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Crane hook rotation reasons and preventive measures

Nov 01, 2018

Hook rotation


Hook rotation is often without any warning occurred during the equipment hoisting operations, when hoisting machinery to lift heavy weights, hook spin, wear around the hook and boom top pulley block between the wire rope twisted together, the lift weights also spin with hook, then can not continue to lift or down the lift heavy things.

The rotation of the hook will affect the normal operation of the lifting operation and seriously threaten the safety of operators and equipment, so it must be avoided.

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The cause of hook rotation is the internal and external factors of crane, and the internal reason of hook rotation is also the fundamental reason.


The steel wire rope used by the crane, no matter what type, specification and brand, will generate torque when under force.

Torque is caused by the way the wire is made, first twisted and twisted together to form a strand, then twisted and twisted together in several strands to form a wire rope.

When the force is applied, the wire and the strand are straightened, but the end of the wire rope is fixed during the hoisting operation so that torque is formed within the wire rope.

Another source of torque is that the pitch of the wire rope becomes longer after being used for a period of time, so that when the end is fixed, the wire rope produces torque without force, and the existence of torque makes the hook assembly have a tendency to rotate.


On the other hand, there are many external factors that directly lead to the rotation of the hook, such as the rotation of the hook driven by external forces such as manpower or wind during the hoisting process, the unsteady operation of the driver leading to the swing of the hook and weight, and the unbalance of the hook leading to the rotation of the hook.

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Hook rotation is related to the following factors:


(1) the larger the crane is, the higher the lifting height is, that is, the longer the steel wire rope between the pulley block and the hook, the greater the possibility of the hook rotation;


(2) it is easier to make the hook rotate when the wire rope of hook is threaded into a single number match than a double number match, and the number of wire rope that is wound is less, so the possibility of hook rotation is greater;


(3) the higher the weight of a single wire rope, the greater the possibility of hook rotation;


(4) the smaller the external dimension of the hook assembly and the size of pulley, the greater the possibility of the hook rotation;


(5) the speed of lifting and landing hooks of the crane is not stable, especially when the weight is off the ground, the possibility of lifting hooks rotation is increased.


Crane hook rotation post-processing method


The handling method after the rotation of the hook when the hook is rotated, the steel wire rope on the hook is twisted together. At this time, the lifting and landing hook operation cannot be carried out again. Otherwise, one of the steel wire ropes may be damaged due to excessive force.


(1) if the weight is not high from the ground and the crane's performance allows, the weight can be lowered by variable amplitude method, and then the hook can be turned forward.


(2) if the weight has been lifted high off the ground, one can only try to get close to the surrounding buildings to turn the hook.


(3) the rotation in the event of a hook, the steel wire rope is released within the torque, the specific method is: put the hook in the ground, to solve the fixed end of the wire rope, in proportion to the number of circle hook rotation base m times the rope matching number n k (depending on the actual situation can increase or decrease), according to the inverse direction of strand wire twisting, turning the end of the wire rope release torque, and then fitted with fixed end.

Lift the arm to the maximum elevation Angle, repeat the lifting hook several times to check the effect, can repeat the above steps until the hook is stable.


Preventive and preventive measures of crane hook rotation


In the actual work, the following measures can be taken to improve the stability of the hook, so as to reduce the possibility of the hook rotation:


(1) when using a hook with multiple pulleys, use the pulley from the outer side as much as possible together with the pulley from the arm;


(2) if the crane has multiple hooks, the pulley with a larger diameter shall be used as far as possible;


(3) use even number of steel wire rope as far as possible;

Use as many pieces as possible when conditions permit to reduce the force on one piece;


(4) do not stagger too much between the pulley of the upper joint of the lifting arm and the pulley of the lifting hook when the wire rope is being worn around the wire rope, so as to reduce the horizontal rotation force generated by the wire rope to the lifting hook when lifting and landing hook;


(5) during the hoisting process, reduce the length of wire rope between the boom top and the hook as much as possible, such as using a larger span method;


(6) during hoisting, slip rope should be used to make the sling controllable. If the lifting height is relatively high, and the hook does not need to be rotated when in place, the hook can be locked;


(7) when hoisting, the driver should operate smoothly, and the lifting hook and turning motion should not be carried out at the same time;


(8) when selecting steel wire rope, try to choose "non-rotating" steel wire rope if other conditions are met;


(9) after the crane's wire rope has been used for some time, it shall be re-wound or the fixed end shall be untied to release the torque inside the rope.



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