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RAPPING. Knocking or jarring the pattern to loosen it from the sand in the mold before withdrawing the pattern.
RELEASE AGENT (PARTING AGENT). A material such as silicone, stearate, oil or wax for lubricating a die, pattern or core box to facilitate easy removal of a casting, mold or core.
REMELT. Sprues, gates, riser, and defective castings returned directly to the crucible furnace.
RESIDUAL STRESS. (See STRESS, RESIDUAL.)
RESPIRATOR. A filtering device which covers the nose and mouth and prevents inhalation of dust or fumes; should have the U.S. Bureau of Mines certificate of approval for the specific contaminant being filtered out.
RIBS. Sections joining parts of a casting to impart greater rigidity.
RIDDLE. A screening device, manually or mechanically operated, for removing coarse particles and contamination from molding sand.
RISER. A reservoir of molten metal provided to compensate for the internal contraction of the casting as it solidifies.
ROLLING OVER. The operation of reversing the position of a flask in which the drag part of the pattern has been rammed with the parting surface downward.
RUNNER. A channel through which molten metal or slag is passed from one receptacle to another, in a mold, the portion of the gate assembly that connects the downgate or sprue with the casting ingate or riser. The term also applies to similar portions of master patterns, pattern dies, patterns, investment molds, and finished castings.
RUNOUT. A casting defect caused by incomplete filling of the mold due to molten metal draining or leaking out of some part of the mold cavity during pouring; escape of molten metal from a furnace, mold, or melting crucible.
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