On several scales which are regularly inspected and kept carefully adjusted, the weighers weigh out the prescribed quantities of the raw materials. “Buggies” holding nearly one ton each are loaded in turn with coke, with proper amounts of pig iron, cast iron scrap, sprues from the foundry castings of the preceding day, and a proper weight of limestone flux. Each charge of two tons of iron requires four buggies for its transportation from the raw-material bins and scales to the cupolas.
The old-time way was for laborers to dump the charges into the cupola and spread the materials by hand, but in modern foundries better ways have been provided. Here a charging machine operated by compressed air lifts into the furnace, one by one, the buggies of coke, and of the other materials, whence, after the dumping of their contents, the buggies are returned to the receiver building to be filled again.
Thus many charges per hour pass through the yawning charging doors of the cupolas, being dumped in fast enough to maintain the level approximately even with the bottom of the charging door.
Reading the Carbons
The higher the combined carbon the darker the nitric acid solution of the iron or steel. The solution is diluted with water or weak acid until the color matches that of a “known” sample or standard. Accurately graduated comparison tubes are used.
In starting, a wood fire has been made on the sand bottom of the cupola. This is covered with coke in such a way and in such amount that, when ready for charging of the metal, a column of glowing coke extends to a distance of one foot or two above the tuyères. Upon this “bed” in alternating layers are piled the weighed amounts of pig iron, sprue, scrap and limestone as described above. Following each charge is a layer of coke sufficient in amount to replace the “bed” coke which is burned away in melting the iron charge, thus maintaining the top of the bed of coke throughout the day at approximately the same height.
Weighing the Graphitic Carbon
The graphite is filtered out on an asbestos pad in a perforated platinum crucible. After drying until all moisture is gone it is weighed, ignited, and weighed again. The loss of weight equals the weight of the graphite of the sample.
Ever since 7 o’clock A.M., when the twelve to sixteen ounces of blast pressure was put on, the charges have been descending gradually from the charging door. Encountering the intense heat in the “melting zone” at the top of the bed of coke a little above the tuyères, the iron melts and trickles down through the three to five-foot bed of glowing coke on to the sand cupola bottom or hearth where it accumulates. The tapper, with his iron bar and “bod stick” with its little ball of moist fire clay, alternately opens and plugs the tap hole at the bottom of the furnace as occasion requires, but throughout the day of ten or more hours there is almost constantly a full stream of iron flowing from the spout. The big “bull ladle” which receives it, in turn gives it up to smaller or “shank” ladles, in which it is conveyed along trolleys to still smaller ladles from which it is poured into the sand molds to form the castings.
