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Hypercon
Fires for Blacksmithing
Background
The predominate blacksmithing fuel of the 19th century in most of the United States was bituminous coal because of its ability to produce high quantities of heat. In remote areas of Texas however, charcoal was used until after the US civil war. This charcoal was made by digging a large pit. At the bottom of the pit was placed hot coals. On top of the coals were placed bundles of hardwood and the pit was then covered with dirt. After a week or more the wood had charred throughout and this was dug up an and then used for fuel. Because of its relatively low density, charcoal burned cooler and fires consumed greater quantities than lump coal. With the increasing penetration of rail lines in the 1860s and 1870s, coal became more readily available and replaced the less efficient use of charcoal even in remote areas.
The Coking Process
When coal burns it passes through several stages. The first stage is coking. As the denser hydrocarbons burn out, releasing sulphur, the source of the yellow smoke from a coal fire, the coal becomes semi-plastic and the pieces begin to fuse in lumps. These lumps are called coke. The coke is lighter, having had the heavier hydrocarbons removed and has a lower ignition point than the coal. When air is forced through the coke an extremely high temperature is achieved.
The Basic Fire
The basic fire is cone shaped with coke surrounding the inside of the cone. As air is forced through the cone, the area inside the cone is superheated by the coke walls. As the coke burns out, it is replaced by new coke from the walls of the cone. This is achieved by tapping the outside of the cone with an iron bar, causing the new coke to fall to the center of the cone.
The highest area of heat is contained approximately 2/3 within the cone. This fire style is appropriate for bending, drawing out and other work that requires a red to orange heat on the iron.
The Welding Fire
A welding fire is designed to generate a much higher level of heat than the basic fire. This is accomplished by capping the cone to hold the heat in and forcing the airflow to be redirected through a mouth under the cap.
A proper welding fire will bring iron to a near white stage. At this stage the iron becomes plastic and will fuse with another piece of iron in the same stage. The hottest point of this type of fire is typically at the midway point between the roof of the cone and its base.
Building the Fire
Both types of fire begin with a base of fresh coal arranged in a circle around the air vent. In the center is placed several loose pieces of coke. The walls of the cone are then built around this coke. When a welding fire is desired the cone is made with a high wall and a low and then capped with a large piece of coke over which smaller pieces of coal can be placed. In both cases the coke if ignited and then air is forced through the coke. This heats the sides of the cone and fuses the cone as the new coal goes through the coking process. Small amounts of water dripped along the outside walls of the cone will help the cone to fuse with fewer air gaps.