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Old 11-02-2010, 09:27 PM
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Greenbuggy Greenbuggy is offline
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Default Any tips for using castable refractory?

Just bought an 18 lb bag of castable refractory from ebay for the forge. Haven't mixed any up but I'm thinking thats the way to go with my forge, in order to get more temperature stability and better insulation. After I get the refractory inside the forge body (which in mine is a pair of freon kegs welded together) I think I'll use the extra kaowool I have to insulate the outside.

Anybody else used this stuff? Suggestions for forming the holes for my burners? I was thinking about using a small weed burner to slowly warm it up and bake out the water before actually firing the forge again. Will that on a low setting be too much heat too fast?

Here's a pic of the forge as she sits currently.
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Don't try this at home - UNLESS you live in a HOSPITAL!
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Old 11-02-2010, 09:32 PM
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CEC CEC is offline
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a long slow heat is best for drying out the refractory.
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Old 11-03-2010, 06:49 PM
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Alright, I'm thinking that a weedburner might get too hot too fast. The seller recommends "leaving it out in the sun for a few days" but with temps to be 40-50* F and dropping in the next few weeks I'm thinking its not going to get very hot just sitting in the sun.

My new plan is to put a 40 watt bulb in the middle and leave it on for 3 days once its gotten hard, then swap out for a 100 watt bulb for another 2 days after that, then weedburner for a few hours and slow initial firing after that.

I'm thinking that because this is going to get exposed to a lot of heat I'm going to use a couple slits of cardboard on either side to separate the two sides when its formed, they'll burn out when its fired and give 1/8" on either side for expansion space. I'll take pics as I make it through this process.
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Old 11-03-2010, 07:45 PM
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rmack898 rmack898 is offline
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If it were me, I'd wait for Jack to weigh in on this.
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Old 11-03-2010, 08:28 PM
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platypus20 platypus20 is offline
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You are doing 18#, we are usually doing 7-8 tons, here are the procedures we use

on for 1 minute - off for 4 minutes for the first 2 hours
on for 3 minutes - off for 7 minutes for the next 3 hours
on for 5 minutes - off for 5 minutes for the next 7 hours
then left on in low fire for 10-12 hours, then the refractory is cured

again were talking tonnage of refractory and approx 23,000,000 BTUs

the light bulb idea sounds okay

I do the 40 watt for 12 hours
then go to 100 watts for 12 hours
then I would go on-off with your normal burner for a couple hours and you should be set.

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Old 11-03-2010, 08:54 PM
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tnmike tnmike is offline
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Slow drying is best. If you use the burner you will get cracks in the refractory do to steam/water escape. I agree with the light bulb idea.

I would not use the wool on the outside. Its a close cousin to asbestos and unless you can contain it there will be airborne fibers, We coat the wool with a high temperature clay to prevent that here.(satanite)
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Old 11-04-2010, 09:07 AM
NC Fabricator25 NC Fabricator25 is offline
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I did pretty much what you are doing using 10" pipe (pretty sure on that diameter), see the pictures below of the forge before paint. I used a piece of 1/4" thick high temperature, high density insulation on the outside of the refractory, between it and steel pipe to allow for any expansion or contraction. I also welded a few studs (1/4" rod) on the inside of the pipe shell to anchor the refractory to the shell. Used a 6" diameter cardboard tube which then was burned out. I think the cardboard tubes are called sonotubes or similar, and used for pouring concrete piers and the smaller sizes are available at Lowes, Home Depot, etc.

I think I let mine sit for a week, then used a regular propane torch on a low setting to cure it out for an hour or so, several times over a couple of days. Still cracked in a few places, but has retained it's shape and integrity.

Pros: durable, looks good, permanent. Cons: cracking, slow to heat up, and I'm not convinced it holds heat like a 2" Kaowool blanket. If I were to do it over, I'd use the kaowool. Good luck!

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Old 11-05-2010, 02:18 AM
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Dave Lee Dave Lee is offline
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Nice job, NC. I like that tripod stand too. Thanks for sharing.

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Old 11-11-2010, 04:18 AM
NickWheeler NickWheeler is offline
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I've had a lot of experience with forges lined with both materials, and I MUCH prefer KaoWool over castable refractory.

It gets to temp MUCH faster, and with a 2" lining (two layers of 1") it holds a consistent heat VERY well. Yes, it drops in temp more when you put a large, cold piece of steel in it, but it gets back up faster too.

The best thing, in my experience, to coat the Kaowool with is ITC-100... it will increase the efficiency and overall output of the forge like you won't believe. It's pretty spendy, but works VERY well.

My forges will definitely get hot
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Old 11-11-2010, 11:11 AM
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Alphawolf45 Alphawolf45 is offline
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I've built three small furnaces for metalscasting. I used home made refractory that has lasted for hundreds of melts in the furnace I use most often,, but it cracks right away and have had to patch it in a few places where the burner impinges on the wall and damaged the refractory... Eventually I developed a recipe that seems indistructable....but I wonder , and there being experts on the matter contributing to this thread.. Does the good commercial mix not crack at all when it is drying? ..I'd buy some good stuff if I could find it within a reasobable drive..
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