What does the continuity law in casting state regarding the flow of molten metal?

The continuity law in casting is fundamentally based on the principle of the conservation of mass. It states that, for an incompressible fluid like molten metal, the mass flow rate must remain constant from one cross-section of the flow to another. This leads to the conclusion that the volumetric flow rate—essentially the volume of material passing through a given section per unit time—must also remain constant throughout the liquid flow, provided there are no additional mass inputs or losses.

In practice, this means that as the molten metal flows through the different sections of a mold, the speed and cross-sectional area of the flow are interrelated. If the cross-sectional area decreases at any point, the flow velocity must increase to maintain the same volumetric flow rate, and vice versa. This principle is crucial in the design and analysis of casting processes because it helps engineers predict how molten metal will behave as it fills a mold.

The other options do not accurately capture the essence of the continuity law as it applies to casting. Some may address aspects related to flow characteristics or pressures but do not reflect the core premise that involves the constancy of the volumetric flow rate in a given system, which is what the continuity law specifically describes.