Ultrasonic Cleaner experiences...and DIY?

[Uncle Bulgaria]

Originally Posted by David G4EBT

The one at the link below looks very tempting, if not too good to be true at £35.99 post free from a uk supplier. 2 litre capacity, 50 Watt ultrasonic power, 100 Watt heater, digital display, includes the wire basket. It’s similar to ones costing four times as much:

https://www.ebay.co.uk/itm/2L-Ultras...-/123734259621

Alas, the address of the supplier purporting to be from the UK is in fact "SHENZHEN DIKANER E-COMMERCE CO LTD
WENJUAN WAN
RM 5G9,F/5,BLDG 1,NO.1 FACTORY,SHENHUA SCIENCE &TECH ZONE,MEIHUA
518000 ShenZhen, 广东省
中國"

I have found that filter to be of limited effectiveness too. How on earth they can offer free postage as well... It's like RS - they must have paid me many times more than I've bought from them on their crazy delivery and packaging!

[Uncle Bulgaria]

Further references...

Caveat emptor - a dangerous cleaner from the Model Engineer forum...

One being taken to pieces on the EEVBlog forum.

[stuarth]

For delicate stuff, would gentle agitation be kinder than aggressive cavitation? Especially for aluminium parts.

Stuart

[Ed_Dinning]

Hi UB, the transducer shown is the "Dalek" type and uses PZT discs. The through hole is not normally for attachment purposes, it is simply a through hole for the clamp bolt.

In production the base of the tank and transducer are abraded and cleaned/ degreased with solvent and DI water. A special epoxy mat is used that is baked to 2 heat levels while the tank and transducer are clamped together. This is a very critical interface!

Transducer have a 1M discharge resistor across then and are normally connected together with tinned copper braid with washers and a pop rivet, not soldered. This area is then coated in a soft epoxy as a damping medium to prevent connections fatiguing.

The transducer design relates back to the earlier Mullard/ Kerry types; price shown is good value.
These transducers can be paralleled for higher power and better coverage of the base of the tank.
In practice they were run at up to 100W/ transducer (actually measured on a dynamometer wattmeter) and tuned , sometimes with a parallel C (HV ceramic, low loss) the reduce the VA and peak the W on the dynamometer.

Note that these discs all have a Curie temp, go above it and they die. Curie temp can reduce with compressive loading. Non compressed types have much lower amplitude excursions (and power handling) before they shatter.

For really high efficiencies the transducer(s) can be connected in a motional feedback bridge circuit the will keep them on tune despite variations in loading (they have a high Q)

Usual method of controlling power was to vary the Vcc of the power oscillator and use a virtually unsmoothed rail to give a bit of frequency sweep

Ed

[David G4EBT]

Originally Posted by Uncle Bulgaria

Alas, the address of the supplier purporting to be from the UK is in fact "SHENZHEN DIKANER E-COMMERCE CO LTD
WENJUAN WAN
RM 5G9,F/5,BLDG 1,NO.1 FACTORY,SHENHUA SCIENCE &TECH ZONE,MEIHUA
518000 ShenZhen, 广东省
中國"

I have found that filter to be of limited effectiveness too. How on earth they can offer free postage as well... It's like RS - they must have paid me many times more than I've bought from them on their crazy delivery and packaging!

I never doubted for a moment that the supplier was anything other than from Shenzhen. Many listings on e-bay are available direct from Shenzhen with a shipping delay of maybe 3 weeks, but for popular items which some customers might wish to receive more promptly, suppliers extensively use UK ‘Drop Shippers’, of which there are many, with UK stocks of selected items and delivery in 3 - 5 days.

The drop shipping process:

https://en.m.wikipedia.org/wiki/Drop_shipping

My own ultrasonic cleaner is UK branded from a UK company, looks remarkably similar to those from China and did cost about 4 times as much. I doubt that the Chinese ones are ‘rip off copies’ - far more likely that items imported from China are branded as UK, implying that they’re not just being marketed by a UK company, but are produced in the UK, rather than imported.

There is a UK woodworking equipment company which refers to itself as a ‘proud British Company’ as indeed it is. It emblazons its stock with union flag logos, but is just a marketing company who don’t manufacture anything and don’t claim to - they import products from China and put there own branding on them.

Incidentally, I use ultrasonic cleaning fluid appropriate to what I’m cleaning - not just water with a few drops of liquid detergent, though that does at least break down the surface tension of the water to assist cavitation.

[Trigon.]

In production the base of the tank and transducer are abraded and cleaned/ degreased with solvent and DI water. A special epoxy mat is used that is baked to 2 heat levels while the tank and transducer are clamped together. This is a very critical interface!

By way of illustration - this is the base of my 110W Kerry 'Pulsatron' tank showing the mat:-



I presume the mat helps create a well defined thickness of epoxy (?), and extends way beyond the transducers themselves to minimise stress at the boundary (?).

And the drive board:-



Note - no DC smoothing to speak of, so the sonics are effectively pulsed at 100Hz. The brochure states 'automatic tuning' so I presume the frequency always hits resonance even with varying tank load.

Cheers

[BulgingCap]

A few years ago I spotted a gigantic ultrasonic tank and ancillaries at a local auction. It was branded as 'Hilbre'. I later found that a friend had bought it for a song. He wanted a pump and some plastic fittings from the assembly. There appeared to be a large tank with heater, a long thin tank with transducers, and a circulator pump and control panel etc. This was all housed in a metal enclosure at least 2m x 1m x 1m. I have no idea as to its original use, but I persuaded my friend to donate the tank and drive pcb (plus spare pcb) to me. It is a fearsome beast and I am always wary of leaving anything too delicate in there for lengthy periods. The drive pcb had dead semiconductors so the spare pcb was used as a donor.
Below is pictured a piece of kitchen foil after a few moments of immersion. I did not record any specs whilst fiddling with it originally, and it has performed perfectly since.
BC

[Uncle Bulgaria]

That is quite significant! I have never had any luck with these local auctions others seem to find excellent bits in - only ugly furniture or hideous ornaments!

It looks like DIY is the way to go for larger tanks, as totting up the parts for the circuit from Practical Electronics (which drives a single transducer) approaches the price for buying one complete up to about 6l, except RS no longer stocks the transformer parts for winding the one required.

David - I know the principle, it is just annoying that eBay is getting harder and harder to trawl through for actually local items rather than Chinese resellers. Even sorting by 'used' can throw up reams of sub-Amazon-quality new stuff.

Thank you Ed. Some interesting material on how to avoid failures through vibration. I think I'm going to buy a small unit and make my own larger one once I've evaluated it as I'm sure I'll come across a myriad of possible uses soon enough that will demand something bigger!

Thank you for all the thoughtful replies.

[David G4EBT]

One point which might be of interest is that almost all ultrasonic baths are marketed on their (alleged!) liquid capacity - for example, 600mL, 1 Litre, 2 Litre and so on. A chum (who isn't on this forum) recently bought one which was described as '2 Litre'. He thought it looked too small to be of 2 Litre capacity, so filled it with water up to the fill line and found that it contained only a little over 1 Litre. (It's gone back for a refund).

Out of curiosity, I decided to check the volume of mine, which I've had some years, and is branded Allendale - a reputable UK company that supplies commercial and industrial ultrasonic cleaners (albeit like most tanks these days, the country of origin of mine is China). The dimensions of the tank at the top are: 15cm x 14cm & 10cm deep. In describing the tank as '2 Litres' they appear to have simply multiplied those dimensions, which would equate to 2,100 CC.

However, the inner corners of the tank are rounded, and the sides slope. There is a fill line which is 3cms below the top of the tank, all factors which reduced the capacity of the tank. When filled to the brim, the tank holds just 1.8 Litres, but when filled to the fill line, holds just 1.4 Litres. In one sense, apart from it's inaccurate and misleading description, what really matters is the size of the wire basket into which items for cleaning are placed, as that further reduces the capacity. In mine, with the basket in place, it is 14 x 12cms at the top, and 7cms to the fill line. Hence, the physical capacity of the basket in 1,176 cms - about half that of the claimed capacity of the tank.

See sketch below.

Really, the key point to bear in mind if thinking of buying an ultrasonic cleaner, is whether or not the basket capacity is large enough to contain whatever items you may need to place in it for cleaning. In my case, that would be say a two-gang air spaced tuning capacitor. Most of the items I've used it to clean are so small that they'd fall through the mesh of the basket so I put them in a small glass jar immersed in the liquid.

Hope that might be of interest when considering what size of cleaner to buy.

I've not attempted to check whether the stated 'ultrasonic power', in mine of 70 Watts was calculated by the same mathematician who arrived at '2 litres'!

They're now so cheap that a '3 Litre' () tank with the following spec is just £58.89, so were I buying one today, I'd probably go for that:

Timer Setting:1-99 minutes Adjustable
- Temperature Setting:0—80 Celsius Adjustable
- Ultrasonic Frequency:40 KHz
- Power Consumption: 100W
- Heating Power:100W
- Tank Material: Stainless Steel SUS304
- Tank Capacity:3L
- Tank Size:240x 140x 100 mm ( L x W x H )
- Unit Size:270 x 170 x 240 mm ( L x W x H )
- Power Supply: AC 220 ~ 240V, 50 Hz

Hope that might be of interest.

[Ed_Dinning]

Hi David, when I was in the industry the power quoted into the transducer *1.414 (because of the 100Hz modulation ) was often used. This is akin to the "watts RMS" used on audio systems.
The actual tank power in terms of sound pressure levels will depend on many things, not least the transducer, which has a higher conversion efficiency if it is of clamped construction.
There really is no definitive way of comparison without running tests on foil or sum such, quoted power levels are not meaningful and tank volumes are misleading. (A similar "power" in a larger tank will have a lower sound pressure level, then if you bring operating frequency in as well..........)

Ed