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Wednesday, May 13, 2015

The Catalan Forge

La Farga Catalana

The Catalan Forge, of the Medieval Spanish era and perfected around the 8th century, was a furnace designed to increase the efficiency and yield from the direct reduction bloomery furnaces that had been used for hundreds of years prior. As tall as 5m and able to produce blooms upwards of 315kg from a single run, the technology quickly outpaced what a crew of smelters were capable of working by hand, and gradually developed into blast furnaces.

Aside from the shape, one of the major differences from the eastern reduction furnaces is the charging of ore and charcoal. A ramp on the wall opposite the tuyere feeds a column of ore, approximately a third the width of the furnace, towards the growing bloom. Traditional cylindrical furnaces take ore and charcoal in layers, allowing the ore to heat as it descends. Here, however, the excess heat of the burning charcoal prepares the large body of ore for melting throughout the run in addition to secondary charges added with charcoal.

Kept wet, the topmost layers of charcoal do not burn as quickly, acting as a control for the speed of fuel consumption. For this run, the mixture of wet charcoal and additional crushed ore was added on top of the depressions made when the column dropped.

Loading the initial charges of charcoal and coal required a steel plate to divide the two. Held two thirds of the way out from the tuyere, that larger volume was filled entirely with charcoal, while the smaller third was mostly ore. At this point, the furnace has been preheated over the course of a few hours and is ready for the smelt to begin.

At first, there was minimal slag, but then the floodgates burst and a heavy river poured out every few minutes until the end.

After three hours, the bloom was ready for extraction. Although the scale of this furnace is considerably smaller than its Medieval parents, the final bloom weight was still around 7.25kg.

Historically, the bloom would be lifted out the top of the furnace so the next smelting crew could come directly to a hot, ready to use furnace. Here, however, we pulled it out the side.

After cutting, the two halves sparked in the mid-lower range of high carbon steel (~.50%C)

Much was learned in the process of running the Catalan Forge, a design which has not wholly survived the ages. Perhaps one day soon a full sized forge can be built, but with the resources demanded by this considerably smaller version, the time, cost and manpower would be substantial.

For more information on the Catalan Forge, kindly see these links:
On this smelt
Jesus Hernandez
Miquel and Josep

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