Bottom is made placing layers of fire sand, that is, sand with about 98 per cent silica, and very free from fluxing impurities, on •the brick work and burning or partly fusing it together. The layers are about one inch thick, and are heat still has to run until ready to tap. After the iron has melted, the slag is skimmed off, and this gives a good chance for refining action, which means the burning out of silicon. The test plug is always taken after skimming, which is often dune for the second time. When the heat is tapped, the men take it off in hand ladles, and pour the molds, throwing the iron into them as quickly as possible so that the necessarily small gates do not prevent the metal from filling the molds by chilling and resulting in "short pours.° The open hearth process (see STEEL CRUCIBLE PROCESS) is by far the best one in general use, but is confined to those works where great quantities are made year in and year out. Thus there are several works where about 80 tons of castings are made daily, and in which the use of the open 'hearth is a pay ing proposition, especially as the same furnace can be used for making acid steel heats in place of malleable cast iron, as desired. The fuel consumption for the open hearth corre sponds to one pound coal for six pounds iron melted; showing a considerable economy over repeated until theproper shape is made. It takes from four to five hours to melt a 10-ton heat after this is charged, depending upon the quality of the bituminous coal used, and the condition of the furnace. From 6 to 10 heats can be made on the same bottom, with but little repairing, but the usual run is from two to four. In order to know when the heat is ready, a test plug, so called, is cast. This plug is about of a diameter equal to the heaviest section of the castings to be made. It is about eight inches long, and the mold for it is made by simply pushing the pattern into the sand in a box. The metal is taken from the bath by a small ladle dipped into it as deeply as possible. After pouring, as soon as the iron is set, the plug is grasped with a tongs, is dipped into water to cool it and then broken across. The fracture is observed, and if properly crystalline, and with but little or no mottling, the heat is ready to tap. If there is too much mottling, that is, too much graphite left, the process is continued to burn out more silicon, and also get the metal hotter, and another test plug taken. Experience will tell just how long a all other methods. The use of a gas producer system, however, where natural gas is not, available, makes the installation an elaborate one, and not desirable where the proper help is not available.
In the case of the open hearth, the furnace is always hot, and hence a heat is finished about an hour sooner than in the air furnace. The iron gets hotter, and can be taken out in five ton ladles to be distributed afterward and as the metal is not as long in contact with the gases as in the air furnace process, it is of better quality. The most economical size of furnace is the 20-ton, with the crane ladle to take off the metal in large quantities, so that tapping is not so long continued a matter as in the air furnace. The latest patented invention to assist in this is the application of two or more spouts to the furnace, so that metal may be taken out at different levels. In this way the surface of the bath, which is punished most by the gases, may be taken off first. Then while this is being poured off, the next part of the heat, now the top, is again taken off, and finally if three spouts are used, the bottom may be taken out as long as half an hour afterward without any deterioration or change in the metal.
From the foundry the castings, after shaking out the molds, go to the hard tumbling room, where they are freed from the adhering sand. This is done by means of tumbling barrels into which the castings, and a supply of made of the same hard iron, are placed. Where castings are liable to crack by this tumbling about, sticks of wood are introduced so that as they strike them, no damage is done. Where delicate castings are made, these are pickled in dilute sulphuric or in hydrofluoric acid.
After cleaning the hard castings, they are has been allowed to get too low in silicon, or ((high) as it is called, in contradistinction to ((low) iron, where the silicon is too high, and the metal mottled or even gray, the sand is apt to burn on so hard that the tumbling all day does not remove it all. Here the sand blast is excellent.
From the sorting room the castings go to the annealing room, or rather to a part of it in which the packing is done. To anneal the hard castings they are placed into so-called or annealing pots. These are simple, box-like shells, with no bottom, about one inch thick, and say 18 inches x 24 inches x 15 inches high. Three or four of these are placed carefully sorted out, the cracked or otherwise defective pieces thrown out, to go back into the furnace again, and the good ones are sent into the annealing room. Where castings are made which crack as soon as they cool, on account of their shape, such as the hand wheels of freight cars for braking purposes, these while still red hot in the sand, are taken into small ovens where they are kept quite hot for a time, and are then allowed to cool very slowly with the oven. In this way they will not be cracked before going into the annealing ovens. The modern tendency is to introduce the sand blast for cleaning, as this removes every particle of sand from the hard castings. Where the iron over each other, and on a high enough to allow a free circulation of the gases under it. The castings are care fully placed in these pots and packed with in such a way that when red hot the whole may not settle and warp the work. This scale is puddle scale, hammer scale, or even iron ore. For that matter, as the process is more of a conversion of the combined carbon into the the castings can be packed in fire clay or sand and good results obtained. But the puddle scale seems to give the best results, with greatest cheapness. The flakes that fall from the annealing pots. these lasting only for 7 to 14 heats, can be crushed and make the finest kind of packing material, being pure oxide 'of iron, and no further scale than the initial lot need be purchased.
The pots, properly filled, are covered with a *mud" made of the sand rolled off the hard castings mixed with water. The joints of the pots are also carefully daubed up with this mud; the pots are introduced into the oven, either run in by a special carriage in the old style ovens, or lowered in from the crane in the new ovens, the tops of which can be re moved. The ovens are now fired and within 36 to 48 hours the full temperature of 1,350 de grees F. in the coldest portion of the coldest pot is reached. This temperature is kept up preferably 60 hours, and the oven then allowed to cool slowly before the pots are withdrawn. The ovens are so constructed that they are heated inside and under the whole bottom, so that a difference of not more than 100 degrees F. throughout the portion filled with work may exist.