Sunday, February 26, 2012

How to make Bloomery Iron

(day 11)

How *do* you make bloomery iron?
Without getting into fine detail, this is a fast description of how it works:

"Briefly, the furnace is a cylinder of clay filled with charcoal, with high combustion temperatures supported by the injection of air into the base of the furnace. Once fully ignited, ore is added in small batches, while keeping the shaft filled with charcoal. Burning charcoal creates superheated carbon monoxide (CO) gas, which reacts with the iron oxide (Fe2O3) contained in the ore. In effect, the more reactive CO rips off the oxygen, leaving metallic iron behind. This iron is heavier, so it falls to the base of the furnace. A liquid glassy slag also forms, composed of melted furnace wall, silica from the ore, and charcoal ash. Falling to the colder base of the furnace, it congeals, forming a bowl shape. The descending iron particles collect inside the liquid pool of slag within this bowl into the bloom mass. Excess slag may have to be tapped off to prevent blocking the air flow at the tuyere. The bloom is finally extracted while hot, either through the top or bottom side of the furnace, then hammered to consolidate it."

" There is a relationship between furnace size, position of the air system, air volume required, the nature and size of the ore particles, the size of the charcoal fuel, and the best sequence of adding both charcoal and ore. Changing any one of these variables will alter the nature of the bloom produced. Using the wrong combination may result in there being no effective production of iron at all. "

The quoted sections are from my just published article 'If You Don't Get Any IRON..." in the journal 'EXARC'
Typical Experimental Iron Smelt set up.
Industrial blower, air gate and metering system, hose to T shaped viewing port in turn attached to tuyere.
Clay 'Short Shaft' furnace, with charcoal fuel stacked ready to consume.
Vinland 1 - May 2009 (Go on for details)

Readers interested in far more detail on bloomery iron making are referred to the Wareham Forge Experimental Iron Smelting web site.

Of special interest will be a couple of fast working guides to building and running an iron smelting furance:

the Econo Norse Smelter
Developed by the DARC smelt team - using standard fire brick packed with sand
Go on Econo Norse Handout.

the Flue Tyle Smelter
Developed by Sauder and Williams - using a ceramic chimney liner
Go on Flue Tyle Handout.

As work with the individual blooms progresses, there will be references back to the individual smelt events which produced each bloom.

Readers may notice a couple of things: First, the grand plan of a blog post every day obviously got overtaken by the flow of other work. Second, days worked on the project bear little resemblance to any kind of 'normal' (M-F) work week. Such is the real life of the artisan!

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February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

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