All cut surfaces of the Band are smoothed, parting Band is sprinkled over the parting thus made, and the cope is placed in position and rammed up. When the cope is lifted off, the sand will part half way down on the arms and rim, allowing the pattern to be taken out with ease.
Still another example in which a single-piece pattern can be used, is shown in the journal-box cap illustrated in Fig. 117. A cross-sect ion of the pattern through two of the bolt-hole core prints is shown in Fig. 118. The pattern is placed on the moulding board in the inverted drag and is rammed up as usual. When the drag is turned over, the position of the pattern in the sand is as shown in cross-section in Fig. 119. The sand that may have entered the curve c d e is lifted out, and the necessary "draft" is given to the sand at the two ends of the opening c d e, as shown at a, Fig. 120. The cope is next placed in position, and when this has been rammed up and lifted off, the sand lying in the curve cde will be lifted with it. The pattern is now removed; the bolt-hole cores are placed in position; and the cope is returned to its place on the drag.
In this case the core prints should be in length at least twice the thickness of the metal through which the hole is to be cast, and the length of the cores will be equal to the thickness of the metal plus the length of the prints.
In the small sheave pully, Fig. 121, we have an example of a casting the construction of the pattern for which, so as to make it easily removable from the sand, may give some trouble to the beginner. The pattern is shown in cross-section in Fig. 122, and is moulded in a two-part flask. At first it would seem impossible to place the pattern in the sand so that either half could be removed when the cope and drag are separated on the parting line of the pattern. This is readily accomplished, however, as follows: The half pattern C is placed in the inverted drag, with the parting downward on the moulding board, and is rammed up in the usual way. After the drag is turned over, the sand is cut away and removed to the center of the rim edge, as shown in Fig. 123. The cut is carefully smoothed, and parting sand applied to the cut surface. The part A of the pattern is placed in position on C, and is rammed up carefully, the sand being then cut away to the center of the rim edge of A. Parting sand is applied to the new surface, after which the cope is placed in position and rammed up.
When the cope and drag have been separated, the upper half A of the pattern is taken out, and the cope is returned to its place on the drag. The whole flask is now turned over, and the drag lifted off the cope, when the ring of green sand Z, Fig. 124, will rest on the cope sand and the part C of the pattern is taken out. We thus have two partings of the Band mould, but only one parting of the flask.
Many other examples might be given, as the case of the common two-flunge pulley, which, when small, is often moulded in this way.
It is frequently the case that parts of the pattern will overhang so that the pattern cannot be removed from the sand in any direction, even if parted. In such cases the overhanging parts are fastened loosely to the main part of the pattern by wires or wooden pins. An example of such a casting is shown in the slide, Fig. 125. A cross-section of the pattern for this slide is shown in Fig. 126, in which the two overhanging parts are held in position by the use of pins. After being rammed up, the part A is removed, leaving the parts b and c still in their positions in the sand, as in Fig. 127. These may now be carefully moved toward the center of the opening and lifted out.
In some cases there is not sufficient room, when the main part of the pattern has been taken from the mould, to remove the projecting pieces. In such cases, the overhanging pieces or projections must be made by using dry sand cores. To illustrate this, we shall consider the pattern for the small cast-iron turbine case illustrated in Figs. 128 and 129. A section view of the casting through A B (Fig. 129) is given in Fig. 130.
The pattern is parted on the line C D and will form its own core. The boss a, however, will prevent the main part of the pattern from being removed from the Band, and if a were made loose it could not be taken out through the narrow space made by the thin side of the pattern.
To overcome this difficulty a core print is fitted on the side, extending from the Darting line CD to the bottom edge of the pattern, as illustrated in Figs. 131 and 132; and in the impression made by this core print a dry sand core formed in the core box shown in Fig. 133, is placed. It will readily be seen that this core will, in connection with the pattern, form a mould which will give the casting required.
Examples in "Methods of Moulding" could bo multiplied indefinitely, but the foregoing, we think, will give such suggestions as will enable the beginner in pattern making to construct all ordinary patterns so that they can easily be removed from the sand without injury to the mould.