Alloy of brass and zink in a home foundry

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ChipsAhoy
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Alloy of brass and zink in a home foundry

Post by ChipsAhoy » Sun Aug 09, 2020 9:00 am

Adding zinc to brass.
Is it as simple as melting tin and zink in the crucible with your brass then mixing before pouring?
Scotty

jkimberln
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Re: Alloy of brass and zink in a home foundry

Post by jkimberln » Sun Aug 09, 2020 6:05 pm

Why would you want to add more Zinc to Brass? Brass is already an alloy of Copper and Zinc.

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ChipsAhoy
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Re: Alloy of brass and zink in a home foundry

Post by ChipsAhoy » Mon Aug 10, 2020 1:53 am

Let me put it this way.
If a person wants to,
is it that simple to add tin and zink to the crucible with the brass? Or are there other steps or procedures to follow to safely do so?
Scotty

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Re: Alloy of brass and zink in a home foundry

Post by Harold_V » Mon Aug 10, 2020 3:01 am

One thing for sure---you'd want to add the zinc to molten metal, and allow it to melt. If you start with molten zinc and heat it to the point of melting brass, you'd distill off a huge amount of zinc. Add the zinc, stir well. In any case, you're going to lose some zinc. The fumes should be avoided.

It goes without saying that you should not introduce ANY metal to a molten mass that has not been preheated beyond the boiling point of water. To do so offers the opportunity of a steam explosion. That could ruin your day, and maybe even your week.

One other thing to consider. Material you melt should be free of oils and grease. That helps limit the amount of hydrogen absorbed in the molten metal.

H
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ChipsAhoy
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Re: Alloy of brass and zink in a home foundry

Post by ChipsAhoy » Mon Aug 10, 2020 9:04 am

That makes sense.
What we were going to do was melt the zink, with glass, then add the brass assuming the liquid zink would wet the brass and help with heat transfer.
Now,
Our zink has been pre-melted and cooled into uniform, weighed ingots, then stored in dry containers.
So then, if I got this right, melt our brass, then add pre heated zink down thru the glass, mix and pour.
Sound safe?
Add tin anytime?
Scotty
(I realize you are not liable)

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Re: Alloy of brass and zink in a home foundry

Post by Harold_V » Mon Aug 10, 2020 3:54 pm

I am not aware of problems with tin distilling, but it melts at a low temp and does oxidize, so I suspect it should be added at the same time one adds zinc. The molten glass covering should go a long way towards protecting the heat against losses to distillation as well as to oxidation. I would still start with the alloy (brass), as it requires a much higher temperature to melt than either tin or zinc.

I have no experience with this process--my experience, which is rather limited, is in melting precious metals (gold, primarily) which are alloyed with base metals. Copper or nickel are used in preparing gold. In these examples, one must be careful to not oxidize the base metals, as that results in inclusions in the alloy.

H
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Re: Alloy of brass and zink in a home foundry

Post by FKreider » Mon Aug 10, 2020 4:12 pm

Speaking from experience- as Harold said above; you will want to melt the brass first (when alloying you always start with the highest temp metal first) and once it has melted then add the zinc. As Harold mentioned you will boil off some of the zinc in the process, its easy to tell when this is happening because it smokes like crazy and is very bright. I use a N95 respirator when being anywhere close to these fumes,

Melting point of Zinc is 787F
Melting point of Brass is roughly 1700F
-Frank K.

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ChipsAhoy
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Re: Alloy of brass and zink in a home foundry

Post by ChipsAhoy » Mon Aug 10, 2020 8:08 pm

Thanks for the hints.
We have had a "zinc fire". When we learned of the glass, we used it in the next melts... works great.
Scotty

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Re: Alloy of brass and zink in a home foundry

Post by John Hasler » Mon Aug 10, 2020 8:45 pm

Tin boils at 4716F. It isn't going to boil off on you (It melts at 450F). Zinc boils at 1665F.

Relevant: https://books.google.com/books?id=6mc4A ... king+brass

Interestingly, the author argues that an induction furnace is best for brass making.

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Re: Alloy of brass and zink in a home foundry

Post by ChipsAhoy » Mon Aug 10, 2020 9:59 pm

When our fire started it was as we mistakenly added bronze swarf to the crucible of molten bronze (Open flame furnace). I don't think it was a case of 'distillation fumes', it appeared that as the swarf passed down thru the hot gasses at the opening of the furnace, some of it must have ignited. The bulk of it did pass down into the crucible. Once it started we had a standing, bright, glowing orb right at the opening in the lid of the furnace. It did not extinguish until we opened the lid in preparation of pouring. It left a yellowish/orange residue. (I am color blind so my appraisal of the residue color may not be exact). What a mess. As I understand, a floating layer of glass on top of the molten material helps prevent fumes from rising and igniting. Subsequent melts with the glass seal surely seemed to do it. We tried using brazing flux as a seal. It helped, but that was the most messy, and left the interior of the crucible coated with uneven blobs of tacky flux residue. We 'assume' it was the zinc burning. Hense my inqusitive post. (Yes, we use 3M brand respirators.)
Scotty

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Re: Alloy of brass and zink in a home foundry

Post by Harold_V » Tue Aug 11, 2020 3:14 am

John Hasler wrote:
Mon Aug 10, 2020 8:45 pm
Interestingly, the author argues that an induction furnace is best for brass making.
He's right, and for a couple reasons. For one, it heats without altering chemistry, but the most important feature is that an induction furnace stirs constantly. The heat becomes fully homogenous as a result.

Scotty,
Would you please address the use of glass as a covering? I understand its purpose, but I have a question about the depth of the layer, and would like to know how you deal with it when it's time to pour.

Thanks in advance.

H
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Re: Alloy of brass and zink in a home foundry

Post by ChipsAhoy » Tue Aug 11, 2020 8:38 am

The way we found that seemed to work the best is pretty simple. BTW, we are amatuers not pros.
The glass is broken up clear glass from an apple cider jug. Pieces range from about 3/8" to 1" Using a #16 crucible, we put in about 1/2 cup of glass. The resulting layer is very thin. I suppose we could make it thicker, and we might yet, but too thick it can over flow the wier. And it seems that too thin a layer it more readily flows thru (under) the weir.
It melts and floats on top. It becomes stringy, if you lower a piece of metal slowly down partially into the melt, the slowly pull it back up and out, it strings along with the consistency of cheese, like motzeralla (sp?) on a pizza. We are careful to add metal very very slowly.
We have constructed a hand held "weir" that a third person holds inside the opening as we pour to keep the glass back.
(Notice what seems to be an overuse of the word "slowly", it is not).
We are still in the 'trial and error' stage, so what I post may not be the correct way. That is why the discussion.
If you wish, I can get a photo of the use of the hand held weir.
Scotty

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