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Technical Discussions
Ramazan Kayikci
Ramazan Kayikci
01:09 Jul-03-1998
contact test

Note:
Email reader need to access to the forum
topic 'contact test' to view the graphic.

I am Ph.D student at Manchester Materials Science Centre. I am
investigating the metal-mould contact area during casting solidification
for heat transfer modelling.

My experimental set-up is schematically shown above. Al-4.5wt % Cu liquid alloy is poured onto a water-cooled copper chill. The solidification is initiated at the metal -chill interface by the asperity contact between the liquid metal and the Cu block (chill). Then, the solidification proceeds upwardsly against the heat flux one diametionally. As my project involves modelling of heat transfer during the casting solidification with various mould surface roughness, I am trying to obtain a quantitative knowledge about the actual liquid-asperity contact occurring at the interface. (immediately after the liquid metal strikes onto cold Cu chill a surface skin solidifies and it obtains its own surface roughness as shown enlarged section and it turns out to be solid-solid contact).

I thought that I can trace the contact area with an ultrasonic pulse-echo flaw dedector as shown above despite I found no example of similar measurements in the literature so far.
First, a backwall echo, from the far end of the Cu block, is seen on the CRT. I usually adjust it to 80-90% of total screen height with the gain adjustment. Then, I pour the liquid metal into the insulating tube (onto the Cu block). With the pouring of the metal the original backwall echo diminishes 10-15% of its height followed by a slight increase within a few sec.

Although, I am using various roughness of the chill surface (preparing with different grade of emery papers) there are little changes in the decrease of original backwall echo.

Now it difficult for me to interpret the results for a quantitative conclusions. Could you help me commenting on the following questions.

1. whether the decrease in the original backwall echo with the pouring is because of the temperature induced attenuation in the Cu block or is it because some of the sound waves are being transmitted across the interface through the casting.

2. I have data from the gain adjustment (gain to compensate the reductions in the BWE to its original position) (dB) . Using this data can I calculate the actual area of contact. How can I take into account the difference in the acoustic properties of two different metals, namely Cu and Al-4.5% Cu.

3. What else I should also consider before going calculation.

I would be grateful if you have a chance to look at these and let me know what you think.

With regards,

R.Kayikci.



    
 
 Reply 
 
Wieslaw Bicz
Wieslaw Bicz
05:10 Jul-08-1998
Re: contact test
: Note:
: Email reader need to access to the forum
: topic 'contact test' to view the graphic.

: I am Ph.D student at Manchester Materials Science Centre. I am
: investigating the metal-mould contact area during casting solidification
: for heat transfer modelling.

: My experimental set-up is schematically shown above. Al-4.5wt % Cu liquid alloy is poured onto a water-cooled copper chill. The solidification is initiated at the metal -chill interface by the asperity contact between the liquid metal and the Cu block (chill). Then, the solidification proceeds upwardsly against the heat flux one diametionally. As my project involves modelling of heat transfer during the casting solidification with various mould surface roughness, I am trying to obtain a quantitative knowledge about the actual liquid-asperity contact occurring at the interface. (immediately after the liquid metal strikes onto cold Cu chill a surface skin solidifies and it obtains its own surface roughness as shown enlarged section and it turns out to be solid-solid contact).

: I thought that I can trace the contact area with an ultrasonic pulse-echo flaw dedector as shown above despite I found no example of similar measurements in the literature so far.
: First, a backwall echo, from the far end of the Cu block, is seen on the CRT. I usually adjust it to 80-90% of total screen height with the gain adjustment. Then, I pour the liquid metal into the insulating tube (onto the Cu block). With the pouring of the metal the original backwall echo diminishes 10-15% of its height followed by a slight increase within a few sec.

: Although, I am using various roughness of the chill surface (preparing with different grade of emery papers) there are little changes in the decrease of original backwall echo.

: Now it difficult for me to interpret the results for a quantitative conclusions. Could you help me commenting on the following questions.

: 1. whether the decrease in the original backwall echo with the pouring is because of the temperature induced attenuation in the Cu block or is it because some of the sound waves are being transmitted across the interface through the casting.

: 2. I have data from the gain adjustment (gain to compensate the reductions in the BWE to its original position) (dB) . Using this data can I calculate the actual area of contact. How can I take into account the difference in the acoustic properties of two different metals, namely Cu and Al-4.5% Cu.

: 3. What else I should also consider before going calculation.

: I would be grateful if you have a chance to look at these and let me know what you think.

: With regards,

: R.Kayikci.

Your contact surface is rough. The soundwave will be scattered at the roughness of this surface.
I think, you should try to measure not the reflected, but the scaterred wave. It could be made very simple if you use the transducer that has a different inclination to the liquid metal - Cu chill interface.
This angle depends on the roughness of this surface. The signal amplitude may be smaller, but it could be possible, that you can find a strong changes, depending on the roughness, temperature and so on.

I think, i could help you in your work, it could be interesting for me. If it is intersting for you, please contact us.

Wieslaw Bicz

Optel sp. z o.o.
Ultrasonic Technology/ Fingerprint Recognition



    
 
 Reply 
 
Massimiliano Pau
Teacher, -
Univ. of Cagliari, Dept. of Mechanical Engineering, Italy, Joined Sep 2002, 25

Massimiliano Pau

Teacher, -
Univ. of Cagliari, Dept. of Mechanical Engineering,
Italy,
Joined Sep 2002
25
05:25 Jul-25-1998
Re: contact test
There are few papers on measurements
of real contact area between rough surfaces in contact
under varying load ( I collected about 40 papers starting
from 1969 to 1997)

During my PhD (that I just finished)
I worked hard on this topic.
Although is not so easy to assess amount of real
contact area, you should use your experimental data
together with some theoretical model of
propagation of ultrasonic waves in contact
interfaces(so called "spring model" or similar)

I studied simple homogeneus interfaces (steel-steel)with different
superficial roughness levels in which is quite simple
to relate amount of reflected (and transmitted of
course) ultrasonic wave and degree
of contact, because you can use some particularizations
of Tattersall equations,obtaining interesting results

I compared also my results with some theoretical
or numerical model (like Greenwood Williamson, Bush Gibson
Thomas etc) with better agreement for lapped surfaces

Unfortunately my PhD thesis is in italian
but I suggest you to take a look at Krolikowski et al.
papers (mid '80-90)and especially at Bruce Drinkwater
and Paul Cawley papers (you can reach the first at
Sheffield Univ and the second at Imperial College)

Massimiliano

P.S. Let's keep in contact....only two or three
researchers in Europe are working on this problem in this way



    
 
 Reply 
 
Massimiliano Pau
Teacher, -
Univ. of Cagliari, Dept. of Mechanical Engineering, Italy, Joined Sep 2002, 25

Massimiliano Pau

Teacher, -
Univ. of Cagliari, Dept. of Mechanical Engineering,
Italy,
Joined Sep 2002
25
05:25 Jul-25-1998
Re: contact test
There are few papers on measurements
of real contact area between rough surfaces in contact
under varying load ( I collected about 40 papers starting
from 1969 to 1997)

During my PhD (that I just finished)
I worked hard on this topic.
Although is not so easy to assess amount of real
contact area, you should use your experimental data
together with some theoretical model of
propagation of ultrasonic waves in contact
interfaces(so called "spring model" or similar)

I studied simple homogeneus interfaces (steel-steel)with different
superficial roughness levels in which is quite simple
to relate amount of reflected (and transmitted of
course) ultrasonic wave and degree
of contact, because you can use some particularizations
of Tattersall equations,obtaining interesting results

I compared also my results with some theoretical
or numerical model (like Greenwood Williamson, Bush Gibson
Thomas etc) with better agreement for lapped surfaces

Unfortunately my PhD thesis is in italian
but I suggest you to take a look at Krolikowski et al.
papers (mid '80-90)and especially at Bruce Drinkwater
and Paul Cawley papers (you can reach the first at
Sheffield Univ and the second at Imperial College)

Massimiliano

P.S. Let's keep in contact....only two or three
researchers in Europe are working on this problem in this way



    
 
 Reply 
 
mehmet kosedag
mehmet kosedag
02:21 Jan-07-1999
Re: contact test
: Note:
: Email reader need to access to the forum
: topic 'contact test' to view the graphic.

: I am Ph.D student at Manchester Materials Science Centre. I am
: investigating the metal-mould contact area during casting solidification
: for heat transfer modelling.

: My experimental set-up is schematically shown above. Al-4.5wt % Cu liquid alloy is poured onto a water-cooled copper chill. The solidification is initiated at the metal -chill interface by the asperity contact between the liquid metal and the Cu block (chill). Then, the solidification proceeds upwardsly against the heat flux one diametionally. As my project involves modelling of heat transfer during the casting solidification with various mould surface roughness, I am trying to obtain a quantitative knowledge about the actual liquid-asperity contact occurring at the interface. (immediately after the liquid metal strikes onto cold Cu chill a surface skin solidifies and it obtains its own surface roughness as shown enlarged section and it turns out to be solid-solid contact).

: I thought that I can trace the contact area with an ultrasonic pulse-echo flaw dedector as shown above despite I found no example of similar measurements in the literature so far.
: First, a backwall echo, from the far end of the Cu block, is seen on the CRT. I usually adjust it to 80-90% of total screen height with the gain adjustment. Then, I pour the liquid metal into the insulating tube (onto the Cu block). With the pouring of the metal the original backwall echo diminishes 10-15% of its height followed by a slight increase within a few sec.

: Although, I am using various roughness of the chill surface (preparing with different grade of emery papers) there are little changes in the decrease of original backwall echo.

: Now it difficult for me to interpret the results for a quantitative conclusions. Could you help me commenting on the following questions.

: 1. whether the decrease in the original backwall echo with the pouring is because of the temperature induced attenuation in the Cu block or is it because some of the sound waves are being transmitted across the interface through the casting.

: 2. I have data from the gain adjustment (gain to compensate the reductions in the BWE to its original position) (dB) . Using this data can I calculate the actual area of contact. How can I take into account the difference in the acoustic properties of two different metals, namely Cu and Al-4.5% Cu.

: 3. What else I should also consider before going calculation.

: I would be grateful if you have a chance to look at these and let me know what you think.

: With regards,

: R.Kayikci.




    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1261

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1261
00:15 Jan-10-1999
Re: contact test
Sorry that my reply comes so late, I could not find Mehmet's
reply so I decided to make a separate repy to Ramazan.

I have reviewed your experimental setup for the heat transfer problem.

It seems to me you are basing your analysis solely on amplitude response. I think this can provide very little quantitative information. As the surface of the contact point is wetted by the molten metal you will of course increase acoustic wave transfer relative to a metal/air interface.
Since heat transfer also includes a velocity change why do you not do a dV/dT study?
A series of rapid fft analyses might also provide an indication of freqency absorption changes with crystal structure changes.
I understand from the description that it is the effects on the copper chill that you want to monitor.
What about a series of through transmission probes arranged along the vertical portion of the chill. Your soundpath from bottom to top can only provide an average effect over the total length of the chill.
A series of probes starting at the contact point and moving down the chill could indicate a dV/dT with respect to distance from the contact point. This could give you a rate of heat transfer based on the various velocity changes.
(You must be careful to correct for any heat sink effect the probes would produce).

Ed




    
 
 Reply 
 

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