KEVOS® MAKEOS · Fasteners
Shear Pin Overload Design (Pin Size for a Break Torque, Break Factor, Hub Bearing)
For a shear pin that protects a drive by breaking at an overload, what diameter should it be, at what torque will the chosen pin break, and is the hub strong enough around it?
Design of a shear pin (breaking pin) through a hub and flange or sprocket: the break torque from the running torque and the overload factor, the pin diameter that shears at that torque from the pin ultimate shear strength, the number of pins and shear planes and the pin circle radius, the break torque and factor with the diameter you choose, and the shear and bearing stresses as a check (as the bolt shear and bearing tool at the break force), against your break factor range and allowable bearing stress.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Running torque | N·m | Torque the drive transmits in normal running. |
| Overload factor to break at | Multiple of the running torque at which the pin should break. | |
| Number of pins | pins | Number of shear pins sharing the torque. |
| Shear planes per pin | choice | Shear planes per pin (2 when the pin passes through a hub between two flanges). |
| Pin circle radius | mm | Radius from the shaft centre to the pin centre. |
| Pin ultimate shear strength | MPa | Ultimate shear strength of the pin material (test a sample batch; it varies widely). |
| Pin diameter chosen | mm | Diameter of the pin you will fit (at the shear plane, often a groove). |
| Limits | ||
| Least break factor accepted | Least break torque as a multiple of running torque (to avoid nuisance breaks). | |
| Largest break factor accepted | Largest break torque as a multiple of running torque (to protect the drive). | |
| Thinnest part in bearing | mm | Thickness of the thinnest hub or flange part the pin bears on. |
| Allowable bearing stress of the hub | MPa | Allowable bearing stress of the hub and flange at the break force. |
Method and formulas
- Break torque = running torque × overload factor; break force at the pin circle = torque ÷ radius.
- Pin diameter = √(4F ÷ (π × pins × planes × τ_u)); chosen pin break torque = pins × planes × π d² ÷ 4 × τ_u × radius.
- Shear and bearing stress at the chosen pin’s break force (as the bolt shear and bearing tool).
- Example: a 7.2837 mm pin breaks at 1,000 N·m; the 7.5 mm pin breaks at 1,060.3 N·m (2.1206 × running).
Limitations
- Ultimate shear strength varies between batches; test pins from each batch for a reliable break torque.
- Sudden overloads; slow overloads can fatigue and break pins early.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a shear pin for a conveyor or mixer drive
- Check a replacement shear pin
- Set the break torque of a sprocket shear pin
Who it is for
- Design engineers
- Maintenance engineers
- Agricultural machinery engineers
What you get
- Break torque and pin diameter needed
- Break torque and factor with the chosen pin
- Bearing at the break force
Interpreting the result
- A groove at the shear plane fixes where the pin breaks and makes the break torque more repeatable.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1535, 1720–1735. Topic reference; no source tables or recommended settings are reproduced.
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