KEVOS® MAKEOS · Mechanics
Vibration Isolator Selection
What mount stiffness and static deflection isolate this machine at its running speed, and how well do my chosen mounts work?
Selection of resilient mounts for a machine: the frequency ratio needed for a target isolation efficiency with damping, the natural frequency, static deflection and stiffness per mount that achieve it, and, for a chosen mount stiffness, the actual natural frequency, transmissibility and isolation, with a warning near resonance.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Machine mass on the mounts | kg | Mass carried by the mounts (machine plus base frame). |
| Number of mounts | Number of mounts sharing the weight equally. | |
| Lowest running speed (forcing) | rpm | Lowest steady speed producing vibration (use the lowest forcing frequency). |
| Target isolation | % | Share of the vibrating force you want kept out of the structure. |
| Damping ratio of the mounts | Damping ratio (about 0.05 for rubber, 0.01 for steel springs). | |
| Chosen stiffness per mount (0 = none) | N/mm | Vertical stiffness of the mount you are considering. |
Method and formulas
- Transmissibility T = √{[1 + (2ζr)²] ÷ [(1 − r²)² + (2ζr)²]}, with r = forcing ÷ natural frequency; isolation = 1 − T.
- Required r solved for the target isolation; natural frequency f_n = forcing frequency ÷ r.
- Static deflection δ = g ÷ (2π f_n)²; stiffness per mount = (m ÷ n)(2π f_n)².
- Example: 90% isolation at 1500 rpm needs 4.5931 mm of static deflection, about 266.88 N/mm per mount.
Limitations
- Single-degree-of-freedom vertical model; rocking modes and a flexible floor change the result.
- Mount stiffness varies with load and temperature; use the maker’s loaded stiffness.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Choose anti-vibration mounts for a compressor, fan or pump
- Check whether existing mounts isolate or amplify
- Explain why soft mounts are needed for slow machines
Who it is for
- Maintenance engineers
- Plant engineers
- Design engineers
What you get
- Required frequency ratio and natural frequency
- Static deflection and stiffness per mount
- Performance of the chosen mount
Interpreting the result
- Isolation only starts above √2 times the natural frequency; stiff mounts on a slow machine amplify vibration.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 197–198, 304–316. Topic reference; no source tables or recommended settings are reproduced.
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