In Figs. 76 and 77, we have another example of flask molding, but for a pattern of different shape to our previous one. The pattern is, in this case, not made iu halves, its flanges on one side being left loose. In Fig. 76, one half of the pattern is shown on the molding board, and the nowel placed thereon and rammed with sand;

Fig. 77.

Sand

while in Fig. 77, the pattern is shown molded and ready to have the cope taken off, A representing one of the crossbars fitted into the cope, and following the outline of the pattern.

CHAPTER IV.

THE FOUNDRY.

ON CORES.

CORES are projecting bodies of sand, either left in the mold by the pattern itself or else made in a separate device called a core box. They are placed, after being dried, in position in the mold. The purpose of a core of the latter description is to leave a hole or recess of such a peculiar shape or in such a position that it is impracticable to make the mold of the necessary conformation by the use of the pattern alone. The use of these cores also permits us to modify the shape of a pattern that would otherwise be difficult to mold. For example, Fig. 78 represents

Fig. 78.

a plate of such length that it is necessary to mold it in the direction indicated by the arrow; as the pendants, which are long and narrow, with their projections at the extrem

ities, would lock the pattern in the mold. Three methods present themselves whereby to overcome the difficulty. First, we may make the projection loose, the vertical line, A, being the joint; it is held in position by vertical dovetails or by horizontal wires, as shown in Fig. 78. In the latter case, the molder, when ramming the sand, withdraws the wires; and when the pattern is withdrawn from the mold, the two different projecting pieces are left in the mold, and are subsequently retracted horizontally, and then lifted out. It is obvious that this can only be done when there is sufficient space to accommodate the projecting piece as it is withdrawn from its recess in the sand, and to admit of its being raised to the surface. To this method there is the objection that the recess left by the projecting piece in the mold cannot be, in many cases, either inspected or dressed, if any reparation is required. A second plan would be to make the projecting piece join the pattern at the horizontal line, B, in Fig. 78, but separable from it; but in this case a three-part flask would have to be used, entailing double work for the molder. The third method is to affix the core prints, CC, to the sides of the pattern, leaving those sides smooth and even; and the pattern will then draw easily out of the mold. If we then core away all we have added to the pattern, as shewn by the dotted lines in Fig. 78, the casting will retain the correct shape of the pattern. To effect this coring away, we make dry sand cores of the shape of the core prints, CC, and place them in the mold. Ordinary dry sand cores are composed of a mixture of sand and flour moistened with water, and they are molded to the requisite shape in the core boxes already mentioned. They are then baked, becoming sufficiently strong to handle; but previous to the baking they are so weak that they cannot be handled without being in some way supported. It is, therefore, as great a consideration to the

pattern maker how the core is to be taken from the box as it is how a pattern shall be drawn from the mold. We may divide cores molded in a core box into three classes: First, those that lie as they are made; second, those that require turning over; and third, those that not only require turning over, but require also a bed of sand made for them to lie upon during the process of baking. Figs.

72, 73, and 74 are examples of the first, in which the cores are represented by C. The core boxes, being made in halves and loose at two of the opposite corners, can be drawn away from the cores, C, leaving them standing, just as they were made, on an iron plate ready for removal to the oven. In a core box made as in Fig. 74, it is necessary to bore in the ends a couple of small holes for the in. sertion of wires to effect ventilation. In cases where suffi

cient draft or taper can be allowed on the core, the core box need not be made in halves, but may be made solid, as shown in section in Fig. 75.

While it is the aim of the pattern maker to form his core boxes to work in the simple manner illustrated in our examples, there are very large classes of cores with which such easy methods are impracticable. This, for instance, is the case with all round cores that are of such length that they are not able to support themselves on end, and with those having branches, as shown in Fig. 79, which represents a core for a straight faucet. If it were attempted to make this core in a vertical position, its overhanging branches would fall away immediately after separating the two halves of the box; hence it is made horizontally, and generally in separate halves, which, after being baked, are