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Crane Hook Skewing: Causes and Practical Solutions

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A large-tonnage, multi-reeved crane hook showed skewing of the hook pulley shaft, which was no longer in the horizontal plane during operation. When lifting or lowering, the hook tilted upward or downward on one side. We analyzed the causes and proposed solutions for reference.

Crane Hook Skewing

Based on the hook arrangement shown in the picture, the winding diagram can be inferred as follows:

winding diagram

Causes of Hook Skewing

Essentially, hook skewing occurs due to uneven tension or asynchronous movement of the wire ropes across the pulleys. For multi-reeved hooks, the level of skewing shown in the picture is a relatively common phenomenon.

When the drum winds or releases the rope, friction exists between the wire rope, pulleys, and pulley bearings. As a result, the wire rope closest to the drum moves first, followed by the second row of pulleys, the third row, and so on. The rope on the fixed-point side changes last.

As the reeving ratio increases, the rope movement on the drum side becomes much greater than on the fixed-point side. At this stage, the hook pulley shaft appears skewed. Once winding or unwinding continues and all pulleys rotate, the rope tensions tend to equalize. Due to the hook self-weight and the load gravity, the pulley shaft tends to return to a horizontal position.

Solutions of Hook Skewing

Dual-drum or four-line single drum winding

In a single-drum dual-line reeving arrangement, the pulleys near the fixed point engage later under high reeving ratios, creating rope tension differences. By canceling the fixed point and ensuring both rope lines wind or release simultaneously, the pulley shaft becomes more stable.

Replace ropes and bearings

Use wire ropes with better flexibility and bearings with lower friction resistance, and ensure proper lubrication of both ropes and bearings.

Increase hook self-weight

A heavier hook provides greater stabilizing torque, reducing the tendency of skewing.

Each method has its own effects and drawbacks, and may involve additional costs. In practice, slight skewing is a natural phenomenon and acceptable as long as safety is not compromised.

Note: If the reeving system does not include a balance beam as shown in the schematic, the two wire ropes may carry uneven loads.

Conclusion

Crane hook skewing is mainly caused by uneven rope tension and asynchronous motion. By improving the reeving system, optimizing component selection, and increasing hook weight, the skewing phenomenon can be effectively mitigated. In practical applications, the most suitable solution should be chosen based on equipment conditions, while ensuring safe operation.

Zora Zhao

Zora Zhao

Expert in Overhead Crane/Gantry Crane/Jib Crane/Crane Parts Solutions

With 10+ years of experience in the Crane Overseas Export Industry, helped 10,000+ customers with their pre-sales questions and concerns, if you have any related needs, please feel free to contact me!

WhatsApp: +86 189 3735 0200
Email: zorazhao@dgcrane.com

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