Thumbs up for ultrasonic record cleaning

When I tested spacing (using SQ as the determining criteria), in my Chinese 10 L/40khz tank, spacing two records at 2" apart has superior SQ, opposed to 1" apart. I could hear the difference.

@jtimothya

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.

With respect to frequency, my reasoning is as follows.

Bass response is a good analogy because both are sound waves in a confined space. Low frequency energy will be present in a listening room regardless of size - the problem is that different frequencies will manifest at different points. The mechanism is constructive and destructive interference. This is a function of reflections and dimensions (spacing).

If you want really good bass response down to a given frequency f, then the room should have at least one distance equal to or greater than c/2f, where c is velocity. Better is c/f, or even more.

By analogy, record spacing will affect the distribution of energy on each record surface. For a uniform distribution of energy (bubbles) which washes the entire surface, at least one wavelength is required. Consider the case of the US cleaner in Imperial measure, as it is more convenient. Then c ~ 5000 ft/sec = 60,000 in/sec. At a frequency of 60KHz = 60,000Hz, a wavelength is 1 inch. At 80KHz, wavelength is 6/8 = 0.75". Of course, records are not planes; they wobble on the spindle, they are slightly warped, etc. Therefore a safety factor of 1.5 to 2 is sensible, for 1 1/8" to 1 1/2" at 80KHz. I use 2".

By theory, the definition of energy is the ability to do work. The work in this case is microscopic bubbles on the surface to be cleaned. Since we know that low frequency US heats the chemistry much more than high frequency US, much low frequency energy is used to heat chemistry rather than clean. That is, the energy is expended elsewhere than on the surfaces. This is evidence that spacing matters.

By experiment, try cleaning a pipette in an ultrasonic bath. If anything is caked on the inside, it will take forever to come clean. The US agitation is negligible in such a confined space. Also, I tried close spacing and had to re-clean nearly a thousand records. I got as much suspended solids off during the second cleaning as I did on the first.

Your analysis of energy may well be correct. Thank you for enhancing my understanding of this by forcing me to think more about it. But in our practical case, it comes to the same thing - something is happening, so either we increase spacing (and reduce the number of records) or we reduce the number of records (and increase the spacing).

In conclusion, the direct evidence is: fewer records with greater spacing removed more solids. This experiment, however, does not differentiate between two potential causes: spacing and energy/record. Both interpretations of theory come to the same thing: fewer records, widely spaced, is better.

Machine is a rebranded ElmaSonic P60H (Fisher Scientific). My thinking was that Fisher is a lab supply company, and so the machine would have to pass two levels of QC. Still going strong after 6000 records, plus misc cleaning chores. Works wonders on wine glasses!

All,

An inherent problem with using ultrasonics to clean PVC is that as a plastic, it is going to absorb ultrasonic energy  http://www.zenith-ultrasonics.com/part_positioning.htm, and https://techblog.ctgclean.com/2011/11/reader-question-baskets-for-ultrasonic-cleaning/, noting that John Fuchs with Blackstone ultrasonics has been in the business of UT cleaning for over 25 years, and is a recognized expert.  This is a good article addressing some of the basics written by John Fuchs, https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19950025362.pdf.

If you overload the UT tank with records, you are going to significant reduce the power available to clean.  Note UT came into promenance 25 years ago when the elimination of CFC solvents forced the industry to develop environmentally suitable aqueous cleaning solutions.  But, this was mostly for metal cleaning.  You can compensate the high plastic load with more power, that is variable, but you are talking industrial units starting at over $2K.  Check the units at Blackstone and Crest Ultrasonics, these companies have been manufacturing USA made UT tanks/consoles & systems for over 25 yrs. 

@antinn

Thank you! That explains why power per record a relevant parameter. If I had ever known that, I had forgotten. Just like I had forgotten some of the basics (i.e. how cavitation bubbles form).