Scaffold
See CHARGING-PLATFORM.
Scaffolding is the formation of highly refractory masses of scoria and iron upon the cupola or blast-furnace walls, which interfere to a remarkable extent with their free working. These obstructions may be caused by the accumulation of refractory slag; from the use of soft fuel that is crushed by the superincumbent charges; uneven distribution of the charges; inferior fuel; too heavy burdens; etc. Most of the conditions enumerated act by obstructing the blast, and thus interfering with a free ascent of the gases; the furnace loses heat, and the slag coagulates and favors the formation of scaffolds. In the ordinary cupola a scaffold may be removed by the introduction of finely divided fuel at the tuyeres, which are directly underneath the offending mass, reducing the blast somewhat until the obstruction begins to yield; and it is sometimes possible to loosen them off by means of a long bar from the charging-hole; but in the case of blast-furnaces more drastic measures must be employed. See CHARGING; RATIO OF FUEL TO IRON; SALAMANDER. Scaling-furnace, as its name implies, is the furnace in which plates have the scales removed by the application of heat.