Trolley & Bridge Derailment, Movement Difficulty and Axle Faults

One of the riskiest mechanical fault scenarios in overhead cranes is the derailment of the bridge or trolley. It causes sudden equipment damage, production stoppage and accidents. Correctly identifying the causes is essential to prevent derailment.

Causes of Derailment

• Rail misalignment: The height difference between the two rails or the lateral axis deviation is out of tolerance.
• Wheel flange wear: Flange thickness has fallen below the critical limit and can no longer grip the rail.
• High-speed travel into the end: The bridge cannot stop at high speed at the rail end; the buffer or end limit switch is not active.
• Foreign object: Weld scale, a bolt or debris left on the rail triggers the wheel to climb off.
• Bridge skewing: In a twin-drive system one motor runs slowly or not at all.

Causes of Movement Difficulty and Jamming

• Rail axle tolerance is off; the wheel flange rubs against the rail.
• Wheel bearing damage: bearings are worn or dry and cannot turn freely.
• Travel motor or gearbox damage.
• The brake does not release (no brake air or the piston is locked).
• Loose rail fixing: rail clamps have loosened and the rail is "creeping".

Response and Correction Procedure

1. 1A derailed bridge or trolley must NEVER be forced back into place; the cause must be investigated first.
2. 2The load is lowered and the system is shut down (LOTO).
3. 3The wheel-rail contact and flange clearances are measured.
4. 4Rail alignment is corrected with a laser instrument.
5. 5Damaged wheels, bearings or flanges are replaced.
6. 6Skewing is resolved with a motor synchronisation (balancing) test.
7. 7Buffers and end limit switches are tested.
8. 8The system is recommissioned after a load test.

A derailed bridge or trolley should never be forced back; intervening before the root cause is resolved increases equipment damage and accident risk.

Frequently Asked Questions