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Pressure of Molten Metal

The conditions of liquid pressure exist in moulds exactly the same as in any other vessel in which liquids may be placed. Solids transmit pressure only in the line in which it is exerted; liquids transmit it in every direction--as may be noticed when in casting the poured metal escapes at every riser, at equal velocities. Molten metal influenced by gravity alone presses in all directions, as will be seen by the following: Let a covered mould be filled with molten metal, and maintain a pressure by a raised runner-basin; if this mould be tapped at the bottom the metal will rush out,--this proves a downward pressure; if it be tapped on the side, the metal rushes out, showing a lateral pressure; and if it be tapped on the top, the metal will escape also, showing an upward pressure. The pressure of molten metal in every direction is proportioned to the depth; hence the necessity of increasing the strength of moulds towards their bases, and additional precautions being taken to hold down the cope when large areas are subjected to a considerable head-pressure. See WEIGHTING COPES; HYDRAULICS; HYDROSTATIC BELLOWS.