•MIXTURES FOR CHILL ROLLS, CAR WHEELS, ETC. 271
tion of the chill is concerned. It is quite obvious wh}r this should be so, since the chill fixes the chemical composition within very narrow limits." In conclusion Mr. Bush says: CiTherefore, to emphasize what has been stated previously, it seems reasonable to conclude that the wear of ccr wheels depends upon the chill, and if chills of various wheels are so closely alike as these analyses show them to be there is really no evidence that the wear of these wheels will differ to any appreciable extent.1' For further analyses of car wheels, see Chapter LVIL, page 448.
The sulphur, it will be noticed, is much higher in Tables 47 and 48 than in Tables 45 and 46. Sulphur from .08 to .15 is now considered by many to give long life to car wheel chills. At the same time, it is also considered necessary to have manganese range from .30 to .80 in order to stand the thermal test described in Chapter LVIL This chapter also treats of methods of testing mixtures, car wheels, and annealing them. The depth of chill reqtiired in wheels ranges from )4 to /& of an inch in the throat and y% to i inch at the middle of the thread. Then again, there should not be over % of an inch variation in the depth of chill in like sections of the rim. In making the mixtures, it must be remembered that Tables 45 to 50 show analyses of the iron after it is remelted or in the castings, so that the iron before being charged' must be higher in silicon and manganese and lower in sulphur, after the principle described in Chapter 45.
Not only has steel and wrought scrap been mixed with cast iron pig mixtures, but steel and wrought iron scrap may, for some classes of chilled castings, be mixed wholly with cast iron scrap, no pig whateverod wheel by Mr. A. Whitney is also given in Table 46.sly the same depth.... Shop scrap ...... 15 x ro x 1.50 i. So 22.50 iS.oo