Rotation-Resistant Wire Rope: When and Why You Need It

Rotation-resistant wire ropes such as 18x7, 19x7 and 35x7 prevent load spinning on high lifts. CML SARL explains how they work, when they are required, and how to handle and inspect them safely.

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Every conventional stranded wire rope tries to rotate when it is loaded. The strands are helical, so tension creates torque. On a short, multi-fall lift this torque is controlled by the reeving. On a high single-fall lift, however, a standard rope will spin the load, twist itself and eventually damage its own structure. That is when you need a rotation-resistant rope. This guide from CML SARL explains how these ropes are built, where they are required and how to look after them on tower cranes, mobile cranes and port equipment in Cameroon. ### How a Rotation-Resistant Rope Works A rotation-resistant rope has two or more layers of strands laid in opposite directions. When loaded, the outer layer tries to turn one way and the inner layer the other way. The opposing torques cancel out to a large extent. The more layers and outer strands, the better the balance. Ropes are broadly grouped as follows: - **Rotation-resistant ropes** with two layers of strands, for example 18x7 or 19x7. They reduce rotation compared with a 6-strand rope but still produce some torque. - **Low-rotation ropes** with three or more layers and at least 15 outer strands, for example 35x7 or 40x7, often compacted. They offer very low rotation and higher breaking force. EN 12385-4 and ISO 21669 deal with the classification and measurement of rope rotation characteristics. ### When Is a Rotation-Resistant Rope Needed? - **Single-fall hoisting**: a load on one rope with a free-rotating hook. - **High li...