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.
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Gating channel cross-sectional area
The gating system of a casting — the set of channels the molten metal travels through, from the pouring basin down to the mould cavity — is sized from the continuity equation: flow rate = area × velocity, that is, Q = A × v. Inverting it, the cross-sectional area of a channel that has to deliver a flow rate Q at a velocity v is A = Q ÷ v. Applied to the various elements of the system (pouring basin, the vertical sprue, the horizontal runner, and the ingates that feed the casting itself), this simple principle is what lets you control how the metal flows. The ratio between the areas of those elements defines the type of system, and there are two opposing philosophies. In a pressurized system the smallest area is at the ingates (the entry into the casting), which keeps the system full and under pressure — easy to build and with good yield, but the metal enters the casting fast and turbulent; it is used on metals that are less sensitive to oxidation (some irons and steels). In an unpressurized system the areas grow from the sprue towards the ingates (the largest area is at the ingates), so the metal decelerates progressively and enters the casting smoothly and quietly — essential for oxidation-prone metals such as aluminium and magnesium, where turbulence is catastrophic (it folds in bifilms). The area ratio is quoted as proportions such as '1:2:2' or '1:4:4' (sprue:runner:ingates). Getting those areas right — starting from the required flow rate (which follows from the filling time) and from the velocities acceptable at each point — is the heart of gating system design, and it determines the quality of the fill and, to a large extent, the soundness of the finished casting. Enter the flow rate and the velocity.
Related Tools
Pouring Velocity
Calculate the molten metal velocity at the base of the sprue by Torricelli's equation, v = √(2·g·h), from the metal column height h (m) and gravity g. The result, in m/s, is the velocity at which the metal enters the gating system by gravity, starting from the pouring basin height. It is the basis of gating system design: the velocity sets the flow rate (with the section area) and the flow regime. Velocities too high cause turbulence (air aspiration, oxidation, erosion); hence gating systems are designed to control and slow the flow. Enter the metal column height.
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.
Casting Metal Yield
Calculate the metal yield of a casting process, η = (part mass ÷ total poured mass) × 100%, dividing the finished part mass by the total poured metal (part + risers + runners + spills). The result, in %, measures the metal utilization efficiency: the rest (runners, risers, flash) is remelted, but consumes energy and adds cost. Typical yields range from 50 to 80%, depending on the part and gating complexity. Maximizing yield (well-sized risers, optimized gating) cuts energy and remelting costs. Enter the part mass and the total poured mass.
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.
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.
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.
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.