BIZOMAT MAKEOS · Fabrication
Casting Solidification Time and Riser Check
Will this cylindrical riser solidify after the casting, and what pattern size allows for shrinkage?
Casting and riser moduli and solidification times by Chvorinov’s rule, the riser-to-casting modulus ratio, and pattern size from a shrinkage allowance.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Casting (section) volume | cm³ | Volume of the casting or the section the riser must feed, from CAD. |
| Casting cooling surface area | cm² | Surface area of that section that cools into the mould (exclude faces joined to other sections). |
| Riser diameter | mm | Riser diameter. |
| Riser height | mm | Riser height. |
| Mould constant B | min/cm² | Mould constant for the metal and mould, from foundry trials or data. |
| Required riser/casting modulus ratio | Riser modulus must exceed the casting modulus by this factor (1.2 is a common foundry rule). | |
| Part dimension for pattern | mm | Finished part dimension to convert to a pattern size. |
| Shrinkage allowance | % | Patternmaker’s shrinkage allowance for the alloy and mould (e.g. about 1% for grey iron, 2% for steel). |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Casting (section) volume
- What it is
- The volume of the casting, or of the section the riser has to feed, taken from the CAD model.
- Units and format
- Enter a number in cm³: cubic centimetres. The form accepts 0.000001 cm³ or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2000 cm³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger volume raises the casting modulus and its solidification time.
- Get it right
- For a casting with several sections, check the heaviest section the riser feeds, not the whole part.
What this means: Casting cooling surface area
- What it is
- The surface area of that section through which heat flows into the mould. Faces joined to other sections or to the riser do not cool and are left out.
- Units and format
- Enter a number in cm²: square centimetres. The form accepts 0.000001 cm² or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 900 cm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger cooling area lowers the casting modulus and its solidification time.
- Get it right
- Leave out faces that join other metal; including them understates the modulus.
What this means: Riser diameter
- What it is
- The diameter of the cylindrical riser that feeds the casting.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 130 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger riser diameter raises the riser modulus and its solidification time.
- Get it right
- The riser is assumed to be a cylinder cooling from its sides and top, with its base on the casting.
What this means: Riser height
- What it is
- The height of the cylindrical riser above the casting.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 160 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A taller riser raises the riser modulus, with diminishing gains.
- Get it right
- Use the height of liquid metal in the riser, not the height of the mould above it.
What this means: Mould constant B
- What it is
- The constant in Chvorinov’s rule for this metal, pouring temperature and mould material, from foundry trials or published foundry data.
- Units and format
- Enter a number in min/cm²: min/cm². The form accepts 0.000001 min/cm² to 1000 min/cm². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 min/cm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Both solidification times rise in direct proportion; the modulus ratio does not change.
- Get it right
- It changes with mould material and pouring temperature, so use a value for your process.
What this means: Required riser/casting modulus ratio
- What it is
- How much larger the riser modulus must be than the casting modulus so that the riser freezes last, as set by your foundry practice.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 3. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.2 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only moves the pass or fail line; the calculated ratio does not change.
- Get it right
- This is a ratio of moduli, not of volumes or times.
What this means: Part dimension for pattern
- What it is
- A finished dimension of the casting that you want to convert into the larger pattern dimension.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 1000000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 250 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The pattern dimension rises in direct proportion.
- Get it right
- Add machining allowance separately; this tool scales only for shrinkage.
What this means: Shrinkage allowance
- What it is
- The patternmaker’s allowance for how much the alloy contracts as it cools in the mould, from foundry data for the alloy and mould type.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 10%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger allowance makes the pattern dimension larger.
- Get it right
- Type the percentage itself, not a fraction.
Method and formulas
- Modulus M = V ÷ A (cm). Riser (top and side cooling): V = πD²H/4, A = πDH + πD²/4.
- Chvorinov: t = B × M².
- Pattern dimension = part dimension × (1 + shrinkage).
- Example: the casting modulus is 2.2222 cm and the riser’s 2.7013 cm, a ratio of 1.2156.
Limitations
- Chvorinov’s rule is an approximation; riser feeding distance and volume (shrinkage demand) must also be checked.
- Exothermic or insulated sleeves change the riser modulus.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check that a riser feeds a casting section
- Compare riser sizes
- Size a pattern for shrinkage
Who it is for
- Foundry engineers
- Pattern makers
- Casting buyers
What you get
- Casting and riser moduli
- Solidification times
- Modulus ratio
- Pattern dimension
Interpreting the result
- Feeding needs both a larger modulus and enough liquid volume in the riser.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1405–1420. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Solidification time and Chvorinov's rule
In Metal Casting by the Numbers
What it covers: How long each part of a casting takes to freeze: the casting modulus, Chvorinov's rule, measuring the mould constant, freezing order, and a riser that froze before the section it fed.
Useful alongside · Library collection
Designing parts for casting: walls, draft, cores, shrinkage and working with your foundry
What it covers: How solidification shapes casting design, the rules for wall thickness, fillets, draft, cores and machining allowances, how to choose between sand and die casting on volume, and how to avoid porosity.
Useful alongside · BIZOMAT original book
Porosity in sections
In Microstructures by the Numbers
What it covers: Measuring casting porosity by area fraction and by density, telling shrinkage from gas pores, why sections cannot show whether pores connect, and tracing porosity to feeding.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
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