Author Topic: Telling metals apart for casting.  (Read 6493 times)

Offline S. Heslop

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Telling metals apart for casting.
« on: November 08, 2013, 08:23:38 PM »
I've been searching around for a while on this topic and haven't found anything satisfactory.

I've got several aluminium castings i've been saving to melt at some point, but now i'm unsure if it really is all aluminium or not since one piece (from a washing machine drum) feels a bit heavy.

I feel a bit dopey asking this question but is there an easy way to check? I could probably do it by density but I want to avoid getting the metal wet if i'm going to be melting it.

Offline mattinker

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Re: Telling metals apart for casting.
« Reply #1 on: November 09, 2013, 01:20:19 AM »
Hi,

if a greyish metal feels "a bit heavy" it's probably of the ZA family of Zinc alloys. Pure Al has a density of 2.7, for every litre of metal, it weighs 2.7Kgs. If you measure the volume of water displaced by the metal when it is submerged, and weigh the metal, if it is a Zinc based alloy it will weigh more than 2.7Kgs per litre. I do this if I'm not sure, A bowl of water, full to the brim in another bowl, emerge the metal in the water, the water that spills into the second bowl is the same volume as the metal. Measure the volume of the water either with a measuring jug or by weighing the water. Water has a density of 1,0 so 1 Kg of water equals 1litre. Weigh the metal, if the weight of the metal is 2.7 times the weight of water, it's Al! Zinc has a density of  7.134, so it's nearly three times heavier per litre than Al. The Zinc alloys aren't very popular as they are often badly used they are difficult to weld and are brittle. The good side, they have good vibration damping characteristics (close to cast iron), Cast very well, machine beautifully and make very good bearing material for steel shafts. The ZA Zinc alloys can be cast at much lower temperatures than Al, with a melting point of around 450C. The thing to avoid with Zinc is overheating it. Over 700C, it boils and gives of white smoke (Zinc vapour) that can give you (fume fever) flu like symptoms! Don't breath it!

I hope that helps! Regards, Matthew

Offline tom osselton

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Re: Telling metals apart for casting.
« Reply #2 on: November 09, 2013, 01:59:45 AM »
I read on one site to use vineger  as it will bubble on the magnisium but not on aluminum although I haven't tested it out to make sure.

Offline RussellT

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Re: Telling metals apart for casting.
« Reply #3 on: November 09, 2013, 06:00:44 AM »
I saw this

http://forum.caswellplating.com/plating-pot-metal/9034-how-can-you-tell-pot-pot-metal.html

I've got as far as buying some hydrochloric acid - freely available in French supermarkets - but I haven't tested it - or considered the chemeistry.

Russell

Offline S. Heslop

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Re: Telling metals apart for casting.
« Reply #4 on: November 10, 2013, 11:18:50 AM »
I saw this

http://forum.caswellplating.com/plating-pot-metal/9034-how-can-you-tell-pot-pot-metal.html

I've got as far as buying some hydrochloric acid - freely available in French supermarkets - but I haven't tested it - or considered the chemeistry.

Russell

I did see that and wasn't too convinced, but i've been planning to try it out anyways next time i'm in the lab.

I might try the density thing too at some point, I figured it'd be a good way to do it but I was hoping there was a less laborous solution.

Thanks for the replies though.

Offline mattinker

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Re: Telling metals apart for casting.
« Reply #5 on: November 10, 2013, 11:30:33 AM »
The Hydrochloric acid method definitely works. I use Hydrochloric acid to make flux for soft soldering Zinc flashing gutters and down pipes it definitely turns Zinc black. I don't use it as a test, as I avoid opening the bottle of acid and I can see the difference between Al and the ZA alloys by their weight colour and texture.  The density method isn't that complicated if you have a good set of scales.

Regards, Matthew

Offline oldgoaly

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Re: Telling metals apart for casting.
« Reply #6 on: November 10, 2013, 12:22:43 PM »
if you break it with a hammer the zinc alloys looks different, magnesium is hard to break, takes a little practice to get the look and feel. But who :bugeye: doesn't like a little fireworks while melting a pot of aluminum!  How many of you have started a small piece of mag and carried it outside and had a less experienced helper throw water on it????  just like to have a little fun!

Offline mattinker

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Re: Telling metals apart for casting.
« Reply #7 on: November 10, 2013, 03:44:21 PM »
if you break it with a hammer the zinc alloys looks different, magnesium is hard to break, takes a little practice to get the look and feel. But who :bugeye: doesn't like a little fireworks while melting a pot of aluminum!  How many of you have started a small piece of mag and carried it outside and had a less experienced helper throw water on it????  just like to have a little fun!

I haven't come across any magnesium yet in my foundry scrounging, but if you don't want to try burning a tiny scrap, the density method works, Mg density 1.74, lighter again than Al. the last time I saw magnesium burn was a Porche engine block on a rally in Wales some forty years ago

Regards, Matthew

Offline vtsteam

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Re: Telling metals apart for casting.
« Reply #8 on: November 10, 2013, 09:47:15 PM »
Looks like there's the possibility above few posts of confusing zinc and magnesium (not yours Mat).

In general:

Aluminum and magnesium are light weight

Zinc alloys are heavier enough to be apparent even when holding them

Zinc produces white fumes if overheated.

Zinc is harder than aluminum, and MUCH slower to file. It usually looks dull, until filed, but takes a good shine as soon as it is.

Magnesium burns intensly and dangerously, and cannot be put out with water. To test for it, take a small sliver with a knife and try to burn it. If it burns with an intense white light, it's magnesium. Don't try to cast with it in a backyard furnace.

Example of magnesium casting:

Volkswagen engine block.
I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: Telling metals apart for casting.
« Reply #9 on: November 11, 2013, 03:54:11 AM »
Tucked away in my 'Round Tuit' area I have not one but TWO alloy analysers. They strike an arc between a carbon point and the sample, and the beastie performs a spectral analysis and works out the percentage of the metals and then prints out a ticket with the results.

One was working fine when I put it in storage, and the other was rather temperamental - just another thing I need to pull out and have a play with. They are very handy as they are 'luggable' ie briefcase sized.

Andrew
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Offline vtsteam

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Re: Telling metals apart for casting.
« Reply #10 on: November 11, 2013, 11:01:18 AM »
What a cool thing to have!
I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: Telling metals apart for casting.
« Reply #11 on: November 11, 2013, 11:51:23 AM »
They are nice boxes of tricks when working. I seem to remember that the firmware was different between them. They both print out % of metals but one of them had a look up table and translated it into the most likely commercial alloy such as LM5 or LM25 or whatever. Too old for your number series alloys !

Modern one are much more compact and fire an X-ray into the sample and do a similar spectral analysis

I also have (again two !!!) more manual ones - again a spark between the sample and a pointed carbon, but this time you look at the spectrum produced yourself and look for the characteristic lines for the metals that you are interested in. I got quite technical when I had my foundry set up  :lol:

If I get time I'll dig them out and start a thread on them.
Andrew Mawson
East Sussex

Offline S. Heslop

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Re: Telling metals apart for casting.
« Reply #12 on: November 11, 2013, 12:31:35 PM »
They are nice boxes of tricks when working. I seem to remember that the firmware was different between them. They both print out % of metals but one of them had a look up table and translated it into the most likely commercial alloy such as LM5 or LM25 or whatever. Too old for your number series alloys !

Modern one are much more compact and fire an X-ray into the sample and do a similar spectral analysis

I also have (again two !!!) more manual ones - again a spark between the sample and a pointed carbon, but this time you look at the spectrum produced yourself and look for the characteristic lines for the metals that you are interested in. I got quite technical when I had my foundry set up  :lol:

If I get time I'll dig them out and start a thread on them.

I'd love to see a thread on them. They sound pretty interesting.

Thanks vsteam and oldgoaly. It does seem like the answer is just more experience. My first casting attempt was a disaster though so I probably won't be trying again for a while. Not until I get at least a moulding bench.

Offline vtsteam

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Re: Telling metals apart for casting.
« Reply #13 on: November 11, 2013, 12:45:52 PM »
Andrew, I once made a spectrometer with a couple razor blades a length of 2" plastic pipe and a piece of DVD.

I've also salvaged carbon rods from dry cell batteries.

you don't suppose..........?


 :zap:
I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: Telling metals apart for casting.
« Reply #14 on: November 11, 2013, 12:53:03 PM »
Ok Ok I give in  :bang:

I'll dig them out and take some photos and start a new thread -  :hammer:
Andrew Mawson
East Sussex

Offline awemawson

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Re: Telling metals apart for casting.
« Reply #15 on: November 11, 2013, 03:20:50 PM »
Andrew Mawson
East Sussex

Offline oldgoaly

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Re: Telling metals apart for casting.
« Reply #16 on: November 11, 2013, 05:08:22 PM »
Cool stuff Andrew!
Seeing magnesium burn in small quantity isn't a big thing,like a medium sized sparklers, I do it to watch the newbies expressions. Now the St. Louis fire department went to a scrap yard fire, a very small fire under a few trailers of mag they had one hell of a fire. trailers were clearly marked magnesium the TV news coverage was right there to show it all. Being mark magnesium didn't stop them from spraying all kinds of water on it. not much left after they got done. Having a crushed limestone floor makes on easy to put out a fire, it keeps molten metal in it place, so much easier on my knees than concrete! Wish a few of you guys were close we could do some serious sand casting!