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CRANE ROPE part 2, bend fatigue, rotation resistance

CRANE ROPE part 2

Today we will look at bend fatigue resistance, and rotation resistance, which are important aspects to consider when choosing crane rope / wire rope.

BEND FATIGUE RESISTANCE;

This is the ability of the wire rope to endure repeated bending under constant or fluctuating loads. As the load increases in any reeving system so the rate of fatigue will increase, as the bending radii decrease in a reeving system so the rate of fatigue will increase.

A wire rope with more strands will have greater fatigue resistance than a wire rope with fewer strands, compacted rope will add extra fatigue life. A compacted wire rope offers a wider bearing surface to the sheave/drum groove. The increased internal fill lowers internal stress levels too and therefore leads to a longer rope life. Compacted ropes can offer up to twice the rope life than that of a conventional wire rope.

ROTATION RESISTANCE;

Every wire rope construction will have natural torque properties where both ends of the rope are secured and an applied force will generate torque at the fixing points. Each rope construction will have a natural turn property where one end is free to rotate and an applied force will cause the free end to turn.

The torque or turn generated will depend on the scale of the force applied and on the construction of the wire rope.

In terms of resistance to rotation of wire ropes, there are three catagories; single, double or triple layer.                                     

 Single layer ropes have a greater tendancy to rotate under load than the 2 or 3 layer wire ropes, which are often referred to as rotation resistant rope. And so the three layer will have less tendancy to rotate than the two layer rope.

Two and three layer wire rope depend on torsional balance between the outer and inner layers creating rotational stability.

Single layer rope however should be considered if the application it will be used for does not require any resistance to rotation, as it can provide a more robust and effective solution.

It is important to note that single layer langs lay ropes have bad rotational properties and so should only be used where both ends are securely fixed.

Our next instalment will discuss resistance to wear and abrasion, corrosion resistance and lubrication of wire rope crane rope.

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