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.

http://i104.photobucket.com/albums/m193/searover1916/furnace1.jpg

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?


:D



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.
http://i104.photobucket.com/albums/m193/searover1916/furnace2.jpg

[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 .)

http://pic40.picturetrail.com/VOL282/9443996/17245530/267594470.jpg

http://pic40.picturetrail.com/VOL282/9443996/17245530/267594479.jpg

[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 (http://www.rockisland.com/%7Emarshall/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 .:rolleyes:

[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 (http://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/oil_fired_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 .:D 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/oil_fired_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 .:D 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 .:D .Fast and it will smell good too !

[S B]

My next will be fired with used fryer oil .:D .Fast and it will smell good too !
Chicken and chips, with a side order of castings:D

[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.


http://i104.photobucket.com/albums/m193/searover1916/Furnacebody1.jpg

[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.

http://i104.photobucket.com/albums/m193/searover1916/flask.jpg

[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]

http://i104.photobucket.com/albums/m193/searover1916/Furnacebody1.jpg

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 :D.

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....

[johngsandusky]

I built a coal fired kiln in the back yard of my old house. Used firebrick and earth to seal and insulate it. A blow drier was the draft. I never did make a successful cast with it, but I did melt metal.

[Jim Ledger]

This is the castable refractory being weighed. You can calculate the cubic volume needed and mix just a bit more than needed. In addition, the water/refractory ratio has to be within a very close range, so weighing is a good method of insuring a correct mix. The butchers balance is surprisingly accurate, a teaspoonful of mix will tip it.

http://i104.photobucket.com/albums/m193/searover1916/weighingrefractory.jpg

Here the refractory mixture is being placed in the central body section of the furnace. The mix is extremely dry and gets tamped down to remove any air pockets. The sticks are spacers to keep the central form in position while filling the cavity. as it gets filled the sticks are withdrawn. The cardboard tube in the center of the form is a piece of Sonotube, primed with paint to reduce water absorption from the concrete. After the concrete sets the cardboard is removed.

http://i104.photobucket.com/albums/m193/searover1916/fillingmold.jpg

The filled section. After filling, the top is covered with a damp towel and left to cure for several days.

http://i104.photobucket.com/albums/m193/searover1916/filledmold.jpg

[PeterSibley]

Thanks Jim ...keep 'em coming !

[Jim Ledger]

Thanks Jim ...keep 'em coming !

Peter, tell me if any of this seems familiar.:D

This is the lid of the furnace, ready for the refractory to be tamped in. The wires are for reinforcement and to hold the refractory in place. A stock garage door handle was bolted on and the angle iron pieces will attach to a lifting mechanism. The pipe in the center is a temporary form and will be removed when the concrete sets. The central hole is an exhaust port where whats left of the flame will exit the chamber.
http://i104.photobucket.com/albums/m193/searover1916/cruciblefurnace1.jpg

Kind of like a Bundt cake, ain't it? Here it is all filled. The central body is finished, in the background. The studs poking out of the sides are for the lifting mechanism, also.


http://i104.photobucket.com/albums/m193/searover1916/Lid.jpg

[PeterSibley]

Looks good Jim .Mine has a cam mechanism down on the base operated by a 30" long handle (with a rod pushing upward ) that allows me to raise the lid about 1" then pivot out of the way .I can see we are looking in the same direction !

[Jim Ledger]

Looks good Jim .Mine has a cam mechanism down on the base operated by a 30" long handle (with a rod pushing upward ) that allows me to raise the lid about 1" then pivot out of the way .I can see we are looking in the same direction !
This design features a foot pedal that raises the lid, allowing it to swing out of the way.

Here's the lid, sitting in place on the center section of the furnace. The stand is starting to take shape, weld, grind, fill, grind, repeat.:D

http://i104.photobucket.com/albums/m193/searover1916/stand1.jpg

[PeterSibley]

Keep 'em coming Jim ! :)

What size crucible is this designed to use ?

[Egon]

As my wife has several electric kilns and a propane fired kiln used for firing pottery I find this furnace very interesting.

The furnace is a very close resemblance of the propane kiln only much smaller.

Are there any licensing conditions for setting up the furnace?

For us I had to build an all metal shed and the entire setup had to be inspected and certified before the wife could get propane hooked up.

It looks like a very nice furnace in the making.:D:D:D

In hindsight a large section of pipe may have been used for the outer casing if such was available. It's only that I have worked around large pipes that I mention this.

[Bob Perkins]

Hi Jim,

Looks good - I took the Bronze casting class at WBS two years ago myself. Our furnace looked nearly the same as yours. We used Propane with a squirrel cage blower for heat.

We had two furnaces for the class. Once worked great and the other seemed to never get hot enough. Me and another guy did a lot of debugging to see why the second furnace would not get hot - swapped the blowers, swapped gas bottles & regulators.. that didn't work.

Finally my stroke of genius - I figured the hole on top of the furnace was too small and we could not push enough air through the system. The furnace was acting a bit like a muffler. My quick test was to put a small rock under the lid to let the furnace breath easier. That was our problem all along. The furnace got too hot and we had to change to smaller rocks to get the right air flow.

Your furnace looks great - it is hard to tell from the pics, but the breather hole in the lid may be a little on the small side. So if the furnace doesn't get hot enough - add a small pebble under the lid or make the hole a bit bigger.

This even had Sam Johnson (Instructor) baffled for a few days until we figured it out. Looking forward to more pics.

[PeterSibley]

Yep ,It's a lot easier to make the lid opening larger and reduce than other wise .Mine is around 5" diameter on a slightly large furnace .I often preheat my metal by hanging it in the vent ...that probably reduces air flow considerably .

[Jim Ledger]

.

Are there any licensing conditions for setting up the furnace?

In hindsight a large section of pipe may have been used for the outer casing if such was available. It's only that I have worked around large pipes that I mention this.

This furnace will run on a portable 50 lb. propane tank and will be used outside, so there's no permanent gas hook-up, hence no inspection required.

Large diameter pipe could have been used, had some been available, and a means to cut it. However, there's no advantage gained with a heavy steel casing, as the insulating work is done by the refractory concrete.

Regarding the diameter of the vent hole in the lid, that's what the plans call for, and I assume it proved satisfactory on other units. This furnace will use an atmospheric burner which, I suppose, creates less draft then a forced air unit, so maybe a small vent might be sufficient. In the worst case, I could chip out the concrete in the lid and re-do it. Anyway, thanks for the tip, and I'll be aware of the possibility that the vent size might affect the performance of the machine.

Peter, the furnace will use a #6 crucible, with a maximum of 20 lbs of bronze, which is a lot more than I'd feel comfortable pouring.;)

[PeterSibley]

Peter, the furnace will use a #6 crucible, with a maximum of 20 lbs of bronze, which is a lot more than I'd feel comfortable pouring.;)

Yes , that's the size I use .I built my furnace to handle a number 10 (I think :rolleyes: ) but I have never felt comfortable with it , even though I have built various jigs and even a gantry overhead .There is something very intimidating about the idea of 40 pound of bronze going everywhere .:eek: I always work by myself .

I'm happy with the 6 and really fill it sometimes .Something that you may find useful is a heat shield on your lifting handle ....however you organise that .It lets you grab the thing closer to the load and gives more control .it stops your gloves smoking too :D.A disc if sheet metal is sufficient .

[Egon]

Just another though on safety equipment.

My wife has a pair of welders goggles with dark lenses that are used when when looking into the inspection ports of the pottery kiln. Something similar may be advisable but with lighter shade of lens when handling the hot material.:confused::confused::confused:

[Jim Ledger]

Just another though on safety equipment.

My wife has a pair of welders goggles with dark lenses that are used when when looking into the inspection ports of the pottery kiln. Something similar may be advisable but with lighter shade of lens when handling the hot material.:confused::confused::confused:

I don't think welders goggles are needed, but face protection certainly is. I intend using a welding helmet with a flip-up shade, which has a clear window to look our of.

Peter, I like the heat shield idea for the lifting tongs. Here's the gloces I picked up for twenty dollars at a liquidation sale of a watchmaking factory. Asbestos, I think, and quite thick. They come up to my elbows. The other gloves are for comparison.

http://i104.photobucket.com/albums/m193/searover1916/gloves.jpg

[PeterSibley]

They look great Jim ....don't breath the dust ! Actually I find welders gloves entirely satisfactory .Something that I have that is very good is a heavy leather apron that goes all the way to the ground (I had to get a local leather worker to make it for me ,I couldn't buy what I wanted off the shelf )....there is nothing like molten metal down your boot tops ...so I have been told .It goes with the leather welders coat .

[Jim Ledger]

Some progress on the stand today.

http://i104.photobucket.com/albums/m193/searover1916/stand2.jpg

[Jim Ledger]

In this picture, the lid-lifting mechanism can still be seen clearly, before being obscured by the furnace body.

The foot pedal, when depressed causes the pipe to raise about one inch. The lid will be welded and braced to this pipe. Raising the lid slightly allows it to be pivoted to one side, exposing the crucible inside the furnace. Metal can be added then, or dross skimmed off.

To answer the comments about the size of the exhaust vent being too small I'd like to point out that there will be an equal sized hole in the bottom of the furnace, primarily to allow the escape of any spilled metal. However, this hole will also help reduce the internal pressure in the chamber.

http://i104.photobucket.com/albums/m193/searover1916/frame3.jpg

[paladin]

Just as a thought ...about welders goggles.......
In the late 60's I had a box dropped next to my desk....a welding unit to assemble, made by Hughes......it would melt metal in a heartbeat as it was a laser welder and wearing welders equipment didn't work too well......I finally gave up and set up a TV set that I could see from the work station, used a small video camera, and got a set of polarized filters then adjusted them until I could see the work getting everything held in place, then trigger the laser with a foot switch from a guitar project....the tv would display a flash but not too strong for the eyes as it would blank the video screen first.....

[Jim Ledger]

Here's the last of the three furnace sections, the base, and the most complex, as it incorporates the burner. The burner nozzle can be seen here, in position, extending into the cavity. It's held in position within a piece of 2" pipe by six set screws.

http://i104.photobucket.com/albums/m193/searover1916/Furnacebase1.jpg

[Jim Ledger]

The base section of the furnace, ready for placing the refractory concrete. A piece of sheet metal has been welded on the bottom. There is a temporary form for the hole through the bottom. This hole is to allow any spilled metal to exit the furnace instead of solidifying in the chamber. The PVC pipe forms the hole through the refractory for the burner.

http://i104.photobucket.com/albums/m193/searover1916/Furnacebase2.jpg

[Eric D]

Jim,

I simply love this tutorial, thank you.

I really like the pictures of the stand and how you plan to address lifting the lid. EXCELLENT!!!

I also like how several guys who have done this are adding/checking in since it really does help to hear from other sides of this discussion.

thanks, can't wait to see what you do as the first cast.

[Jim Ledger]

Thanks, Eric, I appreciate the comments.:)

Here's the base section, all filled up. The escape hole is clearly visible in the bottom. This will be covered with damp towels for a few days, then the cardboard peeled out and the PVC withdrawn, leaving the burner hole through the refractory, into the chamber.

http://i104.photobucket.com/albums/m193/searover1916/Furnacebase3.jpg

[Jack I]

Make your furnace cheap and simple.
I was in Malaysia in 1970 in the Peace Corps. I worked with the Malays on their local brass handicraft. They cast nickelbrass.

The furnace was a hole in the ground 2' X 2' 3' deep. It had a 2" pipe or bamboo that came from the surface at 45 degree angle into the bottom of the hole. A blower or bellows was attached to this pipe. The hole was lined with brick. The bottome row of bricks stuck out about 1". This supported a steel plate that had a bunch of 1" holes in it forming and air chamber in the bottom of the furnace. The plate and the sides of the brick were covered with clay. The hole was 1/2 filled with charcoal a crucible full of brass and nickle was then put in the hole on top of the charcoal. More charcoal was dumped in the hole and into the crucible (charcoal acted as a flux along with a piece of glass from and old green Coke bottle added just before the pour.
The patterns were shaped out of wax and the mold was made by coating the wax with fine sandy clay and then an outer layer of clay with rice husks. These then were dried in the sun for a few days. The molds were then placed in the furnace on top of the charcoal. A piece of sheet metal was then thrown over the hole. The charcoal was lit and the blower or bellows started.The molds baked, the wax evaporated and the brass melted. The red hot molds were removed and then the brass poured into them.

This was simple and much better for them than the kerosine furnace that I built for them, and the sand casting that I taught them.

[S/V Laura Ellen]

Jim: Another great "real time" how-to thread.
Thanks!

[Jim Ledger]

Make your furnace cheap and simple.
I was in Malaysia in 1970 in the Peace Corps. I worked with the Malays on their local brass handicraft. They cast nickelbrass.

The furnace was a hole in the ground 2' X 2' 3' deep. It had a 2" pipe or bamboo that came from the surface at 45 degree angle into the bottom of the hole. A blower or bellows was attached to this pipe. The hole was lined with brick. The bottome row of bricks stuck out about 1". This supported a steel plate that had a bunch of 1" holes in it forming and air chamber in the bottom of the furnace. The plate and the sides of the brick were covered with clay. The hole was 1/2 filled with charcoal a crucible full of brass and nickle was then put in the hole on top of the charcoal. More charcoal was dumped in the hole and into the crucible (charcoal acted as a flux along with a piece of glass from and old green Coke bottle added just before the pour.
The patterns were shaped out of wax and the mold was made by coating the wax with fine sandy clay and then an outer layer of clay with rice husks. These then were dried in the sun for a few days. The molds were then placed in the furnace on top of the charcoal. A piece of sheet metal was then thrown over the hole. The charcoal was lit and the blower or bellows started.The molds baked, the wax evaporated and the brass melted. The red hot molds were removed and then the brass poured into them.

This was simple and much better for them than the kerosine furnace that I built for them, and the sand casting that I taught them.


Thanks, Alan.:)

Jack, that 's one of the things I like about the Forum, the varied experiences and diverse viewpoints that people offer. I'd love to have seen the casting operations you describe or hear anything else you might wish to add.

I could have made a much simpler furnace, charcoal fired or propane, but I decided on this one to start. As I'm learning as I go, there should be a certain predictability about the operation of the furnace, which, once learned, should be repeatable and controlable. This should allow me to concentrate on other aspects of the casting process without being distracted by the operation of the furnace. Besides, I love a gadget and am having a ball building the machine.

Here's a nice shot of the chamber, looking down into the base and center section. The inlet for the burner is in view coming in the side, the safety hole in the bottom.


http://i104.photobucket.com/albums/m193/searover1916/Furnacebase4.jpg

[Jim Ledger]

The three sections of the furnace, sitting on the stand. The L-shaped arms that will raise the center section and top have been placed temporarily in position. These arms will attach to studs on the center section and travel vertically on the roller bearings that can be seen on the rear supports..

http://i104.photobucket.com/albums/m193/searover1916/Stand4.jpg

[PeterSibley]

How much will the centre section lift Jim ?

[Jim Ledger]

How much will the centre section lift Jim ?

That going to depend on the lifting handle and linkages, but the theoretical maximum travel is about ten inches. I said earlier that the furnace would fit a number six crucible, which is what I'll be using to start. The furnace body, lifting ten inches, should permit the handling of up to a number ten crucible, the equivalent of over thirty pounds of bronze. There might even be an advantage to using a large crucible, as there would be less space to heat, more flame, less hot air.

Something to be going on with. These are plinth blocks being made out of refractory material. One goes in the bottom of the chamber, above the safety hole with the crucible sitting on top. The channels allow any molten metal in the chamber bottom to reach the safety hole. The refractory is a difficult material to mold well because it's mixed up very dry and crumbly and doesn't lend itself to a smooth finish.

http://i104.photobucket.com/albums/m193/searover1916/plinthblocks.jpg

[PeterSibley]

That material looks very similar to the cement fondue /vermiculite mix I used for my lid and base Jim .

Not a bad idea ...I need a few new plinth blocks ...my current silicon carbide one is VERY dodgey ! (If the truth were know a complete rebuild is in order ...but I keep putting it off for just a few more firings ).

[Mrleft8]

As usual, very well done Jim! How'd the bandsaw blade(s) work?

[Jim Ledger]

The bandsaw blades worked fine, Doug, as you can see. Being able to easily cut steel angle opens up a whole new world of possibilities. I used to use aluminum for a lot of things because it cuts with carbide tools and welds easily. Steel's a lot cheaper and easier to obtain and often looks better, what with the rust and all.:D

Aaaaaaaaaaaanywayyyyy......

I'm not happy.:mad:

Here's the mechanism for raising the center and top section, built as per specifications, and hastily assembled for a trial. I expected a bit of tweaking to get things to work smoothly, but from the initial trial I'm not sure that tweaking will be enough. We'll see, but it seems a bit flimsy, and the bearings won't be up to the task for long, I'm sure

http://i104.photobucket.com/albums/m193/searover1916/Closed.jpg

This is the open position, showing the crucible inside. It could be that welding the top to the support pipe might steady things up somewhat. I'll report further as things develop.

Might be a good time to go for a sail, I'm thinking.

http://i104.photobucket.com/albums/m193/searover1916/Open.jpg

[PeterSibley]

So ,it's just generally flexible Jim ? I used all RHS for mine as it is far stiffer and does not twist at all .Everything 4mm wall 3x1 1/2 ...over the top of course but my second hand dealer sold me a full length at a very good price . Seeing it never gets moved weight is nor really a problem.

[Jim Ledger]

So ,it's just generally flexible Jim ? I used all RHS for mine as it is far stiffer and does not twist at all .Everything 4mm wall 3x1 1/2 ...over the top of course but my second hand dealer sold me a full length at a very good price . Seeing it never gets moved weight is nor really a problem.

Not generally, Peter, the stand itself is quite rigid, but the lifting handle leaves a lot to be desired. It's much to flexible, but that should be an easy fix. A large part of the problem seems to be the bearings. Sliding door replacement bearings were what the designer called for but they are very sloppy in this application, with this much weight. I found these V-groove bearings for replacements which should perform much better. When in doubt, overbuild.

Now for a little retro-fitting.

http://i104.photobucket.com/albums/m193/searover1916/bearings.jpg

[PeterSibley]

Good to see another post Jim .Those v groove bearings look interesting , I've never seen them before .Mine are quite large (about 1.75" OD ),courtesy of my local auto electrician ,used and no good for motor or alternators but just fine at very slow speed .I think I used 24 ...all free !:)

[Lew Barrett]

Far from the sophistication that this thread has brought out, but along the same lines, here's my article on Sam Johnson, just released. Page 68.I hope you enjoy it.

[Eric D]

Jim, can you show a close up of exactly where these bearings are utilitzed?

Sure look like they should do the trick though.

when is the first casting?

And is that cat boat started yet????

[Lew Barrett]

Including the link to the issue with the article about Sam would have undoubtedly been useful. Here it is. Page 68.

http://www.classicyachtmag.com/currentissue

[C. Ross]

Hew Lew I just read that article last night.

Slight thread drift... Another nicely done article and issue...classicyachtmag.com is definitely worth a read. Lew's profile on Sam, but also nice photography and writing about a couple of boat shows and individual boats.

[Lew Barrett]

Thanks Cris. I always can count on you:)

[Jim Ledger]

Time to light this candle, as they say.:D

I've reworked the whole raising/lowering mechanism, changing the design somewhat and fitted the improved bearings.

Today I'll be reassembling everything and firing it for the first time. The idea is to slowly increase the heat up to melting temps, in order to drive out and residual moisture in the refractory.

Here's a picture of the first lighting of the burner. The charring cardboard is what remains of the tube casting form.


http://i104.photobucket.com/albums/m193/searover1916/Burnertest.jpg

[Jim Ledger]

Here's a couple of pictures of the first burn. It's been burning all afternoon as I slowly increase the heat. I should be able to get some nice shots of the interior around dusk.

http://i104.photobucket.com/albums/m193/searover1916/Burnertest3.jpg

http://i104.photobucket.com/albums/m193/searover1916/Burnertest2.jpg

[Jim Ledger]

I think it's going to work.:D

http://i104.photobucket.com/albums/m193/searover1916/Burnertest4.jpg

[Ross M]

Sweeeet!

[PeterSibley]

:) Very nice Jim ,looks about the right colour .Do you have a pyrometer ?...the next thing to buy !:D A neat good looking job , but then we expect nothing less from you !

[jsjpd1]

Well, it's been almost four years now! Do you still like your furnace Jim?

I've been researching furnace construction and sourcing materials. I'd be curious to know what you thought worked well with your furnace and what you would do differently.

Jim

[George Ray]

Ditto ..... your build was both inspirational and informative. How's it melting and pouring?

[jsjpd1]

Bump.

[Jim Ledger]

Well, it's been almost four years now! Do you still like your furnace Jim?

I've been researching furnace construction and sourcing materials. I'd be curious to know what you thought worked well with your furnace and what you would do differently.

Jim

Jim, George, what a pleasure to see this old thread bumped. It's nice to know that some of this stuff holds some interest in the face of the constant flood of new topics.

No doubt you found this thread also, a kind of companion piece where the furnace get put to some use...

http://forum.woodenboat.com/showthread.php?88357-Casting-catboat-rudder-hardware&highlight=



And then there's some information in this thread, on about page thirty-nine if memory serves, about casting a lot of fairly mundane angles in bronze...

http://forum.woodenboat.com/showthread.php?79099-Lofting-the-Brewer-catboat/page39

And the ever-popular video...

http://www.youtube.com/watch?v=gNcBAYJ4r_k&feature=plcp



(http://www.youtube.com/watch?v=gNcBAYJ4r_k&feature=plcp)


(http://www.youtube.com/watch?v=gNcBAYJ4r_k&feature=plcp)

[Jim Ledger]

To answer your question, I'm very satisfied with the performance of the furnace. It can quickly melt as much bronze as you would care to lift. I don't recommend the plans that I used, David Gingerys book, "Building a Gas Fired Crucible Furnace" The drawings were crude and the description inadequate, and some of the details involved just didn't work. I would, however, recommend reading it for whatever information can be obtained.
The lifting up of the body of the furnace is a feature I built, at great effort, but don't use at all. What is not told in the book is that the furnace needs to be bolted to the floor in order for this to work. I found this video of a guy who built a similar furnace and his is in a permanent location, a luxury I only wich I had. Have a look...

http://www.youtube.com/watch?v=_t5vND-7beU

I'm having difficulty linking videos this morning, so you'll have to click the link.

I'll be back with more later on.

Jim

[jsjpd1]

I was wondering how the lifting body worked out. I'm thinking of just going with a top loader just for simplicity sake, with a propane burner. I've got a handful of fire bricks and thought maybe I could put together a furnace based on that.

[PeterSibley]

http://pic40.picturetrail.com/VOL282/9443996/17245530/401523004.jpg

http://pic40.picturetrail.com/VOL282/9443996/17245530/401523003.jpg

Jim, this is mine. The body is insulated with K26 light weight bricks while the lid is formed with vermiculite ( from your garden store) and thermal cement ( from your pottery supplies).

This forum has some really excellent material on it, including recipes for castable refractories.http://www.alloyavenue.com/vb/forum.php

[jsjpd1]

That is a really good forum. Some of the casting work is out of sight.

[Peter Malcolm Jardine]

Thanks for this thread. I know absolutely nothing about melting smelting and casting, and the forums linked are great!!!

[Jim Ledger]

Thanks for this thread. I know absolutely nothing about melting smelting and casting, and the forums linked are great!!!

Thanks, Peter, this is all new to me too, just not so new.

I've been giving some thought lately to the rigging hardware for the catboat. As the spars take shape and the diameters become fixed I think it will lead naturally into the making of patterns for pieces like the boom bail, gooseneck and various mast bands. I've also got some ideas for a really cool stemhead fitting to hold the bottom end of the forestay. However, several things have to happen first in order to fix the position of a bolt which will go through the fitting, stem and and some of the massive timbering under the foredeck...

Stay tuned.

[seedy]

This has been a good read, thank you to all who've taken time to post info.

For a while I worked in a foundry, one of the last lightning rod factories in the US. Shoveled sand into boxes, shook it down on a Pettibone table, more sand, then the other side, sit it on the row, pull the plug to open the pour hole. When we had a whole row, hoist the crucible from the furnace, slip the long bar with a circle in the middle and a single handle on one end, double on the other underneath, and walk it out and pour down the row, bronze or T6. One paid close attention during this part. There was a story of a worker before me who dropped his end and the crucible jumped out and rolled down the bar toward him, almost cutting him in half with molten metal. Maybe just meant to scare me, but I focused pretty thoroughly for someone under 20. :^)

[Jim Ledger]

This has been a good read, thank you to all who've taken time to post info.

For a while I worked in a foundry, one of the last lightning rod factories in the US. Shoveled sand into boxes, shook it down on a Pettibone table, more sand, then the other side, sit it on the row, pull the plug to open the pour hole. When we had a whole row, hoist the crucible from the furnace, slip the long bar with a circle in the middle and a single handle on one end, double on the other underneath, and walk it out and pour down the row, bronze or T6. One paid close attention during this part. There was a story of a worker before me who dropped his end and the crucible jumped out and rolled down the bar toward him, almost cutting him in half with molten metal. Maybe just meant to scare me, but I focused pretty thoroughly for someone under 20. :^)

There's not much like a pot of two thousand degree molten metal to focus the mind. Well, maybe Formula One racing,or defusing explosives...but you need special training for those.

Thanks for the story, Seedy, but cast lightning rods? Really? Copper, bronze? Wouldn't a lightning rod be like a piece of rod stock? Are there fittings need to be cast. I'd be interested if you care to elaborate further.

Jim

[zeyang]

here is a project we are running. the furnance is an old tempering oven. Plan is to cast portholes in alloy. around 20 of them.We are just at the testing stage now to see how things run. We filmed the first try.http://youtu.be/Q_y-Gh6_YIs