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Full text of "The Flow Of Gases In Furnaces"

VERTICAL FURNACES  FOR TEMPERING             123
to the muffle, and since then has operated in a satisfactory manner,
the following points being worthy of note:
1.  In spite of the large size of the muffler, its temperature was
absolutely uniform, and no differences of temperature could be
detected between the different portions of the furnace, by the use
of a Le Chatelier pyrometer;
2.  By the operation of a damper, this temperature could be
regulated   very  accurately  within   a   wide   temperature  range
(900° to 400°) ;
3.  The quantity of fuel consumed (55 kg 80 per hour) corre-
sponded exactly with the computed fuel consumption.
The only trouble with this furnace resulted from the inter-
mittent operation to which it was subjected. This caused bending
and warping of the muffle which failed completely after about
two months' service, necessitating replacement. That this warp-
ing was entirely due to the intermittent operation of the furnace
is borne out by the fact that a vertical muffle for practically the
same class of work, installed in a furnace in the Poutiloff works,
which is operated continuously, lasts about fourteen months.
In order to eliminate the trouble in the furnace at the Petrograd
Arsenal the muffle was removed and the openings in the hearth
for the removal of the waste gases were relocated. This furnace
works very nicely for tempering and annealing, but it is no longer
a muffle furnace. Finally the furnace was reconstructed with a
new muffle constructed of special thin bricks, and since that time
no operating troubles have developed.
XII. VERTICAL   FURNACES   FOR   TEMPERING,   ANNEALING   AND
HEAT TREATING
The application of the downdraft idea has nowhere given such
brilliant results as when applied to vertical furnaces, and there is
no other form of furnace which gives so little satisfaction and so
much trouble as a vertical tempering furnace. The reason for
this is very simple. In every works " the heat-treating depart-
ment " is the " forbidden ground " of the plant. Secrets, secrets
and secrets! As a matter of fact, the men who possess these secrets
always know less than those who do not possess them.
Nevertheless, tempering and annealing furnaces only require a
working temperature varying from 800° to 1000° and—good or
bad—they may be operated. With regard to the heat-treating