Why a rope turns under load

A wire rope is laid helically, so when it is pulled the wires tend to straighten, and that tendency appears as torque. When one end hangs free, nothing balances the torque and the rope and load rotate. The shorter the lay, the more twist per unit length and the stronger the tendency to rotate.

The direction of rotation depends on the lay. A right-hand lay rope usually turns one way under tension and a left-hand lay rope the other way. Two machines using ropes of different lay can behave quite differently.

The lighter the load and the longer the rope, the more visible the rotation. A heavy load stiffens the rope and suppresses turning; a light load leaves the rope almost unconstrained, and a free length of a few metres can spin several turns. Spinning an empty hook with a swivel is a quick way to see how strongly the rope wants to turn.

Rotation and kinking are not the same

Rotation is the rope turning about its own axis while wires and strands keep their laid relationship, and it usually recovers when the load is removed. A kink is a dead bend formed while the rope is slack, with wires forced into a sharp fold and the structure damaged. The difference is whether the wires have yielded plastically.

A kink is irreversible damage. Even if a kinked rope can be pulled straight again, the wires inside have yielded and cracked, capacity is reduced, and the rope should normally be discarded. A kink near a termination is especially dangerous, because the effect of the fitting is added there.

Rotation does not necessarily damage the rope at once, but it leaves torsional stress that speeds fatigue and can turn the load in a direction people or equipment do not want. Rotation is the prelude to a kink and should not be left alone.

How rotation-resistant rope works

A rotation-resistant rope usually has a multilayer strand structure, with opposite lay directions in the inner and outer layers. Under tension the torques from the layers oppose each other and largely cancel, leaving only a small residual torque. The balance is built into the structure and does not depend on external devices.

Common rotation-resistant constructions include 3-strand, 4-strand and multilayer 19x7 and 35x7 types. More strands and more layers usually balance better, at the cost of higher construction and manufacturing demands. The constructions are described in the rotation-resistant wire rope guide

A rotation-resistant rope is not absolutely non-rotating. Residual torque, the way the ends are fixed and load eccentricity can all produce some rotation. Machines that are extremely sensitive still need guides, counterweights or a two-rope arrangement to control it. When choosing rotation-resistant rope, confirm the match with drum and sheaves at the same time.

When rotation-resistant rope is essential

A single free-hanging line carrying a load that must not turn is the classic case for rotation-resistant rope: single-line grabs, deep shaft lifting and long items lifted from one point. Once such a load turns, its attitude and the load at the lifting point both change.

With multiple lines, a load constrained by guide rails or two synchronised hoists, a plain six-strand rope may be enough, because the ropes balance each other's torque. Whether rotation-resistant rope is essential depends on the constraints, not on the tonnage.

Hoist ropes on tower cranes and mobile cranes are usually selected to the equipment manual. Swapping a plain rope for a rotation-resistant one at will can change the match with drum and sheaves and may upset spooling. A manual selection has usually taken the machine's spooling and sheave layout into account.

• A single free-hanging line with a load that must not turn.
• A deep shaft or high lift with a long free length.
• A light load on a long rope, with rotation visible.
• A load sensitive to direction that must not turn freely.

Can a swivel solve the problem

A swivel lets the load turn freely relative to the rope: it releases torque rather than removing it. Fitted above the load, it lets the load rotate to the torque-balanced position, which may be exactly the direction you do not want. In other words, it moves the problem from the rope to the load.

Using a swivel carelessly on a single line lets the load keep turning during the lift and makes a kink more likely as the rope goes slack. It suits only processes that genuinely need the load to rotate, and only with guiding or anti-swing measures.

The strength and maintenance of the swivel itself also matter. It is one of the weak points in the system, so check it against the working load and dynamic factor, and inspect pin, thread and freedom of rotation at intervals. A pin that has not turned for a long time can suddenly rotate under load and cause a shock.

Reeving practice and operating habits

When reeving, keep the rope lay matched to the sheave and drum arrangement, and avoid feeding a rope onto the drum with twist already in it. Rope on the drum should lie in even turns, without crossing or stacking.

Avoid slack rope in service. Once a rope goes slack, torque is no longer restrained and the rope can spin and kink under its own weight. Raise and lower smoothly, and avoid abrupt stops and starts that make the rope jump and unseat. Slack followed by a sudden load multiplies the shock.

Control the fleet angle as well. A rope entering a sheave or drum at an angle creates side force and extra twist, and long running that way accelerates wear and the tendency to rotate. Where straight length is short, a guide wheel can improve the entry angle.

• Before reeving, confirm the lay matches the arrangement.
• Keep tension on the rope in service and avoid slack.
• Control the fleet angle to limit side force and twist.
• If rotation appears, stop and find the cause before continuing.

The order of selection and layout

Confirm the lifting method first: one line or several, whether the load is constrained, whether it must rotate. Then choose the construction: plain six-strand, rotation-resistant multilayer or single strand. Finally check diameter, lay and termination. Only after all three are confirmed does price and delivery come into the discussion.

Construction and lay options are compared in the wire rope construction guide

To screen constructions by lifting method, use the wire rope selector

One-line rule

For a single free-hanging line, choose rotation-resistant construction first; with several constrained lines, a plain rope may be enough. A swivel releases torque, it does not remove it, and it is not a cure-all. The test is whether the load stays steady during the lift.

Never try to straighten a kinked rope and keep using it. The wires at the kink are already damaged, and carrying on gambles the safety margin on cracks you cannot see.