The casting box. Fig. 180, consists of 2 thick iron surfaces, the top one a serving as a lid. The hinges b are made by 2 protruding pins at one end, fitting loosely into slots c on either side of the bed. By this means, plates of any thickness can be cast, the height being regulated by the steel gauges d placed round the mould. The box is supported in a low upright frame e by 2 swivels f in the centre. The lid a and bed g are held firmly together by a movable bar h, which works loosely on a pin 1 on one side of the bed, and when the lid is closed down, may be swung round and securely clamped by a centre screw k. The month / of the box is slightly bevelled inwards, to admit of the metal being poured without spilling. The casting box being nicely balanced in its frame, but little power is needed in the tilting for pouring, etc. When it is moved either in an upright or horizontal position, it is secured by self-acting springs. The steel gauges d are usually 1 pica thick.
To prevent the metal being too rapidly chilled while it is being poured, it is necessary to heat the casting box prior to placing the mould, usually done by pouring a ladleful of molten metal into the box, and letting it remain for a minute or two, when the box can be opened and the block removed. When first commencing work, this should be done 2 or 3 times. After carefully wiping clean the surface of the box, place the mould in the centre, face upward, and allow the brown paper that has been previously fastened to the top of the page to lap over the front of the mouth of the casting directly to the face of the mould. The gauges are now put round the mould. The lid of the box is next closed, clamped, and secured by the upright screw. The side spring is disengaged, and the box swung into a vertical position, when the mouth will be at the top. If the brown paper before mentioned is liable to obstruct the flow of the metal, place a small wooden wedge at either.
With the skimmer again carefully remove any dross that may have accumulated on the surface of the metal. Ascertain that It is of the proper temperature, as already directed, and take sufficient in the ladle for the whole casting. This is in all cases necessary, as the metal, the casting bos, solidifies, and the addition of a second lot would assuredly spoil the appearance of the plate, as it would be imperfect at the junction. When large castings are made, the ladle is sufficiently capacious to hold the requisite quantity of metal, having a handle at each end to admit of 2 workmen lifting it. As the large ladle cannot conveniently he dipped into the metal, it is filled by a smaller ladle, but prior to this it should be heated by being first filled with hot metal, which can be emptied back again. The casting box must be perfectly dry before pouring.
The metal should be slowly run into the mouth of the casting box, without splashing. Sufficient being poured in, it is allowed to remain for 2-3 minutes, by which time it wilt have set. The box is then swung into a horizontal position, the clamp is unfastened, the lid lifted, and the plate will be found lying on its face. The gauges are re-Q, 2 moved, and the casting is laid on the imposing surface, the workman wearing a long leather apron and being provided with thick blanket-pads for handling the still hot plate and box.
When the casting is sufficiently cool, the superfluous metal at the head, called the "tang," or "pour-piece," is removed by a circular saw or sharp-pointed hook. If more than one page has been cast, the pages most be separated in the same way, and trimmed to a gauge. The newly-cast plate is slightly thicker than is required, and is also uneven on the back, in consequence of the unequal contraction of the metal. It is next subjected to the planing and bevelling processes already described for plaster-cast plates. The circular saw should have a screen of sheet tin or iron, or thick glass, to protect the workman from the flying scraps of metal.
Small complete stereotype-foundries are fitted up for heating by gas, by Harrild's and other firms, at prices ranging from about 20 guineas upwards.
For newspapers, the plates are often made type-high, but with an iron core introduced beneath, to reduce the con-sumption of metal, which core will need heating the same as the mould before casting. Several ingenious contrivances are in the market for casting solid plates of any size without the necessity of having special cores.