Science Fair Project Encyclopedia
Cope and Drag
In foundry work, the terms "Cope" and "Drag" refer to the upper and lower parts of a two-part casting flask, used in sand casting. The flask is a wood or metal frame, which contains the molding sand, providing support to the sand as the metal is poured into the mold.
In the simplest sand casting procedure, the drag is placed on a board, around a pattern of the part to be cast. The pattern is a model of the part to be made. Sand is sifted over the pattern until the model is covered by a few inches of sand. More sand is then dumped into the drag, and rammed with a wooden wedge to pack the sand down. The sand is then struck level with the top edge of the cope, using a wooden or metal strake. A board is then placed on top of the drag and the drag is flipped over.
Then, the cope is placed on the drag, and dowels (or pins) are put in the sand to make holes for the sprue and one or more risers. sand is again sifted over the pattern, and rammed to fill the cope. The pins are then carefully pulled out of the sand, and a gate is cut into the sand. The critical part of the operation is to separate the cope and drag to remove the pattern. The pattern is lifted from the sand, leaving a molding cavity. A passageway for metal to enter the mold, called a "gate", is then cut from the sprue hole to the void left by the pattern, and a runner is cut from the sand to allow metal to flow into the riser.
The flask is then put back together, and metal can be poured into the mold. The metal will flow down the sprue, into the mold cavity, and back up the riser (of which there may be several). Once the metal has cooled enough to solidify, the flask can then be separated again, and the sand removed to reveal the rough casting. The rough casting is separated from the sprue and riser(s) either by sawing them off, or just breaking the thin metal of the gates and runners.
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