The sand goes through a change in crystal structure from low or alpha quartz to high or beta quartz that results in rapid expansion, followed by contraction and then further expansion as the quartz transforms to tridamite and then crystoballite. Veining has long been called an “expansion defect,” linked to the non-linear expansion of silica sand as it is heated by the liquid metal during casting. Many different casting types with cored passageways and unfavorable geometries or sand-to-metal ratios can suffer from veining defects. Ventilated brake rotors may show veining in the “windows” that also are difficult to remove and could cause uneven heating and warpage of the rotor during use. Engine blocks and heads may exhibit veins in narrow oil and water passageways that are difficult to remove, and could cause blockage and engine failure. Veining (aka, finning) has been a perennial problem for certain types of ferrous castings produced with chemically bonded sand cores.
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