DESIGN OF OPEN-HEARTH FURNACES
The pass unit will be different for a different wall thickness,
and it may be desirable to try several variations, in order to secure
the most desirable arrangement. An old rule is that the active
heat-storage capacity of brickwork is comprised in the depth of
1.25 in from the surface, giving a wall thickness for maximum
results of 2.5 in (63 mm). When the brickwork is laid up to
secure stability, 9-in straights give very good results. With
thicker walls the time of the cycle must be increased, to develop
the full weight of the brickwork. With the time cycle assumed,
which agrees fairly closely with practical working, a wall thickness
of 2.5 in (63 mm) utilizes its full heat-storage capacity. With a
fifteen-minute cycle a 2-in wall would be desirable, but is probably
a little too thin to give the best operating results.
Gas on Gas
*Air on Air
Gas on Waste Gas
Air on Waste
By using a 2-in (50 mm) brick, the size of the pass and the space occupied will be reduced : 50-7-0.33=?;= ...............
6 0 in
Brick thickness ...............
2 0 in
Diamet r square pass .........
Wall thickness around pass .....
2 5 in
2 0 in
Area unit pass = 62 = ...........
0 m2 0361
0 m2 0225
Area of pass opening = ..........
0 m2 0162
0 m2 0100
Area occupied by brick = ........
0 rn2 0199
0 m2 0125
As the unit pass was made the same, the volume of brick and pass in the air checker will be changed to Brick = 301. 06X0. 5526= .....
166 m3 37
Pass =301.06X0.4474= .....
134 m3 69
The lineal amount of pass and brickwork is found by dividing
the brick and pass volumes by the area of the brick and pass in
the pass unit. It will generally be found that there is a slight
disagreement between the lengths determined for the pass and the
brickwork. It is preferable to take the highest of the values so
found for determining the size of the space to be occupied by the