RATIONAL CONSTRUCTION OF FURNACES
obtained by reconstructing this furnace upon the downdraft
principle, as shown, in Fig. 88.
IX. FURNACES FOR ANNEALING MALLEABLE IRON CASTINGS
Fig. 89 shows the old style of annealing furnace for malleable-
iron castings, according to Professor Ledebur. Fig. 90 is from the
patent of P. Schnie in 1898, for the same purpose, but upon the
downdraft principle. It is evident that it was practical experience
and not theory which led the inventor to apply the downdraft
principle to these furnaces.
X. CONTINUOUS OR MULTIPLE CHAMBER KILNS
Ring furnaces or kilns, notwithstanding the apparent perfec-
tion of their design, have never worked in a satisfactory manner.
Their main disadvantages are the following:
Too rapid cooling of the burned ware;
The resultant cracking and spawling of the ware, which in
turn results in a considerable loss of product;
An excess of air during combustion, resulting in a very sharp
The high temperature of the waste gases;
The large amount of fuel required for burning the ware.