Rope Rotation & Torque

Being composed of several helically laid components with elastic characteristics, each wire rope has the tendency to turn when subjected to load. This tendency is represented by rope torque factor, which is dependent on rope construction, previous working conditions and applied load.

In a similar way, rope will also oppose forced rotation, depending on its rotational stiffness.

Ropes can be classified on the basis of torque factor, as spin resistant, low rotation or rotation resistant.

Since torque factor depends primarily on rope construction, this has to be selected on the basis of the reeving structure and lifting or deployment height, in order to ensure block and load stability.

Non rotating ropes are strongly recommended for high lifting heights in single fall mode, while for multiple fall other constructions can be considered depending on block configuration.

During the first use of rope wound over a drum, the portion of wire rope coming out from the winch will start to rotate depending on rope construction and applied load.

When the rope is rewound over the drum, the rotation obtained during deployment will be stored into the winch: therefore, if the rope is used to deploy the same load at the same height, no additional rotation will take place.

If the rope conditions are not the same, different behaviour will occur.

Definitions:

Rope torque: Torsional characteristic, the value of which is usually expressed in Nm, at a stated tensile loading and determined by test

when both rope ends are prevented from rotating. NOTE: Torsional characteristics can also be determined by calculation.

Rope turn: Rotational characteristic, the value of which is usually expressed in degrees or turns per unit length at a stated tensile loading

and determined by test when one end of the rope is free to rotate.