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Full text of "Metallurgy Of Cast Iron"

CHAPTER VI.
CAUSE AND EVILS OF SCAFFOLDING AND SLIPS IN A FURNACE.
The factors causing the greatest irregularity in the
working of a furnace are scaffolding1 and slips. This means that a portion of the stock will hang at one point for a period and then suddenly becoming loosened, will slip for a distance and reach material filling* the bottom or hearth of a furnace. There are four factors effecting the hanging of stocks and slips, whicli are evils all furnacemen aim to overcome. The first of these is the lines of the furnaces, the second the manner in which the stock is delivered to the furnace, the third the quality or nature of the ore and fuel used, and the fourth the state of the temperature of the blast and atmosphere causing a furnace to work cold or hot. A. few years ago experts said that the Messabi ores could not be smelted in a furnace, owing to their being so fine and loamy. But the large percentage of iron which, they contain, their low phosphorus, (which makes it a. good ore for Bessemer,) and low sulphur, three very desirable elements, combined with low cost, caused furnacemen to try it and persevere in its use, until to-day it is a large percentage of the ores charged into many furnaces. Nevertheless, furnacemen find much, trouble from slips and wastage of this ore in the form of fine dust being carried out with the gases throug-li is generally largely obtained from the fuel in a furnace. Iron from the ore, as well as the lirne in the flux absorbs sulphur. Which of these two elements, in the process of reducing the ore, will absorb the greater percentage of sulphur from the fuel depends upon the degree of heat obtained. Lime has a great affinity for sulphur, and if the slag is made thin and hot it can counteract the absorbing power ofee reactiony they are often composed of about equal parts of silica and alumina. Bricks should contain silica or alumina in proportion to the amount of heat or friction they are                                                 if j