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. 124. A cross-section of the pattern for this slide is shown in Fig. 125, 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 shown in Fig. 126. These may now be carefully removed toward the center of the opening and lifted out. Use of Dry-Sand Cores. In some cases there is not sufficient room, when the main part of the pattern has been taken from the mold, 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 Fig. 127.
A section view of the casting through the line A D, Fig. 127, is given in Fig.128. The mold is parted on the level cc, and the boss, and the inside and the outside flanges, will be made with dry-sand cores, the three core boxes being shown in Fig. 130. The boxes shown at h and l have their nearer ends removed so as to illustrate the internal construction.
Fig. 129 illustrates a section view of the rim g, and the top outside flange and web patterns e. The boss a, however, would prevent the pattern from being removed from the mold, and even if a were made loose it could not be taken out through the narrow space made by the thin side of the pattern g. To overcome this difficulty the boss a is made in the core box l and the core is bedded in, as shown at l in Fig. 131.
Referring to Fig. 131, which is a section through the vertical center of the pattern, the molding process is as follows: A level bed dd is struck off, and the core i is located on this bed or surface at the center of the flask. Over this core are placed the rim g and the required number of outer-flange cores made in core box h. The core for the lug a is next put into its proper location, shown at I, and the mold is rammed to the top of the rim pattern. The sand inside the rim pattern is struck off level, and the web e is placed in position and rammed down so as to fit the rim into the groove on the under side of the web. The mold is now filled level with the upper side of the web cc and the parting made. The cope mold is now made, and, after being removed, the pattern is drawn. The disk e is removed first, and then the rim g, when it will be seen that these dry-sand cores, in connection with the pattern, form a mold which will give the casting required.
Fig. 129. Section of Rim and Top, Fig. 127.
Fig. 130. Core Boxes for Fig. 127.
Examples in molding practice could be 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 mold.