Free Engineering Tool #081
Flexible Coupling Calculator
Calculate the required torque rating, torsional stiffness, and natural frequency for flexible couplings per DIN 740. Select coupling type and enter operating conditions.
Results
Nominal Torque
The nominal torque transmitted by the coupling is derived from power and speed:
- P — transmitted power (kW)
- n — rotational speed (RPM)
- Tn — nominal torque (N·m)
Required Torque Rating
Per DIN 740, the coupling must be rated for the design torque including the service factor:
Where KA is the application/service factor accounting for dynamic loads.
Torsional Natural Frequency
For a two-inertia system connected by the coupling:
- Ct — dynamic torsional stiffness of coupling (N·m/rad)
- J1, J2 — mass moments of inertia (kg·m²)
Service Factor Guide
| KA | Load Character | Typical Applications |
|---|---|---|
| 1.0 | Uniform | Fans, centrifugal pumps, light conveyors |
| 1.25 | Light shocks | Belt conveyors, generators, centrifugal blowers |
| 1.5 | Moderate shocks | Reciprocating compressors, positive displacement pumps |
| 1.75 | Heavy shocks | Mixers, ball mills, rubber extruders |
| 2.0–3.0 | Extreme/Reversing | Crushers, presses, shears, rolling mills |
⚠️ Note: The natural frequency should be at least 20% away from the operating frequency and its harmonics to avoid torsional resonance. DIN 740-2 recommends fn/fop > 1.2 or fn/fop < 0.8.
Given: P = 15 kW, n = 1500 RPM, KA = 1.5
Tn = 9549 × 15 / 1500 = 95.5 N·m
Treq = 1.5 × 95.5 = 143.2 N·m
Select a coupling with Tmax ≥ 143.2 N·m
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Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
