FUEL AND TOOLS
Coal, co*ke or charcoal may be used as fuel. Charcoal is very clean and there is little to contaminate the metal. It is of low density, however, and greater amounts must be burnt to provide enough heat for bigger jobs. Little air blast is required, but it is still a very expensive form of fuel for the smith's work. Good co*king coal is usually much cheaper than charcoal. Coal must be in the form of small grains, kept wet on the hearth and gradually drawn toward the fire as work proceeds. During this time the coal changes to co*ke and may then be fed on to the fire.
Unco*ked coal should never be fed to the fire. If this is done, vast volumes of smoke and flame are produced, making working conditions uncomfortable. In addition, there is the danger that the metal will be contaminated with impurities such as sulphur from the coal. Sulphur causes a condition known as hotshort in irons and steels. This is a tendency to fracture at high temperatures. Clean co*ke is probably the easiest to use as it requires less management than the other fuels. Grains of co*ke should be small, about 12 to 16 mm.
Tools for managing the fire are a poker, a rake and a small shovel which are usually made by the smith (fig 20).
The forge fire is always changing and must be looked after constantly. It gradually builds up to its best, maintains this level for a while and then deteriorates. Unburnable materials such as earthy impurities melt and sink to the bottom of the fire to form what is called clinker. This must be removed periodically, the length of time depending on the work and quality of the fuel.
When clinker is to be removed, it is best to let the fire cool down for a few minutes, giving the clinker time to solidify so that it can be removed in one piece (fig 21). Clinker must always be removed before welding or at any time when it hampers work. Particles of clinker can be forced up through the fire to impinge on the metal. Fire management is probably the most difficult part of the smith's craft to master. Fire tools should be constantly in use.
FIRE HINTS
- Keep the fire as small as possible for any given job. Fire size should suit the job. A large fire for a small job is a waste of fuel. Use only sufficient blast to heat the job in hand.
- Do not allow the fire to burn hollow. There must be sufficient fuel beneath the workpiece to provide the heat and to absorb the oxygen in the blast. Hollowfires and excessive blast will oxidize the metal and may even burn it beyond any possible recovery.
- The fire is lit by hollowing out a depression sufficient for the size of fire required. Any remaining clinker should be removed, even small pieces. Paper and small pieces of wood or wood shavings are placed in the depression and lit. Hot glowing ash will form close to the blast pipe. Turn on a little blast and feed fuel over the hot ash. Gradually build up the quantity of fuel until the fire is of correct size and high temperature. Work can now begin.
