Brass, Bronze and Dezincification

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FLtenwheeler
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Joined: Sun Jan 05, 2003 8:47 am
Location: Florida, on the Lake Wales Ridge

Brass, Bronze and Dezincification

Post by FLtenwheeler »

Hi All

I found this on the Goulds Pumpsweb page. I think it has some useful information about dezincification.

Tim

The Suitability of Cast Copper Alloys In Chlorinated Water Services

Question:
Which is better for chlorinated water services; Silicon-Brass or Silicon-Bronze? Also, why is it that older pumps made from Leaded-Red-Brass (Alloy UNS C83600) appear to resist corrosion better than the alternative “lead free” materials?

http://locator.gouldspumps.com/download ... Alloys.pdf
He who dies with the most unfinished projects: Should of put more time into their hobby.
RONALD
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Re: Brass, Bronze and Dezincification

Post by RONALD »

Tim, I don't understand, you are about to make valve gear parts by lost wax out of cast brass/bronze, and you are worrying about the effect of chlorine in water. Those parts would never be in continuous contact with water. If you were casting plumbing parts, used continuously in contaminated water, then you might worry.

What they are discussing in that article are long time consequences of immersion in chlorinated( or other chems) water. In the only occasional operation of a model steam locomotive the effect would be almost immeasurable.

I have a large industrial type dehumidifier in my basement that I run in the summer that puts out more water then I could use, all the water has is a little dust in it. Lots of people collect rain water.

I think you could safely use any of those alloys that have been mentioned if you are worrying about chemical degradation. What you should worry about is castability and machinability, because each of those alloys behave differently in that respect.
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steamin10
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Re: Brass, Bronze and Dezincification

Post by steamin10 »

The use of such cast materials for mechanical parts is not nearly as critical as when used for boiler fittings. The heated water that releases not only air but creates a chemistry that can be quite corrosive with carbonates creating acids, (carbonic) and the mix of disimilar metals supporting mild electrolysis, where zinc becomes sacrificial to the iron present, there are considerations.

While the Bronzes mentioned are close in strenth, they are not close in machinability or decorative value. Brass and bronze items, have lead additions for better machinability, (plumbing brass) and the fact that lead is slow to dissolve in water, no matter the PH. So beyond being seen in lead tests, it has the property of holding the zinc inplace unless being overrun by conditions. (cold water, neutral ph). But by putting lead in the brass, it will tarnish easily, and will not hold a shine without either a lot of work or a coating. This holds true of all the casting metals. Bell brass, or bronze you will note has nearly no lead, and the alloys crafted for hardness. Hard metals ring well, the shape and size of the bell holds the pitch, and overtones. You will never find a lead bell. It is too soft to vibrate.

Everdure is a general casting compound, and when I bought mine, its analysis was low zinc. At least that was the spec I was given. It is made for small and fine detail for castings, and works very well, unless you ork up the compound with bad scrap or mishandling. Things in general, I use scrap and create my own mixes which mimic the commercial stocks. Most critical is the silicon, which creates fluidity. The other percentages can float and you get what you put in. I can reduce brass with copper electrical wire, and all that motion, but prefer to use various scrap as is, so it remains close to what material the objects were made from.

That being said, unless you are making a critical part, like an impeller for a pump, where chemistry and other properties are critical, dont sweat it in the model world. Just use bronze for water bushings. Most other things can be safely made of brass, with working parts Bronze of most any grade is suitable. Not only are these noted casting metals, but sheet and bar forms are available in those same compounds. The advantage of castings, of course, is material that is already shaped, and semi-finished in form, supposedly saving time. Fit and finish is nearly as important as function on a model, and apperance in a static model is everything.
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FLtenwheeler
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Joined: Sun Jan 05, 2003 8:47 am
Location: Florida, on the Lake Wales Ridge

Re: Brass, Bronze and Dezincification

Post by FLtenwheeler »

Hi Ron

It has nothing to do with what I am doing right now. But I might need it some day and this is a good place to keep track of it.

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