Overhead bridge cranes have two separate travel systems: bridge travel motors that move the bridge longitudinally and a trolley travel motor that moves the trolley across the bridge. A failure of these motors can halt production entirely.
Symptoms of a Travel Motor Fault
- Motor runs but there is no movement (coupling or gearbox fault)
- Motor does not run while the control signals it (motor winding or brake fault)
- Abnormal noise (gear wear, bearing damage)
- One side motor runs while the other does not (bridge skewing)
- Motor overheats and the thermal relay keeps tripping
Motor Replacement Procedure
- 1LOTO is applied; the bridge or trolley is secured with mechanical chocks.
- 2Electrical connections are labelled and disconnected.
- 3The motor-gearbox unit is released from its bolt and coupling connections.
- 4The new motor-gearbox set is fitted; brake clearance is set to manufacturer values.
- 5Phase sequence is checked; a wrong sequence makes the motor turn in reverse.
- 6An unloaded test run is performed, then handed over after a full-capacity load test.
Gearbox and Brake Replacement
- Gear wear or oil leakage in travel gearboxes may require a gearbox overhaul alongside the motor replacement.
- Brake shoes (disc or drum brake) must be replaced once they fall below manufacturer tolerances; otherwise there is a risk of slipping and collision.
Frequently Asked Questions
If the motor runs but the bridge does not move, what could the cause be?
If the motor turns but motion is not transmitted, the usual causes are a damaged coupling, a broken gearbox gear or a brake that does not fully release. The brake air and coupling bolts should be checked first.
The bridge travels skewed — is this dangerous?
Yes. Skewing occurs when one motor in a twin-drive system runs slowly or not at all; it accelerates wheel-rail wear and increases derailment risk. Motor synchronisation and brake settings must be checked urgently.