NMRV Worm Gearbox Self-Locking – What It Is and When You Need It
NMRV Worm Gearbox – Self-Locking Explained
What is self-locking?
When the worm lead angle is small enough, the friction between the worm and worm wheel prevents the load from back-driving the gearbox when power is off
Self-locking by ratio
| Ratio | Self-Locking Tendency |
|---|---|
| 5:1 – 10:1 | None – freely back-drives |
| 15:1 – 25:1 | Low to moderate |
| 30:1 – 40:1 | Moderate to high |
| 50:1 – 100:1 | Very high |
When you need self-locking:
Hoists and lifting equipment
Inclined conveyors (prevents rollback)
Gate and valve actuators
Trade-off: Higher ratios = better self-locking but lower efficiency (as low as 35-52% at 80:1)
