Hook rotation is often happening without any warning occurred in the lifting motion, when the crane is lifting some weight, hook rotates, the wire rope between hook and pulley twisted together, so it will be the lifted weight, then the lifting operation have to be mid-stop. Hook rotation can affect the lifting operation, seriously threatening the safety of workers and equipment, therefore it must be avoided.
The cause of hook rotation is mixed with the internal and external factors of crane. The internal cause is indeed the root cause of its occurrence.
Crane wire rope regardless of model, specifications, grades, will produce torque in the force. Torque is formed due to the manufacturing process of wire rope, first wires twist together to make a strand, and then several strands twist together making a rope. When there is force in the rope, the wire and the strand will be straightened, but the end of the wire rope is fixed, so it will produce a torque in the wire rope. Another cause of the torque is the rope pitch becomes longer after a period of time usage, thus it makes torque in rope even there is no force in it, the existence of torque makes the hook rotate.
On the other hand, there are many external factors that directly lead to the rotation of hook, such as the human or wind force during the hoisting process. The operator is not steady moving the crane so that the hook and the weight swing cause the hook rotation, the unbalance of hook ect.
In order to avoid the hook rotation happens, the operator should move the crane steadily and smoothly, the hook should be located at the center of lifting material, at the motion of lifting first makes the wire rope straight then lift material up, and yearly re-fix the wire rope to make sure it is free and no force in it when there is no load.
One thing should be noted is that when there is twisting in wire rope the lifting motion should be stopped immediately, otherwise it may cause damage to crane even maybe a dangerous factor for the nearby workers.