Worm gearboxes are self-locking if the gearboxes cannot be driven from the worm gear side.
The self-locking is directly related to the efficiency of the gearbox.
If self-locking is demanded the corresponding efficiency of the gearbox with driving worm must be below 0.5.
If a gearbox must be unconditionally self-locking, or alternatively, unconditionally not self-locking, we ask to contact us for consultation, giving a description of the case of application.
Static self-locking
Worm gearboxes are statically self-locking if starting from standstill with driving worm gear is impossible.
The self-locking depends on the pitch of the toothing.
The angle is 2.5° to 5°.
Please enquire this.
Vibrations may override / deactivate the self-locking.
Therefore a self-locking toothing cannot always take the place of a brake or an anti-reversing device.
Dynamic self-locking
Worm gearboxes are dynamically self-locking if, with rotating gearbox mechanism, continued operation is impossible due to torque action on the worm gear (output side) of the gearbox.
The overrun occurring after switching-off depends on the rotating masses on the drive side.
Dynamic self-locking is only possible with very large gear ratios in the range of low driving speeds.
Please enquire this.
Limits
If driven parts have high mass inertia moments no self-locking must occur during the run-down process.
Extremely high load peaks may occur in case of sudden blocking of the gearbox.
In such cases, a gearbox with multistart worm should be used whenever possible.
Also, if a braking motor or a separate brake is used on the drive side, the braking moment must not be too high, and it must be mitigated by using an additional flywheel mass on the drive side