When properly made malleable cast iron should have a tensile strength of 42,000 to 48,000 lb. per square inch, with an elongation of 5 per cent, in 2 in. Bars 1 in. square, and on supports 12 in. apart, should show a transverse strength og 2,500 to 3,500 lb., with a deflection of at least 1/2 in. The resilience should be at least eight times that of cast iron. Malleable cast iron can be bent, twisted, and abused very much before giving way. thus making ideal for service where a fair tensile strength is required, but especially where often repeated shocks are th rul.
Whil the strength of malleable east iron should be as given above, much of it will fall as low as 35,000 jb. per square inch, and this will still be good for such work as pipe-fittings, hardware castings, and the like, where a certain amount of punishment can be expected, and cracking should not take place. On the other hand, this material can be made exceedingly strong, even 63,-000 lb. per square inch having been reached, as well as a deflection of 2 1/2 in. on the transverse test, with oftentimes 5,000 lb. to cause rupture. This, however, is not desirable, as the softness of the casting is sacrificed in this way, and its resistance to continued shock lessened.
The process of making malleable cast iron may be briefly summarized as follows:-The proper irons are melted in eithe the crucible, the air-furnace, the open-hearth furnace, or the cupola. The metal when cast into the sand moulds must chill white or not more than just a little mottled. After rolling off the sand from the hard castings they go into the annealing department, where they are packed in puddle scale, or other materials containing iron oxide, and here subjected to a period of red heat (1,250° to 1,350° Fahr.), over 60 hours after reaching the proper temperature. They are then cooled gradually, rolled again to remove adhering scale, chipped or ground, straightened, and shipped away.