Making ZA27

Home enthusiasts discuss their Foundry & Casting work.

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jscarmozza
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Making ZA27

Post by jscarmozza » Thu Jan 23, 2020 8:47 am

My casting buddy came by some zinc ingots and suggested that we mix up a batch of ZA27 and see how it pours and how the parts made from it perform. I thought it was a great idea, but then we started thinking about how to melt and mix copper, aluminum and zinc when their melting temperatures vary so greatly. Do we start by melting the highest temperature metal first and work our way down to the lowest melting temperature metal, or do we just put the everything in the crucible and melt the whole thing at once? I would think trying to do the latter would burn off the zinc, but I don't know...does anyone out there know how to do this?
John

John Hasler
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Re: Making ZA27

Post by John Hasler » Thu Jan 23, 2020 9:03 am

I've never done it either but the melting point of copper is above the boiling point of zinc so you certainly don't want to melt the copper first. The melting points of those alloys are a bit below the melting point of zinc so I should think that melting the zinc and dissolving the other metals in it would work. Perhaps grind it all up, heat the mixture to just above the melting point of zinc, and wailt for the other metals to dissolve?

Work with good ventilation so that if you do boil some zinc you won't breath enough of it to make you sick.

Harold_V
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Re: Making ZA27

Post by Harold_V » Thu Jan 23, 2020 3:32 pm

Molten metals are strong solvents of other metals. That's the chief reason why it's NOT a good idea to use steel as a crucible for melting aluminum, which appears to be one of the less than good things that home foundry types just love to do.

This concept is the reason why assaying works, where litharge (lead oxide) is used to collect values from ore samples in an assay. The lead, which is produced as the litharge is reduced, acts as a solvent and collector of other metals.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

jscarmozza
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Re: Making ZA27

Post by jscarmozza » Thu Jan 23, 2020 6:01 pm

Ok, so we should start with the lowest melting temperature metal and 'dissolve' the higher temperature metals in it. I didn't think it worked that way. Thanks guys, I'll keep you posted on how this experiment turns out.
John

Harold_V
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Re: Making ZA27

Post by Harold_V » Fri Jan 24, 2020 5:08 am

While owning one isn't common, an induction furnace makes projects like this a lot easier, as you can melt without altering the chemistry of the charge, and the resulting agitation keeps the metal in constant motion, so it dissolves faster.

I've not tried what you're attempting to do, but you may find that a slightly elevated temperature, below the point where zinc distills, will accelerate dissolution. As is typical of most chemical reactions, heat makes it happen faster. Stirring plays a role in this process, so keep the metal well agitated. When melting precious metals, a carbon rod is used. I don't know what I'd recommend for your project, but keep in mind some metals will contaminate the charge, as anything you choose to use will be dissolved to some degree.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

FKreider
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Re: Making ZA27

Post by FKreider » Sat Jan 25, 2020 9:34 pm

I have melted and poured bronze and brass alloys from their base materials (copper, zinc, tin, lead.)

You always melt the material with the highest melting temperature first and work your way to the material with the lowest melting point. This process can be difficult and frustrating, especially when trying to make an alloy with dissimilar metals. For instance, when attempting to make yellow brass you will need to melt the copper first and then add in the zinc once the copper is molten. You want to stir the metals together and it is ideal to cover the melt in order to prevent the zinc from boiling off. I have heard of using pieces of glass to cover the melt, I have also heard of using charcoal powder or sand. I have successfully made brass from copper and zinc without covering the melt but it was not super fun.

As mentioned above, this needs to be done in a well ventilated area (outside) and I do not stay any closer to the melt and fumes than necessary. Do not breath the fumes given off by zinc (or any fumes for that matter.)

I suggest joining the casting forums on the net and picking up some books. It takes some trial and error to get good castings and a lot of work goes into the process so it can be frustrating however also very rewarding.
-Frank K.

jscarmozza
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Re: Making ZA27

Post by jscarmozza » Sun Jan 26, 2020 1:49 pm

I did some research on the matter and found out some interesting facts, when alloys of metals with greatly varying temperatures are made, as Frank said they start with the highest temperature metal and work their way down. The addition of the lower melting temp metals must be done quickly and done under some type of cover. If however the proportion of the highest melting metal is small, 2% copper, in ZA-27,then it's not practical to melt such a small amount of copper and add the lower melting temp metals to it. So ingots of copper and aluminum are made in roughly equal proportions and then added to the the alloy of the lower temperature metals, aluminum and zinc in this case. They kind of sneak up on the proportions in the alloy, all the while adjusting the proportions for losses in the lowere melting temp metals. So what's the moral of this story...if you want ZA-27, buy the ingots, trying to make them may be more trouble than it's worth, thanks for the replys.
John

FKreider
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Re: Making ZA27

Post by FKreider » Sun Jan 26, 2020 11:28 pm

jscarmozza wrote:
Sun Jan 26, 2020 1:49 pm
...So what's the moral of this story...if you want ZA-27, buy the ingots, trying to make them may be more trouble than it's worth...
:lol: :lol: Yup!
-Frank K.

jscarmozza
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Re: Making ZA27

Post by jscarmozza » Tue Mar 30, 2021 7:52 am

I've been making some pot metal castings and began to run low on metal, so I added a zinc ingot and some thin aluminum trimmings to the pot, melted it and continued to pour with good results. When I ran low again I did the same thing, but threw in a piece of 50/50 lead tin solder this time...that changed things! The mold filled beautifully, the casting finish went from bright shiny silver to frosted whitish silver, BUT, the casting was weak and broke into many pieces when removed from the mold. You could snap the casting easily just like a piece of chalk. Obviously it was the solder that made the difference, do you think I could dilute the problem by adding more zinc and aluminum to the pot?

Harold_V
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Re: Making ZA27

Post by Harold_V » Tue Mar 30, 2021 5:00 pm

No. I suggest you eliminate all traces of lead. I know, from my refining experiences, that lead tends to make some alloys brittle, a total lack of ductility. A trace of lead in gold renders it useless.

That may or may not be true in your case, but considering the success you've enjoyed until you added the lead/tin mixture, I'm of the opinion that you'd be best served by discarding what ever metal remains, and to even clean the pot well before starting over.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

Harold_V
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Re: Making ZA27

Post by Harold_V » Tue Mar 30, 2021 5:07 pm

jscarmozza wrote:
Sun Jan 26, 2020 1:49 pm
If however the proportion of the highest melting metal is small, 2% copper, in ZA-27,then it's not practical to melt such a small amount of copper and add the lower melting temp metals to it.
That's what I was implying when I said molten metals are strong solvents. In this case, you don't melt the high temperature metal, you dissolve it with the molten mass you create with the other elements.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

jscarmozza
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Re: Making ZA27

Post by jscarmozza » Tue Mar 30, 2021 6:43 pm

Yes! Brittle is an understatement, and I didn't add very much solder either.
I poured off the batch containing the lead tin solder and started over with an aluminum zinc mix 1:10 by weight. You are also absolutely correct about dissolving a higher melting temperature metal in an alloy of that metal, I 'dissolved' additional aluminum in the aluminum zinc alloy at 900 degrees F in a cast iron pot on an open natural gas flame. Live and learn...thank you Harold.
John

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