How Does a Coal Forge Work?

Written by john albers
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How Does a Coal Forge Work?

Coal Forge Structure

The basic structure of a coal forge is made from fired brick or heat-resistant iron, depending on the intended use. A larger forge which would generally be hotter would need to be made from brick as an iron forge would begin to melt at extremely high temperatures. In either case the forge is basically a flat plate with a depression in the centre. At the bottom of the depression is a vent downward through which ash can fall and fresh air can be pumped, in order to feed the burning coal. In times past a bellows would've been connected to the side of the bottom vent in order to act as the air pump, but nowadays small electric fans have been designed to do that job. Over the top of the forge should be another vent or flue through which smoke and excess heat can leave safely. Without this flue a blacksmith would sicken from coal fumes, his eyes and skin burning from chemicals in the smoke. With this rudimentary system, blacksmiths created tools, weapons, and armour for several hundred years. Today, small portable coal forges are used by amateur blacksmiths all across the country.

Lighting and Prepping a Coal Forge

A forge takes a good deal of time and preparation to light and get ready for use. Kindling wood and paper were formed into a small pile at the centre depression of the forge and set alight. Some people use lighter fluid for this nowadays, but this is incredibly dangerous as a coal heated too quickly can crack and explode. As the kindling burns, bituminous coal is placed on the plate of the forge, filling it completely with a single layer. The coal closest to the depression is slowly pushed by the metalworker toward the flame and allowed to cook. What many people do not realise is that bituminous coal, which is the most common type, releases sulphur and smoke as it burns. This makes it unsuited for smelting iron and forging other metals as it would release impurities into the metals you're heating. In order for coal to be used, it must be cooked under low oxygen conditions until it turns into something known as coke. Coke burns much more easily and at higher temperatures than coal, making it ideal for a smith's needs. The coal closest to the flame will turn light brown and become porous as it undergoes the change, which should take roughly twenty minutes. More surrounding coal is pressed into the fire until there's enough burning coke at the centre of the forge to do whatever job you had in mind.

Using a Coal Forge

Only once the coke is made and set alight does one engage the fan or bellows to feed the forge more oxygen. The coke should flare and burn more brightly. The smith takes a set of tongs and places the item he intends to work into the hottest part of the burning coke to heat. Depending on what metal is being worked, this may take less than a minute or upwards of ten. Once the metal has been heated sufficiently, it's removed from the forge and worked on an anvil with tongs and hammer until it takes the desired shape. The smith may return the metal to the forge if he takes too long and the metal cools. He may also return the metal to the forge, placing a different portion of the metal into the coke so that too may be worked, as is the case with larger items. The forge should never have any actual flames amongst the coke while it is being used. This indicates temperature flares and would cause metal to heat unevenly, ruining it. To prevent this, the forge often has a cup of water flung over it to bank it back down to manageable temperatures every few minutes. When the smith is done with his forge, he simply disengages the bellows or air pump and allows the coal to die. This leaves a good deal of unburned coke and coal which can be ignited quickly for further use at a later time.

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