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Chvorinov Rule Solidification Time and Riser Sizing Calculator

Chvorinov's rule says a casting solidifies in a time proportional to the square of its volume-to-surface-area ratio. This calculator turns volume and cooling area into modulus and solidification time, then sizes a riser that should freeze after the casting it feeds.

Your numbers

Casting section volume

cm3

Volume of the section or casting that the riser must feed.

Cooling surface area

cm2

Area through which the section loses heat to the mold. Exclude faces joined to a neck or riser contact.

Mold constant B

min/cm2

Depends on metal, mold material and pour temperature. Green sand steel work is often in the range of 2 to 4 min/cm2; calibrate on your own castings.

Riser modulus factor

Your results

Casting solidification time

9.9 min

Chvorinov: t = B x (V/A) squared.

Riser diameter (H/D = 1.5, all sides cooling)

14.2222

In cm. For a cylinder with H = 1.5 D, modulus = 0.1875 D when every face loses heat. Insulated tops allow smaller risers.

Casting modulus (V / A)

2.2222

Volume divided by cooling area, in cm.

Required riser modulus

2.6667

Riser solidification time

14.2 min

Riser height

21.3333

In cm.

First-pass estimate for sand-cast sections. It does not check feed volume, feeding distance, neck freezing or shrinkage demand; confirm with solidification simulation or trial pours before releasing tooling.

Save results:

Solidification time vs cooling area

Sweeps Cooling surface area from 300 to 1500, holding your other inputs fixed.

Link riser and yield history to your ERP

Optional: a short review of how heat, pattern and defect data could feed methods decisions from your ERP.

Optional. The tool and every export work without this. No spam.

How to use the calculator

Measure or pull from CAD the volume of the section to be fed and the area through which it cools, leaving out faces that touch the riser neck or a chill. Enter the mold constant B for your metal and mold system. The tool reports casting modulus, solidification time, the riser modulus after the safety factor, and a cylindrical riser diameter and height.

Treat each hot spot as its own section with its own modulus.
Subtract neck contact area from the casting surface area.
Use a calibrated B from your own thermal trials where possible.

The method behind it

Chvorinov's rule is t = B x (V/A) squared. The ratio V/A is the modulus. A riser should have a longer solidification time than the casting, so its modulus is set to about 1.1 to 1.3 times the casting modulus. For a cylindrical riser with height 1.5 times diameter and all faces cooling, the modulus equals 0.1875 times the diameter, which gives the diameter shown. Exothermic or insulating sleeves effectively raise the riser modulus, so a smaller riser can be used.

Reading the result and common mistakes

The chart shows how solidification time falls as cooling area rises for the same volume, which is why ribs, chills and thin sections freeze faster. A riser must also hold enough liquid to supply the shrinkage, so check feed volume separately: modulus alone does not prove a riser is large enough.

Using the whole casting surface area instead of the section's own area.
Forgetting that the neck itself must freeze after the casting section.
Assuming one B value fits steel, iron and aluminum alike.
Skipping a feed-volume check for high-shrinkage alloys.

Frequently Asked Questions

What is the modulus in casting?

Casting modulus is the volume of a section divided by the surface area through which it loses heat, usually in cm. A larger modulus means the section freezes later. Risers are sized by modulus so they remain liquid until the casting has solidified.

Does the rule work for all alloys?

It works best for skin-forming metals in sand molds, such as carbon steel and many irons. Mushy-freezing alloys and heavy chill use depart from it. The mold constant B changes with alloy, mold material and superheat, so calibrate against your own castings.

Why is the riser factor 1.2?

A margin of about 20 percent on modulus gives the riser roughly 44 percent longer solidification time than the casting, because time varies with modulus squared. Tight designs with sleeves use 1.1, while difficult geometry may justify 1.3.

Is the result enough to release a pattern?

No. It is a screening calculation. Confirm feed volume, neck size and feeding distance, and use simulation or a trial pour for critical parts. Treat the output as the starting point for the methods engineer.

If your foundry tracks pattern, heat and defect history in an ERP, we can help surface riser and yield history next to the quote. A short conversation is enough to see whether it fits.

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