. Transactions . ontraction of cast steel, whichfrequently amounts to T5g- inch per foot; and to the hard dry sandmoulds, which it is necessary to use, in order to prevent the whitehot metal from destroying the mould. There are five different ways of attempting to remedy this evil: 1. By changing the chemical constitution of the steel. 2. By stripping the castings as soon as poured. 3. By mechanical pressure. 4. By large rising-heads. 5. By care in moulding. Chemical Constitution.—A change in the chemical constitution byincreasing the manganese and diminishing the silicon, will nearlyalways ha
. Transactions . ontraction of cast steel, whichfrequently amounts to T5g- inch per foot; and to the hard dry sandmoulds, which it is necessary to use, in order to prevent the whitehot metal from destroying the mould. There are five different ways of attempting to remedy this evil: 1. By changing the chemical constitution of the steel. 2. By stripping the castings as soon as poured. 3. By mechanical pressure. 4. By large rising-heads. 5. By care in moulding. Chemical Constitution.—A change in the chemical constitution byincreasing the manganese and diminishing the silicon, will nearlyalways have the desired effect. This renders the metal more fluid,and lowers its melting-point. Stripping.—A large number of castings can be saved from tearingapart or cracking when cooling, by simply opening the flasks imme-diately after pouring and covering the casting with sand. Mechanical Pressure.—We have been able to save quite a numberof difficult castings by means of mechanical pressure. For example, Fig. Sectional Plan, showing Screw-Arrangement to Prevent Shrinkage-Cracks. at one end of a flask, and immediately at the end of the moulding,a small iron plate is placed. This plate is attached to a screw whichcan be turned from the outside of the flask. The arrangement isadmirably adapted for castings large at both ends and small in themiddle. Suppose, for example, we have a long lever-gear castingto make, such as is sometimes used for hay- or cotton-presses. Insuch a case the shrinkage is away from the centre in both directions,as will be seen by reference to Fig. 2. In this figure, which presents 126 THE MANUFACTURE OF STEEL CASTINGS. a sectional plan of the mould containing such a casting poured onthe flat/ AD is prevented from drawing towards B E by the hardsand between, and, as a consequence, the casting is apt to break intwo at C. By forcing the iron plate G against A D, by means of thescrew S, the sand is broken and allows the casting to contract with-out strainin
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
