Experiments with melting and pouring copper bars.

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a11051605

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Sep 6, 2017
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So after abit of searching on this forum and the internet, with little to no luck on detailed melting and pouring your own copper bars, I decided to have a go at it and experiment and figure it out on my own. Iv included my results so far and figure this might come in handy for some one.

Materials used:
99 copper stripped from electrical wires. (research says most if not all electrical copper is 99.99 but we will call it 99 just to be safe)
propane venturi forge
1 kg clay graphite crucible
1 kg graphite bar molds
graphite stir stick/rod
flux materials (more on these below)

Notes before melt: Copper loves oxygen in a molten state so all melts are done in a reducing flame (orange flame, excess propane to oxygen) Using 1kg bars/values as anything over that will be easy math for flux ingredients and ratios.

Methods and results:
1st attempt, no flux, blow torch on pour. To reduce oxygen contact with bar.
Brought crucible and forge to a nice bright orange glow and deposited copper. Copper melted from solid to liquid in about 1 1/2 min using approx 250 gram bundles of wire at a time. On pouring had a friend hold blow torch on mold to reduce oxygen tell "skin" developed on bar. Noticed during the pour that copper was had a consistency of molten maple syrup and proved a bit difficult to pour and started to solidify fairly quick, even while pouring so I had to hurry and pour up and down the length of the mold to race the copper setting up.
Result on bar: Bar came out ok/acceptable with only light evidence of darkening/oxidation, noticed that you can see a small layered effect on the side of the bar as if it formed seems from the pouring of liquid copper on top of the cooling but not yet solid copper.

2nd attempt 1 tbs charcoal 1tbs borax. Charcoal will burn and pull oxygen out as CO. Borax supposed to form mat that acts as oxygen barrier.
With forge and crucible at a bright orange glow and deposited copper. Copper melted from solid to liquid in about 1 1/2 min using approx 250 gram bundles of wire at a time. Removed crucible and added mix of charcoal and borax to molten copper, stirred in flux using graphite rod and returned crucible to forge to reheat. On pouring did not use a blow torch as I poured. Copper was more runny and poured much better but was still some what viscous, also noted that it appeared to not solidify as quick and also benefited the pour.
Results on bar: bar came out still ok but actually worse then 1st attempt. Noticed significant pitting and cavitation on bottom and sides of bar. Large glass mat on top of bar. Bar itself was free of oxidation and showed a bright luster and shine. Suspect pouring the charcoal and borax at same time may not be correct approach as the bubbles may be trapped CO that could not escape due to borax/glass mat on top of copper? Just a thought?

3rd attempt 1tsp borax 1/2 tsp fluorspar. Borax for mat/oxygen barrier and fluorspar to make pour more runny and better at filling mold. With forge and crucible at a bright orange glow and deposited copper. Copper melted from solid to liquid in about 1 1/2 min using approx 250 gram bundles of wire at a time.
Removed crucible and added 1st fluorspar, stirred, then added borax, did not stir. Found that copper very quickly started to solidify once fluorspar was added and makes time management very critical, also thought it odd that fluorspar appears to mess with solidification curve. Also note that fumes from fluorspar are not good for your health so avoid breathing in any fumes. Returned crucible to forge to reheat. On pouring the copper poured similar if not maybe a hair more runny then 2nd attempt. Bar quickly solidified as in 1st attempt but due to being more fluid and pouring quickly it was less of an issue. Kind of a step in right direction as less flux material used for similar or hair better pour.
Results on bar: bar came out ok and probably the best yet but still not professional/great looking. Bar showed slight spotting between oxidized/darker areas and bright unoxidized areas. Bar itself appears to be the most homogenous yet and appears solid through and through, very small pits on bottom noted. Small glass mat on top of bar.

If any one else has anything to contribute as far questions or ideas or books or sources of info on pouring and working with copper please chime in.
 
Try using sticks of wood to stir with. It will help with the reduction.

That's a lot of fluorospar as well.

A lot of your oxidation is coming from using wire. Too much surface to interact with.

You won't get a shiny copper bar unless you keep it covered with the gas flame the entire time you pour and cool.


Sent from my iPhone using Tapatalk
 
What is the purpose of these bars? Why do you make them? Seems rather pointless.
 
I use waste engine oil to melt my copper. I have no problem melting the copper, its just molten copper loves to absorb oxygen and release it on solidification. This leave holes and pits in the finished bars. You can minimize this by covering the copper with a load of charcoal in the melt. Still doesn't stop it completely though.
 
I could see a wood stick burning and helping with reduction but also think due to the heat it would burn quite quick and also unless very dry would risk a steam burp but it is an interesting thought.

I kind of think its to much fluorspar as well and am going to experiment with less and see if this is a case of "less is more".

Using a reducing flame in the furnace seems to help a lot as far as the copper absorbing oxygen but I will be looking to try and test with a graphite cover on top of the molten copper b4 pour to see if that helps. Kinda difficult managing a "cover" on the molten charge while at same time adding raw solid to fill up the crucible and do enough for a pour. Only thing I can say for sure at this point is Borax is a step in the right direction and does contribute to a better pour and finished product.

Also heard about using vinegar to help shine and clean up the surface of the solid bar but there is some kind of fine line between cleaning and leaving on to long that will actually damage the surface of the solid bar, at this point IDK what that line is.

Will keep adding to this as I get a chance. Last week has been pretty nasty weather here and not good for melting.
 
Adding wood to copper is an old refining method.
https://en.wikipedia.org/wiki/Poling_(metallurgy)
They actually used fresh wood. The heat will make the wood burn fast until the oxygen is removed, then it will be limited by the amount of oxygen that is coming into the furnace.

Göran
 
g_axelsson said:
Adding wood to copper is an old refining method.
https://en.wikipedia.org/wiki/Poling_(metallurgy)
They actually used fresh wood. The heat will make the wood burn fast until the oxygen is removed, then it will be limited by the amount of oxygen that is coming into the furnace.

Göran

Yes it is.

I read it in a copper smelting book written in the late 19th century I believe.

Green Pine trunks were preferred.

It's like making glass. Mixing the batch was best performed by putting a potato on the end of a stick and immersing it below the surface of the glass. It's a very strange sensation (when holding the stick), and a great way to make a quick baked potato.
 
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