# Why bronze for steam?



## Cap'nBill (Dec 27, 2008)

I notice most of the sets of 'castings' offered are of bronze. I also see some kits have aluminum parts. Why bronze as opposed to brass? Bill


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## tacfoley (Jan 3, 2008)

Posted By Cap'nBill on 14 Dec 2009 11:37 AM 
I notice most of the sets of 'castings' offered are of bronze. I also see some kits have aluminum parts. Why bronze as opposed to brass? Bill

Not just bronze, but phosphor-bronze. Easily machined to a very fine finish after casting, if necessary, and does not deteriorate as a result of immersion. It is also capable of retaining oil within its granular structure, and therefore makes good valves of any kind - D or piston - whilst retaining steam-tight tolerances. The same goes for water valves and fittings in the larger scales, right up to full-size.

Aluminium/aluminum has similar properties and is far cheaper to produce, in spite of its rather exotic beginnings. It is, however, hardly a traditional material used in the construction of steam engines, and can lead to problems in designing components using it, as it has a far higher coefficient of expansion - and steam engines get hot. 

Brass is much-favoured by Regner, and with great success, too. It, too, is far cheaper to make components from than bronze of the correct alloying, but has similarly fine machining qualities. 

I'm certain that the experts will come in with more reasons, but that will do for a start.

tac
www.ovgrs.ors


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## xo18thfa (Jan 2, 2008)

Posted By Cap'nBill on 14 Dec 2009 11:37 AM 
I notice most of the sets of 'castings' offered are of bronze. I also see some kits have aluminum parts. Why bronze as opposed to brass? Bill

"Brass" is usually bar stock, round, hex, rectangular etc. for machining purposes. You can fabricate "brass" assemblies with silver solder and finish them by machining. "Bronze", some alloys of it, are better suited for casting purposes. The cast part get finished by machining. The reason "brass" and "bronze" are in parenthesis is because the purist will argue that they are all alloys of copper.

Aluminum is a less expensive material to start with. Plus it has a lower melting temp so other casting methods, help reduce costs even more.


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## coyote97 (Apr 5, 2009)

Good points, Tac!
You can make MANY parts of different materials and find out that most of them DO really work:
-more or less successful
-more or less longlasting.

The most important matter to use bronze may be the two quality-facts of that material: it resist very well all circumstances of steam (water, temperature, aggressive chemical issues with hot water and so on)
second is the good mechanical performance in gliding bearings. 
Tin is therefore the better alloy-component than zinc.
So, brass will work with a life-steamer, but looking ahead MANY years, bronze will be the better material. Especially in fast going bearings bronze stands much longer (not only due to hardness. Bronze has a better gliding performance and stands longer even with missing lubrication).

cutting in any form bronze and brass are very very well to work with. 

nowadays it is no question for the professional engineer:
all thats in contact with hot water is made of stainless steel, barings are balled and gaskets of rubber.
Therefore you have to know about some "steel-mystics" or your project will go down. 
Our grandfathers didnt have that technology, so many parts of a "real" steam engine are made of brass or bronze. (bearings, fittings, tubes, cocks, gliding plates)

Most hobbyists cant work fine on stainless steel, so brass or bronze is the better way. Even though because of the rew-material prices that thing is much more expensive than stainless steel.
But the stability of brass or bronze is really enough for modelling. Therefore is no need or use to use stainless steel.

But in 1:1 scale german steam-engine-supervisors have a new hobby: questioning the stability of all bronze parts on a boiler. They worked on that boiler for over 80 Years now and those parts generally work in the history of railroading for over 170 years...it seems to be high time to find out that they dont work now in 2009!!!! Germans!

Greetings

Frank


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## Steve S. (Jan 2, 2008)

But wait.............................. Wont bronze cause the water in the boiler to deionize it and cause catastrophic failure







Should we store water in the bronze boiler after a run or do we have to drain it completely dry







Just kidding folks.................lets not go there.


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## Cap'nBill (Dec 27, 2008)

Interesting discussion! The reason for the question: I recently got some plans to build a feed water pump. Having limited machinery, I decided to build up various layers in brass, silver soldering. The shape of the steam cylinder, valve chest, and steam chest are rather odd shaped and would require a pretty elaborate casting...as well as the machining. I had noticed some of the pump pics I'd been referred to earlier used the soldered method. Thought I'd ask before I got too far along! Actually, I'm not to concerned if it will last 80+ years. By then, humans will have evolved into having long, skinny thumbs for texting......and permanent bluetoothy gizmos implanted in their ears for talking on d..... cell phones! Steam... what?


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## DKRickman (Mar 25, 2008)

ISTR that bronze, rather than brass, is supposed to be used on a boiler, because brass will dezincify and loose strength, eventually failing catastrophically. I read a model engineering mailing list, and the subject comes up from time to time. Seems there's plenty of anecdotal evidence and some science to back it up. I also understand that some boiler codes prohibit the use of brass on a boiler. 

Now, whether that makes any real difference to a small occasional use boiler is up to you, but I'd prefer to be safe. For non-boiler fittings (valves, pumps, etc.) I see no reason not to use whatever you have on hand.


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## xo18thfa (Jan 2, 2008)

Posted By Cap'nBill on 14 Dec 2009 05:35 PM 
Interesting discussion! The reason for the question: I recently got some plans to build a feed water pump. Having limited machinery, I decided to build up various layers in brass, silver soldering. The shape of the steam cylinder, valve chest, and steam chest are rather odd shaped and would require a pretty elaborate casting...as well as the machining. I had noticed some of the pump pics I'd been referred to earlier used the soldered method. Thought I'd ask before I got too far along! Actually, I'm not to concerned if it will last 80+ years. By then, humans will have evolved into having long, skinny thumbs for texting......and permanent bluetoothy gizmos implanted in their ears for talking on d..... cell phones! Steam... what?

For this kind of thing, a brass fabrication is the way to go. Even if you had a casting, you face the problem of mounting it in the lathe chuck. With a brass fabrication you have nice clean edges for reference.

Brass comes in several alloys. For this job, use alloy #360. It is extremely easy to machine and silver solder. It is widely available from the online suppliers.


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## rkapuaala (Jan 3, 2008)

Correct me if I am wrong, but both my Accucraft boilers are cooper and not bronze or brass. Can I assume that since they are copper there is no issue storing distilled water in them?


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## coyote97 (Apr 5, 2009)

destilled water is always a problem: it is aggressive, even when not used with high temperature.
but copper stands some sort of this attacks, even though you can see that over time it is eroding, too.

But copper has another fine attribute:
its one of the best temperature-transporter with the characteristics of metall (flexibility!)

Therefore using copper with a boiler is energy-effective 

The loco in my avatar e.g. has a copper-firebox, too. later they were made of steel.

Frank


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## jinn (Dec 10, 2009)

Posted By rkapuaala on 15 Dec 2009 11:48 AM 
Correct me if I am wrong, but both my Accucraft boilers are cooper and not bronze or brass. Can I assume that since they are copper there is no issue storing distilled water in them?

I do not believe in "correcting anyone", regardless of the circumstances, but would like to take the opportunity here to mention distilled water, as I have a fair background in Chemistry. The closest to "pure" water we can get easily, is distilled water. The Chemistry textbooks all say this. They also say, "pure" water is defined as water having a Ph of 7.0. Ph is simply a measure of how many H+ ions are free in the water, H+ being Hydrogen nuclei, or centers of the atoms of Hydrogen. The books neglect a MAJOR problem, however.

Traditionally-made distilled water gets exposed to surrounding air in the atmosphere as it is made, bottled, poured, etc. This exposes the water to Carbon Dioxide gas which is in the air; some of it dissolves in the water, causing it's Ph to drop on the acid side to around 5 to 6, from 7.0.

Water having a Ph of 5 to 6 is acidic, which means it will corrode metals used in boilers! Adding the appropriate basic material, like Potassium Carbonate, Sodium Carbonate, or even Baking Soda, which is not quite as good, will RAISE the Ph of distilled water above 7.0, making it VERY suitable for use in model boilers.

I distill my own water cheaply, and have been very pleased with the results. It keeps pretty clean in my boiler; no rust has been seen to come out at all when draining a bit of water off. If anyone cares to see it, please ask, and I will post a description and pics of how I built the water distiller.

Caution: If you reside in UK, it is illegal to build a still!









jinn


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## jinn (Dec 10, 2009)

Regarding brass VS, bronze: I have also heard that the zinc used in making brass tends to leach out at high temperatures, seriously weakening the metal. This does not occur with bronze, which uses tin as the alloying metal with copper, instead of zinc.

jinn


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## Mik (Jan 2, 2008)

IIRC The elasticity of several alloys of yellow brass goes down as the temperature goes up... ie. It becomes more brittle the hotter it gets. So while it may deform at room temperature, it may crack instead when heated... not something you really want to have happen with a pressure vessel. 

Toy steamers do often use brass, but since it's a small amount of water, at a relatively low temperature, for a short period of time, the actuaries say the cost savings outweigh the risk.....


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## RimfireJim (Mar 25, 2009)

Posted By jinn on 15 Dec 2009 04:45 PM 
Regarding brass VS, bronze: I have also heard that the zinc used in making brass tends to leach out at high temperatures, seriously weakening the metal. This does not occur with bronze, which uses tin as the alloying metal with copper, instead of zinc.

jinn
The "bronze=tin & brass=zinc" generalization is just that, a _very _general generalization. Referring to my Metals Handbook, Vol. 1, Properties and Selection of Metals, 8th Edition, I find the following examples (note: this is by no means an exhaustive list):

Format: Common name, metals by percentage (Sn=tin, Pb=lead)

Wrought Alloys
Commercial Bronze - 90 Cu, 10 Zn
Jewelry Bronze - 87.5 Cu, 12.5 Zn
Red Brass - 85 Cu, 15 Zn
Low Brass - 80 Cu, 20 Zn
Cartridge Brass - 70 Cu, 30 Zn
Manganese Bronze - 58.5 Cu, 39 Zn, 1.4 Fe, 1 Sn, 0.1 Mn
Free-Cutting Phosphor Bronze - 88 Cu, 4 Pb, 4 Sn, 4 Zn
Nickel Silver - various ratios of Cu, Ni & Zn (threw that one in just for fun - how many of you knew that it was a CuNiZn alloy?)
Aluminum Bronze 5% Al - 95 Cu, 5 Al

Casting Alloys
Tin Bronzes & Leaded Red and Yellow Brasses - various ratios of Cu, Sn, Zn & Pb - no discernible pattern to the naming
Manganese Bronzes - mostly Cu, with Zn, Fe, Al, & Mn - no Sn


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