Metallurgy Of Cast Iron

CHAKACTKK OK SPECIALTIES MADE OK CAST IRON. 253
many of which call for different grades or mixtures of iron and some of which differ very radically. Those ranging from Nos. i to 9 generally call for variations in what is known as the softest grades of iron. Those ranging from Nos. 10 to 22 generally require variations in the medium soft grades of iron. No. 23 can generally be made of harder iron than permissible in the numbers above it. No. 24 is generally made of the poorest refuse of iron, consisting often of old rusty stove plate, burnt grate bars, and annealing pots, also tin sheet scrap iron. A mixture of these inferior grades generally gives a hard white, or very brittle grade of metal. Nos. 25 to 29 are a class of castings that will generally require a different mixture and a harder iron than those ranging from Nos. 10 1^.22. Nos. 30 to 35 are specialties which generally call for as strong grades of iron as can be finished in lathes, planers, etc. Strong grades of iron can be made so hard as to make it difficult to turn or plane them in finishing such castings. Charcoal iron is often largely used in these latter grades, whereas, in. Nos. i to 29 it is rare that such is used, as coke iron can generally be made to answer all purposes. Nos. 36 and 37 require a grade of iron very distinct from the other specialties shown, owing to such castings having to stand radical, changes of temperatures, which cause an action of alternate expansion and contraction while the castings are in use. Iron of a medium soft character and low in phosphorus, or what is termed regular Bessemer, is found best for such castings. The cannon of No. 38 calls for a grade of iron that should be of fair ductility, but at the same time possess the greatest strength to be obtained. Cannons are generally made from the com-o.n. in ladle 1,772 Ibs. .100" -326 " I.IOO .242 3