Thumbs up for ultrasonic record cleaning

@terry9

Your example of particle size is unconvincing to me. A ’visible glop’ is made up of tiny particles which can be broken loose by US action, and then either deposited as solids or taken into solution as solutes, or perhaps even suspended. It is not necessary (or desirable) to remove the blob of glop all at once - a 1/4" glop would respond best to a frequency so low as to be reminiscent of a file.

Okay. Given enough time leaving an object in a constant stream of water will often result in a clean object. Exposed to the milder implosive power of more small bubbles coming off a higher frequecy may remove a substance - given enough time. But I don’t want to think about the composition of the dirt on a record or continually vary the time of a cycle according to that composition. Through trial and error I arrived at 10 minutes at 80kHz and 10 minutes at 37kHz - and that works. Rarely do I need another cycle.

Wrt the whole wavelength isse, which I see as largely theoretical, hopefully we’ll just agree to disagree. My dual frequency approach can process 5-6 records in 20 minutes and I’m quite satisfied they are clean. But I’m not a dogmatist, I will try using an extra spacer and 4 records though I’m uncertain how I would gauge results unless there is a significant difference.

The use of multiple frequencies within a cycle is common practice for industrial ultrasonic cleaning - I read no articles that talk about wavelength, for example specific item spacing for 40kHz, which is probably the most common frequency used.

When f=.037MHz and c=1480m/s (water)
Wavelength=40mm
My spacing is ~31mm.

Thanks for your engagement on this topic. I appreciate your interest.

@jtimothya, 

Energy supplied to the transducers is actually very close to the energy in the tank, since thin stainless steel is essentially transparent to ultrasonic energy.  If the plastic is easily deformable such as a PVC record, unlike thicker metal, then plastic will absorb energy which will be cause an increase in PVC record temperature, increase in the bath temperature from UT notwithstanding.

Overloading for metals used for UT tank cleaning has been a topic of conversation and analysis for some time with fixturing and spacing applied to achieve acceptable results.  But for metals (and some non-metallic) cleanliness verification has been in use for decades.  For critical applications such as high pressure oxygen were surface contamination levels as low as 5 mg/ft^2 and particles as small as 50 microns (if accelerated by flow) can lead to a fire (that looks like an explosion) NASA and the Navy have very detailed cleanliness verification methods using very specific chemistries and analysis methods - you may find this report of some casual interest - https://p2infohouse.org/ref/14/13872.pdf; I wrote it.  I developed the cleaning and verification procedures and I share the patents for Navy Oxygen Cleaner, the details are now formally documented MIL-STD-1330/1622; so I do have 'some' knowledge in this area.

However, use of UT to clean PVC records is a relatively new application.  But, in the case of PVC records that have a very defined geometry and surface area, overloading can be analyzer by number of records per tank and per watts.  But, this can be complicated by UT transducer location - side of tank or bottom.  If side of tank, will record(s) in the center of the stack see the same cavitation energy?  The record grove is pretty well defined reported as a V-shaped groove that is 56 microns (0.0022") wide at the top, a radius of 6 microns (0.00025") at the bottom, and a nominal depth of 28 microns (0.0011"), with groove spirals are nominally 200 grooves per inch equal to a groove separation of 125 microns (0.005").  Note that since the stylus rides below the record surface, contamination on the surface of the record should have little impact unless it is deep enough to affect the surface the stylus sees, which is why some used records with very fine surface scratches (likely caused by use of multi-stack record changers) can still play perfect.

The chemistry used in the UT tank can have a significant impact.  The very small grooves of the record really need a cleaning agent/fluid that will reduce water surface tension to assist with wetting/getting into the groove.  This is very different from smooth metal surfaces.  Tergitol 15-S-9 is a gentle non-ionic surfactant and at 0.06 wt% is at its critical micelle concentration (CMC) and will reduce the surface tension of the water from 72 dynes/cm to 30 dynes/cm, and with a 13.3 hydrophilic-lipophilic balance (HLB)  categorizes it as detergent.  When using surfactants you target a concentration of 5-10 times the CMC to get acceptable bath life, any more and you only complicate rinsing.  If you do not rinse with water (can be simple tap followed by DI water final simple spray rinse), softly adherent contamination may remain and the surfactant will bind to the PVC in an invisible transparent layer (just angstroms thick) that can affect the record sound and 'gunk' will build up on the stylus.  Using any aggressive solvent based chemistry or high temperature or too much power and you risk extracting or possibly eroding some of the PVC binders in the groove noting that the groove ridges are much smaller than the groove.  

What you are trying to clean, has a significant impact, and for most general type cleaning such as a PVC record, a wide variety of contaminants can be present.  Depending on the type of contaminant, there will be a minimum exposure time, and in precision cleaning for sensitive material such as PVC a maximum duration of 10 minutes would apply (ref MIL-STD-1330).  But, the PVC itself presents a difficult material because particles may be embedded in to the surface.  Temperature always helps since the PVC will expand helping to free up embedded invisible particles (as small as 1 micron and less), and simple oils will soften and flow.

The human eye assisted with bright white light can see particles sized 50 microns (ref MIL-STD-1330D, I wrote it).  So this is not small enough to see the smaller particles that could be in the trough - ~6microns, let alone those between the groove wall ridges.  Have you ever tried Ultraviolet (Black) Light to inspect for particles and fingerprints?  Blacklight can detect contamination at about 25 mg/ft^2 and particles as small as ~30microns?  Animal/vegetable fats will fluoresce. Mineral based oils/greases generally will not fluoresce.  But, like you say, there are currently are no cleanliness verification methods for PVC records other than play and listen.  So, you are still in the experimentation phase.

Otherwise, I do not use a UT tank for record cleaning.  I developed my own manual cleaning procedure (that steps off from what the Library of Congress uses) using the VinylStack record protector that I can clean/dry 6 records in about 45 minutes which is good enough for me; and I am fine with the results.  I am using a multi-step process of pre-rinse with flowing tap-water, clean/scrub with Tergitol 15-S-9, post-rinse/scrub with flowing tap-water, final rinse with DI water spray, then two step dry - medium-pile lint-free microfiber and final dry with anti-static cloth - after which it only takes another few minutes to completely dry.  I developed a fully detailed procedure just for an exercise formatted similar to a Military Standard-Tech Manual.

Hoped the above expands upon the knowledge base, and Good Luck.

R/Neil

@antinn Thanks for your expert contribution.

@jtimothya What I do to gauge results is clean 50 records to the lower standard, allow chemistry to settle overnight, drain drop by drop, and note (e.g. photograph) the solids deposited on the bottom of the tank. Then I change chemistry, retaining a sample of the old, and clean the same 50 records according to the higher standard.

After letting the chemistry settle overnight and draining drop by drop, I compare the solids deposited on the bottom of the tank to the photo, and compare a sample of the newest chemistry to the old. The comparison is therefore of the lower standard to the increment of lower standard plus higher standard, which is approximately (in my experience) the higher standard.

Not precise, granted, but good enough for hobby work. Although I welcome R/Neil’s comment and correction.

@terry9:

This is going to be a long thread, but the devil is in details.

The fundamental challenge with cleaning records, is that we are trying to achieve a cleanliness level better than what we can see.  Right now, the record UT vendors are using post cleaning microscopic inspection to determine the process parameters.  For critical application precision cleaning cleanliness is defined by two parameters - non-volatile residue (NVR) which relates to oils/grease and the like, and particles.  For cleanliness levels that are below visible, very high purity fluids are used to flush for final clean/verification of the surface to determine residual NVR that an be determined by a number of different methods sensitive down to about 1 mg/ft^2, and for particulate cleanliness.  A particle count is used and measurements to 1 micron are common.  Unfortunately, none of this is practical ($$$$$) for a record.  Additionally, the groove design and that fact that the stylus does contact the entire groove surface makes it difficult to determine what is the minimum cleanliness level required, some particulate may be inconsequential depending where it is.  

But, your process of reviewing post cleaning effluent is often used.  You establish minimum process requirements such as chemistry, equipment, temperature and time and then observe the effluent at the end to determine if the process has removed all the contaminants it can.  Although the eye cannot see individual particles much less than 50 microns, in clear water, very small particulate can often be detected as a bloom/turbidity - very small particles act as colloidal suspensions and can conglomerate into larger particles that can then be detected.  

When you try to make the process cost effective, a whole other level of challenge arises.  If you are going to push the bath chemistry, it has to be the right chemistry that will suspend the contaminants to prevent redisposition with enough concentration to get repeatable cleaning performance - the last records in the bath are cleaned as well as the first, and the first records are rinsed or cleaner just as well as the last.  

In another post on UT tank cleaning, I wrote something similar to the following, that I have slightly modified by adding a cleanliness verification step:

If you are using UT to clean a lot of record, consider using a demineralizer, and this is the best value I have found, https://dirinse.com/product/d-i-rinse-pro-50-unit/. If your tap water is of reasonable quality, it can produce about 2000 gallons of demineralizer water at a cost of $0.20/gallon, and it can be refilled ($200 for 2 refills), and the valve arrangement can make a very coinvent install. If you have a source of readily available cheap DI water, then you don't need to worry about bath life or filters/pumps etc to extend the bath life. And, you could easily add an effective rinse/cleanliness verification step as follow:

Step 1. Clean records in UT tank with aqueous chemistry.  You do not need to use a lot of cleaner since you will only be using one tank-bath for each batch of record.  This way you can baseline that every record batch will be exposed to the exact same chemistry.

Step 2. Drain UT tank to household waste drain.  While draining use just warm tap-water to flush over records for first rinse.  This will remove most cleaner residue and loosen contamination.  

Step 3. Refill UT tank with only DI water and using ultrasonic, perform rinse/final clean to remove mostly any remaining very fine particulate.  Hopefully the chemistry in Step 1 removes all surface oils and greases that may trap/cover fine particulate, so that only DI water is required to do the final polish. 

If you want to do a cleanliness verification - at the conclusion of Step 3, obtain about a 100 mL sample of the UT DI water in a clean clear container.  Cap, shake and verify no stable bubbles - this will verify the cleaner has been removed.  To check for particulate, place a piece of white paper behind the container and inspect for visible particulate or turbidity.  You should not see any visible particulate and unless very turbid (and this will take some experience), at this point the process has done all it can do.  If the sample is very turbid, reclean.  Note - if you are constantly having to reclean, then Step 1 needs to be adjusted - it may be the chemistry, the chemistry concentration, the bath temperature, exposure time, record loading, or the tank Hz and watts.   But an occasional (not frequent) reclean is generally indicative of a pretty efficient process.  If you never have to reclean, chances are you doing more than 'required', but that is not necessarily bad.

Step 4. Remove records to dry.; or if cleaning records again proceed to Step 5.

Step 5. If cleaning another batch of records, or cleaning the same records again, just add cleaner to the existing DI bath and begin at Step 1.  This reduces the amount of DI water used.

Quick analysis with a 1.5 gal UT tank volume. The demineralizer should provide enough for 1333 tanks, and assuming you are cleaning 3 records/batch, that is 4000 records. The initial cost is $0.30/tank for DI water, and for the Tergitol 15-S-9 at 6 ml/tank, is ~$0.28/tank for at total of $0.58/tank or about $0.20/record. After the first 1333 records, the DI water cost drops to $0.07/tank, so the total per tank cost drops to $0.35/tank, and the per record cost drops to ~$0.12/record based on the assumptions of this analysis. Clean 6 records per batch, and the per record cost adjusts proportionally, down to as low as ~0.06/record.

This is just a quick analysis.  Like I said, you are still in the experimentation phase.  Good Luck

R/Neil

@antinn

Hello R/Neil. Thank you for the long response. Much appreciated.

My filtration system gets me down to 30ppm of dissolved solids. I use that for rinsing before the distilled bath. Two questions:
1) Is 30ppm low enough to use for cleaning? (have been using distilled)
2) Is 30ppm low enough for polish?

Thanks!!