Ultrasonics 101

[slmjim n Z1BEBE]

Long, geeky post ahead.

Some years ago we were looking for an ultrasonic tank for our Kawasaki Z1 restoration hobby. The breadth & depth of info was daunting, with some conflicting claims & info spread across the interwebs. So, we proceeded to write the article we wish we could have found that covers the basics. The following article we wrote was kindly published in the VJMC NA magazine in 2016 shortly after we submitted it to the Editor. Hope y'all enjoy.

Note - we had to break this up into five parts, as the site software is limited to 10,000 characters per post.

Ultrasonics 101

PART 1
FOREWORD:
Ultrasonic cleaning units sized and priced affordably for individuals and small shops are a commodity in a market where some sellers try all sorts of advertising hype in an attempt to set their equipment apart from others.

In this article I hope to, in plain language, describe what ultrasonic cleaning is, simply distill the theory of operation, define the hardware features most useful to home and small workshops, identify best practices, and cut through the hype that permeates internet marketing.

Information is available regarding every aspect of ultrasonic cleaning to anyone with an internet connection. Much of the information in this article comes from the support and FAQ sections of ultrasonic equipment manufacturers themselves. Where there is sometimes conflicting info between sellers on the same subject, every effort has been made to arrive at a factual consensus based on additional research.

This article is in no way intended to be definitive. It is meant simply to offer anyone who might be contemplating a purchase for themselves or a small shop some basic knowledge to help make a decision.

OVERVIEW:
Ultrasound is defined as any sound frequency that is above the perception of human hearing, generally accepted to be twenty thousand cycles per second, or twenty Kilo Hertz (20 KHz).

To put it simply, ultrasonic cleaning uses the effects induced within an appropriate liquid cleaning solution by high-frequency sound waves (most commonly 40 KHz) to remove many types of contamination from the workpiece being cleaned. The components of an ultrasonic cleaning system are the ultrasonic generator(s), the ultrasonic transducer(s) (driven by the generator) which are solidly attached to the tank, and the tank filled with cleaning solution. Most tank designs are all stainless-steel construction and come in a variety of shapes and sizes, from one pint to hundreds of gallons.

Ultrasonic cleaning utilizes ultrasonic transducers to create cavitation bubbles (aka cavitation, vacuum cavities or bubbles, used interchangeably throughout) within the liquid cleaning solution. This is accomplished by inducing high frequency pressure (sound) waves into the liquid that agitates it at a microscopic level to produce cavitation. The vacuum cavities cannot be seen by the naked eye because they are microscopic in size and exist for only a split second before imploding. Cavitation exerts extreme yet gentle force on the contaminants adhering to the workpiece. Ultrasonic cleaning can be used for many workpiece materials, shapes and sizes, and some items may not even require disassembly prior to cleaning. Ultrasonic cleaning has the ability to clean the INSIDE of complex objects which cannot otherwise be reached by manual spray or brushing. The ultrasonic process penetrates blind holes, cracks, and tiny internal passages and orifices, provided those areas are flooded with cleaning liquid while in the tank. Most materials respond well to ultrasonic cleaning. Ultrasonic cleaning is inherently gentle, although there are exceptions; soft polished metals such as aluminum, some plastics, painted surfaces and a few precious stones. More on that later. Water, specialized detergents or solvents are used, depending on the material of the workpiece and the type of contamination. Contaminants can include insoluble particles such as dust and blast media debris, soluble compounds such as fuel residue (gum & varnish), grease, oil, fingerprints and wax, and contaminant mixtures consisting of insoluble particles embedded within a binder of soluble compound.

Different types of equipment use various ultrasonic frequencies to achieve the desired cleanliness. Lower frequencies aggressively “scrub” larger particles from simple, massive items that have heavily soiled surfaces. Higher frequencies result in gentler cleaning of intricate exterior and internal surfaces on smaller items, and remove smaller particles:
25 KHz creates fewer, larger vacuum cavities that produce aggressive cleaning action. This is because the longer time between alternating positive and negative pressure waves allow larger, more energetic vacuum cavities to form. 25 KHz devices are used to clean large, relatively massive items that;
• are not of complex shape and intricate detail, and;
• are not delicate, and;
• need to be relieved of bulk particulate surface contaminants, and;
•are not easily damaged by the coarser, more aggressive scrubbing action of low ultrasonic frequencies.
Think cast iron blocks or large plates of stainless steel.

40 KHz creates more numerous, smaller cavities that are gentler and remove smaller particles. This is because the shorter time between the alternating positive and negative pressure waves only allow smaller, less energetic vacuum cavities to form more often (higher frequency). 40 KHz devices are the most common, and are the focus of this article. They are available in sizes ranging from one pint home-use units to industrial units with capacities of hundreds of gallons. 40 KHz offers the best combination of cleaning power and speed, gentleness of action, and variety of devices sized and priced for the home or small shop. Consumer items lending themselves to this cleaning frequency can be as delicate as jewelry and eyeglasses, up to carburetors and firearms. 40kHz units are efficient at at removing insoluble particles larger than about 0.7 microns and above.

At 80 KHz – 200 KHz frequencies, correspondingly smaller vacuum cavities of steadily diminishing power are created more often, but the resulting tiny cavities yield the most gentle and finest cleaning power down to sub-micron size contaminants. Devices that run in the 80 KHz through 200 KHz ranges are specialized units typically found in medicine, research and aerospace. Think removing bio-contaminants (blood cells, bacteria etc.) from medical equipment, molecular-level mixing, cleaning delicate solid-state devices that could be damaged by the vibrations of lower frequencies, and achieving ultra-clean-room results needed with delicate aerospace components.

Some high-end units offer multiple frequencies, as in both 40KHz and 80KHz operation simultaneously in the same unit.

Think of frequencies as sandpaper; 25KHz as being coarse, with higher frequencies as becoming rapidly finer. When ultrasonic energy is more evenly distributed in the tank at higher frequencies, cavitating force at any one location in the tank is reduced, although it happens more often and in tinier areas. In other words, cavitation intensity is inversely related to frequency, because as as frequency is increased, cavitation intensity diminishes due to the smaller size of the cavitation bubbles and their less energetic implosions.

THEORY OF OPERATION:
An example virtualization of the cavitation process:

During liquid cavitation, millions of micron-sized vacuum cavities (bubbles) are continuously formed, grow and implode (at 40,000 times per second in a 40 KHz unit) during the alternating positive and negative pressure waves induced in the cleaning solution by the ultrasonic transducer(s). Think cold boiling. Some marketing materials indicate that at 40 KHz, just prior to implosion the cavities are approximately 8 microns (8 µm) in diameter. To put that in perspective, natural spider silk is 2.5 – 4 µm. These vacuum cavities are stretched and compressed at the design frequency and amplitude of the device, growing during the the low pressure phase and being compressed during the high pressure phase when compression causes them implode. Just prior to implosion, the vacuum cavity has an enormous amount of energy stored within itself. Different marketing materials offer sometimes conflicting information, but the numbers seem to be centered around 5,000° F. as the estimated localized, instantaneous energy release of an imploding cavity, with estimated vacuum pressure of 10,000 PSI. Note that these millions of tiny temperature spikes are what causes the temperature of the solution to gradually rise during the cleaning process. (We'll discuss the advantages of heated cleaning fluid later.) The implosion of the vacuum cavity, when it occurs on a hard surface, transforms the cavities' relatively enormous negative pressure into a jet of liquid a fraction the size of the cavity at the time of it's implosion. The resulting very energetic, sub-micron-sized jet impinges on the hard surface at estimated speeds up to 300 ft./sec. With this happening tens of thousands of times a second, soluble contaminants are dissolved and insoluble particles are displaced, quickly and non-destructively from the workpiece. Due to the microscopic size of the jet and the relatively enormous energy it exerts impinging on the surface, ultrasonic cleaning has the ability to reach into tiny internal areas flooded with cleaning liquid that are otherwise inaccessible to manual cleaning, and remove tightly adhered contaminants very effectively.

 

[slmjim n Z1BEBE]

Part 2
EQUIPMENT:
The ultrasonic generator converts incoming AC power from 60Hz to the design frequency of the ultrasonic transducer(s). The generator also matches the incoming voltage (110VAC) to the lower voltage required by the transducer(s).

Modern transducers are usually ceramic piezoelectric devices. Briefly, when a crystal possessing piezoelectric properties is subjected to electrical potential, it changes shape. When the potential is removed, it returns to its original shape. Do this at 40 KHz (or whatever the design frequency), mount the rapidly vibrating crystal on a diaphragm and we have an ultrasonic transducer. Transducers thus convert the high-frequency energy produced by the generators into ultrasonic vibration and, via the diaphragm, emits the resulting ultrasound into the cleaning fluid, thus inducing vacuum cavities in the liquid as the alternating waves of rarefaction create them and compression implodes them. Transducers are usually mounted externally to the tank bottom. The bottom of the tank in fact becomes the ultrasonic-radiating diaphragm, not unlike the cone of a speaker.

Ultrasonic power is rated in watts, stated as energy density or watts/gallon. High powered (high amplitude) units generally mean shorter immersion time in the fluid, but at increased risk of cavitational erosion. There currently seems to be something of a “transducer-count” war, reminiscent of the pocket radio “transistor wars” of the early 1960's (27 transistors!). This is especially evident with some imported units available from certain online marketing and auction sites. In poorly designed systems, multiple transducers placed too closely in too small an area can cancel out some of each others' output due to phase inversions, resulting in lots of watts being dumped into the solution but generating poor cavitation density.

Some ultrasonic cleaning units have a heater built into the tank to warm the fluid prior to cleaning, and to keep the solution warm between cleanings. It has been noted that heat is also generated within the liquid by cavitation during the cleaning cycle. Liquid surrounding the millions of collapsing cavities absorbs the heat generated by the implosions. The result is that even cold liquid warms continuously during operation.

If a unit lacks the heat feature, or if the built-in heater fails, a small, external immersion heater designed for coffee cups can sometimes be adapted. Monitor the temperature of the solution if an external immersion heater is used, as these do not have any kind of temperature regulation.

STANDING WAVES AND SWEEP CLEANING:
Conventional ultrasonic units run at a single frequency. All single-frequency units produce a pattern of cavitation which is distributed in a series of equally-spaced areas known as standing waves. The higher the frequency, the more closely spaced these patterns will be to one another.

Standing waves are sometimes inaccurately referred to as dead spots. They are not really “dead”, they just exhibit more localized cleaning power than in areas immediately adjacent. Sweep cleaning generates slight frequency variations in a single tank by repeatedly “sweeping” the frequency +/- 4 KHz or so either side of the design frequency. In the case of a 40KHz system this means that the running frequency is continuously and rapidly swept from 36 KHz to 44 KHz. Sweep is marketed as helping minimize the effect of standing waves, allowing no single frequency to set up a series of standing waves that resonates continuously in the tank at a stationary, discreet location.

Although effective ultrasonic power is diminished between neighboring standing waves, the energy which is present is likely to be powerful enough to remove the contaminants. This is true provided that the cleaning chemistry effectively reduces bond strength of a soluble to a level where available ultrasonic energy can remove it. Insoluble particles typically do not require much power in order to be displaced.

Since the distance between standing waves diminishes as frequency increases, 80 KHz units produce more evenly-distributed cavitation than 40 KHz units and would theoretically clean items more evenly. However, we have seen that higher frequencies sacrifice cavitating force in gaining this even distribution.

CLEANING CHEMISTRY:
NEVER USE FLAMMABLE CLEANING SOLUTIONS IN AN ULTRASONIC DEVICE.

WEAR CHEMICAL-SAFE GLOVES AND EYE PROTECTION WHEN WORKING WITH CLEANING FLUIDS.

The importance of the cleaning solution (chemistry) cannot be overestimated, since it is largely responsible for cleaning success. Water is a universal solvent, but water by itself is seldom right for ultrasonic cleaning. Various detergents and other water-soluble agents, some of which are very powerful can be added to water in order to:
• lower surface tension and act as a surfactant,and;
• provide wetting action to assist in displacing non soluble particles, and;
• create chemical actions necessary dissolve soluble contaminants.

If at all possible, water-based solutions are preferable to organic solvents. Water-based solutions will also cavitate more effectively then organics at a given energy density.

A contaminant must be dissolved if soluble, or displaced if it is a non-soluble particle. In the case of a mixture consisting of a soluble such as grease or fuel residue acting as a binder that holds insoluble particles, both dissolution and displacement is required.

Ultrasonic activity enhances the effect of many chemical reactions such as dissolution by solvents. For dissolution to occur, the solvent must come into molecular contact with the compound in order to dissolve it. As the solvent dissolves the soluble contaminant, a very thin layer of solvent saturated with dissolved contaminant develops between the contaminant and UN-saturated fluid. This slows or stops dissolution as the layer of saturated fluid is no longer powerful enough to dissolve the compound. Ultrasonic agitation continuously displaces the saturated layer with fresh solvent. This is one reason why ultrasonic cleaning is so effective at cleaning the complex surfaces and internal passages of carburetors.

Some relatively large insoluble particles are only loosely held in place by ionic attraction. Think fine dust or some types of very fine debris left behind by broken media particles used in media blasting. These particles are very quickly displaced by ultrasonic action, often using only a weak detergent/water solution or even plain water.

Detergents usually have a high alkaline content and are designed to remove a number of contaminants, then hold them in suspension. The wetting action of detergents also aids in releasing the ionic attraction that adhere particles to a workpiece. Many Detergent-based metal cleaners are formulated to remove oil, grease and carbon deposits.
Enzyme-based solvents are used for degreasing of stainless steel, aluminum, brass and titanium parts. Enzyme solvents can be more effective than general-use detergents when removing oil and grease. They are designed to clean heavily oiled surfaces when a completely oil-free result is necessary.

The viscosity and vapor pressure of cleaning agents, as well as their concentration when diluted with water will change the power and distribution of cavitation energy.

Sometimes it is desirable for the the part to be rinsed of residue left behind by the cleaning fluid after the part is cleaned. Residue is quickly and completely removed by ultrasonic rinsing in an appropriate fluid, usually a weak detergent/water solution or even straight water

Disposal of used cleaning solution needs careful consideration. Read the labels and follow local laws regarding disposal. Many solutions can be considerably reduced in volume by evaporation.

 

[slmjim n Z1BEBE]

PART 3
HEAT:
The effect of heat on cleaning chemistry is closely related.
Temperature is the single most important consideration in maximizing cavitation intensity. Changing the temperature of the cleaning fluid changes it's viscosity, the solubility of gasses dissolved within the liquid, the diffusion rate of those gasses, and vapor pressure. These interrelated parameters all affect cavitation density and intensity.

The viscosity of most liquids is reduced as temperature is increased. Less viscous liquids cavitate better than viscous liquids.

The vapor pressure of a liquid changes as the temperature is increased. This aids vaporous cavitation, where the vacuum cavities are filled with the non-compressible vapor of the cavitating liquid. Vaporous cavitation is the most effective form of cavitation.

When liquid is cold, the vapor pressure of the liquid is low and considerably more power must be introduced into the liquid to create relatively fewer cavitations. But, those few implosions that DO occur do so with greater energy. Cavitation is more efficient when liquid is warm because the vapor pressure is higher, which reduces the power needed to generate useful cavitation. In other words, the higher vapor pressure of warm liquid lowers the cavitation threshold, reducing the minimum power required to achieve efficient cavitation.

Water cavitates most effectively at about 70ºC (160ºF). Heating aqueous cleaning solutions maximizes efficiency. Aqueous solutions are generally heated to about 50–65°C (122–149 °F) for most applications. The quantity and energy of cavitation bubbles increases proportionally as temperature increases, but only up to a point. Beyond about 65°C, cavitation intensity in most aqueous solutions begins to decline, then stops entirely when heated to within 85% or so of its boiling point as the liquid boils at the cavitation sites.

Increasing fluid temperature will also improve the distribution of ultrasonic cleaning action in the tank. Aluminum foil testing can be used to confirm this observation. As temperature rises, perforations in aluminum foil take slightly longer to produce, but the foil will appear to be more evenly attacked by the ultrasonic energy. Smaller holes will be more evenly distributed instead of the larger holes created in cold fluid, and the dents between the smaller holes resulting from standing waves will be more evenly distributed.

BASKETS AND BASKET ALTERNATIVES:
Most ultrasonic cleaning devices either have baskets as standard equipment or available as an option.

A basket should be designed and supported so as not touch the bottom or sides of the tank. Most can be suspended in the tank by “ears” that rest upon the top surface of the unit.

Many baskets are manufactured of stainless steel wire mesh, which maximize the amount of ultrasonic energy reaching the workpieces. The largest mesh that will hold the parts is preferred over smaller sizes, as small mesh tends to reduce ultrasonic power in the basket. These are most appropriate for general use. Some baskets are no more that solid pans with a few small slots cut in them. These are for specialized lab use.

Basket material can also have a large affect on cavitation power within the basket. Plastic baskets are almost never used in an ultrasonic cleaning device unless absolutely necessary to prevent damage to soft parts. Plastic itself can contribute to ultrasonic shadowing by absorbing some of the energy needed to generate cavitation. A plastic basket design must be as open and thin as possible. Plastic baskets deteriorate quickly due to cavitational erosion.

Alternatives to baskets do exist for some applications:
•Ultrasonic activity will pass through a variety of media. As an example, cleaning solution placed in a Pyrex beaker will cavitate if placed in water that is cavitating in an ultrasonic tank. This technique is often used in medical labs.

•Place the cleaning solvent and the part to be cleaned in a plastic bag, then close the opening securely. The bag containing the solvent and workpiece is then placed in the cleaning tank, which is filled with just enough water to bring the water level up to the tank fill line when the bag is in the tank. Cavitation inside the bag will occur at nearly full power, as the thin plastic of the bag will have little damping effect on the production of cavitation within. The benefit is that the tank itself and the water contained therein will stay clean, as the contaminants removed by cavitation stays inside the bag. Use new bags often to reduce the possibility of erosion perforating the bag.

TESTING:
How to know if an ultrasonic unit is really functioning?

First, the unit should be filled with fresh, degassed cleaning fluid that is heated to normal operating temperature.

Foil test:
Cut three rectangles of aluminum foil to about 4” by 8”. Fold each piece of foil over a support such as a coat hanger or wood dowel and suspend the foil pieces in the cleaning fluid, making sure they do not touch the bottom of the tank: one piece in the center of the tank, and the remaining two at each end of the tank an inch or so away from the tank wall. Be sure the tank is filled to the correct level. Start the cleaning cycle. The foil must be kept completely stationary during this test, just as parts being cleaned would be perfectly stationary. In no more than three minutes (and probably much sooner) remove the foil. Each piece of foil should be perforated at standing wave locations where there is higher energy , and dented and wrinkled in areas of lower ultrasonic power. This presents users with the ability to determine the cleaning properties of any ultrasonic cleaning unit. In a perfect system, the patterns created on the foils would be evenly distributed everywhere across their surfaces. However, due to the presence of standing waves even distribution is never the case. At 40 kHz, patterns of will appear across the surface of the foils roughly every 12mm., with areas affected less (the dents and wrinkles) that indicate less activity found in between these holes.

Lab test 1:
Wet a frosted glass slide with tap water and draw an "X" with a No. 2 pencil from corner to corner. Immerse the frosted slide into a full tank of fresh cleaning solution. Turn on the unit. The "X" will begin to be removed almost immediately, and be removed completely within less than 30 seconds.

Lab test 2:
Using 2 flat glass microscope slides, wipe a line of lipstick on the surface of one, and place the other slide on top of the lipstick. Wrap the slides with a rubber band to hold them together. When the assembled slides are placed into an operating ultrasonic unit containing a heated weak detergent solution, in only a few minutes the cavitation process will remove the lipstick from between the slides.

 

[slmjim n Z1BEBE]

PART 4
BEST PRACTICES:

NEVER USE FLAMMABLE CLEANING SOLUTIONS IN AN ULTRASONIC DEVICE.

Tank size is determined by part size. Generally, the tank should be one third larger than the largest expected workpiece. When a part is immersed in a 40KHz tank, there should be clearance of approximately 20mm. on each side, and 25mm. of unobscured distance between the part and the bottom of the tank.

Nothing should touch the bottom or sides of the tank. This may damage the tank by accelerated erosion, may damage the transducer(s) and will dampen the amplitude of the vibration being induced into the solution.


Layers and shadowing

If stacked parts are cleaned in a horizontal position, the lowermost part will receive the bulk of the cleaning activity since it is closest to the ultrasonic radiating surface. The bottom-most part will reduce the intensity of the cleaning action on parts directly above, an effect known as shadowing. It is for this reason that parts should be cleaned in a single layer, with flat parts oriented vertically as in a dishwasher..


Cleaning Sensitive Materials

Some items, such as soft metals and highly-polished aluminum, can be damaged quickly by cavitational erosion. When this occurs, the polished surface appears mottled, and covered with a pattern of small marks not unlike an exclamation mark (!). These marks are created when the cavitation essentially drills microscopic holes in the polished surface. The “dot” of the mark is the pinhole location of most intense cavitation, while the tail of the exclamation mark represents the direction that the fluid was blasted away during cavitation. Distance between neighboring marks and the severity of damage are dependent upon the frequency used.

When cavitation impinges the surface of a part, nearby liquid is blasted away in a direction defined by the angle between the cavitation and the part's surface. When cavitation is exactly perpendicular to the surface, the nearby liquid is displaced uniformly around the central pinhole activity location, producing a circular erosion mark. This is seldom the case. More often, cavitation is not exactly perpendicular to the surface of the part. Neighboring fluid tends to be displaced in a certain direction, which results in the exclamation mark appearance. This can happen after only a short time of exposure to cavitation. Limiting cleaning time of the part in any one position by frequently changing it's orientation in the tank will minimize or eliminate this artifact by not allowing hot spots to linger in one place for long. Think the rotating platter of a microwave oven.

Painted items may also be damaged by ultrasonic cleaning. Paint that is poorly bond to the surface or in corners or crevices will likely be removed during ultrasonic cleaning, as cavitation tends to concentrate in these areas.

The ultrasonic cleaning process tends to aggressively attack pre-existing areas of defects or cracks in the material. Because of this, ultrasonic cleaning is not recommended for some precious stones, as these have natural defects which are prone to vibrational separation. Anything that has existing cracks must be evaluated. Ultrasonic activity has even been known to find leaks in a tank which does not leak when the ultrasonic system is not running.

Incorrect selection of cleaning fluids can damage some materials. Non-ferrous metals require the use of cleaning fluids specifically formulated for them to prevent discoloration or oxidation of the metal.

After cleaning ferrous parts, some type of rust preventive must be applied immediately to prevent flash rusting.

Cleaning times may vary considerably. How dirty is it and how clean must it be? Two to ten minutes is a good starting point. More powerful units will clean a given part faster. Very dirty parts should be pre-cleaned to extend the life of the solution and hasten final cleaning.

Cleaning efficiency, temperature and solution chemistry are closely related. Ultrasonic cleaning in many solutions is most efficient when the solution temperature is heated to around 145°F.

Very cold parts should be warmed prior to immersion in warm solution.


Degassing

Degassing is the removal of dissolves gases present in liquid. Cleaning liquid must contain as little dissolved gas as possible for efficient cavitation. Dissolved gasses are partially released into the vacuum of the cavities during the growth phase of cavitation, and the gas reduces implosion energy by acting as a compressible cushion. Cavitation will be present, but at reduced power. Fluids that have been degassed are up to twice as effective as fluids that have not been degassed.

The speed of degassing is determined by the volume of liquid in the tank, the watt/gallon power density of the system, and the temperature of the fluid. As liquid temperature increases, the relative amount of dissolved gas in the liquid is reduced due to the change in vapor pressure. Also, at higher temperatures the diffusion rate of dissolved gasses in a liquid increases. This means that a warm liquid degases easier than cold liquid, because warm liquid gives up dissolved gasses more easily than cold liquid. The warmer the fluid, the faster and more thoroughly it will degas.

Degassing is only necessary when fresh cleaning fluid is used the first time. Degassing is done by running the system with the tank filled with fresh cleaning solution, but containing no other objects. Once a fluid is degassed by ultrasonic activity, it does not need to be degassed again.


Loading:

WEAR CHEMICAL-SAFE GLOVES AND EYE PROTECTION WHEN WORKING WITH CLEANING FLUIDS.

Consideration must be given to the shape and mass of parts to be cleaned. If items are large, more power may be needed to overcome the extra mass. The weight of the load should be less than the weight of half the water volume. One gallon of water weighs approx. 8lbs., so in a one gallon tank the maximum work load should be less than 4 pounds. Often it is better to clean two light loads rather than one heavy load.

Plastic absorbs ultrasonic energy, so longer cleaning times or more power may be needed for good cavitation when cleaning plastic parts.

If items heavily contaminated with insoluble particles of dirt, grime, etc. are not pre-cleaned, the large particles sink to the bottom of the tank. In a system with the transducer(s) mounted to the bottom of the tank the debris will settle on top of the transducer(s)/diaphragm(s) and dampen the amplitude of the ultrasound waves. This will causes cleaning performance to rapidly diminish.

Parts shape must be analyzed to determine how to best orient them in the cleaning tank. Orientation should be chosen to ensure complete flooding of blind holes and internal spaces. An air pocket will prevent cleaning in that particular area. Some parts must be reoriented and subjected to multiple cleaning cycles to make sure blind holes and internal passages are flooded to receive sufficient cleaning.

It is best if small parts can be separated so as not to be touching each other when placed in a basket. Sometimes it is not necessary to physically separate parts, such as when many small screws, springs and such need to be cleaned at one time. Cavitation will be able to occur between these parts and allow the solution’s solvent power to remove contaminants.

Very small parts may be placed in fine-mesh tea strainers for cleaning.

Ultrasonic units are tuned to work best when the fluid is at the fill line. Adjust liquid level as needed to compensate for variations in fill level as parts are immersed.

Operating the transducer or heater with an empty tank may damage them. If there is a minimum fill line pay attention to it. If there is no minimum fill line, the upper fill indicator is also the minimum fill line.


Maintenance

Ultrasonic units require no specific maintenance other than keeping the tank clean, as the buildup of debris on the tank bottom will dampen the transfer of ultrasonic energy to the cleaning fluid.

The electronic boards of most units are energized when the unit is connected to a wall outlet even though the unit is “off”. This exposes the electronics to all of the spikes and surges that naturally occur on the power grid. Disconnecting the AC power is recommended when not in use.

 

[slmjim n Z1BEBE]

PART 5
CARBS:

Remove loose exterior dirt and grime, with a quick blast of spray carb cleaner. This helps keep the ultrasonic cleaning fluid free of crud.

Remove all gaskets, seals and rubber. Doing so allows maximum area of the carb to be exposed to cleaning.

Remove the float bowls, floats, jets, needles etc., down to the bare carb body to exposed as much of the carb’s internals to the ultrasonic cleaning fluid as possible.

Think carefully about exposing plastic floats to ultrasonic activity, and don't unless absolutely necessary. Vintage plastic floats may be weakened or perforated by ultrasonic erosion very quickly. Replacements may be difficult to find. If a plastic float must be cleaned, grasp it by the metal portion and immerse only the section(s) that are truly contaminated. Re-orient frequently by moving it around in the fluid to prevent hot spots from developing due to standing waves. Consider also, that even brass floats are usually soldered together, and etching may affect the soft solder at the joints.

Clean small parts separately in a mesh tea strainer or other small fine-mesh basket. It's a _itch to search the dirty bottom of a full tank for one tiny C-clip.

Run the carb in the system for a couple of minutes, and then remove it and check it. Make sure that the parts are all aluminum alloys. Some carbs have other alloys like nickel or plated steel, and process can discolor and pit other metals.

Just because you have a big tank doesn’t mean you should jam it full of all 4 carbs. Ensure there is space around each part you put in the tank.

Choose the right fluid chemistry. There are water-based carb cleaners that do a very good job in ultrasonic systems.


FINAL THOUGHTS:

There are some great deals to be had on robust, used, name-brand units on eBay. Take the time to educate yourself on who the big manufacturers are in the domestic and import arenas so you know what you're looking at in the used equipment market. Of course there are also a number of new units available from eBay and other online marketers, many of questionable origins and advertising claims. Do your research.

Most US manufacturers and many quality importers sell direct to the consumer from their web sites, often at lower cost than large online marketers.


RECOMMENDATIONS:

I can make a few based on personal experience:

I'm not a great fan of Harbor Freight, but they do sell a very good re-branded ultrasonic unit that is manufactured by iSonic, one of the largest import manufacturers. It is identical to iSonic model P4820 (note - this may have changed since original publication in 2016). It comes with a cheap plastic basket that eroded after about 25 hrs. of use. A stainless mesh basket for this unit is available on Amazon. Tank depth is a nominal 4 inches, working depth of 3 inches or so when using the optional stainless mesh basket.

The Sharpertek XPS360-6L offers a sweet spot in features vs price from a US manufacturer, along with a very good warranty. Ask if there are any scratch & dent units available.

2.1 inch dia. stainless mesh tea balls work to keep tiny parts from disappearing from view on the bottom of a tank in the murk of used cleaning fluid. An inexpensive 2-piece set is available from Amazon.


Hope y'all enjoyed & maybe learned a little. We (slmjim at least) had a good time researching & compiling this.

Good Ridin'
slmjim & Z1BEBE

 

[gregb6718]

WOW! Thanks for this great information.