View Full Version : Best Foam for Burnout?
07-10-2005, 01:40 PM
If I were to sculpt in foam for later casting in bronze, what would be the best foam to use, as far as the burnout (moldmaking) process goes? I'm assuming I'd want to use a foam that would burn out more readily and, if possible, one that would produce fewer or no toxic fumes in the process. Incidentally, I'd take it to a foundry, which would probably be equipped to handle whatever I bring them, right?
07-10-2005, 02:31 PM
I talked with a foundry about this and they told me EPS foam is the cheapest fastest and lowest cost. The fumes are not such an issue since respirator should be always be used when cutting or burning foam. Since I did not pursue casting I don't know if the source I spoke to was correct. Maybe others have experience with this.
07-10-2005, 03:34 PM
The dense blue foam used in house construction works extremely well for burnouts. Architectural model shops use it with fine nichrome hotwires; a setup that incorporates a transformer, rheostat and table much like a bandsaw that cuts extremely clean and efficiently.
The fumes and dust are not toxic, but ventilation is still recommended. Also painting the foam with gesso (or several coats of latex paint) will help to maintain the integrity of the form during casting.
Studios I've worked in had great success using a moistened sand mix with the addition of bentonite (5 to 10%) as a binder. Actually using old resin bonded sand, sifted and poured directly into a container/flask, shaken down and packed (rammed up) also worked very well. Large molds using "loose sand" still require the addition of wieghts on the surface to insure that the hydrolic force of the molten metal doesn't breakout the form within the mold.
These were very "direct pours" with straws added at extreme points to make venting more efficient. A splash of molten metal (to initiate the foam displacement) and then "hitting it hard" until the pouring cup is full and vents smolder. This is very practical for casting aluminum, bronze and particularly iron.
Many commercial foundries use a oil/clay binder mix to produce production molds where all of the investment materials are recycled and used repeatedly. This way you can just show up with your sprewed form and they will do the rest.
In Birmingham, Alabama there is Sloss Furnace (http://www.slossfurnaces.com/media/html/home/sloss_story.php) (a historic foundry site) with resident artists and programs that cast iron every month of the year. They also conduct workshops and iron casting conferences on a regular basis that make casting very affordable. There may be something similar close to where you are located.
08-02-2005, 09:24 PM
Fused, I am curious about your statement that burning blue foam is not toxic. If you have some resources that I could see that state this, please foward them on. I have been using white (compressed pellet) foam because I understood that it is created with steam and is the least toxic foam. I would really like to find out that the blue stuff is better becasue it is a lot easier to work with.
08-02-2005, 10:54 PM
Actually, the white stuff (EPS, or Styrofoam) is toxic if you breathe the fumes given off by melting it. Ideally, you should wear a respirator or at least have adequate ventilation when using a hot knife on the stuff.
I have also heard the blue foam is more toxic and shouldn't be used for sculpture. As for polyurethane, you don't use a hot knife to carve it, so it should be safer to carve than EPS (Expanded polystyrene). It's when you sand it that it becomes most dangerous and a dust mask should be worn while doing so.
08-03-2005, 06:21 PM
Yeah, I think burning anything made from plastic or styrene is toxic as all hell, but I had always understood the white stuff to be the least harmful. Its not that great to work with for texture. I always end up using masking tape to smooth the surface.
08-03-2005, 10:10 PM
Well, oddly enough, the white stuff is the stuff to use as a pattern for burnout, since polyurethane doesn't burn out as well.
About texture, no, EPS is not going to sand very smooth; not as smooth as polyurethane. Of course, the higher the density, the better, where that's concerned and also, closed cell works better than open cell.
My objective is to use polyurethane as a core material for fiberglass or Winterstone and, probably Winterstone, since it's non-toxic and polyester resin is toxic as hell (not to mention having a terrible odor). If I do want to cast a bronze, I can use EPS. At any rate, I haven't tried it yet, so everything I'm telling you is what I'm passing on from various sources, including some of the outstanding talents here on this site.
08-04-2005, 09:25 AM
I'm just curious about something. Has anyone tried using micrcrystlline wax over the foam or would it melt the foam. Using an open cell with wax and then ceramic shell around that? I am extremely dumb about casting!
I have gone through the whole process of making a bronze sculpture using the white beaded styro. you dont need hot knives just makes pointless fumes. all you have to do is carve it with knives. it does not melt with wax. very stable. technically i think it is far superior than sculpting clay. lightweight, sturdy *very easy to cast* the only pitfall is if you cant sculpt wax and dont like the material other than that it is very good you can look at pics of the sculpture I made with it
08-04-2005, 12:59 PM
Jamo your link is password protected.
grayem, I worked in an architectural model shop on an upper floor of a high rise, which didn't have great ventilation. One of my co-workers had a brother in law who worked for the EPA and sent him a piece of the dense blue foam to test.
They found it wasn't toxic and contains no known carcinogens. That doesn't mean you don't need to protect yourself from long exposures to fumes and dusts.
08-04-2005, 01:32 PM
That' s interesting. I have looked around and the MSDS sheets I could find concur, but they don't really talk about burning it on purpose :)
It lloks from personal protection for firefighters that self contained breathing apperatus is required, but I would think that would refer to a factory or warehouse full of it burning?
The technique you are speaking of works quite well for shell, and plaster investment. I have done it several times, but dont try to dunk the foam into a pot of hot wax, it melts. Brush it on and you're in business.
It's not a good idea for direct casting or lost foam technique as you probably know the wax would not subliminate the same way as the styrofoam and would cause a lot of damage to you and your work.
08-04-2005, 06:19 PM
Well, one thing to consider is that a foundry will have proper venting to dispose of the fumes, usually. Of course, if you're doing your own casting, that's another matter. It would depend upon the ventialtion in the space you're using. I'll be using my garage, with both doors open, usually, but then, I'm not planning on doing my own casting, either.
I hadn't thought about wax over foam, but then, why would you do that when you can just use the foam and burn it out? I guess the answer is that you could do further sculpting in the wax, using the foam as an armature, right? I wonder if the wax and the foam would burn out at the same rate, though? If the foam takes longer to burn out, it could conceivably ruin the cavity left by the wax coating, since the mold cavity would then be loose around the foam and it would tend to fall or lean to one side in the cavity, due to gravity. Then again, maybe not, if the mold material is rigid enough.
08-04-2005, 06:49 PM
THe wax over foam is actually pretty fast for burnouts. You can build the foam sculpture core and add a thin wax for texture, detail, whatever.
Ceramic shell burnouts are really easy. and wax burns much slower that the closed cell foam i have used making nice wax drainage vents. The benefit is there is little wax to burnout and little chance of a wax fire in the kiln.
Solid plaster investment is going to take all day or 3 days regarless. Its more about getting the moisture out of the plaster and getting it hot all the way through.
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