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LINING AND DRYING OF FURNACES. 43
more fuel than by any other plan, but is quicker in its action of drying. After a fire has been well started, all holes around the furnace and the top, with the exception of a " bleeder" H, Fig. 13, page 57, of about twelve inches diameter, are closed, the '' bleeder '' being left open to create draft. The time taken to dry a furnace ranges from one to four weeks.
The life of a furnace lining not only depends upon qualities described in preceding paragraphs, but also upon the manner in which a furnace is worked. Those that are driven hard by high blast pressures, to get the greatest possible output of iron, have not nearly the life of those driven more mildly. America is noted for fast driving to attain greatest output. For this reason if furnaces run steadily for five years in our country they are doing very excellent work, whereas in Europe furnaces have run steadily for ten to fifteen years; although they are commencing to drive them faster than formerly.
One factor of great protection to linings exists in the formation of a kind of graphite or carbonaceous concrete which accumulates 011 the face of the lining; this comes from the kish, slag, and carbon refuse generated in the furnace, which may be found two to twelve inches thick on the lining, the greatest thickness being found in the hearth or lower body of a furnace.
The factors which destroy the life of furnace linings are defined under four heads by Fritz W. Lurmann in the Journal of the Iron and Steel Institute, 1878, Vol. I., page 200, as follows:
" i. The actual wear due to contact with the descending charge. This is relatively unimportant. 2. The actions of the alkaline cyanides and other substances present in the furnacectice now followed in lining furnaces. This spaceare jf|V