BIZOMAT MAKEOS · Fabrication
Length of Angle or Bar Bent to a Ring
What length of angle iron or bar do I cut to roll this ring inside or outside a tank?
Cut length of an angle, flat or other section rolled into a ring, from the diameter at the back of the section and the distance to its neutral axis, or from a handbook-style length constant, for sections placed inside or outside a tank or stack.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Correction from | choice | Use the section’s neutral-axis distance, or a length constant for the section. |
| Section is | choice | Whether the section sits inside or outside the shell. |
| Shell diameter at the back of the section | mm | Diameter of the shell surface that the back of the section bears on. |
| Back of section to neutral axis | mm | Distance from the back of the section to its neutral axis (centroid) in the plane of bending, from section data. |
| Length constant | mm | Length constant to subtract (inside) or add (outside), equal to 2π × the neutral-axis distance. |
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: Correction from
- What it is
- Whether the length correction comes from the distance between the back of the section and its neutral axis, or from a ready-made length constant.
- Units and format
- Choose one of 2 options from the list: Neutral-axis distance; Length constant.
- Example
- The form opens with “Neutral-axis distance” selected as a worked example. Choose the option that matches your case.
What this means: Section is
- What it is
- Whether the bent section sits inside the shell with its back on the inside surface, or outside with its back on the outside surface; it decides whether the correction is subtracted or added.
- Units and format
- Choose one of 2 options from the list: Inside the shell (diameter is the inside of the shell); Outside the shell (diameter is the outside of the shell).
- Example
- The form opens with “Inside the shell (diameter is the inside of the shell)” selected as a worked example. Choose the option that matches your case.
What this means: Shell diameter at the back of the section
- What it is
- The diameter of the shell surface that the back of the rolled section bears against: the inside diameter for a ring inside, the outside diameter for a ring outside.
- 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 6096 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The cut length rises by π for each millimetre of diameter.
What this means: Back of section to neutral axis
- What it is
- The distance from the back face of the section to its neutral axis (centroid), measured in the plane of bending, from section property tables.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 22.5 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The cut length changes by 2π times this distance.
- Get it right
- Measure from the face that bears on the shell, not from the outer edge of the other leg.
What this means: Length constant
- What it is
- A length constant for the section equal to 2π times its neutral-axis distance, subtracted for a ring inside the shell and added for one outside.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 109.7 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Method and formulas
- Neutral-axis diameter = D − 2x inside the shell, D + 2x outside.
- Length = π × neutral-axis diameter = π D ∓ 2π x.
- Handbook example: 20 ft inside diameter with a constant of 4.319 in gives 754 − 4.319 = 749.68 in.
- Example: 6096 mm inside a shell with 22.5 mm to the neutral axis needs 19,010 mm.
Limitations
- Neutral axis assumed at the centroid; heavy rolling can shift it slightly.
- Add allowance for the ends to be trimmed after rolling.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Cut stiffener rings for tanks, ducts and stacks
- Estimate material for rolled flanges
- Check rolled ring length allowances
Who it is for
- Fabrication supervisors
- Manufacturing engineers
- Estimators
What you get
- Cut length
- Neutral-axis diameter
- Correction to the circumference
Interpreting the result
- Roll a trial ring for new sections and adjust the constant from the measured result.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2593. 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
Rings, stiffeners and flanges
What it covers: Roll a 75 × 75 × 6 angle into a ring on its centroid, not its back: length, toe and heel strains, toe-out against toe-in, splices, bolt circles on the outlet flange, and a ring cut 132 mm short.
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