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Metal hardness and melting point


#1

Hi all…my daughter has her science fair project due and we’re going
to go to my workshop and time metal melting…the only thing is, her
hypothesis she must test is that there is a correlation between
metal/alloy hardness and melting point. Now, the problem is, we can
melt the different metals and time them with a stop watch, and I can
look up Moh’s hardness for pure gold, silver, copper etc…but where
can I find a chart covering the relative hardness of different alloys
like sterling vs 14 kt gold vs brass?? Kind of hard to correlate the
results if half my info is missing. Does anyone have an overveiw of
that or know where I could find one FAST?

thanks,
Jeanne
Jeannius Designs


#2

Jeanne, I think you can find what you need at
muggyweld.com/melting.html

Hope this helps,
Harold


#3

My knowledge, which might be patchy, tells me there’s too many
confounding variables here. What’s considered the metal’s “natural
hardness”? Cooling by oil/water quenching versus cooling with
ambient/flowing air of various temps and wind speeds from liquidus to
solidus affects hardness. Give us torches and kilns and we can modify
hardnesses all day long. Aren’t metal hardnesses measured in Rockwell
and/or other units? Brasses/bronzes vary by hundreds of degrees in
melt point, depending on alloy mix.

Maybe concentrating on fine versus sterling silver and the effect of
alloying on melt point would be a more manageable hypothetical.

With metals prices rallying, a piece on acid testing would be fun.
That was my sci-fair project that never was.

Maybe just giving different brasses the comparison?

Dan


#4

Hi Jeanne

You might contact some gold/silver producer/refiner and ask. I have
some values, mainly gold and platinum alloys and some silver. The
hardness is measured in Brinell or Vickers, common units with most
materials apart from rock and Moh’s grading which is very relative,
the step from 9 to 10 being greater than 1 to 9 on an absolute scale.
Brinell system being a steel ball around 1/4 inch pressed into the
object measured and the force to do this and the resultant
depression, all calculated according to a formula I can’t remember.
Unfortunately all my tables are in german but if your’re not put off
I can scan and email them. Just send me an email.

michaela


#5
I think you can find what you need at muggyweld.com/melting.html 

thanks, but the melting points I have, it’s the relative 'hardness’
to each other we don’t have…like is copper softer or harder than
sterling, is brass harder or softer than copper and sterling…She
needs to be able to put it on a continuum of sorts.

Jeanne
www.jeannius.com
www.rhodes-moen.com


#6

I just skimmed but there might be some info for you here
http://www.zianet.com/ebear/metal/hardness.html Or maybe go to the
atomic table and compare the metals via their density?

Dorothy


#7

Hi,

thanks, but the melting points I have, it's the relative 'hardness'
to each other we don't have....like is copper softer or harder than
sterling, is brass harder or softer than copper and sterling...She
needs to be able to put it on a continuum of sorts. 

As I think someone else has probably already said - it all depends.
If you are comparing the hardness of different metals and only
considering fully annealed metal, you could say that a series would
be 'fine silver - copper - sterling silver - brass - bronze - steel’
but, hammer hardened copper is harder than sterling silver and some
alloys of brass are harder than alloys of bronze. The only real way
to make sense of this would be to consider just two or three metals
and compare the melting points in a fully annealed condition and
then after a standardised amount of work hardening. (I suspect that
the melting point will not change to a noticeable degree).
Alternatively, you could look at the effect on melting point of
changing the amount of one constituent of an alloy - higher
proportions of copper in a silver alloy will raise its melting point
but probably not in a linear fashion and so you could make a graph to
show the effect. Why is it that these school projects always exercise
the minds of parents more than those of the children???

Best Wishes
Ian

Ian W. Wright
Sheffield UK