Cleaning Bottles with Ultrasound

[McHeathen]

A mate of mine who has a hobby involving digging up old bottles (and other items) from old rubbish dumps, came across instructions for cleaning the bottles with ultrasound.

The instructions he showed me involved using a metal tank, signal generator set to 40kHz and a 'transducer'.

I expect that the transducer must be a loudspeaker of sorts with can be used under water, or is it?

Could a plastic tank be used instead of a metal one?

Where would be the best or cheapest place to purchase the 'transducer' and a signal generator capable of generating a signal of 40kHz?

 

[Danger]

Hi, McHeathen.
You can get ultrasonic cleaning tanks for jewelry or dentures or whatever else quite readily. The type of container is irrelevant, as long as it's waterproof.
Technically, a transducer is any device that converts one form of energy to another. That would include microphones, seismic detectors, etc.. In this case, it refers to a piezoelectric crystal that converts an electrical signal to ultrasonic (above human hearing) sound waves.
I can't advise as to the best source, but you might start by checking out jewelry supply houses. A quick 'Google' should turn up lots of sources. They're not expensive.

One thing to watch out for, though, in your case is that you don't want the crystal to get near the natural resonance frequency of the glass. If it matches, the glass could shatter. I'll leave it up to others more informed in these matters to elaborate.

 

[mgb_phys]

I wouldn't worry about the resonant frequency if the object is under water.
It's worth adding a bit of detergent to the water

 

[Danger]

I wouldn't worry about the resonant frequency if the object is under water.
It's worth adding a bit of detergent to the water

I was unaware of both of those factors, Mgb. Can you elaborate?

 

[mgb_phys]

It runs at high frequencies, far above what the vessel would resonate at - the glass doens't move very much, ultrasound relies on creating microbubbles on hard surfaces by caviation.
It's not so great at getting oil off things so a bit of detergent helps - it also stops green goo growing in the tank if you don't clean it for weeks!

It does need a solid surface to create the bubbles - we spent quite a lot of the clients money trying to develop a silent+efficent home washing machine before we worked that out!

 

[Danger]

Cool. Thanks, man. I never saw anything about that before. (I knew about the bubbles, but not that the subject matter wouldn't vibrate as well.) Thanks.

 

[stewartcs]

It runs at high frequencies, far above what the vessel would resonate at - the glass doens't move very much, ultrasound relies on creating microbubbles on hard surfaces by caviation.
It's not so great at getting oil off things so a bit of detergent helps - it also stops green goo growing in the tank if you don't clean it for weeks!

It does need a solid surface to create the bubbles - we spent quite a lot of the clients money trying to develop a silent+efficent home washing machine before we worked that out!

I've also had success using a citric acid based solution in ultrasonic cleaners for removing grease and oil.

CS

 

[McHeathen]

Hi, McHeathen.
You can get ultrasonic cleaning tanks for jewelry or dentures or whatever else quite readily. The type of container is irrelevant, as long as it's waterproof.
Technically, a transducer is any device that converts one form of energy to another. That would include microphones, seismic detectors, etc.. In this case, it refers to a piezoelectric crystal that converts an electrical signal to ultrasonic (above human hearing) sound waves.
I can't advise as to the best source, but you might start by checking out jewelry supply houses. A quick 'Google' should turn up lots of sources. They're not expensive.

Would an electronics shop such as Maplin stock them? He will still need a signal generator capable of generating a 40khz signal. Would such a generator be expensive?

 

[mgb_phys]

Presumably you are in the UK - CPC sell utrasonic baths very cheaply, about £20.

CPC are great for cheap equipement and parts, and you can get all of Farnells parts stock through them. They don't require a trade account - you can just pay with a credit card.

 

[Danger]

Would an electronics shop such as Maplin stock them? He will still need a signal generator capable of generating a 40khz signal. Would such a generator be expensive?

I'm afraid that I've never heard of Maplin. I don't work with electronics at all, but if I happen to need something like a relay or a photo emitter/detector set I just go to Active Components in Calgary and take them off of the shelf.

 

[mgb_phys]

Maplin is a uk high street + catalogue electronics store - a bit like Radio Shack used to be before it became a watered down Circuit City.

 

[hxtasy]

What kind of power are we talking about for the transducer or diaphram to be effective? It seems like a small amount of power would not do much, except for maybe leaving the item in the cleaning tank for a week.

 

[mgb_phys]

They need very little power, all you are doing is creating bubbles from dissolved air in the water. It's the bubbles pushing particles off the surface that does the cleaning.
It's also very efficent to couple the ultrasound power into the water and then to the suface of the part - so very little energy is wasted.

 

[turbo]

Might I suggest that you use a 50:50 solution of rubbing alcohol and water with a few drops of detergent. That is a very effective glass-cleaning solution, and relatively gentle.

 

[hxtasy]

They need very little power, all you are doing is creating bubbles from dissolved air in the water. It's the bubbles pushing particles off the surface that does the cleaning.
It's also very efficent to couple the ultrasound power into the water and then to the suface of the part - so very little energy is wasted.

Do you mean actually using two transducers? one in the water and one close to the part you are cleaning?

I am not very familiar with Ultrasonic cleaning. I guess I need to do some research.

 

[mgb_phys]

There is only a transducer in the water, once the power is coupled into the water it doesn't get out. The part is just dropped in the water - it's the ultrasound hitting the rigid part that creates bubbles.

I suppose you coul dbuild a bath yourself but they are so cheap it probably isn't worth the effort unless you need a very large bath. I imagine you could use more than one transducer in a large bath but you woul dhave to be careful not to create intereference effects / standing waves so that there was no effect at certain points.