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How to Select and Use Your Ultrasonic Cleaner

If you’ve landed on this article chances are you’ve heard about how great ultrasonic cleaners are when it comes to removing all kinds of contamination from all kinds of surfaces. So you’ve decided to look further into the subject. You’ve come to the right place because when it comes to selecting and using your ultrasonic cleaner key considerations are the contaminations and the surfaces being cleaned.

A clear understanding of what you are attempting to clean and the contamination you want to remove goes a long way in helping you decide not only which ultrasonic cleaner you need but also the cleaning solution(s) that do the job the best. This post is written to help you decide.

Ultrasonic Cleaning 101

According to a 2003 article in Controlled Environments ultrasonic cleaning dates back to the early 1930s and work done in an RCA lab. Ultrasonic cleaning systems were developed starting in the 1950s.

Ultrasonic is defined as frequency above the range of human hearing which is about 20,000 cycles per second (20,000 hertz, 20 kilohertz or 20 kHz). Hertz comes from the German physicist Heinrich Rudolf Hertz (February 22, 1857 – January 1, 1894) who developed engineering instruments to transmit and receive radio pulses. These unit of frequency – cycle per second – were named "hertz" in his honor.

When applied to cleaning products, ultrasonic energy is used to create billions of minute vacuum bubbles in a cleaning solution – today usually biodegradable and water-based instead of the hazardous trichloroethylene and perchlorethylene cleaning solvents used in the earlier days. (More on cleaning solutions presented below.)

The bubbles are created by ultrasonic transducers bonded to the bottom (and/or sides) of a stainless steel tank. The transducers are excited by ultrasonic generators designed to deliver an ultrasonic frequency such as 37 kHz. This causes the tank bottom (and/or sides) to act as a vibrating membrane. Vibrations produce vacuum bubbles that pulsate through the solution and implode in a process called ultrasonic cavitation. This creates a powerful jet of cleaning solution against what is being cleaned to blast contaminants from all wetted surfaces.

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Ultrasonic Cleaner Purchasing Decisions

In addition to the cleaning tank and generator, the very basic ultrasonic cleaners will consist of an on-off button. Tanks may also be equipped with a drain. Depending on your requirements other decisions must be made.

Equipment Size

The parts you plan to clean will govern the size of your ultrasonic cleaner – in this case both the dimensions of the cleaning tank and the amount of cleaning solution required for the job. Fortunately cleaners come in a tremendous variety of sizes and tank shapes from small benchtop units to large industrial sized equipment. This assures you that there is a model ideally suited for your cleaning projects.

When considering size take into account not only the size of parts being cleaned but also that cleaning is usually accomplished in cleaning baskets. Baskets are designed to fit into the tank, meaning that their dimensions are somewhat less than tank dimensions in terms of length, width and depth. The point here is that parts must not contact either the sides or bottom of the cleaning tank.

The only exception to the basket criterion is if you suspend parts in the solution from an overhead support or the tank is equipped with a bottom support rack.

Parts being cleaned must be completely immersed in the cleaning solution. You’ll need to know the working depth of the tank, or the distance between the cleaning basket bottom and the surface of the cleaning solution. If this detail is not clear from the manual, ask the manufacturer.

Finally, if you clean extremely small parts you’ll want to investigate fine mesh baskets that can be positioned in regular baskets. Another option is to put these parts in beakers along with the cleaning solution then place the beakers in the basket. Cavitation passes through the glass beaker wall to act on the small parts.

Features Contributing to Cleaning Efficiency

The most basic ultrasonic cleaners are equipped with on-off switches. Manufacturers also offer models with added features that contribute to cleaning efficiency and throughput. Here are examples of options that you can consider:

The cleaning cycle can be controlled by timers that will turn off the ultrasound at the end of the cycle. This allows you to attend to other tasks during the cleaning operation.

In certain cases cleaning efficiently is increased at higher temperatures. Thermostatically controlled heaters bring the solution to the recommended temperature. Some units are designed to activate the ultrasound when the set temperature in reached. Note, however, that ultrasonic energy itself will warm cleaning solutions.

Freshly prepared cleaning solutions contain trapped air that inhibits cavitation action. A degas function drives off air faster than by operating the cleaner without a load, and is particularly time saving when cleaning in larger tanks.

Stubborn deposits of contaminants can be removed faster if units are equipped with a pulse mode that delivers bursts of high ultrasonic power. Pulse also helps degas cleaning solutions.

Uniform cleaning throughout the bath is achieved when the unit has a sweep mode that provides a slight ± variation in ultrasonic frequency. Without sweep there are three potential problems: ‘hot spots’ or areas with a high concentration of cavitation which can be damaging to sensitive surfaces, ‘dead zones’ or no cavitation, and harmonic vibrations. The latter causes parts to resonate which can damage sensitive components such as fine wires or crystals.

When cleaning involves a variety of products with varying conditions of contamination consider equipment offering adjustable power for faster, more effective cleaning. Keep in mind, however, that too much power can damage sensitive or highly polished surfaces. Therefore more power is not always better.

Just as swishing dirty silverware in the dishpan helps remove soils, so parts agitation in an ultrasonic cleaner helps flush away contaminants loosened by cavitation action. It has been shown, for example, that a ± 2 cm vertical oscillation in an ultrasonic bath improves cleaning speed by up to 20% while improving cleaning uniformity.

Selecting Ultrasonic Cleaning Frequencies

Ultrasonic cleaners are manufactured to operate at specific frequencies. Models operating at 37 or 45 kHz are widely used for most cleaning applications; other examples operate at 25, 80, and 130 kHz. Certain models can operate at dual frequencies.

While you’d be hard pressed to see the difference, cavitation bubbles produced at low frequencies are larger than those produced at high frequencies. Lower frequency bubbles implode more violently than higher frequency bubbles. Because of this cleaners operating at 25 kHz are popular choices when cleaning highly soiled fabricated and cast metal parts. Softer materials and those with highly polished surfaces are cleaned at higher frequencies. The smaller bubbles produced at 80 or 130 kHz are also more effective when cleaning parts characterized by cracks, crevices, blind and machined holes. This is because the smaller bubbles are better able to penetrate these hard to reach areas.

Examples of dual-frequency ultrasonic cleaners operate at user-selected 37/80, 25/45 and 35/130 kHz when cleaning a variety of products with differing characteristics.

Ultrasonic Cleaning Solution Options

Two key points apply when selecting an ultrasonic cleaning solution formulation: the parts being cleaned and the nature of contaminants being removed.

Common to most all formulations is that they are biodegradable. This eases disposal concerns; nevertheless local authorities should be contacted to avoid problems.

Here are a few examples. Please contact us for more detailed info on formulations best suited for your jobs.

  1. Alkaline cleaners such as elma tec clean A4 is a universal cleaner/degreaser for all types of metals and most plastics, and is widely used for cleaning automotive parts such as carburetors.
  2. Alkaline elma tec clean A1 is a free-rinsing formulation preferred for applications where the parts must be rinsed free of any chemical residue after cleaning. This includes cleaning optics and electronics, especially printed circuit boards.
  3. Acidic ultrasonic cleaning concentrates such as elma tec clean S1 are used for removing corrosion, oxidation, minerals and rust.
  4. Neutral elma tec clean N1 is a phosphate-free emulsifying cleaning concentrate for gentle cleaning action. It is used for the treatment of highly sensitive pieces.
  5. MedClean C7 removes blood, tissue, ointments and bodily excretions from medical and surgical instruments.
  6. Fine cleaning aluminum and light metal alloys, glass, ceramic, mineral and plastic surfaces is accomplished with EC 260 d&s neutral foam-inhibited concentrate.

Because most solutions are water based there may be a concern about rusting. Rust inhibitors can be added to address this.

Tips for Correct Mixing of Cleaning Solutions

Ultrasonic cleaners are designed to hold a specific level of cleaning solution. Neither overfilling nor under filling contributes to the cleaning process, and under filling may damage the unit. The correct amount is generally indicated by a fill line or some other method.

Because parts being cleaned displace solution we suggest the following procedure when preparing the solution.

  1. Add water until the tank is half full
  2. Add the correct amount of cleaning solution concentrate for a full tank. Dilution instructions are shipped with the concentrate.
  3. Add water to the fill line and activate the ultrasound and/or degas mode to mix and degas the solution.

Draw off and set aside solution that will be displaced by parts being cleaned. When these are immersed the solution level should return to the fill line. Or add enough drawn off solution to make it so. You’re ready to clean.

A related term is called the service volume, which is the minimum amount of solution that can be safely mixed and degassed. It can be useful when accommodating for displacement rather than mixing and degassing a filled tank then drawing off the excess. The service volume should be indicated in the manual; if not ask the manufacturer.

The above may seem complicated at first. But as you develop experience you’ll nail down how much fresh solution to prepare based on the products you are cleaning.

Extending Cleaning Solution Performance

Contaminants removed during ultrasonic cleaning remain in the solution. Those that float to the top should be skimmed off and set aside for later disposal. Spray bars and weirs are available on larger tanks to perform this task. Solid particles that drop to the bottom can be removed by filtering systems also available for larger tanks.

But when cleaning effectiveness drops solutions should be replaced. Abide by local regulations for proper disposal and take the time to clean the tank following user manual recommendations.

Rinsing and Drying Cleaned Parts

If cleaning solution residues are unacceptable consider installing spray stations, rinsing tanks and dryers to your cleaning line. Ask vendors for recommendations.

Sound Advice on Ultrasonic Noise

Ultrasonic cleaners operating at lower frequencies create noise due to tank wall vibrations. Lids (which also reduce evaporation), sound-deadening enclosures and ear protection are ways to reduce annoying ultrasonic noise.

Call the ultrasonic cleaning experts for more information on selecting and operating ultrasonic cleaners that meet your specific cleaning requirements.

FREE GUIDE TO ULTRASONIC CLEANING APPLICATIONS

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