Ofttimes malleable iron castings are made in what are known as “permanent molds” of iron. They are really “chilled castings.” Annealing of these is accomplished in the regular way. Such castings have very smooth and beautiful surfaces but as the iron molds have high first cost they can be used only for castings for which the sales warrant the expense.
While much less malleable than is wrought iron or mild steel, annealed malleable cast iron has considerable malleability. It will resist great shock and can be severely battered and bent without breaking. It has about 75 per cent or more of the tensile strength of mild steel and because of the cheapness of its castings the malleable iron industry has developed wonderfully. About a million tons of this product are produced here each year.
Naturally malleable iron castings are used where a material with properties intermediate between cast iron and steel will suffice. Such are castings for railroad cars, for reapers, binders, and other agricultural machines, pipe fittings, and the cheaper grades of tools.
CHAPTER XIII
CAST STEEL
We have seen how primitive man hunted and fought with no implements and weapons better than clubs, bows and arrows, and stone hatchets, and how his wife cracked and ground the corn between flat rocks or in mortars of stone. In the succeeding “Bronze Age” we found ornaments, idols and tools being made of copper or the copper alloy, bronze. It was only after the next great advance that we found man utilizing iron for his purposes of civilization. This metal, which with us is so common, was in those days very expensive, so much so that it could be used only for purposes of war and as the gifts of kings.
But the world was traveling fast and it was not long before the iron-carbon alloy, steel, was produced. Even so, many hundreds of years elapsed before the present wonderful age was ushered in through the great inventions of Henry Bessemer and the Siemens brothers. And while fine steels for swords and tools have had an incalculably great influence upon the development of the human race, it was the mammoth production of Bessemer and open-hearth steel which permitted its general use as a material for construction of ships, bridges, buildings, and for railroads, that made this the “Age of Steel.”
Speaking in terms of the power house, it is also the “Age of Cast Steel.” Twenty-five years ago the manufacturer and power house man were quite content with their “saturated” steam temperatures and pressures. With cast iron valves and fittings their plants were well equipped.
Steel Castings Showing the Risers on the Flanges
Castings for use on steam, ammonia, water lines, etc., must be of very close-grained metal and require much larger risers than castings for less exacting service.
But the world did not stand still. It became known that by heating the steam out of contact with the water in the boiler it lost the moisture which it carried and became dry and then could be charged with as much additional heat as it was desired to give to it. This “superheated” steam, of course, would do more work and it had also certain other advantages which the old-fashioned “saturated” steam had not.