Cinder block heat safety

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    A photo in the fall-winter Japan Woodworker catalog shows a master chisel
blacksmith working at his forge. The forge is on the ground, and appears to be made of stacked cinder blocks.     This seems like a good way to make a cheap solid fuel forge. My question is how stable cinder block is to high heat? Do you suppose he has firebrick lining his forge?     BTW, his anvil looks like a ~6"x6"x10" chunk of steel, also sitting on the ground.
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Whether or not he does, a firebrick and/or fireclay lining is a good idea for high-heat exposure. Saves time, not rebuilding the forge. Does not cost much. Neither cinderblock nor concrete block take high heat all that well.
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Ecnerwal wrote:

also "proves" it's the man , not the tools ...
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Australopithecus scobis wrote:

I wouldn't trust the cinder blocks right next to the fire, but with a firebrick lining (or just the right sand/clay mix) they should be fine.
Coke is quite an insulator, and it's surprising how little of the heat transfers to the body of the forge, especially with a shallow firepit. I built a reenactor's forge one time, clay/sand mix lining a wooden box. The liner was only a few inches thick, but the wood never burned except some scorches from stray coals and hot workpieces around the top edge.
Conrad Hodson
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On Wed, 12 Jan 2005 09:13:30 -0600, Australopithecus scobis

Cinder block is relatively stable to moderate heat. Nothing like firebrick, but then it doesn't spall so readily as concrete blocks or masonry brick. They're not up to high temperatures but you can use them for the backing of a lined forge without the flying splinter hazard.

I doubt it - not the Japanese way. He probably just has a deep layer of charcoal ash or rice-straw ash on the inside. Rice straw has a lot of silica in it, so the ash is mechanically relatively strong and can make an effective insulator.
It's characteristic of Japanese smelting and forging that the hearth is re-built regularly and seen as a low-cost consumable, not a high-cost piece of long-lived equipment. They're also quite profligate in fuel, as there's little insulation or reflection. If you read Leon Kapp's book there's a description of a tatara smelter being built, used for one smelting, then broken apart. http://codesmiths.com/shed/books/japanese_swords.htm
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On Wed, 12 Jan 2005 23:51:40 +0000, Andy Dingley wrote:

Thanks. ...another snippet for my Dingley.txt file...
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Hey guy's I have worked (briefly) with a Japanese forge before. They are definitely lined with a fire clay type mixture. Which is durable and easy to repair. The shape and proportions are quite specific (and logical). This type of "trench forge" is usually built on the ground and the smith squats or sits in front of it. This is hard on most Westerners knees but with the proper frame of mind.....the body can follow. Or you could just raise the height of the whole thing with more cinder block back filled with dirt. The traditional Japanese anvil is a rectangular block with a flat top and no horns. What book photos don't show is that this block extends 12 or more inches deep into the ground! Like an iceberg, most of the mass can not be seen from above. So what looks like a 6x10x6 is more likely a 6x10x18. The effect is a very stabile solid anvil.
Glen G.
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On Mon, 17 Jan 2005 13:26:12 +0000, glen wrote:

Do you recall the approximate dimensions? ("As big as a cinder block" is what comes to the imagination.)
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Hi Aus & all, The Japanese forges I have seen use cinder block as the outside perimeter. These forges were about 4 blocks long and 2 blocks or less wide. The tuyre (air inlet) is located about 2/3 from the back end. The air inlet is mounted on one side and slightly above the bottom of the forge. You know it would be easier if I posted some pictures. It really is a simple affair but the magic is in the fine details. These forges burn charcoal you know? Anyway, if anyone is serious about seeing my sketches of contemporary /traditional Japanese forge let me know and i will post them .
Glen G.
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Please post! Thanks.
Eide

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But not to the newsgroup - it'ts not a binaries group.
If you don't have webspace of your own to post them on, use the dropbox at metalworking.com, and just post links to the images here. Remember to make a text file if using the dropbox.
Thanks.
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Absolutely!
GA
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On Tue, 18 Jan 2005 21:06:21 +0000, glen wrote:

Yes, please. My flowerpot + hair dryer doesn't make the grade...
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I built a charcoal maker fashioned after the one found a this link: http://www.twinoaksforge.com/BLADSMITHING/MAKING%20CHARCOAL.htm
The charcoal maker uses "cinder blocks" and, to date, several of the blocks have cracks on the inside walls. The charcoal maker does not produce nearly the heat of a forge so I would suspect that the forge in question is lined with some thing.
brad
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Australopithecus scobis wrote:

Could be but I doubt it.
You are expecting the foam type brick ?
I have some very high temp brick used in my wood stove and it looks like cinder block - but it is 1 1/2" thick and cuts with a saw. It is a heavier type of material and is usually backed with steel. (it is a steel wood stove after all)
I could not see having the foam type in a stove I use a shovel in or heave a short log. The temps are in the light red to white in tight spots.
I gave away a bunch after I rebuilt my stove. I suspect a stove dealer would sell you a replacement set - not very expensive. Being semi-solid they make flat sides and can be held in angle iron while the foam type can't.
Martin
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