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How to tell what specification of Bronze and Brass you have

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Adam Harris02/07/2014 17:11:05
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I have inherited (from a hobby lathe user) some large diameter (1"-2" diameter) rods of Brass and Bronze that I thought should be valuable and want to sell but on further investigation I realise that the desirability is based probably on specification for machinability and I have no idea what the specifications are or really what it is that I have got. I also have some reasonable sized blocks of aluminium and the same goes for these. There seem to be so many different grades offered by stockholders. Is there any way to tell what I have got just by looking at it or showing it to a stockholder, or is there some more scientific way of telling? I mainly work on steel.

JohnF02/07/2014 18:40:23
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Adam, short answer is not really, it may be possible to make an educated guess from colour whether it's brass or bronze and maybe by machining a piece might give a bit more guess info. Same goes for the alloy, much the same for steel although you can do a few tests on steels such as a.spark test and a little heat treatment of a sample piece which would give you basic info but as you will be aware this is all you can get without exhaustive scientific tests.

There is of course the "smell test" often enacted on an apprentice ! ! !

Cheers John

Oompa Lumpa02/07/2014 20:03:23
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Spectrometer is the real answer. But I would guess you would be out of pocket by a considerable margin. One of my colleagues bought one recently for his business. £15.000 it was.

graham.

Bazyle02/07/2014 22:54:42
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If you live in a university town you might be able to find a metallurgy student who for a couple of pints can polish up a sample and give you some idea. Or even better put a tiny bit in an electron microscope and have edaxs (Electron diffraction x-ray spectography or whatever the modern equvalent is) analyse it precisely.

fizzy03/07/2014 00:03:12
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err....it looks different! It does, really it does. Brass, shiny like gold, bronze, duller. simples!

Nigel McBurney 103/07/2014 09:31:59
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965 forum posts
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Sell it as mixed selection of brass /bronze on e bay,boot sale or ad in local newspaper etc or take it to the scrapyard,let the buyer take the risk. I was once told that brass and bronze can be identified as brass can be annealed and bronze cannot be annealed,though I have never seen it mentioned in any textbook.

Adam Harris03/07/2014 09:55:08
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Of course it is easy to tell the difference between brass and bronze because bronze is significantly more coppery in colour, but when merchants offer the material on the internet they quote a variety of differing specs of each at different prices presumably because the specs affect machinability and function, just as with different specs of steel. Anyway, maybe model engineers do not fuss about the spec of particular bronze or brass rods they are turning because being soft they all turn easily, and so this is all a bit of a red herring.

Neil Wyatt03/07/2014 10:22:58
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Hi Adam,

Brass machines nicely is great for anything decorative and it has good corrosion resistance, but it shouldn't be used for boiler work (because of de-zincification) and it's no good for bearings taking a real load.

I'll happily analyse the bar for you, but it will be a destructive test and I'm afraid you won't get any back

Neil

Adam Harris03/07/2014 10:38:05
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John, thanks very much for that - very helpful . Adam

Bazyle03/07/2014 18:17:00
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With bronze for machinability you preferably want a leaded bronze to a LB spec like LB2 as it contains up to 10% lead and no phosporus. Hopefully won't work harden and break your drill.

For strength you want a phosphor bronze to a PB spec like PB2 containing no lead and seemingly very little phosphorus but it only takes a pinch. Used for springs and can be deliberately work hardened for a stronger spring. Pray before drilling.

For casting you want a gunmetal bronze to a LG spec like LG2 containing both lead and zinc 5-10% each and less tin that the previous two (and a hint of phosporus).

But they all look pretty much the same (though different from brass.with it's high zinc content).

So you can't honestly sell it as anything specific.

If buying quiz your vendor to see if they understand the difference between the types is not the last digit. I have been offered PB4 as a "nice machineable bronze not like the PB1 that other stand is selling".

Adam Harris03/07/2014 19:07:57
509 forum posts
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Hi Bazyle, nice to hear from you. Very interesting info. The problem is I am the vendor but I do not know what I am trying to sell!! As someone has said, a model engineer having spent many many hours creating a beautiful engine is not going to risk seized bearings because the bronze was not proper PB. It is interesting though that if it is not possible to self-certify a rod then how far can/should one trust any vendor? Adam

andrew winks31/08/2014 00:54:49
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Hi Gents, I too have been looking for answers as I have a huge collection of various sections of brass and bronze and all alloys thereof. When friends and relations know you engineer, you get all sorts of great donations. Short of destructive testing in a lab, you need to rely on colour and how it machines. When it comes to machining boiler bushes, that's where I need to be sure so I've usually stuck with phosphor bronze which does not chip but peels off strings of swarf. It's not as easy as brass to tap but CRC as a cutting fluid, also used for copper, works great. What does throw a spanner in the works are rough castings produced in home foundries which could contain a mix of many alloys so these are used for non critical applications. Adam, does raise an interesting question, how can you trust a commercial vendor who may knowingly or not sell you something that's not as stated. Cheers, Andrew

Michael Gilligan31/08/2014 08:11:28
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Posted by andrew winks on 31/08/2014 00:54:49:

... does raise an interesting question, how can you trust a commercial vendor who may knowingly or not sell you something that's not as stated.

.

Andrew: You have there hit upon one of the reasons why aircraft and aerospace components are so high-priced ... The materials that they are made from are fully traceable; and the 'added value' is the confidence which that brings.

MichaelG.

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