2019 February 18    Metal & Shop  


Introduction


In the first article, I built a wood-fired side-blast forge made from a 55-gallon drum. 

So after building the basic wood forge, I decided to find out how it worked with anthracite coal.

Again, I'm not by any means an expert on blacksmith forges.  This is just to share what I've learned so far.  Let's see how it went.


CAUTION:  Metalworking can be dangerous.  Wear eye protection.  Use proper ventilation at all times.  This is an outdoor forge design that has no chimney.  Indoors, any fire can produce deadly carbon monoxide buildup..  Please read the Disclaimer



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In This Article

Arranging the Bricks

Starting the Coal

First Heat

Re-Arranging The Bricks

Now We're Burning Metal!

What I Learned Here

Conclusion




Arranging The Bricks


The basic cut-off drum is sort of a fire circle with its own floor.  The whole thing sits up on blocks.  Thin firebrick insulates the floor of the drum, with firebricks on edge around the perimeter.  The basic idea was to put scrap wood and branches in there, try to keep the pile consolidated, and occasionally turn on the side blast to increase the heat. 

For coal, I thought a few more bricks might help channel the heat. 

Tamping down the ashes with a brick, I then placed three bricks like so:



These are solid clay bricks.  I would not use concrete pavers for this part.  (As it is, one of the bricks cracked and broke, as you'll see later.)

The way it is at this stage, some of the coal is going to roll into the empty spaces around the bricks.  Should have packed those spaces full of dirt, sand, clay, or ash.  Oh well, next time.

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Starting The Coal


Anthracite is tough to light;  a charcoal or wood fire is necessary to start it.



There's smoke from the wood fire underneath as we add the coal.  It takes a few minutes for the coal to start burning.



As the hair dryer supplies air through the tuyere, there begins an orange glow from under the coal.

Anthracite burns mostly at the surface, like a burning rock (because it is).  The heat radiates away faster than it can stay lit, unless you keep the coal pieces close enough together and provide extra air.  If you turn off the hair dryer, a wood fire can still generate forging temperatures, but anthracite will slowly go out.

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First Heat


Let's start with a rusty old piece of threaded rod.  (That's just what I had handy in a five-gallon pail.)  The galvanizing, if there was any, is completely gone by now. 



The threads make this difficult to forge into smooth stock.  That could involve welding temperatures.

For now, we just want to test out some anthracite.

At this point the coal has a bright orange, concentrated heat zone.  Here's one of the advantages of anthracite over charcoal.  Once you light a heap of charcoal, the whole heap will eventually burn away.  Anthracite will not burn, except in the air blast zone.  That means you can have a reserve supply of anthracite around the fire, as you would with bituminous coal. 



Even at this early stage, it's not difficult to get the steel to a bright red heat:



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Re-Arranging the Bricks


Pieces of coal keep tumbling off the top of the pile.  This makes it tougher to keep a good-sized heap over the hot zone. 

Let's move a couple bricks around and see if that helps:



OK, now we're getting somewhere. 

Even a shallow coal pile can produce enough heat to burn the steel, if you're not careful.



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Now We're Burning Metal!


Even with anthracite, there's such thing as too much air.  There is some ideal amount where the coal stays lit, but it's not an oxidizing fire. 

More air will burn the steel faster, but it's still more than hot enough with the hair dryer on Low. 

A taller pile of coal will reduce the chance of burning steel, because it won't be so oxidizing.  So, build up the sides with brick, dirt, or ash, and turn down the air blast a bit.

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What I Learned


This was not a sophisticated or even very well-thought-out design, yet it was still able to generate forging temps with anthracite.

Like charcoal briquettes, anthracite just sort of glows, gradually turning into ash.  Anthracite is more like gravel, though.  Any upgrades to this forge design should concentrate on keeping the anthracite heaped up around the air-blast zone.

It's shaping up that we'll need a small trench with high sidewalls and open ends, rather than a square firepot.  (That could change, by the way, depending on the size of the coal pieces.)



It would help if the brick sides went up to a flat, table-like region on either side-- made of bricks, dirt, clay, or ash-- to keep extra coal. 

As usual, wear safety glasses.  Anthracite can crackle and throw small bits of hot coal quite a distance. 

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Conclusion


Anthracite works well.  It's denser than charcoal and smokes less than bituminous.  The main drawback is that a pile of it rolls apart like gravel, but there are ways to deal with it.

Even as-is, the forge could heat metal to bright red or orange heat quite easily.



Moving a few bricks around could make this work a lot better. 

In the next article we'll look at an upgraded design, testing it first with with wood / charcoal as fuel.


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