METALLURGY OF CAST IRON.
vary the depth of a chill in castings, as seen by Chapters LI. and LVL, it is best to be guided by analyses of the grey body of the chilled castings or scrap.
The impracticability oi formulating standard mixtures will be realized after a study of the varying , conditions which must be met in actual practice. Each founder must formulate his own mixtures, based upon the principles shown in this and the preceding chapter. It may be stated that mixtures for chilled rolls, which include any scrap used as well as the pig, may often range in analysis when ready for charging as per Table 43. The wide variations in the sulphur, manganese, and phosphorus seen is given for the purpose of showing the range generally necessary to cause the different character of chills often required, as seen by a study of the preceding chapter.
TABLE 43—APPROXIMATE ANALYSES FOR CHILLED ROLL MIXTURES.
Diameter of Rolls. Silicon. Sulphur. Manganese. Phosphorus. Total Carbon.
8" to 10" I.OO .0 to .06 .15 to 1.50 .20 to .80 2.60 to 3.25
12" to 14" .So .0 to .06 .15 to 1.50 .20 to .80 2.60 to 3.25
16" to 18" .70 .0 to .06 .15 to 1.50 .20 tO .80 2.60 to 3.25
20" to 22" .60 .0 to .06 .15 to 1.50 .20 tO .80 2.60 to 3.25
24" to 26" •5° .0 to .06 .15 to 1.50 .20 tO .80 2.60 to 3.25
To illustrate Professor Ledebur's division of carbon
in rolls, referred to in Chapter XXXVII., page 261, Table 44 is given. Iron is melted in both air furnaces and cupolas for casting rolls. The air furnace is the best for melting such mixtures as it gives a purer metal, on account of not compelling- the iron to be in contact with the fuel when being melted, as it is in cupola practice. In melting iron in air furnaces care must be exercised to avoid an oxidizing flame, as this the white to the grey in chilled castingsly the same depth.... Shop scrap ...... 15 x ro x 1.50 i. So 22.50 iS.oo