MUFFLE FURNACE FOR TEMPERING
vertical muffle for continuous service, constructed according to
the designs of the author, was in use at the PoutilofI works (Petro-
grad). In the arsenal the daily interruption of the work resulted
in the rapid wearing out of the muffle, and after a run of two
months it was decided to remove the cast-iron muffle and operate
the furnace with a perforated brick hearth through which waste
gases could pass off. The furnace was reconstructed in this
manner, without a muffle, and upon being placed in operation
worked perfectly, heating very uniformly and fulfilling perfectly
all the demands for annealing and tempering which were made
FIG. 135.—Cross-section through
FIG. 136.—Cross-section through
Waste Gas Ports.
The following shows the computations which were made:
The volume of the heating chamber, according to the design,
was 3 m3 30; the temperature of the gas was to be 1000°, the
combustion being neutral, that is to say, without excess air.
The instantaneous calorific intensity was computed as 2000°,
giving a drop in temperature of the gases of 200° per second, the"
time which the gases remain in the heating chamber being
- = 5 seconds.