Practically all of the phosphorus contained in the fuel flux and ore passes into the product, except a loss when making high silicon foundry iron of about 7 per cent by volatilization, and this loss may be increased to 10 per cent in the manufacture of speigle.
The usual way of handling the pig product is to run the metal while hot into moulds made in sand, forming a runner called a sow and short branches about three feet long, called pigs.
In case of gray iron, this metal is broken hot, when it has first solidified, and then cooled with water and loaded into cars. This iron has considerable sand adhering to the surface of the pigs, and for that reason is unsuited to melt in the open hearth furnace, where the lining is made of basic material. In order to obtain iron free from sand, and to reduce the arduous work of breaking this product hot, and carrying same by hand into cars for shipment, various devices have been constructed.
The Uehling pig machine is the most com mon device employed to make sandless pig. It consists of an endless chain of moulds, which are filled at one point and, after spraying with water, discharge the pig into a transverse pan conveyer, which carries the pig under water, where it is thoroughly cooled and afterward is delivered into cars for shipment.
Another form is provided with moulds and pans made of soft flange steel, and these when filledss into a tank where they are sub the metal cooled and then delivered into cars. Still another form consists of a sub stantial turntable on which the moulds are mounted.
When it is not necessary to obtain sandless pig, the mechanical pig breaker is used. In the operation of this device the metal is cast in sand and the whole bed is removed mechan ically by a traveling crane or trolley to the breaker, where the pigs are broken and fall into cars.
With the pig machines the metal must be first run into cars or ladles, from which it is poured into the machine; but with the pig breaker no ladles are required, the metal going direct into sand beds, as when it is to be handled by hand. Sandless pig may also be obtained by equipping the cast house with cast iron moulds or Itchills,° which are washed with loam while hot, thus making it easy to lift the pig when it is cooled.
Blast Furnace Lines.—In the blast furnace the hearth represents the grate surface, and its area determines the amount of fuel burned per unit of time, hence, the production of the fur nace. The top of the furnace controls the dis tribution of the charged materials, and has an important bearing on the working of the fur nace, the character of the combustion taking place in the hearth, and hence the burden or amount of charge the coke unit is capable of carrying in smelting.
The bosh determines to a large extent, de pending upon its height and angle of slope, the regularity of the working of the furnace, by assisting or retarding the descent of the charge in the smelting zone.
The largest furnaces in the United States are built with the hearth and top diameters practically equal, 17 to 18 feet, while the diameter of the bosh is usually 22 to 23 feet, the bosh height 12 to 14 feet, and the angle of the slope approximately 78°.
The tendency of the last five years has been to increase the furnace diameters, while the bosh has been slightly lowered in proportional height. These changes seem to cause the stacks to work with greater regularity, and larger out puts on burdens composed, largely, of fine ore, and, at the same time, the loss of ore in flue dust has been materially reduced.
Modern practice aims at increased efficiency in all directions. It seeks to increase the effec tiveness of the hot blast stoves by reducing radiation; for this purpose larger checker sur faces are exposed to the gases than formerly. The power plant utilization of gases formerly wasted is gaining more attention. There is also a tendency to save the heat lost in molten iron and slag, by using it to make steam for low pressure turbines. Recovery of the flue dust of the blast furnace is more common. The distribution of incoming ore at the furnace is found to be much more important than used to be supposed. Peculiar ores require to be dis tributed through the mass, so that the furnace will have a uniform ore to work upon at all times, giving a more constant furnace bur den. Improved bin systems are used for ore, coke and limestone flux. It is now universally recognized that to secure steady large product there must be an even distribution of lumps and fines in the furnace. This is accomplished by rotating furnace buckets and also by rotating the furnace top. The revolving principle secures a spiral distribution of the lumps and fines.
Workmen are subjected to less danger around the blast furnace than formerly. The Carnegie Steel Company was the first to suc cessfully plug the tap-hole of a blast furnace with a clay gun, using the blast of the furnace as power. The gun is mechanically swung into position, so that no workman need be near until the hole is well plugged. Other mechanisms tending to increased safety of workmen are in use.