Whenever it becomes necessary to strip an internal surface of a pattern, as illustrated in the socket or bousing for the hardwood bearing used in the holder frame. Fig. 308, some means must be provided to support the molding sand, and this part of the equipment is called a stool. Illustrations of the stool for this pattern are shown in Figs. 312, 313, 323, and 324.
The top surface of these stools are made to the form of the hole or recess which it is desired to strip, and are usually yoked to the underside of the stripping plate. In this case, a projection cast to the underside of the stripping plate serves as a support for the stools. They are to be made of machine steel, and, together with the levers and links, Fig. 325, do not require a pattern, but accurate sketches or drawings, preferably full size, should be made by the pattern maker for these parts for the use of the metal-pattern maker.
Owing to the expense of the stripping plate equipment, this method should not be employed unless some feature of the casting prohibits the use of the simpler methods.
A large part of this pattern which wilt be molded in the cope, has an abundance of draft, and as the other parts are not over 1/2 inch thick, a slight draft can be allowed to these parts, and a draft of fully 1 inch per foot can be allowed in the square hole. Therefore, it will be perfectly practical to mold this side of the casting on a match plate, Fig. 326, and, while a pneumatic vibrator is shown, possibly it may not be necessary. The vibrator is operated while the plate is being drawn or lifted from the cope mold, causing a very rapid vibration to the pattern and plate, and greatly facilitating the drawing of intricate patterns.
Fig. 322. Core Box for Master Pattern Fig. 321.
Fig. 323. Sketch of Stoole. Fig. 312.
Fig. 324. Drawing of Stoel Stool. Fig. 323.
Fig. 325. Machine Steel Lever and Links.
The iron plate should be finished on both sides, as the parting must match that made on the drag machine. The part q1, is a separate casting, and this must be machined to fit the recess q in the stripping plate.
Fig. 326. Match Plate for Cope Mold with Vibrator Attached.
Fig. 327 illustrates the master pattern. Double shrink and a file finish must be allowed.
A pattern for the gate, Fig. 328, must be furnished, and is usually made of cast brass. The location of feeding into the mold and its dimension should be suggested by the molder. It never should feed against a green-sand core, as the core would very likely be washed away.
The parts q1t c1, and the gate pattern are attached to the plate with fiat-head machine screws.
Of course the alignment of the patterns on the cope and drag machines must be very exact to produce perfect castings, but this is the work of the metal-pattern maker. To avoid errors, there should always be a trial casting made and accepted before the outfit is passed to the foundry ready for the commercial product.
Figs. 329 and 330 are illustrations of the cope and drag machines for molding the cover. The distinctive feature of the pattern for the cover is the roll-back method of drawing the pattern on the cope machine, which is illustrated in section in Fig. 331. The pattern c is shown in position for molding and also after being drawn. The patterns cc are assembled on the pin P and mounted in the forged yoke or hanger H, which is bolted to the underside of the stripping plate B. The heads of the set screws which are illustrated on the draw plate A press against the patterns at E, raising the patterns to the desired height. Upon lowering the draw plate, this allows the coil springs which are interposed between the pattern members and the stripping plate to force the pattern out of the mold with an oblique or roll-back motion.
Fig. 331. Sections Showing Mechanism of Machine with Pattern in Plan lor Molding and with Pattern Drawn or Rolled Back.
The master pattern illustrated in Fig. 332 is constructed of three pieces of stock, nailed and glued together. As in the case of all master patterns, use the double-shrink rule and also add a filing finish allowance of about 1/32 inch to such surfaces as form the pattern. Two castings are required from this master pattern for each pattern mounted on the machine. Fig. 333 illustrates the forged yoke H.
A perspective view of the stripping plate for the cope machine is illustrated in Fig. 334. The angle and dimensions of the recess J in the top are determined from the original drawing, Fig. 308, and from the location of the patterns on the machine. A finish allowance of 1/8 inch should be added to the top surface of the stripping plate, and cast-iron filler pieces riveted at the ends of the recess, as shown at K in Fig. 329. The core box tor the cope stripping plate is shown in Fig. 335.
Fig. 333. Forge Steel or Iron Pattern Hanger.
The core prints must be accurately placed, and the length and width shall be slightly smaller than the finish sizes to allow for the accurate alignment of the metal patterns, and the cored hole should be enlarged below the top surface of the stripping plate. This will lighten the labor of fitting these holes to the patterns. The small pieces of cast iron or steel, D, Fig. 331, are fastened to the top of the stripping plate with flat-head machine screws.
Fig. 335. Core Box for Cope Stripping Plate.
Cope the parting to the top of the pattern, and a recess to match this is planed in the top of the drag stripping plate, as shown by the dotted line L in Fig. 336. These features are also to be seen in Figs 329 and 330.
Fig. 330. Pattern for Drag Machine Stripping Plate.
Stop-offs should be screwed to the underside of the stripping-plate pattern, Fig. 334, as the pattern will be weakened by cutting out the stock at J. This recess J can also be made with a dry-sand core if it is desired not to weaken the pattern as suggested above.
Fig. 337. Can Box for Stripping Plate.
The stripping plate for the drag machine is illustrated in Fig. 336, and the core box in Fig. 337. As this construction is largely repetition, the cuts should explain themselves. This skeleton core box, however, has one new feature; it is made in three parts. After the core has been rammed, the end M is drawn, the ends of the sides N N holding the core sand so that end M is stripped out of the core. The sides can then be removed.
This illustration clearly shows the method of enlarging the lower end of the holes which are cored in the stripping plate. The dimension Q shall be the height of the core print plus 3/8 inch, and R shall be the total thickness of the pattern including the core print.
Fig. 338 shows a perspective sketch of the master pattern for the nowel or drag machine. This pattern must be extended to reach through the stripping plate down to the draw plate. The feet marked -uu shall have a metal-finish allowance on the underside, and the weight of the casting can be greatly reduced by coring. The core print is to be made first and the other parts nailed and glued to it. Use great care to have all parts very accurate, keeping the dimensions slightly over size, for the exposed portions will be file-finished. A simple skeleton core box will do for this core.
Fig. 339. Pattern for Part P. Fig. 329.
Fig. 340. Muter Pattern of Gate for Holder Frame Cover.
The part F, Fig. 339, must be finished to the same dimensions as the recess J on the cope machine. This piece is screwed to the center of the nowel stripping plate, as shown in Fig. 329.
The master pattern for the gate is shown in Fig. 340. This is a brass casting and is illustrated in Fig. 329 fastened to the top of part F. A steel pin, shown at W on the cope machine in Fig. 329, locates the sprue.
These machines are in successful operation, the improvements over the hand-rammed castings being more castings per flask, doing away with the expense of making and setting the dry-sand cores, and the uniformity of the castings requiring less fitting.