refractory ideas

[machinemaker]

Hello, first post here. I build commercial equipment to supplement my sculpting and use a bit of refractories. I also have a small foundry that includes a melt furnace and two kilns. I am also active on a casting forum and they have a ongoing discussion on home made refractories here; backyardmetalcasting.com/forums/viewtopic.php?t=6&start=0
For my own personal use I prefer to buy a good commercial refractory that I can rely on its longevity and temperature ratings. My experience is that you can usually find a supplier for commercial refractories with a little searching in most areas. Most will sell small quantities too. You may have to look for boiler repair companies, ceramic suppliers, or other industrial suppliers. One method that I have seen to increase the insulating properties of castable refractories is to load them up with styrofoam beads up to 3-4 to 1 foam beads to refractory. One of the problems of using perlite in refractories is if you reach a high enough temperature they will not only melt, but act as a flux to deteriorate the base refractory material. Granted this is at the upper end of what I have read here about rocket stove temps. What I have seen discussed here in using portland cement is right on. Portland and or masonry cement will start breaking down I believe at around 900 f. I do like to use a low density concrete as a backing material for refractories where it wont see that type of heat. I have used it in boilers and melting furnaces to add structural strength and to cut down on the thickness of refractory to fill a space.
I am still trying to absorb all the information here and we are waiting to receive Ianto's book. I want to play around with some ideas and get first hand experience. I hope that as winter approaches we will have some time to experiment. Thanks.
kent

[hpmer]

Interesting link. One of the posts talks about using a minimal amount of water to get a dry mix to pack in a mold. Is there a chemical reason to minimize the water or is it just so that it doesn't take as long to dry? I've found it easier to work with mixes that are more wet than dry.

[machinemaker]

I think that most castable refractories have a very minimal amount of cement to help them set up, but that the reaction is vitrifying like firing ceramics. the cement is only there for the first setting up until the refractory is fired. It takes very little water to set up cement, it can be mixed like foundry sand or damp beach sand and set up. by adding more water to make a wetter mix you reduce the strength of cement. Once the cement in the mix is heated it looses its strength, but the ceramic bond takes over. At least that is what I was told second hand. I used use a ramable refractory that was like fire clay and grog that was very stiff like potters clay, but it was a very dense refractory.
kent

[hpmer]

Makes sense. My mixes do not include cement, so I guess I'll stick to a bit more water which is easier to work with. Thanks for the reply.

[twohorsepower]

i've experimented with fondu cement and, instead of aggregate, using vermiculite. i read about this first on an italian oven forum, as some oven builders were using this to line their bread ovens, and supposedly this stuff is fit for 1000 degrees centigrade (1800 F)

I've only used it to cast register plates for standard woodstoves so i've no experience of it at rocket riser temperartures. Anyone tried this?

(local builder yard here in ireland were selling the fondu as quick drying cement, and they had no idea it had refractory properties.)