furnace for melting copper

[Mick]

okay, i just whipped up a furnace like in black book companion(or BB munitions #4 - whatever you wanna call it)
a quick overview for those that haven't read it: hole in the ground, pipe in the side with a blower attached, fill with charcoal briquettes, add pot with copper inside.

unfortunatly, it doesn't get hot enough, it gets ungodly hot, but the copper just doesn't quite get to melting point(which i think is around 1800 celcius). it must get so very very close to melting point tho, cause a few bits of copper wire melted slightly, but its unable to sustain that sort of heat for any length of time.

now, has anyone here successfully melted down copper for use in shaped charges?, if so how did you do it?

i was thinking maybe coal might get hot enough?

i've searched around the net to find out about kilns and furnaces but there really doesn't seem to be that much info on the subject. which surprized, cause i figured there would be heaps people into making old school furnaces...

any ideas?

[nbk2000]

Considering how ancient man could melt copper using nothing more than his lungs blowing down a tube, you must have some kind of alloyed wiring.

What're you using to pump air down the tube? Maybe it's clogging up down in the hole.

[Mick]

using a compressor with a gate valve on a piece of 25mm gal water pipe, with 3 1/8 holes in the pit. theres certainly no shortage of air supply.

i've been thinking(scary!), i wonder if its got something to do with the briquettes i'm using...i don't actually think there charcoal, i think there some kind of processed "i can't believe its not charcoal!" stuff.

i'm going to look into building large propane torch. i've wanted one for ages..so i may as well make one.

also, i appeared to have "cracked" into the homemade metal casting web ring. so i found shit loads of info on how to do things.
i hate shit like this, all you need to find is just one site specifically to do with the thing your looking for, and the internet just opens up with a wealth of infomation for you - however, finding that first website is an absolute pain in the ass, and its basicly just luck in picking the right search terms.

anyways, heres the site for people who are interested in this type of thing <a href="http://www.backyardmetalcasting.com/" target="_blank">http://www.backyardmetalcasting.com/</a> (interesting enough, i never even thought to just type what i was looking in the address box)

[nbk2000]

Hey Polverone...think this'd be hot enough to distill phossy? :)

<img src="http://www.backyardmetalcasting.com/bucketfurnace/bucket3_hotfurnace.JPG" alt=" - " />

[A-BOMB]

I too have seen that site, right now I'm trying to cast some small AL gears for my remote control tank like think I'm building. Its just so hard to carve a good gear out of sytrofoam for lost foam casting and make them all the same.

[EventHorizon]

NBK, seeing you know that site I wonder if you lurk around similar sites as I. I may know you and not even know you. :)

EDIT: Just saw that link was posted in the previous reply, sorry.

Anyway, I've made two types of burners for forges and they both work DAMN good. If you can't melt copper with either of them then you shouldn't even bother. I built one forge that I had to crank the propane down to &lt;4 psi to get it below 1500°F. My setup would do 19 PSI. :D

Anyone searching for a burner design, search for "Reil" style burners. Cheap and VERY easy to make. There are may modifications to the design, but the simple one works exceptionally well.

<a href="http://eventhorizon.0catch.com/reilburner.jpg" target="_blank">http://eventhorizon.0catch.com/reilburner.jpg</a>

<small>[ November 12, 2002, 07:37 PM: Message edited by: EventHorizon ]</small>

[Bitter]

Have you tried putting a higher 'chimney' on your furnace, Mick ? I've heard that works, although I haven't tried it myself.

[zeocrash]

ok i'm planning to build a furnace
the furnace will efectively be a hollow bucket, with flame holes on the inside of the bucket.
ftp://ewf:sd332gf@209.195.155.80/hosted%20images/zeocrash/furnace.jpg
(not sure what's up with the image)
ok now i have several problems.
firstly i need an effective method of supplying oxygen to the furnace.
secondly i need to know about the size and quantity of holes to give me a decent burn. i'm not sure of the flame speed of index, but if i get the flame speed too fast the think will look like a prop at a heavy metal gig, and if i get it too slow it will burn back up the pipe.
any ideas

[zaibatsu]

A leafblower could be used, also check the foundry websites and you'll find plans for making a fan. Also heard somewhere about a hairdrier being used for smaller furnaces.

[Tuatara]

Melting point of copper is 1084C. You should be able to reach that easily with a coal furnace.

Ceramic kilns get to 1300C with propane burners!

Recipe for an insulating castable refractory to line your furnace with

By volume :
1 part Alumina
4 parts grog (crushed firebrick)
3 parts coarse sawdust
4 parts fireclay
2 parts Portland cement
2 parts vermiculite

Alumina, grog and fireclay are all available at ceramics/pottery supply stores.
This stuff is mixed with just enough water to make it sticky / mouldable , then packed into your furnace (eg 44 gallon steel drum). Once it is dry I'd suggest a low temp burn out (say 500C , rising slowly to 1000C over half a day). The sawdust burns out leaving voids which improve the insulating properties. This mix will go to 'Cone 10' or 1300C.

[Tuatara]

Induction heater built from a radio oscillator and a flyback transformer?

[ has to stop typing to wipe tears of laughter from eyes]

Sorry mate, you'd get more power out of a box of matches.

Believe me, fire is waaaay easier than making your own high power RF induction heater.

[McGuyver]

Yes, flyback transformers merely put out high voltage, not high current which is what you want for an induction heater. The best thing you could use to melt metal electrically is a arc welder, but for forming things with a fuel powered furnace is way better.

I think the best furnace would be a clay or brick box or whatever shape you want. Then have a decent air blower, like a leaf blower or an electric blower feeding a large amount of air into the bottom of the furnace. I've seen wood fueled fires melt copper so fuel is your choice. As long as you have plenty of air coming in, it should get plenty hot. Maybe those wood pellets used for stoves would work well. You could even make some kind of feed system for it, so you wouldn't have to stop casting.

[klassasin]

If anyone cares I would say propane is the way to go. I have successfully melted aluminum, brass, and copper. Use propane for fuel and air compressor for forced air. It gets hot. Here is a pic. (Server is not always up)

http://www.k3experiments.com/Pics/After.jpg

[McGuyver]

What is your furnace made out of? Also, how big is your compressor? How many psi and cfm does it put out?

[klassasin]

IIRC it is made from a mixture of fireclay, cement(powder), and silica sand. They are mixed with water, put into the form, then allowed to dry. I can't remember the exact proportions. For the compressor(has a regulator) it outputs about 20-40psi. To high and the flame can get extinguished, to low and the flame won't burn hot enough.

[vulture]

Anybody ever tried to feed these things with pure oxygen or air enriched with oxygen?
That should give a huge performance boost.

Ofcourse, if you can get oxygen bottles, you probably can get acetylene too...:D

[GibboNet]

There's no point putting pure oxygen into the furnace, as you want some fuel left to burn....

Dr Karl Kruzelntiski (sp?) Ran a science show around Australia not long ago, and one of the discussions was about getting charcoal ready on a BBQ. A science saavy guy thought of attatching a leaf blower or something to it, and reduced his charcoal "fresh, just lit" to "nice cooking embers" time considerably. He then went one step better, and used oxygen, like you say, and overall time was reduced from about 30 mins to under 3 mins !

Of course, he had to go one step further, and liquid oxygen was poured onto warm coals, and a lit ciggarette thrown on. He had managed to reduce bur time to 3 Seconds :eek:

Of course, he also achieved a 6-7 foot flame burst, and NO charcoal left to cook on. The pictures were impressive too. Dr Karl has a morning segment one day a week on TripleJ Radio here in aus. Others, you might be able to listen on the net, He works with CSIRO, and ABC, (part of which is JJJ) check out Australian Broadcasting Corporation (http://www.abc.net.au)

If you find Dr Karl's site, it has lots of other great stuff on it too.

[SMAG 12B/E5]

The furnaces work well. I use propane and temporary firebrick enclosures. I have three sacks of commercial mix waiting for some spare time to produce a cylindrical furnace. I have melted brass once and aluminum numerous times. I cast fuse blanks for 60mm mortar rounds and will produce several firing grips for RPG-2 type units and fuse bodies/adapters for rifle grenades. The machine waste aluminum is recycled into pyrotechnics and blast-enhanced HE.
Your original use of the copper for shaped charges might be easier if you considered spinning the cones from sheet copper over a form. A homemade spinning machine should not be difficult to fabricate and will produce many identical cones, cheaply.

[Jhonbus]

A compressor wouldn't be my first choice for furnace air supply; most compressors are designed to give a high pressure but probably not a high flow rate. Something like a garden leaf blower would be better.

[klassasin]

We have tried leaf blowers and what not. For us the compressor worked best.

[Microtek]

Having read James Yawn's site on rocketry, I decided to try out his idea of casting nozzles into Al bodies. He uses a large steel can fulle of charcoal and a vacuum cleaner to blow air into a pipe in the bottom.
So, I obtained a steel can ( 25-30 cm diameter, 40 cm high ) and made a 2.5 cm hole near the bottom. A 20 cm long steel pipe ( 23 mm diameter ) was inserted through the hole going 3 cm into the can. A paint stripping gun was attached and the can was filled to a depth of ca 8-15 cm with charcoal.
Starting the paint stripper ignites the coal after 2-3 minutes and after a further 5 min, the furnace is hot. I melted aluminium easily, then copper. Then the thin ( < 1 mm ) steel pipe I was using for holding the copper, crumbled. I think the metal was oxidized rather than melted so I upgraded to heavy-duty water pipe ( wall thickness ca 3-4 mm ) with an endcap. When placed ca 2 cm in front of the end of the air pipe, it went to dull red in about one minute. After another it was bright yellow ( when looking down into the pipe ). Then after yet another minute flames started jetting out from the water pipe, and when I lifted it out of the furnace, I found that the entire endcap and a good 3 cm of the pipe had melted off!!! That means more than 1500 C ( the water pipe IS iron; I tested it for magnetism ).

[the Jackal]

Assuming you melt the copper, how long would you guys estimate it would stay liquid once it was taken out of the furnace?

[Anthony]

Aside from the ambient temperature, that would depend a lot on how much molten copper you have - small amounts would cool disproportionately faster than larger amounts.

[Mr Cool]

Haha, I see someone else has discovered the joys of paint stripper guns and charcoal, Microtek!
It's a good combination, isn't it? :D

I've managed to melt the end off a wrought iron bar that's just slightly over 1/2" thick in a minute or two.

[Microtek]

Yes indeed Mr Cool, the only problem is that the flowrate is very low ( on my paint stripper at least ), much less than a hairdryer. I can see that a lot of CO is produced so if I could up the flowrate without lowering the temp of the airstream.....
This would just lead to another problem: What kind of accessible material could you use for crucible ?
BTW, I stated that my furnace must have gotten to at least 1500 C as it melted the iron pipe. I later realized that this is not neccessarily true as some alloys melt already at 1200 C ( But I also found some molten sand and stones in the ashes, so it does get very hot ).

[Jhonbus]

Graphite comes to mind. You can buy graphite crucibles all over the net, a quick search brought up
http://www.legend-reno.com/minesupply/m58.htm
No pricing from my quick glance but it shouldn't be too hard to find out. I would estimate about $50 for a 400ml one, maybe.

[edit] ah, you just click on the links for the prices. which are even better than I thought.

[Tuatara]

I don't know anything about this book, except whats on the web page, but it might be a good starting point.

Making Crucibles by Vince Gingery (http://www.lindsaybks.com/dgjp/djgbk/cruc/index.html)

[Jhonbus]

Probably a good book. From what I've heard the Gingery books are really detailed and helpful.

(looking at that crucible-making page reminded me I had a dream last night in which I was in a pottery class taught by Hitler!)

[GibboNet]

Totally off topic (sorry)......

But I had to ask.... What does Hitler teach in a pottery class ? :eek:

[Jhonbus]

Well the class had had to make business cards for homework (nothing to do with pottery I know) I was handing mine in, and put it on the desk. Then I'm pretty sure he was about to shout at me but my alarm woke me.

[Jacks Complete]

Sorry to re-open an old thread (I only just worked out how to see them with the drop-downs, rather than the searches) but I thought you might like to hear my experiances.

I have built both a Propane furnace and a charcoal knife forge.

Link to picture of a knife forge (http://www.rubbertreeplant.co.uk/images/110.jpg)

This looks very like the knife forge. The blower on mine is one of those ones you get for inflating mattresses, and is mains powered. I tried the battery ones, but they were crap. This puts through so much air that if I restrict the airholes, the remaining ones blow any of the smaller bits of flaming charcoal all over the place! It takes about ten minutes to get from just lit to embers hot enough for forging. So far, I have made some medeaval type bodkin arrow heads, which I learnt at a craft fair/exhibition, and was why I build the forge, and played about cutting thick steel bars, etc. I also made a rather neat skinning knife, but I can't make it hold an edge fine enough for my likeing.

The propane furnace is quite scary, but mostly for the capacity for things to go very wrong very easily and quickly. I made the mistake of being a bit tight and using a large steel bean tin to melt down some .22 and 7.62mm brass, and so, with my lovely tongs, I lifted it out, only to get molten brass pissing all over the floor (Yes, do this outside!) which I had to break free with a hammer after it had cooled. By the time I got to the mould (two paces) I had lost 90+% of the brass. I turned it all off, and came back four hours later. The furnace was still too warm to lift without gloves! Turns out the heat and flame had turned the whole tin into "scale" and it had cracked when I lifted it.

If anyone wants any info on this stuff, there is loads on-line. The Primal Fires message board seems to have disappeared, the plans I used for the furnace were from here (http://www.aphtrading.co.uk/pages/apage2.htm) and here (http://www.reil1.net/Furnace.shtml) . The first one is UK, the second is USA. You can also ask me, thought I have only limited experiance, as I just followed someone else's plans.

Edit: Changed the picture to a link, as it is quite big.

[Jacks Complete]

See http://www.roguesci.org/theforum/showthread.php?p=69106 for related news.

[Marmaloon]

I noticed you said you were planning on making cones for shaped charges out of copper. Have you considered looking into metal spinning, perhaps with a modified wood lathe? It might be easier to come up with product that way.

[Dave the Rave]

JC, nice forge, but isn´t quite swallow ? I mean, when the blower starts it doesn´t spills the coal and ashes out ? It looks like an AL trays, isn´t ? And by the way, why you "was" Jack´s lack of surprise ?

About the purpose of the topic, I agree with marmaloon, maybe making the cones by melting the copper isn´t an good idea, mainly because it´s very dificult to control the thickness and homogeneity of the cone, which will render on irregular and useless blast jets.

The idea of roll an factory made copper plate on an hardwood cone sounds much more easy and feassible. The resultant cone will be more regular and could be welded with an regular spot welder, and I believe that could be less energy consumible and more readily mass produced.

[Jacks Complete]

I was "Jack's Complete", but I got re-named as my ' was crashing something on the torrents - I was the only person with a decent post count with one, so I got re-named "Jacks Complete", which is a shame, but at the same time a relief, since I couldn't log in, and thought I had been shitcanned!

Anyway, I'm still here :) Yes, the forge is quite shallow. I used a stainless steel pan for turkeys, etc. for mine, and it does work, though the heat-up time and lack of anywhere to keep it really hampers me. Once running, you can heat a fair bit of steel. It will do something the size of a machete, though a lack of steel stock is a real hassle. Mine has a far higher wall than in the plans (though it is hard to tell in that picture), as I decided it was too shallow for what I wanted, which was to do lots of different things. Mine is sat on top of a safe I broke open, as it is too low otherwise, and you can't work long bits easily.

Having said all that, I don't use it often. The latest refinement I want to add is a notch so I can leave the blower on, and adjust the airflow with a collar ring over the notch. I found the little outcut bits too light, as they tend to shift during use, so throttling that way doesn't actually work well.

If you have a metal lathe, you can make a form and "spin" the metal over it as it turns. Just mind how you get dragged in if you slip, as the lathe won't stop unless you hit the button, and it will rip your arm off first. Copper is very soft, so it shouldn't be hard, as it were.

Another way, if you have soft copper sheet, would be to hammer a form into the sheet over the tyre hole in your anvil, and form like that. You drive it straight and it should be ok.

[Dave the Rave]

JC, what I was thinking was on cut an coned shape on the copper plate and then hammer it on the hardwood cone, not use the copper cable and turn it around the form, which is an nice idea...

But there is another one, an fussion between your ideas of the lathe and the hammer.

There is an piece to adapt on the lathe which is caled the tailpipe, and its an steel solid cone, made on several diferent diameters. One can made an female mould on hardwood, which adapts on the shape and size of the male tailpipe cone.

The idea is use the tailpipe and the hardwood mould as an matrix to pressure form the cone on copper plates, and then, with scisors, cut off the excedent material. We can use something like Brainfever´s jackpress (http://www.geocities.com/brainfevert/press.html) to give the necessary force.

Anyway, Gingery´s Books are the best, and he is an conosseur on his metiers, knowing the tools of the trade and writing easily about his job. I´ll look for an copy of that particular book, but on The Forum FTP we can found the other books he wrote.

Graphite crucibles are made of highly pressed graphite powder and then turned and drilled till the shape of the crucible is achieved, but I believe that isn´t necessary to use one to melt copper.

From what I could find, we can make an crucible to the melting of the copper from steel, which can withstand the temperatures used to melt the copper, using one piece of pipe and an small disk to make the bottom of the crucible. It can be arc welded with an double line as we can see here (http://www.backyardmetalcasting.com/crucibles.html).

Another idea is to make the crucible from an ammalgam of powdered graphite, fire cemment and powdered asbestus, but I believe that only us, the inhabitants of 3th world could use high cancerygenous substances like asbestus to make the crucible, the civilized world must stick with powdered graphite and fire cemment, which must be dilluted prior to mix with graphite.

We can use, maybe 10 parts water to one part cemment, as it will only be used as "bind" to the graphite, which is then added till it gets an almost liquid doughnut concistency and it´s then pressed on an 2 pieces wooden mould to form the casing, just do make the pattern of the crucible, and put it to cure. After that, the piece can be baked and used as an regular crucible.

Its the same way they make porcelane dishes and will work nicely.

What do you think ?

[Skean Dhu]

I have the Complete book set from lindsay books on making your own metal shop from scrap, book one is about making your own charcoal furnace and I also own the book on making crucibles. I'll scan those in and up them to the FTP after I get done with exams.
http://www.backyardmetalcasting.com/
is a good site on making refractory, various furnaces, fuels, burners and casting in general

If I have time and you guys think you'd use them I'll scan the rest of the 7book series.