KEVOS® MAKEOS · Power Transmission
Flange Coupling Design (Design Torque, Bolts, Friction Drive, Key)
Is this rigid flange coupling strong enough for the motor power, do the bolts carry the torque by friction or shear, and is the hub key long enough?
Check of a rigid flange coupling: design torque from power, speed and service factor; bolt force and bolt shear stress on the bolt circle with the shank diameter needed, and the torque the bolt preload can carry by face friction (as the flange coupling bolts tool); key force, shear and crushing stress in the hub and the least key length for each (as the key stress tool), with the key length checked against the hub length.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Power | kW | Power transmitted. |
| Speed | rpm | Shaft speed. |
| Service factor | Service factor for the driver, load and duty. | |
| Bolts | ||
| Number of bolts | Number of coupling bolts. | |
| Bolt circle diameter | mm | Diameter of the bolt circle. |
| Bolt shank diameter | mm | Diameter of the bolt shank in the shear plane. |
| Allowable bolt shear stress | MPa | Allowable shear stress of the bolts. |
| Preload per bolt | kN | Tightening preload of each bolt. |
| Friction coefficient between flange faces | Friction coefficient between the flange faces. | |
| Shaft key | ||
| Shaft diameter | mm | Diameter of the shaft in the hub. |
| Key width | mm | Width of the key. |
| Key height | mm | Height of the key. |
| Effective key length | mm | Length of key engaged in the hub. |
| Hub length | mm | Length of the coupling hub. |
| Allowable key shear stress | MPa | Allowable shear stress of the key. |
| Allowable compressive stress (weakest of key, shaft, hub) | MPa | Allowable crushing stress of the key, shaft or hub, whichever is weakest. |
Method and formulas
- Design torque T = 9549 P ÷ n × service factor.
- Bolt force = 2T ÷ (n_b D_bc); shear stress = force ÷ (π d² ÷ 4); friction torque = μ n_b F_i D_bc ÷ 2 (as the flange coupling bolts tool).
- Key force = 2T ÷ d_s; shear = F ÷ (w L); crushing = F ÷ (h ÷ 2 × L); least length for each (as the key stress tool).
- Example: the design torque is 429.72 N·m; the bolts see 22.797 MPa and friction can carry 960 N·m; the key needs at least 53.715 mm.
Limitations
- Steady torque with a service factor; shock and reversing loads need a fatigue check.
- Bolts in shear assume fitted (reamed) bolts; clearance bolts rely on friction.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a rigid coupling when fitting a larger motor
- Choose bolts and keys for a fabricated coupling
- Decide whether fitted bolts are needed
Who it is for
- Design engineers
- Maintenance engineers
- Millwrights
What you get
- Design torque
- Bolt force, shear stress and friction capacity
- Key stresses and least key length
Interpreting the result
- If friction alone carries the design torque, the bolts are not loaded in shear and clearance holes are fine.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2441–2450, 2460–2486, 301–302. Topic reference; no source tables or recommended settings are reproduced.
WORKOS 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.
Open the Flange Coupling Design (Design Torque, Bolts, Friction Drive, Key) calculator
