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Cores for Ceramic Shell Casting
Daniel Rotblatt -
Monday, October 15, 2007 - 2:14am
Casting bronze casting | bronze sculpture | ceramic shell | core | lost wax casting New here - hope I'm doing this right! I have a question about cores for ceramic shell casting. I teach a foundry class, so I am no newbie. Generally for hollow pieces I cut out a section or make sure the piece is designed so that the center will build up a shell and be able to dry properly. But, I am now doing some foundry work for another artist out of my studio of some small animal figures. These are a little too big to cast solid (though I can if necessary), but a little too small for a large enough opening to allow the shell to make a strong core -- soooooooo.....I have been looking into using some sort of core material. Several options I have found so far: 2) a mention of cement fondue (which seems to be a high alumina cement) mixed 2:1 refractory to cement. Stucco can be used for the refractory. This is in "fine art metal casting" by Richard Rome and Hamish Young. 3) If there is an opening that will close up after 4 dips or so, do the 4 dips, then fill the inside with dry stucco and seal with some slurry. Allow to dry and continue to dip - the stucco will support the thin inner shell. Question, does anyone have any experience with this? With the quick burnout times of the ceramic shell, I imagine this could cause an issue with solid cores. I could put some vents in the solid core - but would the burnout times or temperature be different? Other ideas? If you would like to see my work take a look at my website: http://www.rotblattsculpture.com  Thanks for the reply Mr Fink
Daniel Rotblatt -
Thursday, October 18, 2007 - 10:07pm
Thanks for the reply Mr Fink - I've read a number of your comments on different forums and gotten a lot from them. I have played with sodium silicate/CO2 so I am familiar with it. Will it hold up to the burnout? As I recall the sodium silicate does not degrade at the 1500°F that I would be burning out (it is in fact good for fireproofing wood), but I would be afraid that the wax would dissolve the core when it melted out. I have found it to be somewhat fragile. On the other hand, if I could get one or two layers of shell inside the piece, then back that up with sodium silicate/CO2 sand, I think that would make a great core. A thought off the top of my head - could one add porosity/venting to a solid core like this by adding something that would burn out - styrofoam beads, wood chips or fiber for example? These pieces are either too small or too detailed for me to want to cut them in half and replicate the detail over the welded areas. Thanks again - Dan www.RotblattSculpture.com » reply Sand cast cores and sawdust
Bill Wolff -
Wednesday, December 5, 2007 - 9:06am
Although most of my sand casting experience is with Linocure (a two part resin), I can tell you that it is common practice to add a healthy percentage of sawdust into the mix for cores. I guess the porosity helps improve venting (maybe), but it helps substantially with evacuating the core after casting. I`ve also heard it argued that the combustible wood helps keep the metal hot (an issue with iron and cold molds), but I`m not sure I believe that. I read a wikipedia article last night about pre-cast ceramic shell cores...can you build or cast the wax around a ceramic core? Bill Wolff » reply core materials
visitor -
Monday, February 18, 2008 - 12:17pm
I've heard about sawdust sand and an additive wich links all these together » reply |
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ArtMetal
The core material for Ceramic shell
I no longer do ceramic shell casting so this draws from what was used about 35 years ago when I did. Then we would use a sand / resin binding material that would not need any burnout.
That means no drying, and no baking for it to work. In this class comes pre made cores of sand and sodium silica hardened with an injection of CO2, or sand and one of the oil / acid hardening binders.
Also be sure to put some vent holes in the actual metal parts being cast so the core can still vent out somewhere. You can not trap it in totally but can almost. Those vents can be small copper or bronze or aluminum tubes or pipes (depending on what metal you are casting, or just core extensions that go through the new cast walls and will need to be removed and welded shut later. For most of our larger works we would have some exit for the core at a later time and if this means doing it in two, sometimes very unequal sections, that was always a preferred good trade off. bpfink