The chief impurities to he removed from cast iron to make it into wrought iron are silicon, manganese, phosphorus, and carbon. To remove these by the puddling process. SI special puddling furnace is employed. These furnaces are of various forms, but the ordinary form is n single bedded reverberatory furnace. Briefly described, such a furnace eonsists of a combination cham ber of oblong shape. At the front of this cham ber are the grate-bar, to the rear of which rises a vertical wall, and back of this, at a higher level than the grate-bars, is a shallow receptacle for the charge. A common roof covers the two chambers. This roof is horizontal over the grate bars, but curves downward as it extends back ward until at the llue-entrance it descends below the level of the charge. There are two doors at the side, one for feeding the fire and the other to give access to the charge. Structurally the furnace consists of cast-iron plates and fire-brick. In operation the combustion of the fuel takes place on the grate-bars, and the hot gases and flames rise to the roof and are beaten hack or reverberated upon the charge as they move toward the flue. Generally two men work at a furnace. The puddling process consists of four stages. Previous to describing these stages it will be necessary to state briefly the manner of preparing the furnace for work. The basin for the charge is made of east-iron plates. These are covered with a layer of oxidizing material a few inches deep, and the fire is then started and urged until the heat is intense enough to partly fuse this material and the fragments cohere. The sides of the basin are banked up with similar material. Stag is then shoveled in, and the pig iron to he treated is plated in this couch of slag. The lining of the basin lasts for many successive charges, with occasional repairs as wear occurs.
The furnace having been charged, the door is closed, and rendered as nearly as possible air tight by banking with cinder. Beating is con tinued until the top of the pig iron is red hot, when it is turned by opening the door. which
is afterwards closed until the iron melts, the workmen stirring up the mass with a rod at intervals to hasten the process. This completes the melting-clown stage. One of the workmen next introduces a hooked bar and vigorously -stirs the molten mass until its appearance to his skilled eye indicates that the silicon has been expelled. This completes the second or clearing stage. The next process is to reduce the tem perature, and vigorously continue stirring until the metal and cinder become thoroughly mingled, part of the slag flows ofT, and the metallic iron and residue of slag form a porous cake in the melting basin. This completes the third stage, known as the boil. The final stage is to break up the porous cake, and form the separate parts into balls by manipulating them with a bar. These balls are taken from the furnace and ham mered or squeezed to press out the slag, when the iron is ready to be manufaetured. During these various stages of the puddling process the impurities of the cast iron (silicon, manganese, phosphorus, and carbon) are removed. As pre viously stated, various forms of puddling furnace are used, and other variations in apparatus and methods employed; hut the general process is al ways essentially as described.
The crude puddle ball which is drawn from the furnace is composed of imunnerable globules of nearly pure iron, the interstices between which are filled with slag. Much of this slag is re moved in squeezing, and each subsequent working removes a further quantity, but it is never all removed. The piece of iron made in the first rolling of the puddle ball is a rough, crude prod uct known as muck bar. To make merchant iron several of these muck bars are bundled to gether into 'piles,' so as to give a bloom of proper sectional area, and this after being, heated to a welding beat is rolled into the desired shape. See