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I Forge Iron

Holes in the Bottom of my Copper Ingots

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Welcome aboard from 7500' in SE Wyoming.  Glad to have you.

If you put your general location in your profile we can give better answers to your queries.  A surprising number are geography dependent.  This is a world wide forum and we don't know if you are in Lapland, Arizona, or Tasmania.

This is just a guess but might your mold be too hot and is reheating the liquid copper and you are seeing copper vapor bubbles preserved in tche bottom of the ingot.  Just a SWAG and other folk may have a more accurate response.  This might be more likely if your liquid was particularly hot and near its liquid/vapor temperature.

"By hammer and hand all arts do stand."

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In principle, that is a sensible answer George. However, boiling point of copper is 4643F and has a fairly low vapor pressure at temperatures below the melting point of iron which I am sure was not exceeded here.

Caveat - I do not cast copper but I am a chemist so do understand something of the issues. Consider this a [guess].

Oxygen is quite soluble in copper (up to about 1%). From the look of the ingot, you could well be seeing outgassing at the center where it looks as if you are pouring the molten metal. The oxygen would form a gas as the metal cools in this region forming the bubbles that you see in the ingot.

You could consider pouring at a lower temperature which would mean less oxygen in solution and having the mold hotter for slower cooling to allow the gas to escape more effectively. From the look of the ingot, the metal cools pretty rapidly on contact with the mold.

Also consider how you pour to minimize the contact of the copper with air.

Commercially, I think that they use phosphorus or lithium as a deoxidizer to avoid this issue.

Let us know how it progresses.

Edited by Mod34
Edited for inappropriate language
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Yes; molten metals often absorb gasses while molten that then come out as the metal cools leaving porosity.  You can use flux to help prevent gasses being absorbed and materials to "degas" molten metal before pouring.  (I've used very DRY charcoal rods to help remove gas from silver for instance.)

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  • 1 year later...

Novice here, but I would agree with Thomas. 

I pour my copper bars as soon as I can stir the pot with a graphite rod and not feel any solid pieces. The longer it is molten the more problems you will have.

He mentioned an iron mold. How is he keeping the the metal from sticking?

I coat my mold in soot from my furnace after I cut off the oxygen making it fuel rich. Similar to oxy/acetylene torches.

The soot allows a route for the gases to escape around your bar vs trying to rise up the center.

I also use an plate iron mold that isn't very tall to facilitate the escaping gases.

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