Thursday, August 09, 2018

Charcoal / Ore / Burn Rates?

On 2018-08-08 2:19 PM, Jeff wrote:
I remember that both you and Lee abide by the 1:1 weight ratio of charcoal to ore. But I can't remember how big and fast the charges were. Was it (like) 1kg every 10 min?

In North America, we normally calculate time per standard charcoal measure.
Most of us us a standard galvanised bucket - which runs about 1.8 kg dry charcoal (sized ) slightly depends on species.

'Bucket on a stick' standard measure (Icelandic / Hals furnace)
The standard is usually 8 - 10 minutes to burn that measure.
Anything below 6 is way too fast - cut back on air
Anything over about 14 is running too slow - increase air volume

The Europeans normally will report kg per hour
(most of us here just don't bother running the math)
The ideal amounts / time works out similar.

On ore
there is typically a ramping up of volume of ore over the progress of the smelt.
My group typically starts with 1 kg charges per charcoal bucket.
At first there will be a slight damping of temperature / increase in burn time as the cold ore works down the column.

A portion of ore charge (analog) added before being covered with a part bucket of charcoal.
Once the reduction reactions start, and the slag bowl starts to form, you should see the temperature / burn time shorten.
Adding increasing amounts of ore will help to keep the burn rate consistent - even though there is more and more ore inside the furnace column.
This makes the 'magic' ration even out to roughly 1: 1 ore to charcoal (by weight)
Expect in the later part of the sequence to be able to increase the amount of ore per charge - with the same burn time.
We usually hit at least a few 3 kg ore to 1.8 kg charcoal. I have managed a couple of times (on much larger total ore amount smelts) to get to 4 kg per 1.8 ! (Our usual is 30 kg ore, so we don't get to those big numbers often).
There is likely a 'type of ore' effect here too. Working with our bog ore analog, we have a high Fe2O3 content, without much silica (rock) impurities.

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

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