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Guru

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very old ultrasonic cleaning bath- current needed!

10/24/2009 4:27 PM

Hi,

recently I got a very old ultrasonic bath that has not the piezo-exciters as I expected but something that looks like a transformer and acts very likely using magnetostriction.

Photo below.

Does anybody know the electronics that was used 50 years ago?

There should be a mechanical resonance (elasticity and velocity acting as energies) and if I add a capacitor also an electro-magnetical resonance.

Questions:

A.: Maximum allowable current? Only heat in the coils critical or something else? Overload in the brazing areas of exciter to bath?

B. Operating inside or outside one of the resonances or tuning both to be the same?

C. Let it oscillate at a frequency between 10 and 50 KHz (estimated range of the fundamental mode of lengthwise oscillation of the "transformer" bars)? Or?

Any information and ideas?

I have seen some more modern ultrasonic baths out of order because the glue between the piezo and the bath was broken by overload caused by empty baths or nonloaded parts.

This old one seems to be immune to these problems.

RHABE

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Guru
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#1

Re: very old ultrasonic cleaning bath- current needed!

10/24/2009 10:37 PM

Might be nickel rods and magnetostriction indeed.

Magnetostriction can peel nickel plate

drill here

http://www.google.ca/#hl=en&source=hp&q=nickel+%2Bmagnetostriction&btnG=Google+Search&meta=&aq=f&oq=nickel+%2Bmagnetostriction&fp=7cb5519368a1228f

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Guru
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#2

Re: very old ultrasonic cleaning bath- current needed!

10/25/2009 8:36 AM

Yes, you do have a magnetostrictive transducer. They are very rugged and reliable. They were replaced by piezoelectrics for cost reasons - not performance. You can likely power it with a good quality audio amplifier and an oscillator. Originally, most units operated with a DC bias through the windings to establish a more efficient operating point. You should operate at the resonant frequency. The height of the stack is 0.5 wavelength. The solder or braze joint to the tank is a stress node, so the stresses at that location are not very high. That is why piezo powered cleaners can get by with an epoxy connection. The highest stress is at the center of the stack. You can either tune to resonance, or use a FM sweep that includes the resonant frequency.

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Guru

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#3

Re: very old ultrasonic cleaning bath- current needed!

10/25/2009 5:58 PM

Dear contributors,

your answers helped very much, but still some questions remaining.

In: Introduction to Magnetic Materials; B. D. Cullity, C. D. Graham, (found in the link) there are two interesting plots:

A.: Magnetostriction in Nickel is parabolic if excited (plotted) by flux-density.

A1.: Symmetric with saturation if excited by field-strength (amperes-turns).

B.: Magnetostriction is enhanced by 50% at tensile stress of 120 MPa and totally suppressed at a compressive stress of -120 MPa.

So if excited with a sinusoidally changing current there will be a changing length of twice the exciting frequency plus higher order (even only) frequency-components.

By the resulting stress level this may be changed to unsymmetric behaviour if the stress is above 10 ? MPa.

This is highly or total nonlinear behaviour so no linear oscillator-circuitry can be used.

Pre-straining in tension or equivalent magnetisation will establish a working point, near this working point a linear oscillator is existing that may be used with feedback to establish a stable oscillation that is self regulating, changing its frequency if coupling or other effects causes the natural frequency to drift.

I assume -but not sure- that the objects to be cleaned in the bath will change the part of the water that is coupled to the oscillations and are thus part of the oscillator and its characteristics.

So one suggestion from you: use an external frequency generator and an audio-amplifier will certainly work. I will try if I can get sufficient excitation.

I would like better a self tuning oscillator, but mechanical prestress is not suitable and if a magnetic prestress can be introduced is not clear as I do not know the direction of the magnetic field lines inside the 4 bars of the "transformer".

If you have additional comments I would be happy.

Thank you, any results will be posted here.

RHABE

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#4
In reply to #3

Re: very old ultrasonic cleaning bath- current needed!

10/25/2009 10:33 PM

Your curves are for FeCo alloy [Permalloy]. Although it is also magnetostrictive, its properties are very different from Nickel. I'm going to have to do some thinking to try to answer the rest of your questions, but suggest you use data for nickel.

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#5
In reply to #3

Re: very old ultrasonic cleaning bath- current needed!

10/25/2009 10:54 PM

If you excite the transducer symmetricaly around a zero magnetic field, you will find many complications. This is the primary reason for the DC bias current. When properly biased, most of the problems you mention, disappear.

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