So far the patterns used have been made in one piece, but a flat joint is the most economical for the molder, when many castings are required. Generally such pieces as bushings, pipe connections, and symmetrical machine parts are made in halves; one piece of the pattern remaining in each part of the flask when the mold is separated. There are many cases, too, where, to make a flat joint for the mold, the pattern maker can separate one or more projections so as to have the main part of the pattern in the drag and to let these loose parts lift off in the cope.
The small punch frame and the gas-engine piston, shown in Fig. 44, are examples of these two classes of patterns. At A, the sections through the patterns show the methods of matching them together. B shows the drag parts of the patterns in position for molding. At C, is the section through the mold and the plan of the drag showing how the gates are connected. Attention is directed to the use of the horn sprue - the sprue pattern is shown at a - by which the metal enters the mold at the bottom, If the gate were cut at the joint surface, there would be danger of cutting the sand on top of the green-sand core b as the metal flowed in upon it. Loose-Piece Mold. It often happens that bosses or projections are required on a casting at right angles to the main draft lines of the pattern and below the joint surface. Examples of such cases are shown in Pattern-Making. In molding such work, care must be taken that the overhanging portion of sand shall be strong enough to support itself. Where the projection is deep, the mold should be strengthened by nails or rods, as shown in Fig. 45. These should be wet with clay wash and set into the sand, when the mold is rammed. Use of Green-Sand Core. Some work has projections on it which lie above or below the parting line in such a way that it cannot be molded by either of the foregoing methods. Examining the patterns for some of this work, we find two entire parting lines with the pattern made to separate between the two. Such patterns require between the drag and cope an intermediate body of sand, from the top and bottom of which the two parts may be drawn. In small work, as illustrated by the groove pulley, this intermediate form is held in place by the sand joint of the cope and drag, and is termed a green-sand core. The method of molding such a piece is given in Pattern-Making, Part I. To provide for pouring the casting, a runner should be placed on the hub of the first part packed C, Fig. 46, which shows a section of the mold before either part of the pattern has been removed. When the flask is rolled over to remove the final part C of the pattern, the runner is on top ready for pouring.
Another method used does away with rolling the entire flask. A core-lifting ring is first cast slightly larger in diameter than the flange of the sheave, and having such a section as shown in a, Fig. 47. The ring is set in position in the middle of the inverted drag, the pattern is held central inside of the ring by the recess in the mold board. Pack the drag, roll over, and remove the mold board. Tuck the green core all around and slick off the top joint of the core. Pack the cope in the usual way, lift it off, and draw the cope pattern. Now, by means of lugs cast on this lifting ring, the green core may be lifted off of the drag pattern, allowing it to be removed. Replace the ring and close the cope; and the mold is complete, as shown in section, Fig. 48.
In larger work, where the parting planes are farther apart, this intermediate body of sand is carried in a cheek part of the flask, and we speak of it as three-part work. Fig. 49 shows a casting for a 10-inch nozzle, the mold for which illustrates this class of work. Here the pattern is separated just above the fillet of the curved flange. Fig. 50 gives a view of the mold, showing the way the joint is formed. This casting should be made on the floor.
Select a square flask, 4 inches on a side larger than the diameter of the flanges. The cheek should be as high as that part of the pattern which is molded in it. There should be two projecting bars on opposite sides of the cheek to support the sand, and crossbars in both drag and cope.
These should be well wet with clay wash before using the boxes-Set the pattern centrally inside the cheek, and place a runner stick just the height of the pattern in one corner of this box. On account of the depth of the cheek, the sand must be rammed in two courses. Sift enough facing sand into the box to cover the joint and 5 inches up around the pattern to a depth of about 1 1/4 inches, tucking about the pattern with the fingers. Fill in about 5 inches of loose sand and before ramming tuck around the ends of the side bars, compressing the sand between the finger tips, having a hand on each side of the bar, as illustrated in Fig. 51. Now use the peen end of the floor rammer in the same general way as the hand rammer is used in bench molding. Guide the rammer around the sides of the flask and bars first, then direct it toward the bottom edges of the pattern. As the sand gradually feels properly packed at this level, direct the blows higher and higher up. Proceed in this way to within about 1 inch of the drag joint. Make this joint by ramming in sifted facing sand, being careful to tuck it firmly underneath the flange. Cope this joint to the shape of the curved flange.
Fig. 49. Carting for Ten-Inch Nossle.