It is important to determine whether there is a requirement to use a rotation resistant rope.

Six or eight strand rope constructions are usually selected unless load rotation on a single part system or "cabling" on a multi - part reeving system are likely to cause operational problems.

When loaded, steel wire ropes will generate:

- “Torque” if both ends are fixed.
- “Turn” if one end is unrestrained.

Torque
When both ends of a rope are fixed, the applied force generates “torque” at the fixing points.

Turn
When one end of a rope is free to rotate, the applied load causes the rope to turn.

The torque or turn generated will increase as the load applied increases. The degree to which a wire rope generates torque or turn will be influenced by the construction of the rope. Having recognized what can happen when a rope is loaded it is necessary to select the correct type of rope. It should be noted that all ropes will rotate to some degree when loaded .

The diagram below serves to illustrate the differences in rotational properties between the three basic types of stranded rope.

Specific information including the torque factor and the turn value expressed in degrees per lay length for individual rope constructions can be found in Summary Technical Information and Conversion Factors.

The tendency for any rope to turn will increase as the height of lift increases. In a multi - part reeving system the tendency for the rope to cable will increase as the spacing between the parts of rope decreases. Selection of the correct rope will help to prevent “cabling” and rotation of the load (see Rope Torque).

“Endurance” Rotation Resistant ropes ensure that problems associated with cabling and load rotation are minimised.

Bridon is pleased to offer advice on any specific problems associated with rope rotation.

Bridon is able to verify the rotational characteristics of individual wire ropes through testing on its specially designed in house machine. All Bridon products intended for lifting applications have been subject to this “Twistcheck” testing programme.