Peter King wrote
>Early blast furnace linings were apparently
usually of stone, <
Sandstone is pretty good for blast furnace hearths as long as the slag is
not too limy. It has a transformation which causes a large expansion on
heating which closes up the joints. I can't remember from which phase to
which. Maybe tridimite to cristobalite. Molten pig iron has a low surface
tension and will creep out though anywhere. It also, if reasonably pure, has
a high melting point, perhaps above 1600 deg Celsius.
These properties are not useful in the stack, which does not get so hot,
and firebick is easier to fit together with gas tight joints. Modern lining
practice uses shaped bricks to make this even easier. Some of the clay at
Ironbridge may have been used as "mortar" when laying the firebricks. Some
would have been needed for stopping the taphole, though this wouldn't need a
lot.
Peter Hutchison
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