Refractory Formula

[j.w.s.]

Just wondering what people's experience with making their own refractory has been and what formulations they found successful. Doing a little research I've found mixes from 13:1:1 vermiculite, Portland cement and lime to just 5:1 vermiculite and Portland cement with 80% the called for amount of water. I'd like to form my own bricks to line the inside of a new gasser. I've got plenty of vermiculite, I use it for annealing blades and the rest is easy to pick up. Any help?

-J

[WayneCoeArtistBlacksmith]

Castable refractories are not all that expensive, especially when you can buy it in 6# bags and have no waste. You will have spent way more and have an inferior product by the time you buy the bag of vermiculite, Portland cement and lime.

[j.w.s.]

That wasn't the question though, i understand there's refractories for sale in small quantities but some of us like the act of making things we could readily buy, especially when we have most of the components necessary. I guess its part of the discovery, probably the same reason Popular Mechanics was so, well, popular - building a project at home that you could buy across town, with the understanding that comes along with the creation. I was merely asking if anyone found success in making their own and if so, could they share their experiences?

-J

[ThomasPowers]

You might want to see what successes they have had in a backyard metal casting forum.

While I build my bloomeries from adobe dirt and straw I have always sprung for my forges as they see a lot more travel, vibration and thermal cycling---all hard on refractories!

[knots]

Google "2 buck furnace" and have a look at what one member of the Backyard Casting group has done. If I were to make one of these I would consider it experimental and not expect it to last a long time. Perhaps someone on that forum will be able to comment on how their home mix refractory holds up under service.

My first gas forge was made from an alumina based castable. It worked but was heavy, took a long time to reach forging heat (because of it's mass), and had a tendency to develop heat stress cracks. I built this forge in the mid 1980's before internet. If I had had the information resources available today, I would have built a fiber based forge.

Having said that I understand where you are coming from. If I were to build another castable forge I would use a cylindrical fireclay flue liner as the inner lining for my next one. It would either be jacketed or bound with strap . Good luck. Show us what you come up with, and share your comments on it's performance.

[Frosty]

The vermiculite has a melting temp around 2,000f so any very near the inside will degrade. I've had some success with 2pts fire clay to 3pts silica sand (sharp is better it seems) to 1/2pt portland cement. Mix thoroughly dry and have your brick molds ready before you add moisture.

Add only enough water so it will clump hard when squeezed in your hand and break cleanly. If it stains your hand it's too wet, if it crumbles it's too dry. hammer it into your brick molds with a wood mallet till it bounces then strike it smooth with a bar.

If you really want insulating brick replace a portion of the mix's sand with saw dust and lay it in the molds so it rams to about a 3/4" - 1" layer next to the fire, then ram it with the hard refractory. When using saw dust it helps to moisten the sawdust and add it to the other ingredients after they're mixed. You will have to mix it a lot though or it will separate.

The portland cement is there to get the bricks to set up before firing but if you use too much it will spall and degrade the bricks. The sand will help prevent it from shrink checking as it dries as will using the absolute minimum water it takes to work. Sand will also help prevent checking with the thermal cycles as it allows some movement when expanding/contracting. This makes me wonder why sharp sand seems to work better than aluvial (stream/beach rounded) sand.

The sawdust will burn out leaving voids in the refractory just like light insulating fire brick, (it's how they make it) providing some insulation and not having any silica sand in it will make it more flux resistant. I've wanted to try using small styrofoam beads instead figuring spherical voids would be strounger but I'll bet it'd be pretty stinky firing the things.

Lastly you need to cure and fire your bricks. Let them dry completely, days if necessary or put a light bulb next to them but dry Dry DRY is a must. Now for the first fire, charcoal briquettes work really well for this, lay a single layer on/around the spaced out bricks and light em up. Allow it to burn out and cool completely. Now move them apart a little so you can put lots more charcoal briquettes on/around them and repeat the first firing process. Lastly stack them for your forge and mount your burner (if it's a gasser) and bring it up to a nice cheery orange heat and let it soak for a couple hours and you're good to go. Well, as good as it'll get for home made firebrick that is.

Best luck.

Frosty The Lucky.

[Robert MacVeigh]

Making Insulated clay firebricks: http://www.bioenergylists.org/stovesdoc/Still/VC%20Stove/vcstove.html These bricks even look and weigh like the ones we buy from ceramic houses. Excellent read with several batch designs (but they are not specific about quantities or ingredients) wouldn't be any fun if we didn't have to experiment. These bricks are fired at 1000C but there is no discussion on their maximum rating because they are intended for use in third-world cooking stoves to conserve fuel. Holds some promise if we find the right clay for casting/firing as we know that industry uses sawdust to manufacture the production bricks we buy today...

[Sweany]

Here are a couple formulae from the old Keenjunk.

Kevin, depends on the rating of the clay you have, you'll have to add some stuff to it to keep it together. You'd need some stuff in the mix to keep it together. And a flux to, sinter it. If you exceed the heat limits of the refract it will melt .

Kawool is faster heating and lighter.

I realize the following is a crucible recipe but it shows some of the principals involved.

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Crucible recipe from a clayart thread

I saw one a couple of months ago a Behrens' formula I think

Epk 40
Calcined Kaolin 20
Tennessee Ball Clay (OM #1) 20
Grog 10
Flint

mix with about 500ML of water per 1000 grams mix. After an initial
wetting period of about 24 hours allow to mature for a week before
wedging and throwing. Fire to Cone 4 or higher

There's another way to go with the help of your friend.
You'll need to get investment from him. Then mold a lump of clay into a
mound. This will shape the bowl of the crucible. Set the lump onto a
smooth surface and build a wall around it with clay. Mix the investment
in a ratio of 38-40 parts of water to every 100 parts of powder by
weight. Then stir in 1/3 to 1/2 as much pumice as there is investment.
Pour the mix into the form. Vibrate it to remove air bubbles. Let it set
up overnight then fire it to 600 degrees Fahrenheit. Let it cool slowly
in the air.
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another one from the junkyard
Ed

I have had pretty good success making my own castable refractory material. 4 parts premixed concrete, 4 parts fire clay (available at masonry supplies), 1 part vermiculite. Mix with water to the desired consistency. Let sit over night and bring heat up slowly for first fire.
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I've read pearlite is better in this mix, pearlite does not soak up water like the vermicullite.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~another one
Here's a recipe from a potter ,Florida Bob. Bob makes his own kilns, burners etc.





Cone ten refractory

Mike Sweany and anyone else interested:

Sure do, and it's Easy to remember: 1:1:2:2:4. Courtesy of Lowell Baker at the Univ. of Alabama.

1 part (all by volume) Portland cement

2 part alumina hydrate

2 parts fireclay, native clay sometimes works -- *Always* have a local potter toss a couple samples in the kiln for testing, make sure they get fired at least as hot as your duty temp.

2 parts grog - this is potterese for ground and sized fired clay, crushed old soft firebrick . find the temp rating on the brick 1/2" screen to size

4 parts sawdust or vermiculite

mix with approx 2 parts water, should be almost loose & ram into form.

May need to gently heat for a good set after a day or so, looks like a soft concrete fresh & cork after firing

Have fun,

Bob

castable questions: Alumina hydrate & correction
Mike, et al:
Yup, pottery suppliers will have it, also try the local chemical supply house, you want 200 mesh, not necessarily reagent grade, but low iron, metal & flux able salt content. Also, Lowell Baker told me that calcium aluminates cements are also used in the cement boatbuilding industry for their high initial setting strength. The whole point of adding alumina is to imitate these cements. Look for cement-boat yards in your area if appropriate. Also Portland is a flux at high temps, so if anyone is going for copper, iron,
etc & can find this stuff in your area, might want to use the Ca-Al+? mixes in the articles(there are 9 or 10 of them).
1 part alumina hydrate
4 grog
3 coarse sawdust, as from a sawmill
4 fireclay
2 Portland cement
2 vermiculite
SO, there is some leeway, but always test before you commit to a recipe. Be sure to test under use conditions, too (toss some in your forgr, smelter, whatever -- in pottery, things that survive in an oxidation atmosphere sometimes degrade in a reducing atmosphere. (an excess of fuel gas or gasified solid fuel) And you might be working in contact with fuel, metal, fluxes - GOK what effect that'll have on a refractory, especially if you dig the clay. Preferably test to destruction, lets you know the idiot margin. Check at www.potters.org, under kiln construction. um, GOK = God Only Knows :->
Later, Bob.
alumina hydrate
Mike, You can order alumina hydrate and other ceramic/pottery supplies from National Art Craft, 1-8888-937-2723, or 1-888-we-r-craft, they carry a complete line of supplies from submersible pumps to glass oil lamps etc. and all the kiln supplies you might need to incorporate for your forge.
Looks like another overcast day in King George, Va.