KEVOS® MAKEOS · Gears
Plastics Gear Power Rating
How much power can this nylon, acetal or other plastics gear transmit?
Power rating of plastics spur, helical and straight bevel gears by the handbook’s Lewis-type formulas in metric form, from face width, tooth form factor, module, safe bending stress, pitch-line velocity and service factor, with the corresponding torque.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Gear type | choice | Gear type. |
| Face width | mm | Face width. |
| Tooth form factor Y | Lewis tooth form factor for the tooth count and system (from the handbook table or the material supplier). | |
| Module | mm | Module (normal module for helical gears). |
| Safe bending stress for the plastic | MPa | Safe bending stress of the plastic at the operating temperature and lubrication (from the material supplier). |
| Pitch diameter | mm | Pitch diameter, for the pitch-line velocity. |
| Speed | rpm | Speed of the gear. |
| Service factor | Service factor for the load type and running hours. | |
| Pitch cone distance (bevel) | mm | Pitch cone distance of a bevel gear (must exceed the face width). |
Method and formulas
- V = π d n ÷ 60,000 m/s.
- Spur: kW = F Y m S_s V ÷ [327 (3.05 + V) C_s].
- Helical: kW = F Y m S_s V ÷ [179 (5.56 + V) C_s]; straight bevel: the spur value × (C − F) ÷ C.
- The metric constants match the US-customary forms (55 (600 + V) P C_s and 423 (78 + V) P_n C_s).
- Example: a 10 mm wide, module 1.5 spur gear at 600 rpm is rated about 143.19 W.
Limitations
- Bending strength only; wear, heat build-up and creep often govern plastics gears.
- Plastics strength falls with temperature and moisture: use the stress for the service condition.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check whether a plastics gear can replace a metal one
- Size face width or module for a plastics gear train
- Rate a molded gear at a new speed
Who it is for
- Design engineers
- Product engineers
- Gear designers
What you get
- Pitch-line velocity
- Power rating
- Torque at the rating
Interpreting the result
- Plastics gears running against metal pinions wear less and run cooler than plastic-on-plastic pairs.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 604–606. Topic reference; no source tables or recommended settings are reproduced.
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