Ultrasonic Cleaning

It will make a lot of noise, but the liquid is what transmits the ultrasonic energy to the surface to be cleaned.

The cleaning action of a ultrasonic cleaner is due to cavitation of bubbles at the surface. The energy that would be applied to the part that causes this would be a lot less. The water being a better conductor. Not so sure that heat that would build up on the horn would cause it to burn out prematurely.

As shown, the ultrasonic energy is coupled through the liquid to the surface to be cleaned. The liquid is non compressible and thus is an effective coupling agent. The coupling through air from below will be very low, due to the large impedance mismatch caused by the air gap.

Ultrasonic cleaning, can use high energy that uses cavitation. It can also use lower energy and rely on oscillation of fluid to provide cleaning action. This looks like a low energy application, but may not be. Possibly more info will help. I am curious about the 'horn' mentioned. Horns are usually used to couple the high impedance of a transduccer to the low impedance of ambient space, in this case, air. yet it is shown as embedded in luquie. It might be an ultrasonic whistle, and common way to create ultrasound for cleaning and mixing?

The horn is attached to a converter driven by a 750 controller, typically we will not run it a maximum. It is used in a chemical process stream to clean an optical window that gets contaminated by the chemistry sticking to it. It is usually programmed to come on in short bursts (5 seconds) every so often (15 minutes).

What we actually manufacture and sell is the device with the optical window.

There are a few "problems" with the ultrasonic cleaner as we currently use it:

1. It has to be in the process stream.

2. It has to be close to the optical window. It is a given length because it is tuned to the wavelength of the ultrasound. This means that if the diameter of the proess stream is large, the tip of the horn cannot be placed close enough to the window to be effective.

3. It is another device that has to be installed.

If it would work from the other side, we would have a much better product, since everything would be self contained in our actual product.

Here's how this all got started. if you hold the horn close to the side of a ceramic (or whatever) coffee mug you can see the liquid inside the cup move.

So, what is the mechanism that transports those ultrasonic waves to the other side of the mug?

1. Is it truelly mechanical ? the horn moves an air molecule, the air molecule moveing a mug molecule, the mug molcule moving the liquid inside?

2. Is it more like a radio wave ? where the wall of the mug is basically transparent to the energy and it just passes thru the mug ?

What we do know is that if we place the horn directly on the window..................we shatter it

Hi,

any discontinuity in material will reflect ultrasound.

Think of a material with its E/ρ as similar to an optical material with an index of refraction, this will handle elastic waves: reflect, transmit, absorb, refract and rough (compared to wavelength) will generate stray energy.

E= elastic modulus, ρ = density, refractive index = sqr(E/ρ)

Here only longitudinal waves to be considered, pressure changes are in the direction of wave travel.

So - as in visible optics - you can design the thickness of your "membrane" as an antireflection device: the surface reflects some energy, the backside reflects some energy, these two cancel if they are 180° of phase, this is if the thickness is a quarter wavelength.

Wavelength in steel is near 4.5mm at 1MHz.

You can easily judge if your approach is working by inspecting the bubble density at cleaning. Be sure to use degassed water else the cleaning effect is better done with a liquid jet.

RHABE

"Wavelength in steel is near 4.5mm at 1MHz."

Are you saying that if the material was steel, i could make it 4.5mm/4 thick and it would transmit a 1MHz wave ??

thanks

we have a customer that uses a high velocity liquid jet to clean the window. He erodes the material (Hastelloy) around the window and has to replace our device at fixed intervals (hopefully before the seal breaks )

it might be possible to couple the ultrasound to the window without shattering if you use a viscoelastic coupling media. A typical material might be silicone on the horn, say 1/2"thick, cured flat against a piece of aluminium which you then etch off with caustic. To make this easy use aluminium foil flat on plate glass, then little to etch.

Then place this against the window with a drop of silicon oil to further increase coupling.

Suggest this be tested on a piece of window, or otherwise ex-process, to avoid risks, to see if it will stand up to the U/S.

An elastic solid like steel or glass will transmit U/S, but glass shatters if local stress exceeds a certain level, steel does not. That means you would make a cell window with a horn built into it in such a way that it blasted the US from the side to clear the window. U/S can be fed down a fixture and round a corner. I suggest you ask horn makers about the fabrication limits of horns and US and frequency. Some aspects to horn size will affect the frequency they can deal with.

Antireflection would be λ/4 (quarter wavelength) or 3λ/4,

so 1.1 or 3.3mm thick. (Steel, 1MHz).

Half wavelength or full wavelength will be reflecting!

RHABE

thanks for your replies......

what do you mean by reflecting????? i'm not trying to reflect the energy, i'm trying to get it to pass thru????

is that correct? also, will multiples of that thickness work? or does it really have to be 1/4 or 1/2 wave thick ?

if the energy passed through the deposit with zero loss = no work done cleaning it.

The energy is going to reflect off the window back into the space. Very little will go into the air with a liquid on the sound side and air on the other. A horn can be curved with air on the outside and steel on the inside and the sound will go down the horn by internal reflection.

So the horn send sound into the deposit, which absorbs it and it starts to vibrate with the sound. This chattering back and forthbreaks the forces that stick it to the window and off it comes.

You could make a curved horn that brought the sound onto one side and swpt the surface clean and it might be less intrusive. In fact the horn could be external and feed through a solid steel window to a position where the curve in the horn woulod direct the sound at the back of the glass.

To do it from the front it cannot go thrugh air, so you need the silicone washer to keep the air out with flexibility to prevent the steel horn from shattering the glass by bashing at it at a high frequency.

Hi,

λ/4+nλ/2 will let pass (antireflection),

nλ/2 will reflect (enhanced reflection).

n is any integer 1, 2, 3, ...

Important: your horn shall be submerged into water or any other similar liquid,

as coupling from air on one side to steel and passing to water will be very difficult because the difference in density is so high.

RHABE

Hello Reefdiver,

I have some expertise on Ultrasonic cleaning, let me know if the horn is immersed in the liquid container like an transducer and also what is that you want to clean?

Normally you require 8 Watts/litre of water Ultasonic.

Ultrasonic creates resonance with its high frequency pitch to dislodge hardened or intricately stuck particles, pieces of loose metals etc from various bodies.

If the Ultrasonic device is brought near to the cleaning surface, it may distort or disturb the material characteristics like remove, paint, plating, phosphating etc of even damage the superficial layer of the part to clean.

"I have some expertise on Ultrasonic cleaning, let me know if the horn is immersed in the liquid container like an transducer and also what is that you want to clean?"

As currently used, the ultrasonic horn is immersed in liquid, located approximately 1" away from a diamond window. It is pulsed to clean chemical residue from the the surface of the window. If works fine as is.

What we have been debating here is: Can the ultrasonic horn be located on the opposite side of the window immersed in air, and still be used to clean the surface on the opposirte side that is in the liquid. Please refer to my origianl post for a diagram of existing and proposed.

One thought is that the ultrasonic waves can pass through the diamond (like radio waves pass through a wall) and still clean the surface in the liquid.

The other thought is that the only way the ultrasonic waves can get to the liquid side is by physically vibrating the diamond, which will vibrate the liquid. If this is indeed the way it works, it is of no value to us because we know we will crack the diamond.,

"Normally you require 8 Watts/litre of water Ultasonic."

It appears that you are talking about an u,trasonic bath? We are using a 750w power supply, and aiming the waves directly at the window. We can make wood burn by holding the horn directly on a peice of it.

"If the Ultrasonic device is brought near to the cleaning surface, it may distort or disturb the material characteristics like remove, paint, plating, phosphating etc of even damage the superficial layer of the part to clean. "

We can easily shatter the diamond if we move the horn closer or run the system wide open for a long period of time. That is why clean in short bursts of energy.