WROUGHT IRON 9. Manufacture. About 500 pounds of cast iron is put into the hearth of a puddling or reverberatory furnace (Fig. 4), and a fire built in the furnace. The heat melts the iron, the impurities form a slag with the iron oxide lining of the hearth, and the carbon burns out. The purer the iron, the higher the heat that is required to melt it; and therefore, as it becomes purer, the heat of the furnace being insufficient, the iron becomes pasty or "comes to nature," as the puddlers call it. The puddler, by means of an iron bar or poker, collects the pasty mass into several balls called puddle balls. When these are of the right consistency, he takes them out and places them in a squeezer.
The squeezer is a cam-like machine which squeezes most of the slag out of the ball and welds the entire mass into a homogeneous whole. This mass is then put through rolls, and comes out in bars which contain from one to two per cent of slag. These bars are called muck bars. The muck bars are then cut in strips and piled up in piles (Fig. 5), which are tied with wire, raised to a welding heat, and again rolled into rods, bars, or other shapes. The effect of this last rolling is to squeeze out more slag; and the piling helps to form a product in which all the fibers do not run the same way, as was the case in the muck bar. It takes about two hours to run a charge and recharge the furnace.
10. Characteristics. Wrought iron is dif ferent from cast iron, in that it can be hammered into almost any shape, can be bent double when cold, and can be welded. Wrought iron may be defined as pig iron with its impurities, all of the graphitic or uncombined carbon, and almost all of the combined carbon, burnt out. Silicon, car
bon, manganese, phosphorus, and sulphur occur more or less in all ore, iron, and steel, and in fact in most metals. They are called metalloids. During the process of puddling they are largely eliminated, so that wrought iron is nearly pure iron.
11. Effect of Metalloids. Too much carbon or sulphur will cause the iron to be "red short." This condition causes it to work poorly in the rolls; and the edges of the piece are rough— somewhat the same result as if one tried to work clay that was too dry. Phosphorus is bad, as it tends to lessen the welding properties of the metal.
It has been claimed that the small amount of slag that is left in the iron, usually less than 2 per cent, increases its welding properties and strength, but tests do not seem to substantiate this.