The Cleaning Machine That Uses Collapsing Bubbles as Tiny Tools.
An ultrasonic cleaner looks almost disappointingly simple: stainless tank, liquid, basket, buttons. Then it begins turning pressure waves into millions of microscopic cavitation events that reach recesses, threads, channels and textured surfaces a brush may never touch. Elma's current Elmasonic Select makes that invisible process programmable, repeatable and scalable from a small benchtop bath to an 89-liter machine.
By Dr. Rob Urban · On cavitation, 37kHz ultrasound, sweep and pulse modes, degassing, heated chemistry, reproducibility, watchmaking roots and why the most interesting cleaning tools sometimes never touch the object they clean
First, the current-product check
Keep Elmasonic Select. It remains Elma's current programmable general-purpose ultrasonic-cleaning platform, spanning models 30 through 900 rather than one obsolete fixed-size machine.
Elma's current lineup separates its benchtop ultrasonic cleaners by job. Elmasonic Easy is the simpler entry platform. Elmasonic P adds switchable frequencies for more complex applications. Elmasonic Med addresses regulated medical-device workflows. Select sits in the middle as the broadly programmable workhorse.
The current Select family runs at 37kHz and offers five ultrasonic modes, four memory locations for custom programs, heating from 25 to 80°C, temperature-controlled start, automatic degassing, wipe-clean membrane controls and a bright status display.
The family is unusually broad. Elma lists models from the Select 30 through the Select 900, with recommended operating capacities stretching from 2.7 liters to 89 liters. The smaller machines belong comfortably on a bench. The largest are serious floor-scale cleaning equipment with optional noise-protection lids.
That breadth is why I am treating Elmasonic Select as a platform rather than pretending one tank size represents every use. The fascinating part is the control architecture and ultrasonic process shared across the family.
The cleaning tool is a bubble that exists for almost no time
Ultrasound makes liquid alternately stretch and compress until cavities appear and collapse.
Sound is pressure variation traveling through a medium. At ultrasonic frequencies, those pressure cycles occur too quickly for human hearing but still transmit mechanical energy through the cleaning bath.
During the low-pressure portion of a cycle, microscopic cavities can form in the liquid. During subsequent higher-pressure conditions, those cavities collapse. This phenomenon is cavitation.
The collapse is highly localized. It produces tiny jets, shock effects and intense mechanical disturbance close to surfaces. Multiply that behavior across an entire bath and contamination can be attacked in grooves, holes, threads, recesses and textured geometry that would be tedious or impossible to reach consistently with a brush.
The important thing is scale. Ultrasonic cleaning does not work because the entire tank violently churns. It works because an enormous number of microscopic events distribute mechanical cleaning action through liquid that is already in contact with the part.
The liquid therefore becomes the delivery system. If cleaning solution can wet a surface, ultrasonic energy can potentially act there too.
A brush has to reach the dirt. Cavitation asks whether the liquid can reach it.
Frequency shapes cavitation behavior
Thirty-seven kilohertz is a deliberate general-purpose compromise.
Ultrasonic frequency influences how cavitation develops. Lower ultrasonic frequencies generally produce larger, more energetic cavitation events and are often favored for robust contamination. Higher frequencies tend toward smaller, more numerous events that can be gentler and better suited to fine structures.
Elma's more specialized Elmasonic P machines make that trade visible by allowing 37kHz and 80kHz operation. Elma describes 37kHz as appropriate for coarse contamination, mixing, dissolving, dispersing and degassing, while 80kHz is useful for capillaries and more delicate or quiet applications.
Select stays at 37kHz because it is meant to be broadly useful rather than frequency-specialized. Watches and tools, laboratory glassware, machined components, instruments, automotive parts and many other robust objects can all benefit from a strong general-purpose field when the cleaning chemistry and operating mode are chosen correctly.
Frequency does not determine cleaning quality by itself. Power density, bath geometry, liquid chemistry, dissolved gas, temperature, part placement and contamination type all matter. A headline frequency without process control is just one number.
This is why Select is more interesting than a bargain ultrasonic tank that simply turns on. Elma treats the bath as a process that can be tuned.
The five modes are really five ways of distributing ultrasonic energy
Same tank. Different sound field.
Standing waves are an awkward consequence of putting sound into a bounded tank. Pressure maxima and minima can form in repeatable locations, creating zones where cavitation is stronger and zones where it is weaker.
That is why Sweep matters. Instead of allowing one perfectly fixed acoustic condition to dominate, the system varies the ultrasonic field around its nominal operating frequency so the distribution of mechanical action becomes more homogeneous across the bath.
Pulse changes the behavior in another direction. Elma uses a pulsating sound-field pattern intended to attack stubborn contamination more aggressively.
Dynamic alternates or combines Sweep and Pulse behavior to pursue both strong cleaning and broad distribution. Eco runs a gentler, quieter version of sweep-like operation for sensitive cleaning and lower device stress. Degas is designed to remove dissolved and entrained gas from fresh cleaning liquid before serious cleaning begins.
These are not decorative software presets. They address physical conditions inside the bath.
Spread the action
Frequency variation helps prevent fixed hot and cold zones in the acoustic field and improves cleaning uniformity.
Attack stubborn contamination
Pulsating operation emphasizes stronger mechanical action when ordinary cleaning is not enough.
Combine distribution and force
Elma pairs sweep and pulse behavior to increase overall cleaning performance without giving up bath coverage.
Degassing sounds like a laboratory footnote until you understand cavitation
Fresh liquid can contain exactly the wrong kind of bubbles.
Water and cleaning solutions naturally contain dissolved gas. Freshly mixed solution may also trap air during filling. Those gases affect ultrasonic transmission and cavitation behavior.
Before the bath settles into consistent cleaning performance, some ultrasonic energy can be spent driving unwanted gas out of solution rather than producing the cavitation field the operator actually wants.
Degas mode accelerates that conditioning process. Elma explicitly uses it both for freshly prepared cleaning liquids and for laboratory applications such as degassing HPLC samples.
This is one of the most elegant aspects of ultrasonic cleaning because it reveals that not every bubble is useful. The machine wants transient cavitation cavities generated by the pressure field, not a bath full of ordinary dissolved and entrained gas interfering with energy transfer.
Good process control begins before the dirty part even enters the tank.
Ultrasound is mechanical assistance, not universal chemistry
The cleaning solution still has to be compatible with the dirt and the part.
Cavitation can loosen and disrupt contamination, but chemistry determines whether oils emulsify, oxides dissolve, residues wet properly and the substrate survives the process.
This is why professional ultrasonic cleaning is rarely just “fill with water and press start.” Elma sells application-specific cleaning chemistries and recommends matching the detergent to material and contamination.
Heat becomes part of that chemistry. Warmer cleaning solutions often reduce viscosity, improve reaction rates and help dissolve or mobilize certain contaminants. Select provides controlled heating from 25 to 80°C and can wait until a target temperature is reached before beginning the timed ultrasonic process.
That temperature-controlled start is a small feature with large implications. If one cycle begins at 28°C and another at 55°C, the cleaning outcomes may differ even when time and ultrasound settings are identical. Waiting for the setpoint makes the process more reproducible.
There is no universal ideal temperature. Some materials, adhesives, coatings and chemistries are heat sensitive. Volatile or flammable liquids can be unsafe and may be prohibited. The process has to be engineered around the object, contamination and approved chemistry.
This is where the machine starts to look less like a gadget and more like process equipment.
The four program memories are the quiet professional feature
Once a cleaning process works, the next challenge is making it work the same way again.
Select can store four individually configured programs for fast recall. In a hobby setting, that is convenient. In a workshop, laboratory or production environment, it is process discipline.
A known part family might need a specific mode, bath temperature and cycle time. Another assembly may need gentler conditions. A third process may include degassing first. Saving recipes reduces the chance that each operator reconstructs the process differently from memory.
Elma's display shows operating states, time and temperature, while acoustic and visual feedback communicate completion or overtemperature conditions. The front uses membrane keys and a closed surface that can be wiped clean, which matters around wet chemical processes.
The Select line also includes an adjustable temperature limit and automatic safety shutdown after eight hours. Those features are not glamorous, but professional equipment is defined as much by failure behavior and repeatability as by maximum cleaning power.
A machine that cleans one watch bracelet beautifully is interesting. A machine that can reproduce the validated conditions for the hundredth bracelet, component or laboratory sample is useful.
The product family scales without changing the operating idea
From 2.7 liters to 89 liters, the interface stays recognizable.
The smallest current Select 30 has a recommended operating capacity of 2.7 liters and a working volume of 1.6 liters. At the opposite end, the Select 900 reaches 89 liters of operating capacity and 63.7 liters of recommended working volume.
Power scales accordingly. The Select 30 is listed at 120 watts effective ultrasonic power and 480 watts peak, with a 200-watt heater. The Select 900 reaches 960 watts effective ultrasonic power, 3,840 watts peak and a 2,000-watt heater.
Intermediate models cover long narrow tanks, deeper tanks and broader footprints so the bath can match the geometry of what is being cleaned. From Select 60 upward, current models also include drain fittings. The 500 and 900 can be configured with noise-protection lids.
This matters because tank geometry is not an afterthought. A long instrument, wide machined component or deep basket may need a very different vessel even if its total volume resembles another part.
Elma has effectively made Select into a platform: same 37kHz process philosophy and control language, scaled across different physical work envelopes.
The basket is part of the acoustic system
Do not put the work directly on the tank floor.
Elma specifically warns that parts should not rest directly on the bottom of the ultrasonic tank. The instruction is practical and physical.
The tank floor is coupled to the ultrasonic transducers. Loading it directly with hard parts can interfere with vibration, create concentrated mechanical stresses and eventually damage the tank or transducer system.
A basket suspends parts in the active liquid while keeping them mechanically separated from the vibrating tank surface. It also makes loading, unloading and draining cleaner.
Placement affects results too. Overloading a basket can shadow surfaces, trap air and reduce liquid circulation. Deep cavities may need orientation that lets air escape rather than remain trapped inside.
Again, the machine is not doing magic to an object simply because the object is underwater. Ultrasonic energy, chemistry and liquid access all have to reach the contamination.
This is a useful parallel to precision manufacturing, where fixturing often determines whether a theoretically capable process actually reaches the surface or tolerance that matters.
Elma began with clocks, which explains more than it first appears
Precision cleaning was in the company before ultrasound was.
Hans Schmidbauer founded Elma in 1948. The name came from “electric machines,” and the company's first defining product was what Elma describes as the world's first electric clock cleaning machine.
That origin is almost perfectly suited to what the business became. Clock and watch mechanisms contain small metal components, lubricants, recesses and contamination-sensitive interfaces where careful cleaning matters enormously.
Under the next generation, led by Manfred Schmidbauer, Elma expanded into ultrasonic and industrial cleaning technology. The company is still family managed, with third-generation family members in leadership.
Today Elma spans small tabletop units, medical cleaning equipment, laboratory devices and fully engineered industrial cleaning systems with frequencies extending well beyond the fixed 37kHz used by Select.
The continuity is satisfying. A company founded to clean delicate mechanisms evolved into a specialist in controlling the physics and chemistry of cleaning across increasingly complex parts.
That makes Elmasonic Select an especially good object for this series. It is not a novelty in Elma's catalog. It is a modern general-purpose expression of a problem the company has been solving since 1948.
Hans Schmidbauer founds Elma and develops an electric cleaning machine for clocks.
Manfred Schmidbauer grows the family company into a specialist in ultrasonic and industrial cleaning technology.
Elma develops dedicated benchtop ultrasonic families for general, laboratory, medical and advanced multifrequency applications.
Third-generation family leadership continues, including Mirja Schmidbauer and other family members in management.
Elmasonic Select remains current as the programmable 37kHz general-purpose platform across a 3-to-90-liter class product family.
Ultrasonic does not mean universally safe
A cleaning method that can reach everywhere can also reach surfaces you did not intend to disturb.
Delicate coatings, porous materials, glued assemblies, soft gemstones, damaged plating, unstable finishes and components containing trapped liquids may be poor ultrasonic candidates. Cavitation and chemistry can expose weaknesses that manual wiping never touches.
Electronic assemblies may be ultrasonically cleanable in some controlled industrial processes and completely inappropriate in others. Bearings may emerge visually spotless but stripped of lubricant. An intricate mechanical assembly can be cleaned so thoroughly that its next required step is relubrication.
Flammable solvents create another serious limitation. A heated electrically powered ultrasonic bath is not a casual place for volatile combustible liquids unless the equipment and process are specifically engineered for them.
The right conclusion is not that ultrasonic cleaning is dangerous. It is that professional cleaning is materials science plus process control.
Elmasonic Select is compelling because it exposes more of that control than cheap consumer cleaners do, but the operator still has to understand the object entering the tank.
The machine's real luxury is reaching geometry without disassembly-level hand labor
Ultrasonic cleaning converts access from a tool-shape problem into a wetting problem.
Traditional cleaning tools have geometry. A brush has bristle length. A swab has diameter. A pick has a tip angle. Every physical tool can only touch surfaces it can physically reach.
A liquid conforms to geometry in a different way. It surrounds threads, enters holes, wets mesh and flows around complex contours. When the cleaning force is transmitted through that liquid, the process can act at surfaces that would otherwise require miniature tools and patient hand work.
This is why ultrasonic cleaning shows up in watches, jewelry, laboratories, machine shops, optics, electronics manufacturing, dental and medical preparation, automotive work and precision production.
The dirt changes. The part changes. The chemistry changes. The underlying appeal does not.
It is a good example of industrial product design solving a difficult physical-access problem by changing the medium through which work is performed.
Why it goes in the digital time capsule
Because it makes invisible physics feel like a shop tool.
The Things Worth Wanting collection tends to favor objects where the underlying technical idea is legible once you know where to look.
Elmasonic Select is almost perversely good at hiding its trick.
There is no robot arm. No dramatic blade. No laser line. No visible jet of abrasive. You lower a basket into liquid, select a mode, and hear the peculiar high-frequency chatter of a process whose important events are microscopic.
Yet the machine is doing something mechanically extraordinary. Pressure waves are creating and collapsing cavities throughout the bath. The geometry of the sound field is being deliberately altered. Heat and chemistry are accelerating contamination removal. Dissolved gases are being driven out before the serious work begins.
The current Select adds another layer that matters to me: reproducibility. Four stored programs, temperature-controlled start, five acoustic modes and clear status feedback turn a fascinating phenomenon into a controlled workflow.
That is the transition from science demonstration to useful equipment.
The company history makes the object even better. Elma began by cleaning clock mechanisms, objects defined by tiny surfaces and inaccessible geometry. Nearly eight decades later, the company is still solving the same fundamental problem with much more sophisticated physics.
There are cheaper ultrasonic cleaners. There are more advanced Elma machines with multiple frequencies. There are massive industrial systems that move baskets automatically through several cleaning, rinsing and drying stages.
Select is interesting because it sits exactly where the technology becomes understandable.
Stainless tank. Liquid. Heat. Sound. Time.
Then millions of bubbles become tools.
A few practical questions
About the current Elma Elmasonic Select
Is Elmasonic Select still a current product?
Yes. Elma currently sells Elmasonic Select as its programmable general-purpose ultrasonic cleaning family alongside Easy, P and Med product lines.
What frequency does Elmasonic Select use?
The entire current Select family operates at a nominal ultrasonic frequency of 37kHz.
What are the five ultrasonic modes?
Eco, Sweep, Pulse, Dynamic and Degas. They change how ultrasonic energy is distributed or used in the bath for gentle cleaning, uniformity, stronger action, combined performance or liquid degassing.
Can it save cleaning programs?
Yes. Elmasonic Select provides four memory locations for individually configured cleaning programs.
How hot can the bath get?
Current Select models provide temperature control from 25 to 80°C, with temperature-controlled start available for repeatable processes.
What sizes are available?
Elma currently lists Select 30, 40, 60, 80, 100, 120, 150, 180, 300, 500 and 900 models, with recommended operating capacities ranging from 2.7 to 89 liters.
Why should parts not sit directly on the tank bottom?
The tank floor is part of the ultrasonic transducer system. Elma warns that direct contact can damage the tank, so parts should be suspended in a suitable basket or holder.
Is ultrasonic cleaning safe for every object?
No. Material, coating, adhesive, geometry, contamination and cleaning chemistry all matter. Delicate or incompatible objects require process-specific evaluation.