Casting Cooling Time Calculator

Chvorinov's Rule states that solidification time t = B x (V/A)^n, where V = casting volume (m^3), A = casting surface area (m^2), B = mold constant (s/m^2), and n = 2 for sand casting (the standard exponent). The ratio V/A is called the modulus of solidification.

The mold constant B depends on the mold material, pouring temperature, and metal-mold interface conditions. For green sand molds with gray iron, B is typically 5 x 10^6 to 8 x 10^6 s/m^2. For steel poured into green sand, B is approximately 6 x 10^6 s/m^2. B must be determined experimentally for each specific combination of metal and mold.

Casting geometry is captured by the modulus M = V/A (volume divided by surface area). A sphere has the highest V/A ratio and thus the slowest cooling. A flat plate has a low V/A ratio and cools rapidly. This is why spherical (or roughly spherical) risers are used: they solidify last, feeding the casting.

The solidification modulus M = V/A (m) is the key geometric parameter. For a simple solid cylinder of diameter d and height h: V = pi x (d/2)^2 x h and A = 2 x pi x (d/2)^2 + pi x d x h. Riser design uses Chvorinov's Rule to ensure the riser has a higher modulus than the casting section it feeds.

Chvorinov's Rule was developed for sand casting and is most accurate for that process. For investment (lost-wax) casting, the mold is preheated, which changes the heat transfer boundary conditions significantly. Modified versions with different exponents (n closer to 1.5) and different B values are used for investment and die casting, but Chvorinov's n = 2 remains the standard for sand casting per foundry engineering textbooks.