How to Select Ultrasonic Parts Washers

One or more cleaning procedures are generally involved in the manufacturing, finishing and maintenance of thousands of industrial and consumer products.  In this post we provide suggestions on how to select ultrasonic parts washers that find wide employment in preparing and repairing most anything that comes to mind.  These range from printed circuit boards in your PDA to aircraft jet engines.

But first we’ll provide information that may be useful for those of you not that familiar with the ultrasonic process.  For the cognoscenti, feel free to scroll down to the Tips section. 

What is Meant by “Parts Washing?”

The answer seems obvious, but there are other ways of describing what’s going on.  Yes, parts washing means removing dirt, grease, grime and most any contaminant from any product that can be safely immersed in a water-based cleaning solution. 

Parts washing can also be described as parts cleaning and parts degreasing. 

The degree of cleanliness is an important consideration when it comes to ultrasonic parts cleaning.   This can vary all over the map.  For example:

• Cleaning newly manufactured automotive transmission gears is important to remove fines and other contaminants that may induce wear.
• Cleaning stamped metal parts to be painted, plated or anodized is very important to insure proper adhesion of the finish.
• Cleaning carburetors and other engine components helps ensure reliable operation of outdoor power equipment such as garden tractors, motorcycles, motorboat engines and snowmobiles.
• Properly cleaning medical, surgical and dental instruments is obviously a critical application for ultrasonic parts washers.
• Cleanliness standards may be prescribed by government, trade and technical associations. A procedure to measure this is described in our post on determining technical cleanliness.
• And so on….

What Distinguishes an Ultrasonic Parts Washer?

Good question.

Maybe the best way to address this is to first describe what it isn’t.

Several methods can be employed to remove contaminants from new or refurbished surfaces. 

A basic (albeit somewhat dangerous) method employed by shade-tree mechanics is to wash parts in gasoline using a brush to remove grit and grime.

Lawn & garden, and automotive repair shops may employ what are generally described as solvent-based wash tanks.  These circulate a jet of cleaning solvent against parts being cleaned and held by the mechanic who may also wield a bush to dislodge dirt.  Solvent aerosol sprays may also be used.  Both methods are somewhat environmentally unfriendly.

Enclosed spray wash cabinets employ high-pressure jets of heated water-based cleaning solutions.

But to your question:

Ultrasonic parts washers use a technique called cavitation to remove contaminants from all surfaces of parts immersed in a biodegradable cleaning solution.  It is proven far superior to any other cleaning process because cleaning action reaches all surfaces of parts immersed in the solution. 

These include cracks, crevices and blind holes very difficult or impossible to reach by manual processes employing solvents, sprays and brushes.  

Components of an Ultrasonic Parts Washer

Ultrasonic parts washers come in a variety of sizes and performance characteristics.  They range from small tabletop units to multi-featured benchtop and floor mounted industrial models.

Common to all are

• A stainless steel tank to hold the ultrasonic cleaning solution.
• Control panels that can range from a simple on-off switch to managing sophisticated operating parameters.
• A generator to power the
• Ultrasonic transducers bonded to the bottom of the tank or, in some cases the sides and in larger units immersed in the solution. Transducers convert electric energy to mechanical energy by vibrating at ultrasonic frequencies.

How Ultrasonic Parts Washers Work

When the ultrasonic parts washer is activated the generator-powered transducers are excited and vibrate at ultrasonic frequencies.  This is generally defined as frequencies above the hearing range of approximately 20,000 cycles per second (20 kHz).

The vibrations cause the tank bottom (and/or sides and the container of immersed transducers) to vibrate as a membrane.  This causes the formation of microscopic vacuum bubbles that implode violently on the surfaces of parts immersed in the solution. 

These powerful  implosions blast loose and carry away even the most tenacious contaminants from the surfaces.  And by powerful we mean just that.  Shock waves may be on the order of 15,000 to 150,000 psi and at temperatures of 5,000 to 10,000⁰C.  Yet the process is so fast that sonic cleaning is safe when the correct frequencies are used.  That said, never reach into an operating ultrasonic parts washer bath.

Contaminants removed during the parts washing process have to go somewhere and we cover that later in this post under cleaning solution maintenance  tips.

Tips on Selecting your Ultrasonic Parts Washer

Tank dimensions

How large or what number of parts to be washed?  Measure the dimensions of largest parts to be cleaned  and make sure to select a tank that will accommodate them.  In addition, pay attention to the  dimensions of the parts baskets, which are slightly less than tank internal dimensions .  Baskets must be used to keep parts from contacting the bottom of the tank  and  interfere with cavitation .   An option used for large industrial parts washers is suspending parts in the solution from overhead supports.

Know the working depth of the cleaning fluid, which is the distance from the inside bottom surface of the basket to the surface of the liquid in a filled tank.  Parts being washed must be fully immersed in the liquid.  

Product specs for benchtop ultrasonic washers may not include this information.  If they do not, feel free to contact the manufacturer or supplier for this information. 

Ultrasonic Frequency

Most ultrasonic parts washers operate between 35 and 45 kHz.  This frequency range is well suited to the vast majority of cleaning tasks.   Examples include the Elmasonic E+ series of ultrasonic washers.

Lower frequencies such as 25 kHz produce larger cavitation bubbles.  When these bubbles implode they release a larger amount of cleaning energy.  For extremely dirty parts such as removing lapping abrasives or polishing paste, a lower frequency will be more effective. 

A higher frequency produces smaller cavitation bubbles.  These cover fine featured complex surfaces more thoroughly and are gentler than low frequencies.  For fine cleaning of very delicate jewelry, electronics, and soft metals with polished surfaces consider a unit operating at 80 – 130 kHz.

When washing a variety of materials consider a dual-frequency ultrasonic cleaner.  An example is the Elmasonic X-tra ST unit that can be set to 25 kHz for basic cleaning and to 45 kHz for fine cleaning.  Other models operate at 35/130 kHz or 37/80 kHz.

Other Ultrasonic Washer Features

• Temperature controls let you set cleaning solution temperature to the level recommended by the cleaning solution manufacturer.
• Timers control the duration of the cleaning cycle. Some units are designed to start cavitation when the selected temperature is reached and shut down at the end of the cycle.
• Freshly prepared cleaning solutions contain entrained air that inhibits cavitation. It can be removed by allowing the equipment operate for a period of time without a load or specifying a parts washer with a degas mode for faster results.
• Sweep provides a slight ± fluctuation in the ultrasonic washer’s ultrasonic frequency and serves to even out the cleaning action. This avoids what are called “hot spots” or more intense and possibly damaging cavitation action, “dead zones” or no cleaning action, and harmonic vibrations that can damage delicate parts such as PCBs.  
• If you are cleaning products with particularly tenacious contaminants specify an ultrasonic pats washer equipped with a pulse mode. Pulse mode boosts ultrasonic power 20% on some models to remove stubborn contaminants.
• While more ultrasonic power usually indicates faster and more effective cleaning, more power is not always better. Too much power can damage electronic parts, the surface finish on a soft metal (e.g. aluminum), and other delicate items.  For cleaning extremely sensitive items, adjustable power is a useful feature.  Examples is the P series. 

Selecting Cleaning Solutions for your Ultrasonic Parts Washer

Successful ultrasonic parts washing procedures are most likely achieved when thought is given to ultrasonic cleaning solutions that deliver the desired results.  There is a vast variety of ultrasonic cleaning solution chemistries available to satisfactorily accomplish your parts washing tasks.

In fact an improper choice of cleaning solution chemistry (just as the wrong ultrasonic frequency) can damage parts or surfaces being washed. 

Most but not all ultrasonic cleaning solutions marketed today are in the form of biodegradable concentrates formulated for specific cleaning tasks.  They are shipped with instructions regarding dilution, recommended cleaning temperatures and material safety data sheets (MSDS). 

Container volumes vary by manufacturer; 2.5, 10 and 25 liters are typical examples.  Biodegradable formulas eliminate handling, health and disposal concerns associated with trichloroethylene and perchlorethylene solvents formerly used for ultrasonic parts cleaning.  We invite you to check our post on selection guidelines for cleaning solutions.

How to Maintain the Cleaning Solution in your Ultrasonic Parts Washer

Contaminants removed by ultrasonic parts washing end up in the bath.  Removing these helps maintain the bath allowing it to perform longer. 

Particles that float to the surface should be skimmed off and set aside for later disposal.  Larger capacity cleaners can be fitted with weirs, skimmers and filters that contribute to maintaining the effective life of the bath.  These also help remove solid particles that sink to the bottom and, if not removed, can eventually “drill” into the tank bottom and cause leakage.

Please check our post  on using oil skimmers and solution filters for tips on extending the life of the solution in your ultrasonic parts washer.

Cleaning and maintenance instructions for your ultrasonic parts washer are provided by the manufacturer.

Please contact the Tovatech ultrasonic cleaning professionals for the information you need to get the most out of your ultrasonic parts washer equipment.