the internal diameters, and the cores were printed with internal vents for gases generated during casting. To ensure conditions were
consistent, all tubes of the same diameter were cast at the same time and were fed from a common feeder at the bottom of the tube. Figure 1 shows the tubes, feeder and two down sprues, which in- creased the feed rate so the tubes would fill before freezing off. The tapered area at the end of each tube was a riser to feed the tube as metal shrunk during solidification. This design allowed the use of a single core for all six tubes of the same diameter. The core resembled a harp with a core print sur- rounding the cores, and the cores running parallel between them like strings on the harp. Figure 2 shows the CAD model of the core, which contains a passage through the base to allow the tubes to be bottom fed. The core would be ex- tremely difficult if not impossible to create by conventional means. To create the molds, matchplates
were created for each of the tube diameters, is shown in Figure 3. T e matchplate included vent lines that would connect the vents from each of the cores to the outside of the mold. Each of the mold cavities also was vented to the outside to allow complete fi lling of the mold. The molds were positioned so
that they were vertically parted. The pouring cups were elevated to increase the static pressure of the metal during pouring. A vacuum manifold was attached to the mold where the vent lines emerged so that a low level vacuum (supplied by a shop vacuum) could be used to assist in drawing out gases gen- erated during filling. On the fi rst casting, the pouring cup was positioned 2 ft. above the mold, which fi lled quickly and metal fl owed up and out of the vents. On successive casts, the head height was reduced until it was found that a head height of 3 in. suffi ced. In all, 12 pours were done, two for each of the six core diameters.
Nov/Dec 2015 | METAL CASTING DESIGN & PURCHASING | 29
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The primary aims of the study were to see whether cores were strong enough to hold up during pouring and whether gases could be vented from the mold through internal passages in the core.”
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