Thickness | of casting. J Percentage ) of silicon, j %" i" ll/2H 2* 2^" 3" ZYs" 4"
.90 •7° .60 •50 .40 •30 •25 .20
In melting1 white iron mixtures the iron should be brought down " hot," and care taken not to let it get too near the danger point of becoming sluggish before pouring. White iron, being low in silicon, or high in sulphur, will cool very rapidly when it reaches a temperature where the eye can detect it commencing to lose fluidity. As a general thing the gates for pouring white iron castings should be made from one-third to one-half larger than for gray iron, in order that the iron may fill the mould rapidly. If castings over 2 inches thick are desired to be solid on their interior, feeding will be found necessary and much care and skill are required in the feeding, as white iron has great shrinkage and contraction. These two factors are about as great again as in gray iron. A contraction of about % inch per foot is generally allowed for white iron in castings ^-inch thick. As they increase in thickness the less of course the contraction.
White iron can be made gray and malleable by annealing; in fact, malleable castings are white iron annealed. The principle involved consists in packing the white iron castings in cast or wrought pots or boxes surrounded with iron oxides, generally in the form of rolling mill scale and wrought or steel turnings, the whole sometimes treated with a solution of sal ammoniac. Then again, hematite ores are used. In the selection of such iron oxides care is taken to have them as free of sulphur as possible, especially for 302, will permit any founder making a study of this chapter to intelligently formulate a mixture which will work well for any thickness of castings to be used for electrical purposes.castings in the cupola that would stand the tests of the United States Government for gun carriage work rightfully belongs to Messrs. Robert Poole & Son Co. of Baltimore, Md., and Muirkirk pig iron made by me. This was in 1893. The War Department at first refused to accept cupola iron as gun iron, but when it was fully demonstrateduois Iron Co., Illinois Steel Co., Jefferson Iron Co., Kittan-ning Iron & Steel Co., C. A. Kelly Plow Co., Lebanon Furnace, Longdale Iron Co., Lackawanna Iron & Steel Co., Logan Iron........................ 16,720 " t-