Crucible furnace for melting bronze.

[Jim Ledger]

I've been reading up on building a crucible furnace in order to melt and cast bronze fittings. Although casting involves a lot more than melting metal, it is the necessary first step, after which the patternmaking and casting can follow.

There's quite a range of designs available, from charcoal fueled coffee can machines useful for making jewelry, on upward to gas fired units capable of melting more bronze than you might want to handle without an overhead gantry.

It might be prudent to start simple and make a fairly basic unit to get started, however, the more sophisticated designs incorporate more features that make handling the molten metal a much safer operation.

This design is taken right from David Gingery's book "Building a Gas Fired Crucible Furnace". It seems a well thought out design and I see little reason to modify it.

These various bits of sheet metal will form the body of the furnace itself. The round bits are 16 ga. black iron, rolled at the sheet metal shop to close to their finished diameter. They're heavier than called for, but that's what was available. There's a bit of exhaust pipe from an auto parts store and some galvanized stuff for a temporary form.



T'ain'tmuch, but it's a start. I'll put up a few photos as things progress.

[Lew Barrett]

Jim, I was there when Sam mailed you his manual. You're taking this quite seriously!

[StevenBauer]

Didn't Norm use a popcorn tin for his?






Steven

[Jim Ledger]

Jim, I was there when Sam mailed you his manual. You're taking this quite seriously!

And I read it a couple of times at least, although this is not the design in Sams book.

Steven, a popcorn tin will work. But this will be better.

Coffee can, popcorn tin, sheet metal, whatever you use here is only the outer shell. the real work of insulating will be done by two or three inches of refractory cement applied to the inside of the shell. Here, three plywood forms are being used to coax the metal into a proper round shape. The furnace body consists of three parts, a base which holds the crucible of molten metal, a center section which lifts up to allow the crucible to be grabbed from the side, and a top which can swing aside to allow metal to be placed in the crucible for melting.

An attempt must be made to get the three parts as nearly round and alike as possible so they stack atop one another neatly.

[kc8pql]

Jim, here's a link you may find interesting. Back in the late 60's early 70's I helped out in this fellows original foundry. The furnace was an up-sized version of what you're building. The link has some photos of his latest Foundry.
http://bluefieldfoundry.com/about.html

[PeterSibley]

Jim ,here's another site for you ............one I can thoroughly recommend !

http://home.iprimus.com.au/cmckeown/foundry.htm

I've learned a LOT from this one , the man really knows his stuff .

[Jim Ledger]

KC, thanks for that. What a fantastic opportunity, working with somebody doing interesting creative work like that. What led up to you working there, if you don't mind my asking?

Peter, that's great. His new furnace is based on the design I'm using, but built much heavier with some interesting modifications, a set of wheels for one thing. I'll have to give it a good read, there's a lot there. It's good to see a finished example as the book has no photos, only diagrams. Thanks

[PeterSibley]

For your interest Jim ,here are couple of photos of mine .It shares ideas with the Gingery but the lifting mechanism is a little different and lets me stand further away and behind .They get hot ! (details if you need them .)

[Jim Ledger]

Peter, I remember you posting those pictures of your furnace in a previous thread. I'd be very interested in some details if you don't mind, particularly the lifting mechanism. What did you use for the rollers? Gingery used sliding door rollers, but I thought that that could be improved upon and I see McKeown (if that's his name) used ball bearings for his. Both of these machines look bigger than the one I'm putting together. Mine should handle a #6 crucible, which should be enough for any fittings I might need. I take your point about the rear handle, letting you stand behind and further away, however, it makes the machines footprint much larger and harder to store in a limited space. What fuel are you using, and what kind of burner? I was intending using a fairly simple propane burner. I see that there are many complicated burner designs available which are probably more efficient but that would be a easy thing to upgrade in the future should the simple design prove inadequate.

It's funny, I thought Gingery went overboard making the fan for the burner from sheet metal when theres so many inexpensive blowers available that would do the job. Then I looked at that website and see a blower custom cast in aluminum, shell, rotor and all. A beautiful thing it is too.

[PeterSibley]

Jim ,as you guessed the large square section at the bottom houses 4 x bearings (same on the other side) .They are used alternator bearings from my local repair guy .A valuable resource ...things that are no good at 3000rpm are just fine at 10 .

The pivot arm is obvious ,then a loose swing section.It's balanced to be an easy lift .On the Gingery , if I remember rightly you have to pull the arm over the top of the furnace ...some thing I didn't want to do .Yes it does have a bigger footprint but perhaps you could modify my idea and add a some ballast to the lifting end .

As you can see I can lock it open one handed .Mine will take an A20 crucible but I haven't worked out how to do it by myself (safely ) ,so I stick to an A10.The body is lined with Thermal Ceramics K26 light weight bricks ,the lid is vermiculite and cement fondue (high temp cement ).It has lasted very well ..3 years& 60 odd firings with minimal wear ....cheap too !

The lid lifts up and swings sidewaysf to add metal or adjust things .There is a cam operated lift mechanism which unfortunately isn't visible in the photos , you can see the pivot at the top though .It is very useful ,especially topping up a crucible as the metal settles .

Fuel is LPG ,although I think Cameron McKeown's oil burner (it in there at the bottom of the main page ) is a very good idea. I'm going to do it myself .My burner design came from this site ,
http://www.abana.org/ronreil/design1.shtml
( I think ....it was a while ago ,any local potter can help you here .)By the way ,my burner doesn't use a blower .

Anything else , just ask .
Peter

[Tylerdurden]

I have one but it is buried now. If you can afford it buy some commercial crucibles. I still have a couple left and they do stand up better. Problem is you will need to fab tongs to fit as the do it yourselfs are not the same.
I had one let go when I first started so I switched and haven't had a failure since.

Make sure you spend money on sound safety equipment and apron.
Even with all the gear the first melt of the season gets me nervous.

I forgot to add, if your serious get into lost wax method. Its the trick way to go for small parts.

[PeterSibley]

I have one but it is buried now. If you can afford it buy some commercial crucibles. I still have a couple left and they do stand up better. Problem is you will need to fab tongs to fit as the do it yourselfs are not the same.
I had one let go when I first started so I switched and haven't had a failure since.

Make sure you spend money on sound safety equipment and apron.
Even with all the gear the first melt of the season gets me nervous.

I forgot to add, if your serious get into lost wax method. Its the trick way to go for small parts.

I agree wholeheartedly about the safety gear ,leather welder's coat and a long leather apron , gloves and face shield .Ventilation is also essential ...there are some strange compounds formed at furnace temperatures .

As to lost wax ....maybe , I can make most anything you would need faster and in multiplies with sand and a well made pattern .As a tip I recommend acrylic sheet as a brilliant material .

For me metal shrinkage has always been the worst problem to solve .

[Tylerdurden]

I agree wholeheartedly about the safety gear ,leather welder's coat and a long leather apron , gloves and face shield .Ventilation is also essential ...there are some strange compounds formed at furnace temperatures .

As to lost wax ....maybe , I can make most anything you would need faster and in multiplies with sand and a well made pattern .As a tip I recommend acrylic sheet as a brilliant material .

For me metal shrinkage has always been the worst problem to solve .

For small intricate parts that is the best way I have found. As far as shrinkage goes I have found the formulas to be lacking at times.
Practice makes it easier but I mess it up on more than a few occasions.
I had a long term GF whose father was a jeweler, he showed me the lost wax method and then I bought several books on the matter. Once you start doing it you will enjoy doing it. I no long have all the supplies but I made a simple vacuum fixture which served me well. Would not take a lot to start doing it again.

[kc8pql]

KC, thanks for that. What a fantastic opportunity, working with somebody doing interesting creative work like that. What led up to you working there, if you don't mind my asking?

I was fresh out of art school, sub-contracting finish carpentry to eat and doing some photography to feed the soul. I did a Dorothea Lange inspired series of B&W photos of what goes on every day on a construction site that came out pretty well. One of the sculptor/partners in the foundry saw them in a gallery and asked if I'd be interested in taking some photos of their casting process to hang in an upcoming sculpture show they were preparing for. I agreed and one thing led to another.

[S B]

IF you need to cast bronze "on the cheap", this is probably the most cost effective furnace you can make. Line the inside of a galvanized garbage can with 2" of Kaowool or Fiberfrax blanket, attach with ceramic buttons,mushroom shape with a hole in the stem,and wire. Cut vent hole in bottom,top eventually, and hole in side, angled to get spiral action from flame. Build platform from brick, top layer IFBs ,23s good enough. place 2 hard brick in the middle to hold crucible. Place loaded crucible on hard brick, invert garbage can over crucible,insert burner, fire up, when melt completed turn off burner, lift can off "carefully" and carry on as usual.

[PeterSibley]

For small intricate parts that is the best way I have found. As far as shrinkage goes I have found the formulas to be lacking at times.
Practice makes it easier but I mess it up on more than a few occasions.
I had a long term GF whose father was a jeweler, he showed me the lost wax method and then I bought several books on the matter. Once you start doing it you will enjoy doing it. I no long have all the supplies but I made a simple vacuum fixture which served me well. Would not take a lot to start doing it again.

I have to agree with you with small or intricate parts .There is professional investment caster about 100 miles North of here that can do the most amazing work on an industrial scale .Cast threads ,accuracy to .5 mm ...the whole bit !

However for most work that I have had to do ,things like my windlass parts and straps for wood shell blocks I am able to achieve acceptable results and very much faster .There is a place for both techniques , indeed the company I mentioned has both methods side by side .

[Tylerdurden]

I guess my point is its worth trying just for the experience. When one needs it ,it will be a skill already saved.

[Jim Ledger]

Peter, you've got me rethinking the naturally aspirated burner option. Sam Johnson doesn't like them, but there seems to be some pretty good designs available. Check out the T-Rex here..http://www.hybridburners.com/products.html

Much more efficient and quieter. I wondering what kind of inlet is used into the furnace itself? The design calls for a 2 1/2" tube for the fan blower, but this is probably much larger than would be needed for the thinner gas burners. any chance of a close-up photo of what you're using?

Mark, I couldn't agree more about the safety issue. I picked up a #6 silicon carbide crucible, can't see making my own. for gloves I got a pair of THICK asbestos gloves that come about to my elbows from a watch making firm that was going out of business. they did investment casting, but most of their gear was on an industrisl scale, but the gloves were a good score. Thich shoes, no problem. Leather apron, I've got a big piece of hide that'll do to make one, and face shields, have a few.

The lost wax seems interesting and I'd ike to try it eventually, but I'm going to start with sand casting, as most of the parts I want to make are of a fairly good size. I'm going to use Petrobond, and bypass the green sand learning curve while I figure the rest out.

KC, just wondering, if you had the initial experience in casting, why didn't you do your own fittings on the boat? Or maybe I don't want to know?

[kc8pql]

KC, just wondering, if you had the initial experience in casting, why didn't you do your own fittings on the boat? Or maybe I don't want to know?

Time and expense. I spent between 7 and 8000 hrs. building the boat. I imported most of my bronze fittings from Toplicht before the price of bronze went through the roof and the euro was at 75 cents. For the parts I did need to cast, it made more sense, in both time and money, to just make the patterns and have them cast rather than going to all the trouble of setting up a foundry.

[Tylerdurden]

Jim, the apron is essential. I did most of my pours on a sand pit I made just for that purpose with quick escape routes on either side.
If you can cover your run area all the better as wet sand an slag can cover some good distance when steam launched.

Have fun with it, I know I did and the neighborhood kids would come to watch whenever they heard the foundry start to roar.
I would not bank to hard on atmospheric burners unless just pouring aluminum. Speed of melt is essential as you tire fast near all that heat.

[PeterSibley]

Well, as far as non blower burners go ,no problem .I can melt phosphor bronze easily enough ,my usual is manganese bronze .What we call HBT2 , I don't know your US standard designation .The slowest thing about melting metal is heating the furnace itself ,mine is quite a large structure , lots of brick and other ceramic .For me the first melt takes 60 to 70 minutes , after that 20 minutes per 8 kg shot .
Jim ,I'll try to find a photo of the burner or I'll take one ..........it's not as pretty now as it was !

As to safety gear , it sounds like you are doing it well .The only thing I'd suggest is that the apron goes down very low at the front .You don't want molten metal down the tops of your boots.You can buy gaiters from a welding supply shop too .

[PeterSibley]

Jim ,these are drawings of my burner from the McKeown site.
http://home.iprimus.com.au/cmckeown/139SHT001.gif
http://home.iprimus.com.au/cmckeown/139SHT002.gif
http://home.iprimus.com.au/cmckeown/139SHT003.gif
About half way down the main page ....Burners , a few photos too .

as to sand , yes petro sand would be much better for you .We are able to use greensand with our mild (non freezing) temperatures .It's probably a better sand too .I wonder if you will need a muller ?

[S B]

Well, as far as non blower burners go ,no problem .I can melt phosphor bronze easily enough ,my usual is manganese bronze .What we call HBT2 , I don't know your US standard designation .The slowest thing about melting metal is heating the furnace itself ,mine is quite a large structure , lots of brick and other ceramic .For me the first melt takes 60 to 70 minutes , after that 20 minutes per 8 kg shot .
Jim ,I'll try to find a photo of the burner or I'll take one ..........it's not as pretty now as it was !

As to safety gear , it sounds like you are doing it well .The only thing I'd suggest is that the apron goes down very low at the front .You don't want molten metal down the tops of your boots.You can buy gaiters from a welding supply shop too .

Why are you heating 60 to 70 minutes of deadload at 1/4 million BTUs per hr? Must have money to burn?

[dennisbur]

You could also get Stewart Marshall's book on how to build small cupola furnaces. http://www.rockisland.com/~marshall/index.html A small 7" furnace will give you 16lbs. of bronze every ten minutes.

[PeterSibley]

You could also get Stewart Marshall's book on how to build small cupola furnaces. http://www.rockisland.com/~marshall/index.html A small 7" furnace will give you 16lbs. of bronze every ten minutes.

If you can get the coke ...which I can't .I wish I could ...not for bronze , I prefer a furnace , but for cast iron .

[PeterSibley]

Why are you heating 60 to 70 minutes of deadload at 1/4 million BTUs per hr? Must have money to burn?

Agreed , but I haven't found a faster one the size of mine .A smaller one is faster...less mass to heat to 1300 C ....but after the first "wasted " 45 minutes it sure is good .

[johngsandusky]

I don't mean to change direction on a fun thread, or deprive Jim of the opportunity to build a furnace. But, Jim, I have an electric ceramics kiln that might do the trick. I bought it at a tag sale a few years ago, never did use it. Let me know if you want it, I'll help you put it in a truck.

[S B]

Agreed , but I haven't found a faster one the size of mine .A smaller one is faster...less mass to heat to 1300 C ....but after the first "wasted " 45 minutes it sure is good .

Soakin' the heat out of the brick?

[PeterSibley]

Soakin' the heat out of the brick?

Suckin' out the cold .

[Jim Ledger]

I have an electric ceramics kiln that might do the trick. I bought it at a tag sale a few years ago, never did use it. .

Most generous of you, John, but I'm not sure that a kiln would be the best way to go. If it reached the 2000+ degree temp required it would probably take all day as the requirements for firing clay and melting bronze are much different, the clay needing a long, slow bake in a large oven, while you want to melt bronze fast in a faily compact space. There's also the matter of opening a kiln at the high temperature, it's probably not something that's done firing clay, whereas bronze smelting requires it.

Just out of curiousity, what's the amperage on a thing like that?

[S B]

Most generous of you, John, but I'm not sure that a kiln would be the best way to go. If it reached the 2000+ degree temp required it would probably take all day as the requirements for firing clay and melting bronze are much different, the clay needing a long, slow bake in a large oven, while you want to melt bronze fast in a faily compact space. There's also the matter of opening a kiln at the high temperature, it's probably not something that's done firing clay, whereas bronze smelting requires it.

Just out of curiousity, what's the amperage on a thing like that?

An open kiln is all radiation heat, doesn't travel far.

[andrewe]

All good stuff here,from people who have hands on,thanks. I bought a CD from www.myhomefoundry.com which gives a complete design and all the other bits one needs, plus manuals on `how to´. It is close to the top of my projects list. One point, it shows a venturi in the burner (as in the drawings above) but uses a blower (vacuum cleaner) If blown, there is no need for a venturi. Better would be some small vanes to promote swirl. Control was via an adjustable reducing valve for the propane and a waste gate for the air ( presumably so as to avoid back pressuring the vac. cleaner) It is all back yard, low precision engineering but looks (to my untrained eye) close to the artists foundries I visit. Heat time around 45min. for alu.
Andrew

[PeterSibley]

Agreed , but I haven't found a faster one the size of mine .A smaller one is faster...less mass to heat to 1300 C ....but after the first "wasted " 45 minutes it sure is good .

Actually Jim and SB , there a note about an oil burning furnace on the McKeown site ,

http://home.iprimus.com.au/cmckeown/...ed_furnace.htm

that has some info on an oil fired furnace .He reports 1300C in 15 minutes on a furnace about my size .Remarkable and it's the next foundry project ........after ,the biodiesel processor and roof on the new cabin . it uses used hydraulic oil .Definitely worth looking at .
One thing to remember though is that very quick increases in temperatures reduce crucible life (according to the bloke at Thermal Ceramics ) and they are $100 each !

[johngsandusky]

Jim, I'm not sure. It's buried under sails and stuff in the storeroom. I don't recall a lable on it, might be homebuilt. It's steel, with a cover, electric coils, and some kind of insulation. I've seen instructions for building smelting kilns that way.

[S B]

Actually Jim and SB , there a note about an oil burning furnace on the McKeown site ,

http://home.iprimus.com.au/cmckeown/...ed_furnace.htm

that has some info on an oil fired furnace .He reports 1300C in 15 minutes on a furnace about my size .Remarkable and it's the next foundry project ........after ,the biodiesel processor and roof on the new cabin . it uses used hydraulic oil .Definitely worth looking at .
One thing to remember though is that very quick increases in temperatures reduce crucible life (according to the bloke at Thermal Ceramics ) and they are $100 each !

Thermal shock will take its toll on the refractory, but wasting expensive energy to slow down the inevitable, seems like the wrong way to look at the problem. There is a small foundry, just outside St. John's, that fires up with charcoal, make their own.

[PeterSibley]

My next will be fired with used fryer oil . .Fast and it will smell good too !

[S B]

My next will be fired with used fryer oil . .Fast and it will smell good too !

Chicken and chips, with a side order of castings

[Jim Ledger]

As with most infrequent welders, my first efforts after a period of absense leave much to be desired. Once the projects finished I'll find myself starting to get back in the groove, as much of a groove as there ever was, anyway.

Ugly welds , but serviceable, here are the three parts of the furnace body, the base, body and top.

[LLaver]

I spent aprox 12 yrs as a jeweller and did (still do) a lot of lost wax carving and casting. If you are only doing small items then lost wax is easy but for larger items sand is simpler and quicker.

Lost wax has the advatage of excellent detail down to a tenth of a millimetre but is slow and expensive compared to sand.

I always used either an induction coil or a torch for melting metal but the torch (oxy LPG with a melting tip) is way cheaper. and can melt 1/2 kg (bit under a pound) in a few minutes in an open crucible. I have heard of people making their own induction coils but I am not that brave/smart.

Lee

BTW induction coils are really cool(hot) and fast.

[emichaels]

Interesting thread ! I was wondering if there was a significant advantage to using a gas fired crucible vs an oil fired one.

Eric

[Jim Ledger]

Interesting thread ! I was wondering if there was a significant advantage to using a gas fired crucible vs an oil fired one.

Eric

As I understand it, the usual practice is to start an oil-fired furnace on gas and bring it up to a certain heat, then switch over to oil. This is to properly vaporise the oil for combustion. Why this should be, I'm not sure, as my home oil-fired boiler seems to light up fairly regularly, from cold, with an electric arc to start combustion. However, a boiler oil gun is a much more sophisticated piece of equipment than most of the equipment found on melting furnaces. The gas burner I'll be using has no moving parts at all, compared to an oil guns fan, oil pump, sensors, electrodes, nozzle and circuitry.

No doubt the oil burner would be more economical to run on a commercial basis.

[emichaels]

Jim in Gingery's book does he go over oil fired furnace at all ?? It sounds like, from what you said, the gas burners are quite a bit simpler to make and probably to use also.

Eric

[Jim Ledger]

Davic Gingery wrote quite a lot of books on metalwork and casting, but in this book he describes the building of a particular gas burner design with a fan supplying a forced draft.

Some of the websites posted earlier in the thread by Peter Sibley show some interesting furnace projects, including some oil-fired units. I'm going to deviate from the Gingery design and use an atmospheric gas burner, which should create its own draft, eliminating the need for a blower.

[Jim Ledger]

[quote=LLaver;1910014]

Lost wax has the advatage of excellent detail down to a tenth of a millimetre but is slow and expensive compared to sand.

Lee quote]

Lost wax sounds very interesting and I hope to try it out one day, but for now, I'll stick to trying to cast in sand while I get a feel for the process.

This is a wooden flask, a two part box in which to pack the molding sand around the pattern. It was made as one box, then sawn around the center to produce two halves that fit closely together. The mahogany pieces screwed onto the ends are guides to accurately position the halves. The coves on the inside of the box are to keys to prevent the packed sand form falling out.

[emichaels]

Jim how large is that box, and what wood is suitable for the flask.

[Jim Ledger]

Jim how large is that box, and what wood is suitable for the flask.

That particular box is made of inch thick soft maple measureing 9"x9"x15" inside. It's a good general purpose size but the final dimensions were dictated by the size of the plank. The rule of thumb is to hace two inches of sand between the flask and the pattern. You can make flasks from pine, butted and nailed, or anything else you might have, so long as its seasoned. Flasks get used up after a while from spilled metal burning them, so I may have overdone this one a bit. No matter. I can see that using more than one flask at a time would be an advantage because once you have a melt going you can keep pouring into more molds. Odd sized or shaped pieces could have one-off flasks made, used and discarded.

[emichaels]

Jim who do you like to get raw bronze material from ??

[PeterSibley]

Great stuff Jim ..I cheated , I used a steel hot water cylinder as the basis for my furnace .Actually I've used them for quite a few projects ...my lead melter for the boat's keel( 5600 pound of lead ),the furnace and currently a biodiesel processor .$5 each from the tip , good steel ,1/8" thick in a huge variety of sizes !

It's amazing how my welding improves after a few days ! Smooth and pretty with a wonderful lack of blow holes .

As to that flask ,mate I'd have to varnish it .Mine get knocked up from off cuts of 4x2" and one difference is that I use x2 metal alignment pins welded onto a steel pad and screwed to the cope box ,the pin passing through a reasonably close hole in a section of angle screwed to the drag box.It helps me to lift things straight up away from a pattern .(in 2 dimensions ...not just one ).

[Emma56]

Jim I think that these burnners are the best on the market www.abana.org/ronreil/Hybrid.shtml

[Mrleft8]

Back in the dark ages, when I was a teenager, I took a class in casting. The blower on the furnace we had in that class was an old electolux vaccuum with the hose hooked up to the exhaust side, and run to a fitting on the base of the furnace. I seem to remember that there was a rheostat, but that could be my imagination improving reality....