[TheForge] Water on your coal forge fire? A Novel

Mon May 31 17:58:04 EDT 2004

You don't have to worry about "flames"; I'm too tired after reading your
novel.  Lots of good info there, some of which I knew and some of which I
had never heard of.

I have learned a lot of my blacksmithing by watching others; I know what to
do, but I don't know why it works.  Stuff like your reply gives me a the
why, as well as the what.

Thanks

Murf

> -----Original Message-----
> From: theforge-bounces at mailman.qth.net [mailto:theforge-
> bounces at mailman.qth.net] On Behalf Of info at reciprodyne.com
> Sent: Sunday, May 30, 2004 3:26 PM
> To: Sponsored by ABANA
> Subject: [TheForge] Water on your coal forge fire? A Novel
> 
> Dear Dave and List,
> 
> Coal is a coarse mixture of various fuels: most importantly the carbon in
> the coke, and the flammable gasses trapped in the coal. Sulfur, peat,
> oils,
> and other combustible impurities in the coal can also act as fuels, but
> will
> be disregarded for the moment. The coke (carbon) is the most important
> component where heating metal for forging is concerned. Coals are classed
> according to their carbon content, Anthracite (most carbon), Bituminous
> (Most common for forging), Sub Bituminous, and Lignite (least carbon).
> 
> The gasses in the coal have a lower ignition temperature in air than the
> coke (carbon). Some coal with a lot of volatile material will burn by
> itself
> without forced draft, just from the combustion of the gasses. This type of
> fire will not heat metal to a forgeable temperature, because the gasses
> are
> burning off at a relatively low temperature. On the other hand, some coals
> have so few volatiles that they will not burn at all without forced draft.
> 
> With the addition of atmospheric oxygen from the forge blower the carbon
> in
> the coke becomes incandescent, and the radiant heat from the glowing coke
> then heats the metal in the fire to a useable temperature. By the time the
> coke in the coal is blown and heated to a sufficient temperature for
> forging, the gasses are long gone as "steam", smoke, or flames. The steam,
> smoke or flames do not heat the metal.
> 
> In the heap of green goal surrounding the fire itself, the radiant heat
> from
> the fire (and some escaping heated air) begins to drive off, or "distill"
> off the volatile gasses, which, if heated to combustion temperature,
> become
> large romantic flames which heat the smith, but not the work.
> 
> Wetting the green coal does several things, but most importantly, it keeps
> the carbon (coke) in the green coal below it's combustion temperature
> while
> the more volatile gasses are being driven off. That way, the all important
> coke is preserved from premature combustion while the distilling of gasses
> is taking place. When the gasses are gone, the coke is ready to be raked
> or
> pushed into the heating portion of the fire.
> 
> The presence of water in the green coal immediately surrounding the fire
> also keeps some of the gasses from reaching combustion temperature, so
> that
> they boil off in the steam, rather than creating unpleasant flames.
> Whether
> you steam off or flame off the gasses is largely a matter of preference,
> but
> you generally get more useable coke for heating your metal if you keep the
> surrounding green coal below the combustion temperature of the coke. You
> get
> less flames and smoke if you keep the rapidly departing gasses below their
> combustion point.
> 
> The cost of BTUs absorbed in the vaporization of the water are completely
> insignificant compared to the BTUs preserved by preventing the premature
> combustion of the coke. The water (and the gasses) in the green coal are
> being boiled away by the stray radiant heat that escapes from the center
> of
> the fire, heat that is not doing useful work anyway.
> 
> The amount of water necessary to produce the maximum quantity of usable
> coke
> varies widely with the quality of the coal, and the size of the coal
> particles. Some fine, high carbon coals burn well almost dry.
> 
> The more carbon (and less gasses) in the coal, the less water generally
> will
> be needed to keep the coking process under control. Coal with more carbon
> and less gasses is (in general) "better" for forging purposes, ignoring
> the
> melting temperature of the slag for a moment. If you just buy coke already
> made, you don't need any water at all, except perhaps to keep the fire
> from
> spreading too much, but you have to blow it continuously, or it goes out
> pretty fast.  Pure metallurgical grade coke is my forging fuel of choice,
> and charcoal second.
> 
> Finer coal particles help keep the hot (burning coke) portion of the fire
> contained, and less draft air escapes through the surrounding green coal,
> so
> that the fire spreads less readily, and the available air blast is more
> effective. If the coal is too coarse, enough blast air can escape through
> the loose pile to make it difficult to reach forging temperature. The
> coarser the coal, the more wetting and packing may be necessary to keep
> the
> fire hot and contained.
> 
> Ok, let's talk about clinkers.
> 
> Coal comes from the ground, it is comprised from carbonaceous materials
> (such as old trees and dinosaurs :-), and also contains a more or less
> percentage of dirt (ash). This dirt (ash) is comprised of a fantastic
> variety of materials, but largely silica, minerals, etc... you know, Dirt.
> 
> In the high temperature of the forge fire this dirt mixture forms a very
> crude glass or slag know as clinker. Some rare forms of dirt (like pure
> silica) may have such a high melting point that they are not a melting
> problem at forging temperatures, but these are not often found in coal, so
> the best way to prevent clinkers from forming is to obtain coal without so
> much dirt (ash) in it in the first place.
> 
> All coals contain some ash (dirt), but whether it becomes problematic
> during
> forging depends on the melting temperature, friability, etc. Some clinkers
> are sticky, some are not. Some coals may be dusty grey, have 25% by weight
> of ash, and only 50% of carbon, but forge very well because the clinkers
> do
> not clump. Some coals are very shiny black, very little ash, a rating of
> 15,000 BTUs per pound, a high price tag, and immediately turn to a sticky
> mess at forging temperature. Most coals are somewhere in between.
> 
> The free coal that comes the from the stoker bin in the old farmhouse may
> be
> fantastic or horrid for forging, the only way I know to tell is by trying
> it
> for a couple of days. Some coals may work OK at "forging" temperatures,
> then
> become sticky when blown to "welding" temperature.
> 
> Clinkers are caused by dirt mixtures being exposed to temperature above
> their melting point in a forge fire, not by the apprentice who doesn't
> hold
> his jaw right, too much stirring, or by the phases of the Moon. You can't
> "cause" clinkers by improper treatment of the coal. You CAN prevent them
> entirely by buying "better" coal, or using coke or charcoal.
> 
> I have found that "clinkery" coal can sometimes be made to work better if
> kept very wet, which tends to keep the clinkers solidified, and broken
> into
> smaller pieces.
> 
> Once, when I had some sticky coal, I put a wide, heavy ring of 1" thick
> steel plate around the blast hole in my forge, and kept the coal (and the
> plate) very wet around the fire. Instead of raking the newly formed coke
> into the center of the fire, I pushed it in from the side with my hands.
> The
> relatively cooler ring o'plate caused the clinker to form a solid
> "doughnut"
> of glass around the hole, and kept most of it out of the tuyere. Every 45
> minutes or so, I would pour a liberal amount of water around the opening,
> and lift out a perfect ring of clinker with my poker. I would hang these
> on
> a hook, just because I could. If I raked the top edge of the "volcano"
> into
> the fire, the little free clinkers would melt together over the air hole
> and
> shut me down. Getting some good forging coal solved the issue completely.
> 
> There are many different kinds of tuyeres, grates and air holes, and they
> all have their place, experimentation is the best teacher.
> 
> Excuse the over "blown" response. I will ignore all "flames".
> 
> 
> --
> Tom Troszak
> Reciprodyne
> 47 Panola St.
> Asheville, NC 28801 U.S.A.
> 
> Phone and Fax: 828.251.1112
> Cell phone: 828.731.7828
> e-mail: info at reciprodyne.com
> website: http://www.reciprodyne.com
> 
> 
> 
> 
> 
> 
> 
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