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Re: acoustic speed of liquid metal
Posted by: Tom Nelligan , E-mail: nelligant@panametrics.com, on May 13, 1997 at 17:55:55:In Reply to: Re: acoustic speed of liquid metal posted by : Steffen Bonss on May 13, 1997 at 08:45:12:
: The cooled coupling plate is planned to make of an AlMg-alloy.
: The maximum temperature at the point of transducer contact shall
: be about 373 K. At the back site of the titanium plate the
: temperature raises to about 873 K, but very localized beneath
: the melting bath. The liquid titatium is in fact a pool on top
: of the solid titanium, but a pool wandering along the surface.
: While the transducer position is fixed beneath the titanium, the
: liquid pool moves through the sound field. The method suggested
: by Linas for measuring the melting depth should be possible, if the
: echos are measurable. The second way for measuring the melting depth
: is cutting and polishing the specimen after processing. The position of
: transducer and specimen, the track speed and the moment when the
: measuring starts are exactly known. In this way it should be possible
: to determine the melting depth too.: Steffen Bonss
Thanks for the update. My additional thoughts would be as follows:
The surface temperature of 373K/100C is beyond the safe limit for most standard, commercial broadband contact transducers. So the first consideration is that you will need a transducer that is capable of withstanding this temperature without failure. You should discuss this in detail with your vendor, as a special fabrication may be required to prevent thermal damage.
As an aside, I would probably not recommend a high temperature delay line transducer because it would introduce additional delay line echoes into the mix, and I would not use a high temperature dual element transducer because it would probably lack sufficient resolution for the precision echo-to-echo measurement required here.
We haven't discussed the typical depth of the liquid pool. Assuming it is a couple millimeters, I would try a 5 MHz broadband longitudinal wave transducer. Coming from the bottom, if everything is properly coupled and aligned, you would see an echo from the cooling plate/titanium boundary, probably a second multiple of that echo (based on the rough dimensions from the drawing, an echo from the solid titanium/liquid boundary, and then an echo from the top surface of the liquid. You will want to measure the interval between the last two echoes. Depending on the exact material thicknesses and gain levels required, you may also have a third multiple of the cooling plate/titanium boundary echo in here somewhere.
I suspect that experimentation with an actual assembly will be required to optimize both transducer selection and setup parameters. As a start, I would try coupling through the cooling plate/titanium assembly when it is cold to verify that I was getting a strong signal from the top of the titanium. Based on a total thickness of about 20 mm, and assuming good coupling, I think a 5 MHz broadband transducer would be a good place to start.
--Tom Nelligan