Among the following examples showing typical ways of setting and securing cores in molds and of connecting vents, the bolt-hole core, shown at A, Fig. 70, illustrates the simplest form of core to set. Only a drag print is necessary; the flat top of the core should just touch the cope surface of the mold. The level may be tested by a straight stick or by sighting across the joint. If the core is too long, one end may be filed off a little, if too short, a little sand may be filled into the bottom of the print. For longer cores, especially hub cores, a taper print is placed on the cope side of the pattern, and the same taper is given to the end of the core; this guides it to the exact center when the mold is closed. Numerous examples are shown in Pattern-Making. The exact length of the core should be obtained from the pattern with a pair of calipers, as shown in Fig. 71. One point of the calipers should then be placed on the taper end of the core, and the print filled in, or the core shortened in case of variation from the right length. It is well to make a vent hole from the center of each print before setting the core.
Fig. 71. Calipers.
With pattern and core boxes properly made, little difficulty should be experienced in setting small horizontal cores for hollow bushings, pipe connections, etc. (See Pattern-Making, Figs. 110, 203, and 210.) The core must fit the print or a poor casting will result. The sand supporting the prints must be tucked firmly enough to withstand the lifting pressure on the core. A scratch with the point of the trowel along the joint surface from the end of the print to the edge of the flask, will usually take care of the vent.
For larger cores of this character crossbars made to fit snug against the core print are nailed in both drag and cope. See aaaa, Fig. 72. These hold the core absolutely firm. The spaces bb in the cope, are not packed until the core is set, when it is a simple matter to ram these spaces and take off an air vent directly from the center of the core.
Fig. 73. Setting Core below Surface.
There are two methods of coring holes below the level of the joint. One is shown clearly in Fig. 73.
A stock core is set in the bottom of the prints; a wooden template, shown at b and b', is set over the core, and the print a is then packed with molding sand, or stopped off, as|it is termed.
The other method is shown at B and B', Fig. 70. Here that part of the core which will shape the hole through the casting, is formed on the end of a core which exactly fills the print. A single operation sets the core and stops off the print. For this reason this method is used where a large number of such holes are to be cored.
In setting chaplets, the height of the lower one may be tested with a rule, with a straightedge rested on the prints, or by a gage similar to that shown in Fig. 74. A small boss is usually formed by pressing the trowel handle into the mold where the chaplet is to go.
The cope chaplet is not fastened until the mold is closed, then the stem can be properly wedged down under a bar clamped across the top of the mold.
In work where a hole must project well into the casting, but [not all the way through it, a balanced core is often used. Such a case is illustrated by the rammer head, Fig. 75. When making this core, let the vent extend through the entire length, then stop up the vent at the small end with a bit of clay after the core is baked.
It is not always practicable to enlarge the print as shown here, but when possible, it reduces ■ the length of print necessary to balance the projecting end and ensures accurate depth to the hole.
Heavy projecting cores must be supported by chaplets, as illustrated in Fig. 76. Vents may be taken off through a channel and air riser as explained in the section on Venting. Fig. 77 shows the shape of the print on the pattern for this mold at a, the pockets formed by the core are shown at bb, and c indicates the position of the gate.
Fig. 74. Gage for Setting Chaplets.
A core is frequently used to avoid a deep lift for the cope. Suitable wire hangers, shown at a, Fig. 78, are bedded in the core when it is made. In setting the core, small annealed wire about No. 20 or No. 24 gage is looped through the hangers, passed through small holes made in the cope, and fastened with a granny twist over an iron bar on top. This bar should bear on the sides of the cope and the core be brought up snug in its print by wedging under its ends. The rigging need only be strong enough to support the weight of the core, for the pressure of metal will force this core firmly into its print with little danger of shifting it. For heavy cores, a lifting eye, as previously illustrated in Fig. 66, takes the place of the wire hanger, and the core is hung by means of a hooked rod with a nut on the end. As shown in Fig. 79, this rod passes through a long washer which bears on a pair of rails, or similar stiff rigging. Bottom-Anchored Cores. Where possible, the placing of cores in the bottom of molds should be avoided, for in this position, being much lighter than molten iron, they must be secured against a pressure tending to float or lift them. This pressure is proportionate to their depth below the pouring basin. But the metal at the bottom of a mold is cleaner and more sound than that at the top. Therefore, planer beds, large faceplates, and pieces of this character are usually cast face downward, making it necessary to anchor the T-slot cores in the bottom of the mold.
Fig. 77. Shape of Print on Pattern for Projecting Core.
Fig. 78. Section Showing Use of Wire Hangers.
In some cases, such cores may be held down by driving nails so that their heads project somewhat over the ends of the core, as shown in Fig. 80. If this method is not strong enough, pointed anchors, with a foot on one end, are run through a hole in the core, and are carefully driven into the bottom board, as shown in Fig. 81. Where the work is bedded into the floor, a plank must be set to receive these anchors just below the cinder bed. As in the case of lifting eyes, the holes in the core, into which the foot on the anchor is driven, are smeared with oil and stopped off with green sand.