The pattern for the flask will be molded by striking a green-sand core, lagging this to obtain the thickness, and molding the lower flange with a dry-sand core, and the upper flange with loose segment pattern bedded in. Where iron pulley-rim or similar patterns are available, they may be used for the flask pattern without much expense. Allow a metal finish on the outside face of the flanges, and the inside of the flask for a depth of about 3/4 inch is to be turned true, but no finish allowance need be made on this surface. Drag Flask. The drag flask will be of the same diameter as the cheek flask, but the depth need be only long enough to include the steel shaft. A hub is fitted at its center i, which will be machined to fit the finished end of the shaft. A shoulder is turned on the shaft, and the upper end of this hub is finished so as to locate the vertical height of the shaft. The drag flask is rammed on a cast-iron mold plate, as illustrated in Fig. 380. The flat disk dry-sand core is placed on this plate and rammed in, as illustrated in Figs. 380 and 384. For this core a wooden core box should be furnished.
The cope flask, Fig. 381, is similar to the drag flask excepting the ring k and the radial bars. This ring should be large enough to provide space for the two sprues l. The upper inside edge of this ring is finished to a bevel to fit the centering ring m. Fig. 384. A sketch of the pattern for this ring is shown in Fig. 382.
The mold plate j, illustrated in Fig. 381, can be used for both drag and cope molds.
Fig. 383 illustrates the wooden core box for the inside of the mold. The rings n are made of two layers of segments glued and screwed together, and the walls of glued lagging firmly nailed and glued to the top and bottom rings. It should then be mounted on a faceplate and turned true on the inside and on the ends. A very slight draft - about 1/16 inch - should be allowed on the inside, and the height of the box will be 12 inches. The print o, hub p, and arm q patterns are fastened to the bottom board r; the ends of the arms centering the outside of the core box with the print o. This print o should be at least 1/16 inch larger than the steel shaft used. Two cores with the arm mold are required, and a center core without the arm mold. The length of this core is varied to produce rolls of different lengths. A bottom board is furnished without the arm and hub patterns, and the length is struck off to the height desired.
Fig. 384 illustrates a section of the complete mold.
It may have been noticed that while great accuracy has been insisted upon, there have been no difficult problems of pattern making required in the adaptation of patterns to the molding machine.
The permanence of the master patterns is not a question, as they are usually molded soon after being completed, but these parts must be very accurately made.
There is plenty of opportunity for the display of mechanical ingenuity, but always consult the foundry experts regarding any new venture, for, as stated at the beginning, many patterns have been adapted to machine-molding that have proved to be failures when tried out in the foundry.
Vertical And Longitudinal Sections Of 3-Flue, Double-Ended Return-Ture Boiler.