The description of Hoffman kiln.
The description of Hoffman kiln.
A “Hoffmann kiln”, “ring oven” or “ring kiln” was a massive oven in which clay was baked at a temperature
of around 1,000° Celsius (1830°F) to produce bricks and tiles. It was a circular, elliptical or
rectangular brickwork structure that consisted of an endless tunnel, divided into 12 to 24 chambers, all
interconnected to each other and to a main flue leading to a large chimney. Each of the chambers also had
an opening through which the bricks were loaded and unloaded, to be closed by a door or a temporary brick
wall.
The chambers were filled with bricks (some 25,000 of them) and fired one after the other. The heat in one
chamber was not only used to bake the bricks inside, but also to preheat the still to be fired bricks in
the succeeding chambers. Meanwhile, air that was drawn in, through the door of the chamber where bricks
were unloaded, travelled in the opposite direction and cooled down the already baked bricks in the preceding
rooms. The fire was “chased” around the building in a never ending process that was extremely energy-efficient.
Depending on the size of the kiln, it took between one and six weeks for the fire to complete a full circle.
The ring oven was patented in Germany by Frederick Hoffmann in 1858. It revolutionized the brick and tile
production industry because of multiple reasons: it allowed for a better and more uniform quality of
ceramic goods, it was much more economical both in terms of fuel consumption and labour costs, and it
raised the production output spectacularly – up to 10 million bricks per factory per year. Population was
growing fast at the beginning of the industrial revolution and brick producers were struggling to keep up
with demand. The Hoffmann kiln allowed for mass production of bricks and tiles, but despite its complexity
the whole firing process was executed without the use of machines.