CHAPTER XXXVIII.
MIXTURES FOR CHILLED ROLLS, CAR WHEELS, ETC.
The use of chilled castings has grown to such an extent that we find the following chilled specialties being manufactured: Rolls for various purposes, car wheels, crushers for breaking ore, etc., squeezers for balling iron, die presses, anvils, armor for inland fortification, shot and shell, axle bearings, grinding and grist machinery, switches for railroads, turn-tables and transfer plates, boiling pans for various chemical purposes, cutting tools, plows, and numerous other specialties that might be mentioned to illustrate the extent to which the manufacture of chilled castings is used.
In making mixtures for chilled rolls, it is generally necessary to consider the thickness through the neck and body of the rolls, the thickness of chill desired in the castings, and whether they are to be used for cold or hot rolling; also the thickness of the chill mould used and the temperature of the metal in pouring, as seen by Chapters LI. and LVI. The thickness of chill is, in some cases, desired from j/£ to j£ inch, and then again from 3/£ to i inch. It is rare that more than \y^ inches thickness of chillis desired in rolls. The founder is supposed to have such a control over mixtures that he can attain to within a % inch ofiven either, in producing the combined carbon. It is very important in assisting to prevent " cold shuts" or " chill cracks," when pouring a mould, to have the metal run freely, and hence the advantage of manganese over sulphur, as above stated.*