Endless tunnel of Hoffman kiln
Endless tunnel of Hoffman kiln
Apart from mismanagement, another risk was the weather. If a chimney is used to create draught, a storm
will create irregular heating. Therefore, in some later kilns, large fans were positioned to obtain a
more powerful and perfectly steady draught (also speeding up the production process). Large temperature
differences also were a challenge.
Although it simplifies the explanation of the Hoffmann system, in reality most of these continuous kilns
did not really consist of 12 to 24 separated chambers. The so-called chambers were basically theoretical
sections of the endless tunnel that indeed could be separated from each other by very large metal dampers
(which could be raised and lowered from the outside) or – later – sheets of paper or fabric (which were
automatically torn apart at the right moment by the approaching hot air).
But, at any time in the process, a maximum of 3 shutters were in effect and so a Hoffmann kiln in reality
never contained more than 3 chambers – one being a very large one. The basic function of the shutters was
to prevent the cold air drawn in from going the wrong way around the kiln.