Casting Riser Sizing Calculator (Modulus Method)
Shrinkage porosity usually means a riser was too small, badly placed or froze too early. This calculator uses the Chvorinov modulus method to size a cylindrical riser and then checks that its volume can supply the shrinkage of the section it feeds.
Your numbers
Volume of the casting section the riser must feed.
Surface area through which that section loses heat, excluding the contact area with the riser.
Riser modulus divided by casting modulus. 1.2 is a common starting value.
About 3 to 6 percent for carbon steel, much lower for graphitic cast iron.
Your results
Planning aid for first estimates. Real riser design also accounts for riser neck size, hot spots, chills, alloy, mold material and solidification simulation. Validate with trials or simulation.
Riser diameter vs casting cooling area
Sweeps Casting cooling surface area from 400 to 2400, holding your other inputs fixed.
Connect methods data to ERP costing
Optional: we can review how pour weight, yield and riser data feed costing and quoting in your ERP.
Optional. The tool and every export work without this. No spam.
How to use it
Enter the volume of the casting section to be fed and the surface area through which it loses heat, excluding the contact patch with the riser. The calculator gives the casting modulus as volume over area. Choose a riser modulus factor, normally 1.2, so the riser freezes after the casting. Pick a height to diameter ratio and the feed efficiency of your riser type. Read the diameter and height, then check the feeding margin. A margin of at least one means the riser holds enough liquid to feed the shrinkage.
- Use the cooling area without the neck contact
- A factor of 1.2 is a common start
- Compare plain, insulated and exothermic efficiency
The method behind it
Chvorinov's rule says solidification time is proportional to the square of the modulus, where modulus is volume divided by cooling surface area. If the riser modulus is 1.2 times the casting modulus, its freezing time is about 1.44 times longer. For a cylinder with height to diameter ratio r, cooling from the side and top, the modulus is D times r over 2 plus 4r, so the diameter follows directly. The second check is volumetric: a riser feeds only a fraction of its own volume, roughly 14 percent for a plain sand riser, so the riser must also hold shrinkage volume divided by efficiency.
- Time to freeze scales with modulus squared
- Modulus governs for compact castings
- Volume governs for large shrinkage or low efficiency
Worked example and common mistakes
A 10 by 10 by 20 cm block has a volume of 2,000 cm3 and an area of 1,000 cm2, so the casting modulus is 2.0 cm. With a factor of 1.2 the riser modulus is 2.4 cm. At a height to diameter ratio of 1.5, the diameter is 12.8 cm and the height 19.2 cm. Riser volume is about 2,470 cm3, far more than the 714 cm3 minimum for 5 percent shrinkage at 14 percent efficiency, so modulus governs. Common mistakes include using the total casting area, forgetting the neck must also have adequate modulus, and applying steel shrinkage to graphitic iron.
- Do not include the neck contact in the cooling area
- Size the neck larger in modulus than the casting
- Use the right shrinkage for the alloy
Frequently Asked Questions
What is casting modulus?
Casting modulus is the volume of a section divided by the surface area through which it cools. Larger modulus means slower cooling and longer solidification. It is used to compare sections and to size risers so the riser stays liquid longer than the casting.
Why use a riser modulus factor of 1.2?
A factor of 1.2 makes the riser freeze about 44 percent later than the casting section, because solidification time scales with modulus squared. Some foundries use 1.1 to 1.3 depending on alloy, neck design and experience.
What is riser feed efficiency?
It is the fraction of riser volume that can actually be delivered to the casting before the riser freezes. A plain sand riser is often rated near 14 percent. Insulating and exothermic sleeves raise it, which lets you use smaller risers and improve yield.
Does this replace solidification simulation?
No. It is a quick first estimate for compact sections. Complex geometry, hot spots, chills and neck placement need simulation software or proven trial practice before tooling is cut.
If your methods engineering notes live in spreadsheets, we can help connect pattern, gating and riser data to routings and costing in your ERP. The calculator is free and stands alone.
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