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New lining for the iron furnace

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The old iron furnace has been through a fair number of changes -- originally intended as a charcoal burning sawed off cupola. That was an experiment which didn't pan out. The lining was fire brick set in fireclay grog mix. The firebricks were set on edge to the bore, which was a little over 7". The lining was 4" thick.

A few attempts were made with different configurations to get iron to flow in the cupola using charcoal. But I never got hot flowing iron. My feeling at the time was that it might have worked with coke - the density difference meant a lot lower fuel weight in the bore with charcoal. An attempt to change the tuyeres and furnace height didn't improve it enough to pour iron.

The furnace was then converted to an oil crucible furnace by adding a modified Kwiky burner and I was successful with iron in that configuration. The bore was still a little over 7" and that made it difficult to get tongs around even a number 6 crucible. It was do-able but not ideal. Also the furnace took about an hour and a half to two hours to melt a crucible of iron from cold start.

Since then, I haven't used the iron furnace -- I've mainly been casting aluminum, zamak, and occasional brass using my smaller and more convenient plaster-lined propane furnace. But last year I wanted to cast some engine parts in iron. The lining of the iron furnace had got wet and needed repair -- it was still viable, but the bore was actually smaller than the propane furnace, so I decided to tear out the old lining and try the Ironman's insulated type: ceramic blanket covered with a painted-on ceramic hot face compound. I could then increase the bore to about 10" and, I hoped, cut down substantially on melt time.

The hard part of lining with insulating blanket in the past was in trying to find a substitute for the Zircon hot face compound Ironman uses -- apparently only available in Australia. Afew years ago I had called a couple of manufacturers of similar compounds but they wouldn't sell to non-trade individuals. But since then ITC 100HT has been become openly available and is used here in the States by gas forge hobbyists. So I decided to try some.

The stuff is not cheap....$500+ a gallon. But it is sold in pint sizes at an affordable price on ebay. So a year ago I ordered that and some 2" Ceroblanket insulation for my furnace. I figured a pint would probably coat the furnace.

Last week, a year after I had ordered the materials, I installed and coated the new insulating lining, and today with temps of 14 degrees F by noon (not ideal :loco: ), I decided to bake the lining. That is supposed to be done below maximum heat for the first 6 hours. That's a lot of fuel! Instead of propane or oil (which would require the compressor and blower to be set up) I decided to do it the low tech way I did all my other linings; build a small kindling wood fire in the barrel, then let the charcoal embers heat soak the furnace for a few hours.

So, I loaded the barrel with some crumpled newspaper, and 8 small sticks of kindling. The fire caught easily, probably the insulation and hot face compound helped focus the heat.

When the kindling sticks dropped below the top of the furnace, I swung the insulated lid over it to heat that as well. I didn't close it right away, so the whole lid face would get some heat including the sealing edge. After about 15 minutes I lowered the lid.

What surprised me after that was that the whole interior of the furnace gradually took on a bright orange glow. Just from a small amount of kindling charcoal in the bottom. There was no blast, mind you, this was all just from an inch and a quarter burner hole at the bottom as a vent and natural draft with the lid closed. The burner had been removed.

This really illustrated the reflective and insulative qualities of the blanket and coating. To have a 10 inch bore furnace walls glowing orange from just a few pieces of charcoal, and no blast is really surprising.  :med:

This is looking through the top vent at the furnace wall:

I'm thinking to myself, cherry red, that's aluminum melting heat.  :scratch:

So naturally, I start looking around for my casting stuff, a crucible, spoon tongs, etc. I don't have a mold -- all my greensand is frozen anyway, but just for the heck of it, let's see if we can melt some Al.

I find some scrap aluminum bar cutoffs and pop them into the crucible:

I set them into the furnace. There's some snap crackle popping going on from the somewhat dirty cast iron plumber's pot I'm using as a crucible. Well I just set a crucible and aluminum at 14F (-10C) into a hot furnace, so you might expect a little complaint from the items in question...  :hammer:

The walls cool quickly, since they have little thermal mass, but the charcoal is still glowing. I swing the lid back into place:

I drop a couple more small sticks in, just to get the fire going again. But in only 5 more minutes I'm seeing a pot of the shiny stuff under a small skim of dross, ready to pour:


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