Foundry Can't Melt Copper?

Hello,
Recently I made myself a casting foundry using a 5 gallon steel bucket, lid, a lot of refractory cement, and a propane burner I got off eBay.

Aluminum melting is of no problem. Copper, not so much.
It got the copper in my clay-graphite crucible red hot, but not enough to melt it down.
I put a rock over the the 3" hole in the lid to try to help keep the heat in a bit, seemed to work, but not quite enough.

Any ideas?
Can a propane burner get hot enough for my copper goals?
If not, any upgrades I can do?

It's called a furnace, furnaces are situated in a foundry. These guys should be able to help you: https://forums.thehomefoundry.org I would expect you'll need to increase your rate of burn to overcome any heat losses. That will involve anything up to a forced air blower and a higher flow gas regulator. A 5 gallon bucket may not allow thick enough refractory for the job so wrapping it in some high temp insulation or even a jacket filled with expanded perlite will reduce rate of heat loss enough to do the job.

It should get that hot, it probably needs to be tuned or adjusted. Also if you have reflective coating on the refractory that will keep heat from absorbing into the refractory. Something like ITC-100, its made for this:
Buy Ceramic Coating - ITC 1�� Refractory — ITC Coatings
Oil will melt iron so you can always step up to that if you can not get the propane to work, it could be a poorly designed burner.
If you had a way to dribble oil into your furnace it will get HOT, just read up on that and be carefull.

Rob F. said:

It should get that hot, it probably needs to be tuned or adjusted. Also if you have reflective coating on the refractory that will keep heat from absorbing into the refractory. Something like ITC-100, its made for this:
Buy Ceramic Coating - ITC 1�� Refractory — ITC Coatings
Oil will melt iron so you can always step up to that if you can not get the propane to work, it could be a poorly designed burner.
If you had a way to dribble oil into your furnace it will get HOT, just read up on that and be carefull.

Click to expand...

Neat material, thanks for the lead.

I looked up the melting point of copper, 1984 F. I wonder if that is where George Orwell got the name for the novel? I routinely melt silver at 1763 F with a natural gas/air burner. The main problem with burners using air is that air is 80% nitrogen, which does not burn, so it is like blowing cold on it while trying to heat it.

Sculptor Arthur Towata described a furnace that was simply fire brick piled up with an opening for a gas jet and the air regulated by sliding a brick across it.
He was firing pottery, which takes a lot higher temperature.

Bill

bxb301 said:

Hello,
Recently I made myself a casting foundry using a 5 gallon steel bucket, lid, a lot of refractory cement, and a propane burner I got off eBay.

Aluminum melting is of no problem. Copper, not so much.
It got the copper in my clay-graphite crucible red hot, but not enough to melt it down.
I put a rock over the the 3" hole in the lid to try to help keep the heat in a bit, seemed to work, but not quite enough.

Any ideas?
Can a propane burner get hot enough for my copper goals?
If not, any upgrades I can do?

Click to expand...

copper closer to yellow heat not red heat. some furnaces you can just increase fuel flow and watch fuel air mix is still ok. many furnaces might burn 8 lbs per hour but as it up to temperature you can reduce to 4 lbs per hour. otherwise it might get too hot.
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i have use furnaces with 2 burners and often it was just easier to turn one burner off once furnace up to temperature. basically i used 200% more fuel the first 30 to 60 minutes to warm things up and after i could reduce the burners to avoid overheating. furnace needing a hour to warm up is not unusual

Propane absolutely gets got enough to melt copper. The flame temperature is about 3,600°F and it's the typical fuel in many foundries. The question is whether the burner is large enough. It's the total heat being generated (over time) , not peak temperature, that matters. Without knowing more about your burner and furnace, it's hard to make diagnosis. (In my experience, "red hot" for most people is "it's starting to warm up in there." for me. Ambient lighting can also affect judging temperature by eye so you may need to adjust for that as well.)

You need to think about the problem correctly to find the solution. The peak temperature in your furnace is the temperature at which the heat escaping the furnace equals the heat being generated by your burner. If it's not high enough you can either keep more heat in (covering the vent is one way) or generate more heat.

More insulation might help, in my experience hard refractory materials, like cement, are less efficient insulators. If your furnace is almost hot enough then wrapping it in refractory blanket could nudge it over the line. If it needs more than that, larger or multiple burners are the way to go.

Thank you everyone for the reply.

Peter from Holland ; Do you have those photos of your build still?

fciron, you are correct, some photos of my setup might help a bit. (posted below)

I'm thinking I might have some heat loss out of the burner hole; its a bit large and the burner flops around in there.
Perhaps I can get some more cement and make this hole a bit tighter.
The rock over the lid hole sure helped I think.

It was darn hot in there, no doubt. The copper pipe I was trying to melt was glowing and became soft and pliable, just not quite there to its melting point.

that ceramic coating might help a lot. a pint is $50, but might be enough to paint the inside of the oven. Anyone have any experience with it?

Have you tried reducing the air?

with a air fuel burner using the waste heat to preheat air going into burner you can increase flame temp from 3000 to much higher.
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a air fuel burner can usually get furnace up to 2500F or melt cast iron at a yellow/white heat and with preheating air get even hotter. you actually have to not have burner flame directly on crucible cause with preheated air you can actually damage crucible and easily see burner marks on the crucible where flame touches it.
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then usually the crucible sits on a much taller block so flame touches the base block first not the crucible. with lower flame temperatures its not as much a concern so flame might directly touch crucible if only melting aluminum. if flame is oxidizing it might actually burn the carbon or graphite thats part of many crucibles especially if over a red heat like a yellow or white hot temperature

bxb301 said:

Thank you everyone for the reply.

Peter from Holland ; Do you have those photos of your build still?

fciron, you are correct, some photos of my setup might help a bit. (posted below)

I'm thinking I might have some heat loss out of the burner hole; its a bit large and the burner flops around in there.
Perhaps I can get some more cement and make this hole a bit tighter.
The rock over the lid hole sure helped I think.

It was darn hot in there, no doubt. The copper pipe I was trying to melt was glowing and became soft and pliable, just not quite there to its melting point.

that ceramic coating might help a lot. a pint is $50, but might be enough to paint the inside of the oven. Anyone have any experience with it?

Click to expand...

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use 2 burners at opposite ends. also 20lbs tank might not be enough to sustain pressure. that is tank starts at 100 psi but gets cold and pressure drops often below 20 psi cause the propane gets cold.
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if each burner burns 4 lbs per hour thats 8 lbs per hour for the first hour. once furnace warmed up then normally can reduce fuel burn rate to maintain temp

I'm with DMF_Tomb, that burner looks small for what you're trying to do. A second burner on the opposite side would be the easiest fix.

I bought a 100lb tank for my forge and that helps a lot with the pressure drop. (My two burner forge will freeze up a, twenty pound tank when it's only half full. I Have put the tank in a tub of water as a heat sink to finish a job.) There are rigs to gang up two small tanks, but they cost about the same as the 100 lb-er.

my burner has .040" orifice hole using 3/4 and 1.5 NPT pipe, usually maximum is about 4 lbs per hour
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if much different size than you would have flow volume and velocity problems

Two things . I don't see a base block in your picture. New propane tanks have a valve that can limit the gas flow. Put together a bank of tanks to make sure your can supply more fuel than you need and the pressure does not fall off. If its cold out even 2 or 3 tanks can frost up and you will lose gas flow.

Not much to add to the suggestions above, but ...

1) Add a gauge to your setup so that you can see how much psi you are feeding to the burner

2) That is not a lot of refactory, and as others have said that burner looks too small. For your "Model 2" furnace, consider using a larger container to gain more refactory, and/or include some ceramic wool in the design. And increase the burner size, or add a second burner.

3) Rather than plugging the hole around the burner with cement, use some ceramic wool.

4) 1 pt. of ITC 100 will do your furnace and leave some left over.

Looks to me like your whole furnace is a little small to have enough insulation around that crucible to melt copper...of course if you stuff enough fuel through it, you will do it.

Your flame should be blue with only a little yellow. Yellow means not enough oxygen, but once you are all blue, you can no longer tell if you have too much air which is only cooling things down

You do need a block under the crucible, direct the flame so it swirls around under the crucible, or most of the heat will whoosh out the opening at top before it does much to your charge......back to needing a bigger furnace.

Also worth noting that pure copper is rarely cast, because you get problems with oxide embrittling the casting. A little phosphorus, tin, or zinc solves that problem, as well as lowering the melting temperature

some people leave propane tank on a bathroom scale so they can see the weight change as it empties. it also gives a better ideal how much fuel you are using and when it will run out.
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if you see snow or frost on side on tank that also sort of indicates propane level

Looking at your photos, the hole in the lid is a bit too small to get the exhaust gasses out quickly. As the fuel burns you'll get a drastic increase in volume of the gasses and your lid hole is not much bigger than the tuyere/burner hole. A modest increase in diameter will double the surface area and flow rate...at present that small lid hole is choking off combustion. Without forced air induction the hole size becomes critical. Dry diamond blades for an angle grinder are cheap and will let you resize the hole easily.

Well, that is a lot to go through.
While trying to do the copper, having it on for quite some time, I did notice some round flame damage to my crucible, but, hardly noticeable after it cooled.
A block in there would do it good for the time being. I only have an inch or two before the crucible touches the lid.

I'm getting an occasional "burp" while in use. I thought that was just because I don't know how to adjust the flame correctly. Perhaps that is caused by too small of a vent hole, and gasses building up.

I didn't think I was going to have a problem of it being too small, I thought it was too big!
That used 4 tubs of that refractory cement, at $50 a pop making it larger will have some sticker shock to it.

One problem I don't have is that tank freezing up.
Its a pretty old tank, but with a new label on it. Local place wouldn't fill it because it wasn't new tank, so I put that plastic sleeve on it from my buddies barbecue; problem solved!

I have a large heater for the garage and I can run that thing empty and it wont freeze up.

The burner does have a gauge on it. I usually have it about 10psi, anymore and the burping increases and it puts itself out. (Back to the vent problem I suppose)
...that lid hole was made with pipe with an OD of almost 3" I thought it would do just fine.

ebays seller specs are:
Output 130,000 btu
The feed tube is 1"O.D stainless steel.
The air choke is 1-3/8" stainless steel.
The tip or expansion chamber is 1-3/8"O.D. 1/8" thick wall - 3" long

I thought it was too big also.

So,
should I build a new one?

or

band-aid this to meet my copper goal by-
Ceramic lining
Spacer block
Larger vent
2nd (or larger) burner
(possibly) more propane.