Ultrasonic Cleaning FAQs
Questions about ultrasonic cleaners and the process of ultrasonic cleaning? We've collected a list of common questions and provided answers below. Click on your question to see a detailed answer.
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At the very minimum water and a few drops of dishwashing liquid. Best cleaning results are obtained when using an ultrasonic cleaning solution formulated for the cleaning tasks at hand. These are offered as biodegradable concentrates with instructions on dilution and cleaning temperatures. Do not fill the tank with flammable solvent unless the unit is designated as explosion proof. For more details see our post on cleaning solution selection tips.
Most ultrasonic cleaning solutions marketed today are biodegradable, are shipped as concentrates and are formulated as: acidic, neutral, or alkaline.
- Acidic solutions are used to remove rust and mineral deposits from ferrous metals, but not for light alloys susceptible to corrosion.
- A mildly alkaline ultrasonic cleaning solution is suitable for removing oil, grease, dust, soot and other organic compounds on glass, plastic, ceramic, rubber, iron and non-ferrous metals. Mildly alkaline detergents containing enzymes are used to remove blood and tissue from medical instruments.
- An ammonia-containing alkaline solution cleans laboratory appliances, work pieces and jewelry made of glass, ceramic and precious metals. It also brightens jewelry and non-ferrous metals.
- Strongly alkaline (caustic) solutions are used to strip burned on plastic residues from metal injection molds.
- Very delicate materials made of plastic, glass, metals and rubber call for a neutral solution to remove impurities such as dust, grease, pigments and other organic compounds.
- Nonflammable semi aqueous organic microemulsions are used to strip paint, coatings, adhesives, grease, and shellac from metal surfaces. These formulations may be either acidic or neutral and are not classed as biodegradable.
- Nitric, sulfuric, formic, or hydrofluoric acid should only be used when an acid-resistant plastic tub is placed in the tank to protect the stainless steel. These solutions are not biodegradable and must be disposed of properly.
Our post on ultrasonic cleaner solution selection tips provides added detail.
Before you set up the cleaning process it’s important to define ‘clean’. DI water is used when a spot-free surface is required after cleaning. In most cases it is adequate to clean with a cleaning agent dissolved in tap water and rinse with DI water to remove residues. (Also, see answer below about water containing chlorides.)
Yes under certain conditions. The potential for damage is increased when using cleaning media with pH values in the acid range. If tap water contains chlorides, we recommend using cleaning chemicals in the alkaline range. If the cleaning job requires an acid cleaner use distilled water instead of tap water.
Yes but care must be taken to avoid condensation that can damage transducers.
This is generally not allowed in an open bath. Instead you can treat a limited quantity of a flammable medium when it is placed in a separate, closed container (e.g. beaker with a lid) immersed in a tank containing water and a surfactant. Flammable solvents may be used in an explosion proof ultrasonic cleaner in an area suitably equipped for hazardous vapors. Check our post on cleaning with flammable solvents for more information.
Here are some suggested frequencies.
- 25 kHz for the removal of coarse and tenacious adhesive contaminants and for pre-cleaning of robust surfaces such as stainless steel and cast iron
- 35-45 kHz is the standard frequency range for most cleaning jobs and for cleaning tasks in the laboratory and sanitary sector
- 80-130 kHz is used for the finest cleaning jobs and for the cleaning of highly sensitive surfaces such as micro electronics, precision optics, and polished aluminum
For more details please check our post on how ultrasonic cleaners work.
Two points to keep in mind. Tank size and basket size. Basket dimensions are smaller than tank dimensions. Determine the dimensions of the largest parts you will be cleaning and select equipment with a basket size that accommodates those parts. For example, the 4.7 gallon Elmasonic Select 180 has tank dimensions 12.9 x 11.8 x 7.9 inches deep with basket dimensions 11 x 9.8 x 4.5 inches deep. Caution: separate, do NOT stack parts in the basket for optimal cleaning results.
The short answer is yes. Baskets are designed to suspend parts at the proper level above the bottom of the tank and also prevent damage to the tank. Large parts cleaned in industrial-sized tanks can be suspended in the cleaning solution. Check our ultrasonic cleaner video for more information.
Keep in mind that ultrasonic cavitation increases bath temperature. Heated solutions are best for highly contaminated greasy parts. Suggested cleaning solution temperatures are recommended by manufacturers. For example, the recommended cleaning temperature range for widely used degreaser Elma tec clean A4 is 50⁰ - 80⁰C (122⁰ - 176⁰F). For removal of blood and biological tissue from used medical instruments, the bath temperature should be under 40⁰C to prevent blood hardening; no heating should be used at all.
Cleaning cycle time depends on the number of parts being cleaned, the extent of contamination, and how you define "clean." Cleaning baskets allow you to safely remove parts from the bath for inspection but be aware they will be hot. With experience you'll be able to set cleaning cycle length on the ultrasonic cleaner timer. Limit wear and tear by cleaning for the shortest time that does the job.
Ultrasound at a fixed frequency creates fields of high and relatively low ultrasonic intensity, which can yield uneven cleaning results. Sweep is the term used to describe a continuous slight modulation of the ultrasonic frequency. This produces a more uniform distribution of the cavitation process and delivers better performance in the cleaning bath.
The pulse mode provides brief spikes in power to remove stubborn contaminants or for mixing and sample prep.
A freshly filled ultrasonic tank contains air, as exemplified by bubbles observed when placing an item in water. Unless removed by degassing, the bubbles inhibit the cavitation process. Equipment should be operated in the degas mode when filled with fresh solutions and before starting the cleaning operation. If the unit has no degas mode, degassing can be accomplished by operating the ultrasonic power for about 15 minutes. The sound produced by the unit during operation changes discernibly when the liquid has been degassed.
The Eco Mode, a feature of the Elmasonic Select series, is selected for gentle cleaning and a quieter operation, achieving a lower intensity cleaning cycle with sweep frequency.
Oscillation, also called agitation, is precisely controlling the up-and-down movement (± 2 cm) of cleaning baskets to maximize the efficacy of the cavitation process. Precision is critical because if movement is more severe it will in effect reduce or even eliminate the cavitation action. Oscillation is offered as a Move option on the Elmasonic xtra ST industrial ultrasonic cleaners.
The lifetime of the solution depends primarily on how much soil is being removed from parts. Soils removed during ultrasonic cleaning cycles either rise to the surface or are suspended in the solution. Hard contaminants settle to the tank bottom and unless removed will cause damage. Solution replacement is signaled when cleaning efficiency drops off. Drain the tank and dispose of spent solution according to local regulations, and take the time to clean the tank following user manual instructions. Check the section "where contaminants go" in our post on how ultrasonic cleaners work.
While "ultrasonic" is generally defined as sound above the hearing range, ultrasonic cleaners do make noise due to the vibration of the equipment. Low-frequency (25-45 kHz) cycles are noisier than higher frequency cycles. For long-term exposure options are available: hearing protectors, lids (that also reduce cleaning solution evaporation) and placing the unit in a noise protection box. Some models have an option of a hinged insulated lid to further reduce noise,
Detailed maintenance instructions are provided in the user manual. For day-to-day operation be certain that your tank is properly filled with cleaning solution - designated by the fill line when parts are in the basket. Avoid overfilling and under filling. Continually skim off floating contaminants and set them aside. Replace cleaning solutions when efficiency drops off and dispose, along with skimmed off contaminants, following local regulations. Clean the tank to remove settled contaminants but do not scour.
It's a good idea to run a performance check on your ultrasonic cleaner from time to time. This is especially important if you are cleaning medical instruments and must meet CDC standards. But optimum performance is also important in any cleaning operation to help assure thoroughness and improve throughput. The easiest and most popular method is the aluminum foil test described, along with other alternatives, in our post on ultrasonic cleaner performance validation.
In addition to the correct ultrasonic frequency, cleaning solution chemistry, temperature, cleaning cycles (sweep, pulse, degassing, time…) and bath maintenance we suggest this: Remove gross contaminants first, disassemble complex components, separate parts in the basket, inspect and reposition if necessary. The user manual provides information on effective operation, and running a performance validation will indicate your unit is operating properly or needs attention.
Absolutely no! Chances are the solution will be hot, but more importantly cavitation will pass through your skin and act on your blood stream.
You don't need to but covers perform important functions. They reduce cleaning solution evaporation and they reduce noise. Covers on some models can be inverted after the cleaning cycle, serving as trays allowing solution to drain back into the tank.
Not recommended because the heaters will cause discoloration on tank walls. When the ultrasonic power is operating the solution circulates in the tank to carry heat away.
It is the erosion of the tank surface by cavitation associated with ultrasonic cleaning and can in the long run lead to tank failure. Tank life is prolonged with regular cleaning to remove settled particles that abrade the tank bottom when subjected to ultrasound, by not placing items being cleaned directly on the tank floor, and by operating the tank at the proper fill level.
Discoloration, also called furring, can result when highly calciferous water contacts hot surfaces and usually occurs around the heating elements. It can be prevented by using ultrasound to circulate the bath during the heating cycle to minimize hot spots. Furring can be removed fairly easily and gently with standard citric or phosphoric decalcifiers. Never use an abrasive cleaner on tank surfaces. We cover this in our post on tank discoloration.
Because this is a complex operation, we recommend that repairing or replacing transducers be done by a qualified technician in a service center.
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