(9) Put on the blast when ready for the metal, and leave the tap hole open. Bott up when the metal begins to run freely - generally about 7 minutes after blast is on.
Bott clay should be mixed with about 1/8 sawdust, to make it more fragile when tapping, and is made up in small balls, and shaped onto the end of the bott stick A, Fig. 128.
(10) Tap when sufficient metal has collected to supply the first ladles.
(11) Drop the bottom, when all the iron has been melted and run off. This is done by pulling away the bar that supports the bottom doors. Throw water on the dump by bucket or hose, to deaden the heat, and leave it to cool off over night.
Fig. 128. Tapping Bars.
Fig. 129 A
Fig. 129 B, C
Like C, with bail
Single or double hand shank
Bail with single or double hand shank
Worm gear on heavy bail
9 to 15
14 to 26
20 to 75
9 to 15
1/2 to 3/8
14 to 26
3/4 to 1
l to 4 1/2
6 to 7
1/2 to 3/4
8 to 13
3/4 to 1
12 to 23
18 to 66
l 1/2 to
As the melted metal flows from the spout of the cupola, it is caught in ladles. The sizes of these are designated by the weight of metal they will hold; they vary from 30 pounds to 20 tons capacity.
Table V, containing references to Figs. 129 and 130, give compact data regarding foundry ladles.
The names of ladles relate to the method of carrying them. Hand ladles are made of cast iron or pressed steel. The larger ladles are built up of boiler plate. Cast iron is poured from the top of the ladle, which should therefore be provided with lips.
Ladles must be lined to protect them from burning through. Up to 1-ton capacity, the cupola daubing mixture is used. The bowl is smeared with thick clay wash, and the clay pressed in hard with the hands, being rubbed smooth on the inside. The lining should be kept as thin as possible, 5/8 to 3/4 inch on hand ladles, 1 inch to 1 1/2 inches on large ones; the bottom lining being from one-third to one-half thicker than sides, as it receives the first fall of the incoming metal.
The larger ladles are first lined with fire brick of thickness proportionate to their size, and then daubed on the inside with clay mixture similar to cupola lining. The lining must be well dried before use, to drive out moisture. In stove-plate and hardware shops, where most of the pouring is done with hand ladles, a special ladle drying stove similar to a shallow core oven is provided. A wood fire is built inside of the larger ladles to dry them out. To preserve a lining as long as possible, slight breaks are repaired daily. As with the cupola, the slag formed by the hot metal forms the best coating possible for the inside lining.
The first thing to be considered in connection with pouring is skimming off the slag which collects on top of the metal. This should be done on the larger ladles before leaving cupola, and again while metal is being poured. For this, a long iron rod is used, with blade shaped as in D, Fig. 128. This is rested across the top of the ladle near the lip, and effectively holds the slag back; the long handle permits the skimmer to stand well back from the heat of the metal. On small ladles, skimmers are of course shorter, and the end is bent up more, for convenience, as the ladles will be much nearer the floor when pouring with them.
Hand and bull ladles are shown in Fig. 129, while Fig. 130 shows a crane ladle.
Much skill is required in pouring a mold. A molder must know the character of the work, and judge whether it must be poured fast or slowly. In general, light work cannot be poured too fast. Heavier work is poured more slowly. Care must be exercised to keep the stream steady from the first, and not to spill into the mold, as this may cause cold-shuts or leave shot iron in the castings. The runner basin must be kept full, for gates and runners are made with this express purpose in view, as has been stated previously.
Fig. 129. Hand and Bull Ladles.
Metal must not be allowed to chill or freeze in the ladle, as this would destroy the lining when it came to removing the cold metal. Metal left in the ladles when the mold is full, must be poured back into a larger ladle or emptied into a convenient pig bed. These latter are built in a sand bed usually near the cupola; or stout cast-iron pig troughs or chills are provided. The chills should taper well on the inside, holding about 60 pounds each. Some are arranged to swing on trunnions for convenience in dumping. They should be smeared with a heavy oil and dusted with graphite, to prevent the metal sticking in them. It is safer to heat these pig molds as well, so that no moisture will form and cause a kick or explosion when hot metal is first poured into them.