So I think this is the final conclusion of my research on refractory materials. There are two major types of refractory. The first is standard firebrick that is commonly used in making things like clay ovens. This firebrick is generally quite dense and contains a lot of alumina (28% to 80%+). It conducts heat well, which works especially well for transferring heat to food which you are trying to cook.
The second major type of refractory is insulating firebrick. This also often contains a large amount of alumina, but is likely to contain more silica as well. Insulating firebrick is usually very light and contains a lot of air. The best example of this is the HRSI (High-temperature reusable surface insulation) tiles used on modern space shuttles. These tiles conduct heat so poorly that they can be held in hand, while white hot, without burning the skin (see the Wikipedia article Space Shuttle thermal protection system). These tiles contain only 10% silica and 90% air.
The type I am looking for is the insulating firebrick. First, it should be simple to mix good portions of alumina with the clay, to get a high alumina content, which should help prevent cracking. Since I do not have access to the silica fiber material used for HRSI tiles, my next best option is to add some perlite, specifically smaller pieces. Large pieces are likely to weaken the finished product too much, but if I mix in a moderate amount of perlite consisting solely of pieces between 2mm and 3mm, I should be able to add enough air to offer good insulating properties without weakening the fireclay significantly.
I think that the clay may actually have sufficient alumina to work fine if I were to add around 25% perlite to the clay (by volume). This time around, I would prefer to add some extra alumina anyhow, just to be safe, but I would guess that the 30% alumina is probably plenty for the forge. Once I have the forge working, I plan on trying different mixtures. I will make small balls or bricks (very small bricks) of the various different mixtures, then use the forge to heat them until they glow, then allow them to cool. I will repeat this procedure on each mixture, either until the pieces crack, or until I get tired of testing them and can conclude that the particular mixture is sound and unlikely to crack for some time.
My current bottle neck is producing alumina. I am still looking for a good source of scrap aluminum (since most "aluminum" cans produced currently are actually made of steel). Maybe I will have my parents save soda cans for me. For now, I am producing some alumina, but very slowly and in very small amounts.
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A few good sources of aluminum are empty soda cans and used, but not dirty, aluminum foil.
ReplyDeleteSince I do not drink much soda I did not even consider soda cans, but so many people around me drink soda that I can still get as many cans as I need for this.
With the foil, I have discovered that the foil tends to rust out in circular areas. This means that there are many very small fragments of unoxidized foil in my alumina. These need to be picked out. Cans should not do this (because of their thickness in comparison to foil), but I may need to sand off some of the paint on the outside of the cans, to allow access to the water and the electric current.
On a side note, you can use a regular can opener (not the side opening ones) to take the top off of a soda can. This gives you something that can be used as a cup, or for cooking over lower temperatures. The two cans I have done this with have not had any sharp edges, because the soft aluminum presses down against the inside of the rim.
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ReplyDeleteThanks for the feedback. Having been in college full time for the last few years, I have not had much time to do much experimenting worthy of posting. I graduate fairly soon though, so you can expect me to be a little more active here. I have experimented a little with casting aluminum, and I will probably be making (and writing about) an aluminum smelter before the end of the year.
ReplyDeleteIt's a nice information about types of Refractory Materials. I have learned many things from this. It really helped me a lot…I really appreciate your post and you explain each point very well. I will love to read your next post too.
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