Moderately alkaline compounds, the ones with a pH ranging from 11.0 to 12.5, are ideal for most metals, including steel (stainless or not), cast iron, zinc, aluminum, brass, copper, and tin. In addition, they also effectively clean glass (including neutral glass), ceramics, and most types of plastic.

Acidic solutions

Acidic solutions are a bit trickier to use in the sense they are very specific and have to be utilized with suitable materials – some acids might damage certain materials, while the same acids have no effect on others. Knowing which is which is essential for a successful ultrasonic cleaning process.

This type of solvent has a pH of 5.0 or lower, with lower pH solutions being the most aggressive.  Acidic solutions are perfect for removing oxidation from almost all metals, providing the solution has inhibitors in order to protect the base material.

 

Deionized water

Deionized water will work on nearly any material out there, as long as it can be safely immersed in water: glass, metal, epoxies, hard rubber, plastic, just to name a few.

The quantity of deionized water used in the solution has to be calculated carefully because many items will oxidize quickly once taken out of the ultrasonic cleaner tank. In order to prevent this, immediately after the washing process is done, the item has to be placed in a wetting solution and dried. Some of the items that need special post-cleaning handling are switches, printed circuit boards and small servo motors.

 

High caustic solutions

These solutions are actually alkaline solutions that contain caustic soda. Although they can be used should the need arise, the first option must be more moderate formulated alkaline solvents.

Highly caustic detergents contain hydroxides and silicates and are great for removing oils, wax, or heavy grease from objects made of steel, stainless steel and cast iron. Special attention has to be given to the interaction between magnesium and highly caustic solvents — in case magnesium is added in the ultrasonic cleaner tank, then a low caustic solvent should be used or else it may cause damage to the object.

Enzymatic solutions

This type of solution is utilized mostly for cleaning tools and instruments used in medical facilities and in pharmaceutical and food processing industry. It is specially designed to remove contaminants that are based on protein and it is good for brass, titanium, aluminum, stainless steel, but also for lab equipment made of plastic and glass.  

 

 

 

What can you clean with an ultrasonic cleaner?

 

If you’re wondering what can you clean with an ultrasonic cleaner, the answer might surprise you – long story short, just about everything. This popular method of cleaning can be used at home, for passionate coin collectors for example, or in industries ranging from medical facilities to weapons manufacturing and automotive workshops.

Why is ultrasonic cleaning so widely spread?

This cleaning method’s popularity makes perfect sense considering items have to only meet two requirements in order to be scrubbed with ultrasonic cleaners.

Firstly, the object must not be damaged by immersion because the basic process of ultrasonic cleaning, cavitation, only occurs in a liquid environment. Secondly, the item has to dry fairly easy, which means only things that absorb fluid are not suitable for ultrasonic cleaning.

 

Electronics

The idea of immersing electronic equipment in water or any other kind of liquid might seem counterintuitive, but providing proper drying techniques are used, it is actually very safe. Moreover, ultrasonic cleaning is much more efficient in terms of thoroughness and duration than any other method out there.

Previously, trichloroethylene was used to clean electronics, but the ultrasonic method is more convenient, requiring only water and some mild water-soluble detergent.

 

Glass, ceramics and other delicate items

We have all watched those sci-fi movies where high-frequency sound waves are used to shatter windows, flower vases and basically anything that’s made of glass. Yet, in real life, ultrasonic cleaning is the best method to scrub items like glass beaker sets, high precision lenses or cannulae.

Using ultrasound on glass or other fragile objects is not only perfectly safe, but it can save money in the long run because this cleaning system is so gentle and it requires so little handling, that there is a very low risk of damaging or scratching these delicate things.

Medical equipment and implants

As previously stated, ultrasonic cleaning is excellent for scrubbing all sort of glass and plasticware, including lab equipment, medical instruments, and implants. This kind of equipment has always to be spotlessly clean, and there is no other method that can clean like the one using high-frequency sound waves.

However, it should be noted that ultrasonic units do not sterilize, so viruses and spores have to be eliminated using specific methods. On the other hand, there is so little handling when it comes to this type of washing, that the risk of contamination is very low.

 

Aerospace components

Along with medical facilities, the aerospace industry is another field of technology where quality expectations are enormous. Whether we are talking about the manufacturing process or simple maintenance, everything has to be perfect and mistakes are not allowed. Luckily, ultrasonic cleaning is up for the challenge.

These systems excel in eliminating contaminants quickly and thoroughly, whether it’s about removing grime from a hydraulic part or cleaning oil off some newly machine components or simply making some stainless steel part shiny and spotless.

 

Large industrial items

Ultrasonic cleaners come in a wide variety of sizes, from tabletop units designed to clean items like coins or jewelry, to large systems created for industrial use. When it comes to industrial molds and engine parts, the most important thing to consider is the sound wave frequency of the ultrasonic device.

These large industrial items are often contaminated with difficult to remove residues and, if that’s the case, then it is the right moment to bring in “the big guns” – large ultrasonic cleaners that eliminate even the most resistant grime. The best units for such a task are those that function at a frequency just above the human hearing range (which is 18 kHz).

Other tools, machined parts, and equipment

If an object has been machined, lapped or polished there will be residue like cutting oil, dust, chips or polishing compounds on it. Ultrasonic cleaners remove all that quickly and gently. As long as the object is immersed, it gets cleaned and this way there is no chance of ruining the next step of the manufacturing process of the part like painting or applying some other needed coating.

Similarly, equipment like piping from an oil refinery or carbide cutting tools is rendered spotless with the help of an ultrasonic cleaning unit. Moreover, using ultrasounds saves time and money considering ultrasonic cleaners are fast and do a more thorough job than any other method available.

 

 

 

A short history of ultrasonic cleaning

 

Ultrasound was initially used only for image processing and it was discovered by John Wild – the so-called father of modern ultrasound. Wild managed to identify transducers that emit sound waves which then reflect back and project images of different internal organs.

Nowadays, ultrasound has many applications in a multitude of industries: automotive, pharmaceutical, engineering, and weapons manufacturing, just to name a few.

There is a number of additional uses for ultrasound, including humidification, disintegration, welding, identification, as well as a wide range of medical applications. Whichever field ultrasound may be used in, it is helping companies in their effort to become more environmentally friendly, and more efficient in terms of costs, time and labor.

What is ultrasonic cleaning?

Just like the name suggests, ultrasonic cleaning is a process that uses ultrasound (non-audible sound waves) and a cleaning solvent or a detergent in order to clean certain items. Ultrasonic cleaners are able to function using just water as a cleaning solution, but choosing a type of solvent suitable for the object to be cleaned will enhance the efficiency of the process.

Ultrasonic cleaning is nowadays a conventional cleaning method utilized in a plethora of industries, ranging from laboratory equipment (used for items like glass beaker sets) to jewelry workshops and hospitals. There are even ultrasonic denture cleaners out there and ultrasonic cleaning systems used for carburetor components, as well.

 

How does it work?

This method of cleaning is based on a process called cavitation – small bubbles are produced with the help of high frequency sound waves and then they implode on the surface of the object immersed in the cleaning solvent.

Through the process of cavitation, contaminants are removed both from the item’s surface, and from the small cracks and recesses. Contaminants can be dust, soil, rust, algae, limescale, bacteria, grease, mold, and so on.

The advantage of ultrasonic cleaning is that it can be used for products made of different materials (like plastic, ceramics, rubber or glass) and of different shapes and sizes, and it is possible not to require the object to be disassembled before cleaning.

Discovered by accident

The history of ultrasonic cleaning started almost 90 years ago, in the early 1930s. One of the Radio Corporation of America (RCA) laboratories, located in New Jersey, discovered that ultrasounds can be used for cleaning by accident.

While trying to cool the inner components of a radio with freon, they noticed a wave movement around a crystal operating at 300 kHz. Although this process was considered interesting, it was not researched as a cleaning method for years to come.  

 

Taken out of the laboratory in the 1950s

During the 1950s, the Bendix Corporation in Davenport, Iowa, created an ultrasonic department that experimented with multiple applications of ultrasound only to discover that ultrasonic cleaning was the most profitable. In 1952, this method of cleaning was used in production for the very first time.

Bendix tried to pioneer ultrasonic cleaning in several industrial environments.  The process was highly effective and its popularity in the manufacturing industries increased rapidly. That included electronics companies, those in the medical equipment field, the aircraft industry, automakers, and even missile manufacturers.

Ultrasonic cleaners become popular

In 1959, Time Magazine published an article entitled “Ultrasonics: Unheard Progress” and it was such an optimistic piece of writing that the possibilities seemed endless. “Someday we’ll be cleaning clothes with ultrasonic equipment”, the author wrote.

The Time article focused on a few innovative companies that were researching non-audible sound waves and their applications in industry and everyday life. These companies developed ultrasonic tanks and used them to clean anything – from pens to cash registers and electric shavers.

Most ultrasonic cleaners developed in the late 1950s were operating with frequencies ranging from 18 kHz to 40 kHz. 18 kHz is the lowest frequency and it is still widely used nowadays. Even though Russia developed a 6 kHz system, it wasn’t very popular so it was quite short lived. Until the late 1980s the majority of systems available on the market operated at 25 kHz to 40 kHz.

 

 

 

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