Ultrasonic Cavitation & Cleaning Explained

Neil.Antin

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With the growing interest in ultrasonic cleaning of records, the following information is being provided in the hope of providing some guidance on what is ultrasonic cavitation, what does it look like, what are the design rules for ultrasonic tanks, how do cleaning agents/surfactants play-in, how to manage bath life. The following information has been extracted from this free book - Precision Aqueous Cleaning of Vinyl Records-3rd Edition - The Vinyl Press.

What is UT cavitation and what does it look like? Ultrasonic tanks 'grow' bubbles Principle-of-ultrasound-cavitation-16-The-initiated-bubbles-grow-due-to-evaporation.png (850×553) (researchgate.net) until the bubble collapses. Watch this video between 6:19 and 8:30 Cavitation - Easily explained! - Bing video to see how the bubble collapses. This is going to happen whether the tank has objects in it or not. However, for side firing transducers in a very small tank, like the KLAudio, the Degritter, or the Humminguru, operating without a record or sometime between the transducer's could be a problem.

These are some of the basic design rules for UT tanks.
-The power to produce cavitation is proportional to the kHz, so a 120kHz UT needs more power than a 40kHz.
-For ultrasonic tanks, the bubble diameter is inversely proportional to the kHz, so a 40 kHz UT produces a large bubble than a 120kHz UT.
-The cavitation intensity is proportional to the bubble diameter and the tank power (watts/L) but there is a maximum power above which no addition cavitation intensity is obtained.
-The number of cavitation bubbles produced is proportional to kHz, so a 120kHz produces more bubbles than a 40kHz, but smaller bubbles.
-The smaller the tank volume, the more power that is required. It has to do with the ratio of the tank volume to its interior surface area.
-For lower kHz units (<60kHz), if the tank bath flow rate (from filtering or spinning) >50% of the tank volume per minute, cavitation intensity decreases.

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-The KL Audio 40kHz 2.5L 200W is a very powerful machine and so is the Degritter 120kHz 1.4L 300W machine. And, given the high power (most of the energy goes ultimately goes to heat) and small volumes, the bath can heat up quickly. The Degritter mitigates this with a cooldown mode if temperature >95F while the latest KLAudio with its external pump/filter system mostly avoids the overheating. But by the experience of others, the high powered Elmasonic P-series UT tanks need a cooler/radiator if high throughput serial cleaning is performed.

-The Elmasonic P-series with its dual frequency 37/80kHz variable power and pulse power for record cleaning is near ideal. The two frequencies can target the different types of soils that may be present with the higher 80kHz targeting the very fine particles and films that the lower frequencies are not as effective. The reason has to do with the boundary layer. The fluid flow at the record (or any) surface develops a static layer that is separate from the bulk fluid that is moving. The boundary layer thickness is dependent on the ultrasonic frequency (high kHz = thinner boundary layer), acoustic energy, and fluid properties (viscosity & density). To get the most effective cleaning, the complete cleaning process has to penetrate the boundary layer to remove the soil and particles that are contained within it. At 40-kHz, the boundary layer can be as thick as 5 microns, while at 120-kHz, the boundary layer can be as thin as 2 microns.

-Lowering the surface tension of the fluid reduces the energy needed for cavitation and can improve cleaning efficiency - better opportunity to penetrate the boundary layer. But there is a delicate balance with using chemistry with UT that can improve the cleaning efficiency more than the small expense to the cavitation intensity (more an issue with low power units). But use too much chemistry or the wrong chemistry and it's all downhill.

-The benefit of the nonionic surfactant Tergitol 15-S-9 is its very high performance. For a no-rinse wetting solution, you want the lowest concentration that will lower the surface tension of the water enough to wet the record.
  1. Surface tension of the water is ~72 dynes/cm.
  2. Surface tension of the record is ~37 dynes/cm.
  3. 10 ppm (0.001%) Tergitol 15-S-9 reduces the surface tension of water to ~45 dynes/cm.
  4. 20 ppm (0.002%) Tergitol 15-S-9 reduces the surface tension of water to ~37 dynes/cm. This is enough to 'wet' the record. Wetting the record has the advantage that water runs off the record and does not bead-up on the record significantly quickening the drying time. Drops take a long time to evaporate.
  5. 52 ppm (0.0052%) Tergitol 15-S-9 reduces the surface tension of water to ~30 dynes/cm. Adding anymore will not lower the surface tension any further and is known as the critical micelle concentration (CMC) and at >52 ppm, and you begin to get detergency.
  6. 3xCMC (0.016%) for a filtered UT tank will give the full detergency that Tergitol 15-S-9 can give and good bath life.
-Note that Triton X100 (now banned in the EU) CMC is 189-ppm, so it's not very efficient and requires much higher concentration which now complicates rinsing. Note that the one disadvantage of Tergitol 15-S-9 (and Triton X100) is that it foams. Some UT units like the Degritter whose filter system acts as a surface skimmer is very sensitive to producing foam, so any surfactant use is pretty much limited to very low concentrations.

-A challenge with UT tanks is bath management. If you reuse the same fluid for sequential cleaning the bath will progressively get dirtier after each use. Filtration can extend bath life, but not all filters are created equal. Most soils removed from records using just water or surfactants are not soluble so they can be filtered.

1. The Degritter filter is tiny and is only a simple reticulated foam with pore size at best 80-pores/in (ppi) which is about 150-micron.
2. A 1-micron filter is common, but the very cost units are rated 'nominal' that can pass particles 10X greater.
3. The very best (but require better pumps) are absolute rated meaning they filter >98% at the micron rating and 0.2-micron absolute (that can filter bacteria, but not the surfactant) are readily available and can last upwards of a year, allowing 2 to 4-week bath life.
4. For extending bath life with filtration using water or nonionic surfactant, monitoring with a total dissolved solids meter such as Amazon.com: HM Digital 716160 COM-100 Waterproof Professional Series Combo Meter, 7", White/Purple : Industrial & Scientific is valid. Over time the water TDS will increase from contaminants and absorption of air, replacing at +5-10 ppm above baseline is the general recommendation.

-One option for bath life, is to make your own purified water in large enough quantities to frequently refresh the tank, and that can be done with RO/demineralizer units such as 5 Stage RO/DI Water Filter System - 75 GPD (1-OT-75) | For Fish Tanks, Aquariums, Reef, Water Filtration Machine | RODI – LiquaGen Water. For RO, there is a water usage rate that is 3-4 gallons of water used for each 1-gallon of purified water produced. The ‘brine’ wastewater is disposed to a drain. RO production rates can be impacted by the tap-water inlet temperature and pressure, and filter life will be dependent on inlet tap-water TDS. For homes with higher tap-water TDS, 2-stages of demineralization may be required.

If the above info spurs your curiosity, further details with over 80 linked references is available in this free book - Precision Aqueous Cleaning of Vinyl Records-3rd Edition - The Vinyl Press. Chapter XIV discusses only ultrasonic tank cleaning.

Take care,
Neil
 

Neil.Antin

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(Excellent synopsis on many topicd! We are fortunate for Neil's participation here.
Tim,

Thank-you for the kind words and your and @dminches willingness to learn, reap the benefits and share openly with others so that they may likewise benefit.

Take care,
Neil

PS/I recently assisted someone using an Elmasonic P60 (6L) spinning at ~0.15-rpm, 20 minutes reaching a temperature of 50C (122F). For sure at least one record (1960's) was damaged - the record was left with a mottled dull finish. Increased the spin speed to 0.3 rpm, adjusted chemistry and added a radiator/filter/pump because he was cleaning a lot of records. UT tank vendors can advertise all the power they want, but what gets into the water is what matters. The power rating of some UT tanks may be questionable, but not so with the Elmasonic P-series, they are powerful units.
 
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Klaudio/Peter

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It is said that the cleaning power in ultrasonic cleaners is that the small bubbles created by cavitation are shaken to push out the dust. However, according to Klaudio's cleaning design concept, vibrational energy is transmitted by resonance of ultrasonic waves into the groove, and the dust vibrates and is blown off. At theat time, the suitable frequency for resonance with the groove is 36-38KHz and at this time through out the long testing, the most energy is transfered to the inside of the groove and the most current flows (200 Watts). Without LP, it drops to 40% and consumes only 80 Watts power and is sprayed with water. Almost all 3rd party Ultrasonic cleaners have the same power consumption regardless of whether or not LP is inserted. This means that almost of the energy is wasted as heat and vibration of the water as it is sprayed with water, and less energy is only used to work in resonance with the groove.
 
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Neil.Antin

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Please see these videos that are computer generated simulation of the cavitation event - Simulations of the acoustically-driven growth and collapse of a cavitation bubble near a wall - Bing video and Inertial collapse of a single bubble near a solid surface - Bing video. Pay attention to the pressures and temperatures (which are theoretical) associated with the implosion event. There is a lot of energy with the event.

There is an entire science to the removal of particles - example the 573-page book Particle Adhesion and Removal, Editors K.L. Mittal and Ravi Ja, John Wiley & Sons, Inc, 2015 - Particle Adhesion and Removal | Wiley Online Books. The paper Adhesion and Removal of Fine Particles on Surfaces, Aerosol Science and Technology, M. B. Ranade, 1987 Adhesion and Removal of Fine Particles on Surfaces: Aerosol Science and Technology: Vol 7, No 2 (tandfonline.com) shows for aluminum oxide particles, the force (acceleration) required to remove a 10-micron particle is 4.5 x 10^4 g’s, a 1-micron particle is 4.5 x 10^6 g’s and a 0.1-micron particle is 4.5 x 10^8 g’s. So, as the particle gets smaller, the energy to remove increases exponentially.

Semi-conductor chips that cleaned to the nano-level are cleaned with mega-sonics of which there is little or no traditional cavitation, instead its acoustic streaming with target velocities about 3-6 feet per second - that develops the shear force to get into the boundary layer - Tech briefs on the basics of acoustic treatment in wet processing (prosysmeg.com).

All ultrasonics units are subject to standing waves. In a traditional UCM with bottom firing transducers, the acoustic waves that are propagating upward through the liquid will reflect downward from the fluid surface. When reflected downward, the acoustic waves will combine with the upward acoustic wave and the subsequent wave can be constructive(amplifying) if in-phase or destructive (attenuated) if out of phase. Ultimately areas/layers of higher acoustic energy/cavitation (standing waves) will form and there will be areas/layers of lower acoustic energy/cavitation. The standing waves tend to layer at a distance 1/2 of the wavelength associated with the UCMs frequency. The spacing of the standing wave is relative to themselves. Their position in the tank relative to a fixed point is dependent on the reflected surface – is it hard or soft; water height and other factors such as the type of transducer and water temperature. Based on an article by the late John Fuchs Ultrasonics - Near Field and BEYOND! - Ultrasonics - Near Field and BEYOND! - CTG Technical Blog (ctgclean.com), the first standing wave reflected from a hard surface (such as a tank metal wall) is about 1/2 the wavelength, while the first standing wave reflected from a soft surface (such as the water surface) is about 1/4 the wavelength. So, for UCMs with bottom firing transducers and the Degritter™ with side firing transducers into the record (soft surface), the location of the first standing wave relative to the water surface or record could be as close as 1/4 wavelength. Subsequent standing waves will be spaced about 1/2 wavelength apart. However, for side firing ultrasonic tanks, with limited width, absent the record between the transducers, there may be no standing waves if the frequency (and associated wavelength) and the tank width supports destructive/out of phase attenuation.

Sweep Frequency: Many ultrasonic tanks advertise a “sweep frequency” function. The “sweep frequency” function essentially modulates the main ultrasonic frequency about +/- 1 to 2 kHz. The intent of “sweep frequency” is to minimize narrow standing waves that will form in the tank when using a fixed frequency which is valuable for cleaning parts that are layered static in a UCM. There is debate in the industry as to the effectiveness of sweep frequency which is intended to equalize the cavitation intensity throughout the tank. But the record(s) is rotating and standing waves (from bottom firing transducers) may be beneficial since the record is exposed to a scrubbing type action as the record alternately moves from areas of lower cavitation intensity to areas of higher cavitation intensity.
 
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Neil.Antin

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Following up on standing waves and wavelength, below are the wavelengths for the common UT tanks used for record cleaning noting that wavelength is the speed of sound (in the fluid) in mm/sec divided by the frequency (cycles/sec or just Hz) and the speed of sound in water increases with temperature.

Frequency..................Distilled Water @20C......................Distilled Water @40C
37kHz..............................40.1mm...........................................41.3mm
40kHz..............................37.1mm...........................................38.2mm
80kHz..............................18.5mm...........................................19.1mm
120kHz............................12.4mm...........................................12.7mm

Note that for UT cleaning, frequency determines the wavelength while the power to the transducers determines the amplitude b826f935885f1b6144eb3dd76838178b.jpg (960×720) (pinimg.com), and the amplitude determines the acoustic pressure that can form in the cavitation bubble and the higher the acoustic pressure the more violent the implosion event. The greater the implosion event the greater the fluid agitation - pressure waves & turbulence - created in the vicinity of the implosion event which essentially scrubs the surface.

HOWEVER, the fluid boundary layer has a significant impact on the effectiveness of ultrasonic cleaning and this article by the late John Fuchs is a pretty good summary Ultrasonics - Frequency - Barrier Layer - CTG Technical Blog (ctgclean.com) of what is a fairly advanced concept with the takeaway "...that cavitation bubbles can form closer to a substrate surface at a higher ultrasonic frequency.".

HOWEVER, this is not to say that a 40kHz UT cannot clean a record or that a 120kHz is required to clean a record. A very high-power UT machine like the 200W KLAudio is going to produce very intense cavitation that by all accounts can penetrate the boundary layer sufficient for cleaning the required small micron size particles from a record.

BUT absent chemistry using only pure water with any UT machine will be challenged by organic viscous-type detritus films. Chemistry (such as surfactants) provides the assistance needed. But too much chemistry or the wrong chemistry and you now trade one problem for another. The organic viscous-type detritus film is removed only to be replaced with a potentially even more tenacious surfactant film.
 

tony22

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We are fortunate for Neil's participation here.
Indeed! I was AXPONA and wandered into the marketplace. I stopped at a table of an ultrasonic cleaner brand (who shall remain nameless :)). I began asking about the rotation speed of his cleaner, and whether it was correct to provide the most effective cleaning for the number of records that could be supported. He gave me a quizzical look. I asked “well, you are familiar with the analysis done by one of the most knowledgeable people on the subject”. He said “I thought I was the most knowledgeable person on the subject”. As he had given me answers to this point that proved this to be false, I gave him a dead look and said “You are not”. I asked if he was familiar with Neil’s excellent treatise. Blank stare. I called it up on my iPhone and showed him the first page. It was clear he had never seen nor heard of Neil’s phenomenal work. He took a picture of my screen and mumbled something about planning to take a look at it.

I repeat - someone who makes and markets ultrasonic record cleaners, and not a newbie in the hobby, either! Clueless.
 
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Jeffy

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Its funny because Fremer brought a record he cleaned on his KL Audio machine and then had Kirmus clean it. Kirmus showed the KL did not do a very good job.
 
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Neil.Antin

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@tony22, thanks for the acknowledgement.

One item to add to this thread is the use and interpretation of cavitation meters. Long story short, an objective analysis of the various available meters was done, and the summary is here - An objective comparison of commercially-available cavitation meters - PubMed (nih.gov) and the actual report is available here (PDF) An objective comparison of commercially-available cavitation meters (researchgate.net) but note that it downloads as a MSWord document. Read and draw your own conclusions if you are interested.
 

dminches

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Its funny because Fremer brought a record he cleaned on his KL Audio machine and then had Kirmus clean it. Kirmus showed the KL did not do a very good job.

How did they illustrate that?
 

Neil.Antin

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Its funny because Fremer brought a record he cleaned on his KL Audio machine and then had Kirmus clean it. Kirmus showed the KL did not do a very good job.
In what way was the record not very well cleaned? Was it an organic detritus or was it particulate?
 

mtemur

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In what way was the record not very well cleaned? Was it an organic detritus or was it particulate?
(As far as I can see from YT video) A white substance came out when Mr. Kirmuss sprayed his activator fluid. Pretty controversial situation cause it’s hard to be sure what was that white thing.
 
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Neil.Antin

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A white substance came out when Mr. Kirmuss sprayed his activator fluid.
Very simply, there are three basic types of surfactants - nonionic, anionic and cationic. Nonionic surfactants are compatible with any ionic surfactant. But anionic and cationic surfactants are not generally compatible and can form a sticky white paste. Without knowing the ingredients of the Kirmuss spray, but from anecdotal discussions, it appears to be a cationic surfactant. If Fremers record was a used record, and if it was ever 'cleaned' with any of the ubiquitous brush cleaning fluid (i.e., diskwasher, etc.) or Dawn, there could have been a thin film of anionic surfactant. So, a thin film of a spray-on cationic surfactant in contact with the anionic surfactant residue film and you can get white sticky type paste to form.

But as I said above - "...absent chemistry using only pure water with any UT machine will be challenged by organic viscous-type detritus films.". Used records can generally benefit from a pre-clean with surfactants. But the use of cationic surfactants needs to be approached with some caution. Cationic surfactants are known for their disinfection properties and being very hydroscopic are effective as anti-static agents. BUT from 1830476 (osti.gov) sponsored by Lawarence Livermore Labs who is nothing to sneeze at "Because of the negatively charged nature of most surfaces (the PVC of the record one of the most), anionic surfactants tend to be more efficient for particle removal than cationic surfactants (cationic surfactants themselves are also difficult to remove from these surfaces). Nonionic surfactants are usually more effective in particle removal than cationic surfactants but not as anionic surfactants.". Note that the difficulty in removing cationic surfactants is what then provides a somewhat 'durable' anti-static coating. But if the goal is a residue free surface, then the use of a cationic surfactant is contradicted.

However, one wrinkle in the use of cationic surfactants is that the RCA record formula from the early 1960's uses a cationic surfactant to coat the vinyl pellets. But in this case, it provides an inherent reservoir and is leached to the surface in a much more controlled fashion, ref: article Anti-Static Phonograph Records, G. P. Humfeld, begins page 18 1960-10-11.pdf (worldradiohistory.com).
 
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tony22

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@tony22, thanks for the acknowledgement.

One item to add to this thread is the use and interpretation of cavitation meters. Long story short, an objective analysis of the various available meters was done, and the summary is here - An objective comparison of commercially-available cavitation meters - PubMed (nih.gov) and the actual report is available here (PDF) An objective comparison of commercially-available cavitation meters (researchgate.net) but note that it downloads as a MSWord document. Read and draw your own conclusions if you are interested.
Neil, all I can say is that if someday soon you see an US cleaner manufacturer suddenly claiming they’ve “discovered” new and heretofore unknown techniques to clean records, and they start using phraseology that sounds vaguely derived from your paper, you’ll know who to sue for copyright infringement! :eek: ;)
 

Neil.Antin

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No Fremer’s record was brand new never cleaned in past just once with distilled water with his machine as noted.
If you watch the video starting at time 21:00, Axpona 2023 Video Coverage Begins Here | Tracking Angle, the records that Fremer provided may not have been new or if they were they were new old stock since Fremer mentions a dollar store label on one.

However, noting the record label is RCA and noting the RCA used an anti-static cationic surfactant to coat their pellets, the Kirmuss cleaner which is known to at least have propylene glycol, he calls it "diol" which is short for propanol 1-2 diol which propylene glycol, his cleaner may actually be an anionic surfactant and the reaction is with the cationic anti-static surfactant in the record vinyl formulation.
 
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Neil.Antin

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I will give my opinion as I ordered a kirmus and will compare to my degritter.
You will not be the first to do so, and those that have generally use it in a very traditional pre-clean with Kirmus and some chemistry and then rinse-dry using only DIW or just a touch of nonionic surfactant for wetting only with the Degritter.
 

Neil.Antin

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Neil, all I can say is that if someday soon you see an US cleaner manufacturer suddenly claiming they’ve “discovered” new and heretofore unknown techniques to clean records, and they start using phraseology that sounds vaguely derived from your paper, you’ll know who to sue for copyright infringement! :eek: ;)
Tony,

The book is free, and it based mostly on what I did 20-30 years ago when I was developing precision cleaning procedures for the Navy (which was not a one-man show, I had a large technical support group consisting of PhD scientists, chemists and field engineers) and a lot is in the public domain, so more power to them. If they paraphrase, so what. If they quote, then it's appropriate and professional to acknowledge the source. To do otherwise would be unethical and not to be trusted.

Take care,
Neil
 

tony22

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Understood, Neil. My comment was only partly in jest, but also reflective of what I feel are way too many in our hobby who seem to have no real depth of knowledge yet proclaim themselves to be “experts”.
 
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