Alloying Bell Bronze

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FLtenwheeler
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Alloying Bell Bronze

Post by FLtenwheeler » Wed May 18, 2016 7:21 pm

Hi

I would like to cast a small bell using bell bronze. 78% Copper and 22% Tin. Do I melt the Copper and add the Tin?

Thanks

Tim
He who dies with the most unfinished projects: Should of put more time into their hobby.

jkimberln
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Re: Alloying Bell Bronze

Post by jkimberln » Wed May 18, 2016 7:30 pm

FLtenwheeler wrote:Hi

I would like to cast a small bell using bell bronze. 78% Copper and 22% Tin. Do I melt the Copper and add the Tin?

Tin boils at a much higher temperature than copper, so you could melt the tin first then add copper. It might not make much difference, however. Normally one would melt the lowest melting component first then the next lowest, and etc.

JerryK

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NP317
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Re: Alloying Bell Bronze

Post by NP317 » Wed May 18, 2016 7:45 pm

The best sounding steam locomotive bells contained some percentage of silver, to harden them and allow better ringing sound.
The logging locomotives I restored varied significantly in the sound quality of their bells. The Climax steam locomotives had the dullest, poorest sounding bells. Understandable, considering they were known as the "Poor-Mans" logging locomotives. Undoubtedly no silver...
~RN

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Re: Alloying Bell Bronze

Post by Harold_V » Thu May 19, 2016 3:29 am

jkimberln wrote: Tin boils at a much higher temperature than copper, so you could melt the tin first then add copper. It might not make much difference, however. Normally one would melt the lowest melting component first then the next lowest, and etc.
Interesting comment.
If one was working with pure gold, it would be the gold that would be melted first, even if the target alloy was white gold, where nickel is often the alloying component. It is best melted in that sequence because gold does not oxidize. That limits the time that metals that oxidize are exposed to higher temperatures, and has the added benefit of an overall lower melting temperature. Remember, molten metals are also solvents, so they are capable of putting in to solution a metal that is not at its melting point. In a controlled atmosphere it may not make much difference, but in an oxygen rich atmosphere, it is certainly something to consider.

Personally, I'd be inclined to melt the copper first, as it melts at the highest temperature of the elements in question (including silver, assuming it was to be added). Once the copper was molten, I'd then introduce the other elements, in reverse order from their melting temperatures, highest one first. That way, as the alloy that's created was cooled somewhat, the lower melting temperature elements would still be melted, and if not, at least dissolved.

I an not familiar with proper foundry practice. My comments are flavored by my years of refining and alloying precious metals. I welcome correction if I have backward thinking.

Harold
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jkimberln
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Re: Alloying Bell Bronze

Post by jkimberln » Thu May 19, 2016 6:09 pm

I don't really know either Harold. Even though I worked in a foundry, I was not a melter. I do know that if you melt copper first, then add zinc, you will get a volcano. This is because the boiling point of zinc is lower than the melting point of copper (I think). But tin has a very high boiling point that is much higher than the melting point of copper, but a melting point that is lower than copper, so one could do the melting either way without any superheating problems. I think one way to tell would be to look up the melting points and boiling points of all the metals (see Engineer's Edge, for instance). and make sure the lower boiling point metal is started first. Otherwise, you are liable to get a face full of hot metal.

JerryK

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Re: Alloying Bell Bronze

Post by Harold_V » Thu May 19, 2016 8:00 pm

Thanks, Jerry. I now better understand your thinking, and certainly have to agree, at least in part. Zinc, I know, is troublesome, so dealing with it is always a challenge. Luckily, in refining, it wasn't an issue, and was used only for the recovery of values when in solution, if even then. There were other options in many cases.

I appreciate you sharing your knowledge.

Harold
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Re: Alloying Bell Bronze

Post by steamin10 » Fri May 20, 2016 2:16 pm

Although I have never done component alloying, just adjusting scrap, I think it was in Ammans book that copper is melted first, and such additions are made to lowering temps on the melt. I made my additions by weight without the benefit of true analysis, so it was best guess.

Brass is usually covered to avoid the burning at the surface, usually crushed white bottle glass. The mass is then hooked off just before pouring. It limits the exposure to the caster, who sometimes came down with 'founder's augh' from the heavy metal absorption.

If you want a dull bell, use common brass bearing material. Not only will it not hold a polish, but the lead content will kill the tone. Bell materials must be hard to achieve a good tone. Lead content must be very low. While desirable for machining parts, as lead will allow brass to cut like butter, it is least desirable for bells, and that includes the copper-tin bell bronze, that will have a deeper tone than brass in the same shape. Brass dings, while bronze dongs.

Gassing and porosity is always a problem, and holding a heat is asking for problems. Melt quick, and pour quick with as quiet a stream as possible. So making additions on rising temperatures is asking for trouble.
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