Solidification Time (Chvorinov)
Calculate the solidification time of a casting by Chvorinov's rule, t = B × (V ÷ A)², from the mold constant B (min/cm², depending on the mold material and metal) and the ratio of the part's volume V to its surface area A. The result, in minutes, is the time for the metal to fully solidify. The rule shows that parts with a higher volume/area ratio (more 'massive') solidify more slowly — a fundamental casting design principle: risers (metal reservoirs) must have a larger modulus than the part to solidify last and feed the shrinkage. Enter the mold constant, the volume and the part area.
Result
—
Solidification time (Chvorinov's rule)
Chvorinov's rule is one of the most fundamental relationships in metal casting: it predicts how long molten metal takes to solidify inside the mould. The formula is t = B × (V ÷ A)², where V is the volume of the casting, A the surface area in contact with the mould (through which heat escapes) and B the mould constant (in min/cm²), which bundles together the thermal properties of mould and metal (latent heat, conductivity, temperatures). The central insight lies in the V/A ratio, raised to the square: chunky parts with a lot of volume and little surface solidify slowly, because they have a great deal of heat to lose through a small area; thin, spread-out parts solidify fast. Since time varies with the square of that ratio, doubling the 'bulkiness' quadruples the time. The rule is the basis of riser design (the metal reservoirs that feed the casting as it contracts): for a riser to do its job, it has to solidify after the casting — that is, it needs a larger V/A (modulus). Chvorinov's rule turns that requirement into a calculation: by comparing the moduli of casting and riser, the correct order of solidification is guaranteed and shrinkage cavities (internal contraction voids), the commonest casting defect, are avoided. Enter the mould constant, the volume and the surface area of the part.
Related Tools
Casting Cooling Modulus
Calculate the cooling modulus (or geometric modulus) of a casting, M = V ÷ A, dividing the volume V by the surface area A in contact with the mold. The result, in cm (length unit), is the parameter governing solidification speed: the larger the modulus, the slower the solidification (Chvorinov's rule says the time is proportional to the modulus squared). It is the basis of riser sizing in foundry — the modulus rule requires the riser modulus to be about 1.2 times that of the part, so it solidifies later and feeds the shrinkage, avoiding shrinkage cavities. Enter the part volume and area.
Mold Fill Time
Calculate the fill time of a casting mold, t = V ÷ Q, dividing the cavity volume V by the metal flow rate Q of the gating system. The result, in seconds, is the time to completely fill the mold with molten metal. It is a critical parameter: filling too slowly lets the metal cool and solidify before filling everything (cold shut, misrun defects), while too fast causes turbulence, gas entrapment, mold erosion and inclusions. The optimal time depends on the part's weight and thickness and the metal. Sizing the gating system for the right time is central to casting design. Enter the cavity volume and the flow rate.
Metallostatic Pressure
Calculate the metallostatic pressure exerted by molten metal at the bottom of a mold, P = ρ × g × h, from the molten metal density ρ (kg/m³), gravity g and the metal column height h (m). The result, in pascals, is the pressure the molten metal exerts on the mold walls and bottom due to its own weight — analogous to hydrostatic pressure, but with the high density of metals. It is essential to size the mold strength (which can 'burst' or deform under pressure), predict core flotation and metal penetration into gaps. Dense metals (iron, ~7000 kg/m³) generate high pressures. Enter the metal density and the column height.
Solidification Volumetric Shrinkage
Calculate the volumetric shrinkage on solidification of a metal, ΔV = (ρ_solid − ρ_liquid) ÷ ρ_liquid × 100%, from the metal densities in the solid and liquid states. The result, in %, is the volume reduction that occurs when the metal goes from liquid to solid — because the solid is denser (more compact) than the liquid. This shrinkage is the main cause of shrinkage cavities (internal voids) and is exactly what risers must feed with extra molten metal. Each metal has its solidification shrinkage: steel ~3%, aluminum ~6.6%, copper ~5%. Gray cast iron is an exception (graphite expands, reducing the liquid shrinkage). Enter the solid and liquid metal densities.
Shrinkage Allowance
Calculate the pattern (mold) dimension accounting for solidification shrinkage, dimension = part dimension × (1 + shrinkage ÷ 100), from the desired final part dimension and the metal's linear shrinkage coefficient (%). The result is the larger dimension the pattern must have so that, upon solidifying and cooling, the part shrinks to the correct size. Each metal has its linear solidification shrinkage: steel ~2%, gray cast iron ~1%, aluminum ~1.3%, bronze ~1.5%. Patternmakers use shrink rules ('contraction rules') already scaled up. Ignoring shrinkage results in undersized parts. Enter the part dimension and the shrinkage coefficient.
Gate Area
Calculate the gating channel section area, A = Q ÷ v, dividing the desired metal flow rate Q by the metal velocity v. The result, in the consistent area unit (cm²), is the cross-section the sprue (or gate) must have to deliver the needed flow at the calculated velocity. It is the application of the continuity equation to the casting gating system. Correctly sizing the areas of the system's elements (basin, sprue, runner, gates) controls the flow rate, velocity and flow regime of the metal, avoiding turbulence and ensuring proper filling. The ratios between the areas define the system type (pressurized or unpressurized). Enter the flow rate and the velocity.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.