CHAPTER 3
THE BLACKSMITH'S FIRE
FUEL
Both coal and coke breeze are used for blacksmithing, and the choice seems
to depend mostly on local custom. Although first class work can be done with
either, a blacksmith familiar with one is usually embarrassed by the other.
Good blacksmithing coal should be bituminous and free from sulphur, and as
regular supplies are now hard to obtain the beginner may be well advised to
use breeze. This must be good smithy breeze free from dust; the most suitable
size is known as `beans'. Crushed or brokenup boiler coke or furnace coke
is not suitable for forging.
FIRE TOOLS
Four tools are used to manage the fire: a poker, shovel, rake (Fig. 26 above
left) and swab (Fig. 27 below right). These vary in more ways than can be
imagined. Some blacksmiths never use a rake, and others scorn the swab altogether,
but the tools shown are a fair example of a practical set.
THE
FIRE
Coal and coke require slightly different management both in lighting the fire
and in keeping it burning properly. To confine the burning part of a coal
fire to the required size, soak the coal with water. This will retard combustion,
assist coking and impede the passage of the blast. It is not necessary to
wet breeze, because its flame does not spread so readily and in any case wetted
breeze does not form a draughtproof barrier. As long as enough fresh breeze
is fed on to the fire, which must be kept clean, the fire will remain sufficiently
concentrated of itself. This difference should be borne in mind when reading
the description of managing the fire later in this chapter.
The blacksmith's fire does not burn steadily indefinitely. It gradually builds up to its best, maintains this condition according to the fuel and the work, then dies down until it becomes useless. With good fuel the fire may last all day on rough work, but with poor fuel on fine work it may be dead in an hour. When using coal, make sure before starting a job that an adequate well-soaked supply is available and banked up ready to replenish the fire as required.
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Gradually increase the blast and as the fire breaks through (Fig. 31 right) it can be made up directly with fresh breeze. New coal should never be heaped on top of the fire, but always worked in from the outside as in this way the impurities in the coal are burnt away before it comes in contact with the metal. Wet coal should be packed all round and gradually driven into the heart of the fire with the edge of the shovel. |
MANAGEMENT OF THE FIRE
There are three aims in managing the fire.
(i) To keep the fire as small as possible. The whole purpose
of the fire is to heat metal and anything more is both wasteful and a nuisance.
Never use more blast than is necessary to keep the fire at the size and heat
required for the job.
(ii) To prevent the fire from burning hollow. The heat in
the fire must be in the middle, immediately below the piece of metal being
heated. A hollow fire has no fuel to produce heat where it is wanted. Also
the unburnt blast air will get at the hot metal and oxidize the surface or
may even burn it beyond recovery.
(iii) To defeat clinker. Clinker is the blacksmith's worst
trouble. Cold, clinker is like a crude black glass; hot, it is like black
treacle. It is produced by the combination of oxygen in the blast with impurities
which are more or less present in all fuels. This is a further reason for
not using more blast than necessary.
As the fuel burns, clinker is formed in a molten state and trickles down to
the bottom of the fire, just in front of the blast hole. Here the clinker
obstructs the blast and bits are blown upwards and stick to the hot metal
giving it a molten coating. Metal in this state cannot be welded and when
it is struck, the molten clinker spurts out from under the hammer and burns
the hands. This not only hurts but interferes with the work.
Unless very good fuel is used, the fire will become dirty almost as soon as
it begins to burn freely. kt this stage the only thing to do is to persevere
for one or two heats in spite of the dirt. The blast is then cut off for a
few minutes to allow the liquid clinker to cool and solidify sufficiently
to be hooked out in one piece with the tip of the poker, which is flattened
and curved for just this purpose (Fig. 32).
A great deal of judgment is required to know exactly how long the clinker
must be allowed to cool, when it is ready to catch, and just where to find
it. Even so, it is a feat of considerable skill to remove it all without disturbing
the fire. Nothing but practice is any real help in this. Sometimes the clinker
does not form into one lump or else the lump breaks up, but in either case,
the pieces can be distinguished from the dully glowing fuel of the cooling
fire by their brighter red heat, their smooth surface and, as soon as they
begin to cool, by the characteristic `clink, clink' they make when touched
by the fire tools. Hell to a blacksmith is not a place of fire and heat, but
of clinker.
The metal which is being heated should be kept near the top of the hot part
of the fire with a good bed of live fuel underneath it and a sufficient covering
of glowing coke on top. Remember that a coal fire always produces some coke
as it burns. This covering not only prevents the heat from being radiated
from the metal, but burns up the free oxygen from the air above the fire before
it can reach the hot metal and oxidize it.
For this reason metal should never be brought to a red heat on top of the
fire-always keep it below the surface where it is protected from the air and
where the fire is hotter.
