APPENDIX VII

DESIGN OF OPEN-HEARTH FURNACES
By A. D. WILLIAMS

IN designing an open-hearth furnace the first point to be settled
is the size of the hearth. Molten metal weighs 430 Ib per cubic
feet, so that 5.23 cu ft of bath will be required per ton of metal
capacity. The depth of bath permissible depends upon the work
to be done. With a shallow bath the reactions will be completed
faster than in a deep bath. The boil will be more violent and the
depth allowed for the molten cinder will be greater. Furnaces of
the mixer type, used in the Talbot and duplex process, are much
deeper than those used in the regular process.

In the pig and ore process the boil will increase the volume of
the bath to from 2 to 2.5 volumes. In the scrap process the bath
may boil to 1.5 to 1.7 its original volume.' The manner of handling
the cinder, whether it is retained in the furnace until the heat is
tapped or is to be drawn off by a cinder skimming notch, affects
the depth. In the early furnaces room had to be provided for all
of the cinder, and overflows were not infrequent. One advantage
of the Campbell tilting furnace was the facility it offered for
running off a portion of a heavy cinder. Later furnaces were
built with a cinder notch which permitted draining any excess
amount of cinder.

Table 1 gives the approximate hearth area in square feet
required for bath depths ranging from 1 to 3 ft. It was com-
puted by the formula:

nV 4

in which V—volume of molten metal in charge;
d = depth of bath, metal only;
yi=area of hearth.
194