The main causes of crane rail pad migration are:

Lateral wobbling of rail fasteners: If the fasteners are not properly secured against the rail foot, or if they move back under the effect of cyclic lateral loading, this creates lateral wobbling of the rail, allowing it to move sideways. This can vary from 0.5 mm in the least affected areas to 5 mm in the most affected areas. The behavior of rail fasteners over several load cycles, fastener design, production quality and installation precision all influence lateral float. Correct installation, using a torque wrench or RailLok™ fasteners that allow the use of impact wrenches, can eliminate any initial deviation and improve fastener movement under load, thus reducing lateral float.

Insufficient clamping force: Crane wheels generate a “wave effect” in the rail, creating an upward force just before and after the wheel position. If the clamping force of the rail foot is insufficient, the rail can move upwards, resulting in a rocking effect and lateral forces that can expel the pad or cause fatigue failure of the pad’s steel reinforcement. To optimize clamping force, it’s essential to select the right combination of fastener height and nose length to ensure perfect nose compression. RailLok™ fasteners offer a variety of nose heights and lengths to suit different rail types.

Dirt infiltration between the rail foot and the rubber pad: The presence of dirt particles can damage the pad over the long term, contributing to its failure under high cyclic loads. This problem is more common in floor applications, but can also occur in crane runways. RailLok™ pads have a patented “mustache” shape that prevents dirt from penetrating between the rail and the pad.
It’s important to note that high loads and the cyclical nature of crane activity are given factors and cannot be reduced. Other root causes must therefore be tackled by using an optimally designed, quality-controlled and correctly installed rail system.