Ultrasonic Cleaner / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Ultrasonic Cleaner

1 2 next

Move Thread

LAN_403

IntraWinding

Sun May 23 2010, 03:47PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

I bought a 5 Litre low cost Chinese ultrasonic cleaner (120W Ultrasonic power) and it has two problems.

First it makes a lot of really unpleasant mains frequency modulated ScreecH

despite having a nominal operating frequency of 40KHz.

Second, it produces much less cavitation (cleaning power) than the silly little Â£30 one I had before.

It's pair of transducers look good and solid. They each have the same hand written frequency near 40KHz written on them.

Anyone here an expert on these things by any chance? I wonder if the power problem could just be down to the drive frequency needing a tweak. Or perhaps 120W is just too low for 5 litres?

I don't have any theoretical understanding of how the system is producing audible undertones of 40KHz but I know the ultrasonic cleaner at my dentists' just makes a sizzle rather than a screech.

Nicko

Sun May 23 2010, 03:59PM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

Sounds similar to the one I bought on eBay a while ago - there are a few out there. Mine was the 4L version of this:

(Eumax US100SH-4) but the price seems have gone bonkers since I bought mine - I paid about USD 130.

Whilst I know little about these things, mine had a loose transducer and the main PCB had broken a mount - I fixed both those issues - the transducers are bonded to the bottom of the tank - the wire basket also generates a lot of noise and I found that by putting some rubber pads to support the basket so it wasn't actually in direct contact with the tank helped. Also, the lid rattles and acts as a sounding board - rubber pads good there too... (I used those little stick-on rubber feet that come in a sheet).

Also, use clean water and run the tank for a good few minutes before cleaning objects to get the water settled and up to temperature. I also use a decent additive (3% Tikopur @ 45C). A big tank takes a while to get going... I was told that you need to get the air out of the water by running for a while before adding the basket with your bits - this may be apocryphal YMMV...

It is noisy - the cats & dog hate it, so it lives in the utility room with the washing machine!

I've had good luck with mine - e.g. see

Cheers

Proud Mary

Sun May 23 2010, 04:01PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I would expect the following: f1, f2, (f1 - f2) (f1 + f2) - and that would be if f1 and f2 were pure single frequency sine waves.

Is there a direct relationship between cavitation and what you call 'cleaning power'? The tank will very likely be home to all sorts of standing waves, nodes and troughs, and what have you, where local 'cleaning' action, or agitation, may be weaker or stronger. Who can say?

Id there any sonoluminescence?

radiotech

Sun May 23 2010, 04:19PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Two evil old treatments for aching fingers-dip them in the cavitation bath and dry them in the10kMhz feedhorn .

Pity the best solvents for those things is illegal now.

IntraWinding

Mon May 24 2010, 01:13AM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

Mine looks to be this

The transducer on my earlier 30W cleaner came off. I epoxied it back but eventually it burnt out. My present tank has the transducers glued on but with a layer of gauze sandwiched in with the glue. This, I imagine, is to stop the spread of delamination. Anyway, the transducers seem to be solidly attached, but I'll check again.

The initial run is supposed to degas the water to allow to cavitate aggressively. You certainly see bubbles released so I'd say this myth is likely to be proved true.

I'd accept the noise if they all sounded so bad, but like I say, the ones at the dentist are sufficiently civilised to be operated in the room with a patient and staff without creating a noise issue at all.
I've been wearing earplugs, but I've had complaints from neighbours in the past: "I can't hear anything but my grandchildren say it's awful."

f1, f2, (f1 - f2) (f1 + f2) is the usual thing, but for F1=100Hz, F2=40KHz, all the high pitched tones should be inaudible. Somehow a high pitched but all to perfectly audible racket gets generated.

I understand the idea that standing waves will result in variation in cleaning action throughout the tank volume, but a standard test for an ultrasonic cleaner involves strips of aluminium foil arranged hanging at the centre and close to each end of the tank, filled with water. After 5 minutes all 3 foils should be uniformly perforated. My old cheap 30W tank had no trouble perforating foil, but this big thing really struggles. I only found perforations after running it with a very low level of water fill.

What solvent are they? Hope your fingers are still working!

radiotech

Mon May 24 2010, 04:20AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

The last time I was at the dentist they used a "Cavitron" a teeth cleaning machine Cavitation + High speed water jet in the handpiece. Seems you can heat through your teeth too.

Ultrasonic baths are used with mild detergents too.

Bjørn

Mon May 24 2010, 05:03AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Whenever there is two of something it is a good idea to check that one is not wired the wrong way around.

IntraWinding

Mon May 24 2010, 08:29AM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

radiotech wrote ...

The last time I was at the dentist they used a "Cavitron" a teeth cleaning machine Cavitation + High speed water jet in the handpiece.

New to me! Just to clarify, The ultrasonic cleaner in my dentists treatment room I'm referring to is for cleaning dental instruments, presumably before sterilisation. It looks like most ultrasonic cleaners in having a tank, but is shaped as a large area shallow tank so that lots of instruments can be lay next to each other without touching. I suppose it could be quieter just because it's lower power than mine, but I suspect it's actually a better design. I wonder if mine drives the transducers with a square wave whilst machines that cost 8 or 10 times as much but otherwise look similar, use sine waves, for example.

I will double check the wiring of the transducers in case that's the problem.

I just found this paper, illustrating that the sound generation is still a bit of a mystery:

Noise generation in bench-top ultrasonic cleaners
D.H. McQueen

Abstract
A theory of audible noise generation in bench-top ultrasonic cleaners is presented. Strong audible noise is generated when the ultrasound intensity exceeds a cavitation threshold with harmonic, subharmonic and broad-band noise generation. In conventional bench-top cleaners the highest intensities occur in the immediate vicinity of the ultrasonic transducers. According to the proposed theory the audible noise is produced there. A method of avoiding this ultrasound concentration and audible noise generation using point source transducers is described, and experimental results supporting a theory of their operation are given.

Anyone got a copy by any chance?

I haven't seen any sonoluminescence yet, but I haven't looked (too keen to get away from the awful noise!).

Alan

radiotech

Mon May 24 2010, 05:11PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Here are 3 pages from manual for a cleaner that works well.

IntraWinding

Mon May 24 2010, 06:54PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

radiotech wrote ...

Here are 3 pages from manual for a cleaner that works well.

Thanks very much for those scans

Could you possibly add the circuit diagram (and perhaps the rest of the circuit description, if it gets complicated)?

I'm going to try that foil test on my tank with cooled boiled water at 80C. I'll degas for 10 minutes first and then stir in a squeeze of washing up liquid. I think that's giving it the best possible chance of working and will give me something to compare any improvements to if I decide to try tweaking this.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob