Failure Analysis of Wire Ropes in Lifting Systems

Wire ropes are fundamental mechanical components that find their application in lifting and hauling devices including cranes, lifts, mine haulages, and aerial tramways. Out of these, wire ropes for lifts are the most critical safety components since they are involved in the lifting of humans directly. These wire ropes have an intricate service environment with different loading forms of axial tension, bending through pulleys, torque, and dynamic loads because of starting, stopping, and emergency braking actions. The wire ropes in lift systems are very susceptible to fatigue damage owing to their frequent start/stop cycles and bending around small diameter sheaves. They are more prone to fatigue failure in the form of micro-crack formation in individual wires followed by propagation leading to eventual rupture of strands. Moreover, the requirement of traction imposes stringent conditions of wire rope surfaces, friction properties, and suitability of grooves in sheaves.

Several critical concerns specific to lift wire ropes include:

§  Fatigue and Bending Stress: Continuous cyclic loading reduces rope life significantly, especially when improper D/d ratios (sheave diameter to rope diameter) are used.

§  Wear and Abrasion: Contact between rope and sheave grooves leads to external wear, while internal wire movement causes fretting wear.

§  Corrosion: Moisture, humidity, and environmental contaminants (especially in outdoor or high-rise glass elevators) accelerate corrosion, weakening wires internally.

§  Loss of Lubrication: Inadequate lubrication increases internal friction between wires and strands, accelerating wear and reducing flexibility.

§  Unequal Load Distribution: Improper installation or tensioning can cause uneven load sharing among ropes, leading to premature failure of specific ropes.

§  Traction Loss (Slippage): Surface wear or contamination (oil, dust) can reduce friction between rope and traction sheave, affecting lift performance and safety.

§  Wire Breakage and Bird caging: Localized damage, shock loading, or improper handling can cause deformation such as bird caging, compromising rope integrity.