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The improvement of the capacity of lifting machinery in hoisting operations has reduced people's labor intensity, but it has also increased operational risks and some new problems. Among them, the rotation of the crane's hook during hoisting operations is a problem that affects safety and progress.

1. Hook rotation phenomenon

Hook rotation often occurs without any warning during equipment hoisting operations. When the hoisting machine lifts a heavy object, the hook rotates and the wire rope threaded between the hook and the pulley group at the top of the boom becomes tangled together (as shown in Figure 1). The lifted heavy object also rotates with the hook. At this time, it is no longer possible to continue to lift or put down the lifted heavy object. The rotation of the hook will affect the normal progress of the hoisting operation and seriously threaten the safety of workers and equipment, so it must be avoided.

Hook rotation is related to the following factors:

　(1) The larger the crane, the higher the lifting height, that is, the longer the wire rope between the boom top pulley group and the hook, the greater the possibility of the hook rotating;

　(2) It is easier for the hook to rotate when the hook wire rope is wound into an odd-numbered match than an even-numbered match, and the smaller the number of wire ropes that are wound, the greater the possibility of the hook rotating;

　(3) The greater the weight a single wire rope bears, the greater the possibility of the hook rotating;

　(4) The smaller the overall dimensions of the hook assembly and the size of its pulley, the greater the possibility of the hook rotating;

(5) The speed of operating the crane lifting hook is unstable, especially when the heavy object is lifted off the ground, the possibility of the hook rotating increases.

2. Reasons for hook rotation

The causes of hook rotation include internal and external factors of the crane.

The internal cause of hook rotation is also the fundamental reason for its occurrence.

Regardless of the model, specification, or grade of the wire rope used in the crane, it will generate torque when it is stressed. Torque is caused by the way the wire rope is made, first the wires are twisted together helically to form strands, and then several strands are twisted together helically to form the rope. When force is applied, the steel wire and strands will be straightened, but the end of the wire rope is fixed during hoisting operations, so a torque is formed in 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 generates torque without being stressed. The existence of torque makes the hook assembly tend to rotate.

On the other hand, there are many external factors that directly cause the hook to rotate. For example, external forces such as manpower or wind during the hoisting process push the hook to rotate. The driver's unstable operation causes the hook and the weight to swing, causing the hook to rotate. The way the hook is wound causes the hook to be unbalanced and cause the hook to rotate.

3. Prevention and avoidance measures of hook rotation

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

　(1) When using a hook with multiple pulleys, try to use the outer pulley together with the pulley on the boom;

　(2) When the crane has multiple hooks, the pulley with a larger diameter should be used as much as possible;

(3) Try to use an even number of wire ropes; when conditions permit, try to use more wire ropes to reduce the stress on a single wire;

　(4) When threading and winding the wire rope, do not stagger too much between the pulley of the boom top section and the pulley of the hook, so as to reduce the horizontal rotational force generated by the wire rope on the hook when lifting the hook (Figure 2);

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

　(6) When hoisting, use a slide rope to control the hoisted object. If the lifting height is relatively high and the hook does not need to rotate when it is in place, the hook can be locked;

(7) When hoisting, the driver should operate smoothly, and the lifting hook and slewing movements should not be performed at the same time;

　(8) When purchasing a wire rope, try to choose a "non-rotating" wire rope if other conditions are met;

(9) After the crane's wire rope has been used for a period of time, it must be re-threaded or the fixed end must be untied to release the torque in the rope.

4. What to do after the hook rotates When the hook rotates, the wire ropes on the hook are kinked together. At this time, the lifting hook can no longer be operated, otherwise one of the wire ropes may be damaged due to excessive stress. The following methods can be used to deal with it:

　(1) When the weight is not high from the ground and the crane performance allows, you can use the luffing method to lower the weight and then straighten the hook. (2) If the heavy object has been lifted very high from the ground, you can only find a way to get closer to the surrounding buildings, or use other cranes to lift the cage to straighten the hook.

(3) After the hook rotates, the torque in the wire rope must be released. The specific method is: put the hook on the ground, untie the fixed end of the wire rope, multiply the number of turns m of the hook by the matching number n of the wire rope as the base k (it can be increased or decreased depending on the actual situation), rotate the end of the wire rope in the opposite direction of the twisting direction of the wire rope strands to release the torque, and then install the fixed end (as shown in Figure 3). Raise the boom to the maximum elevation angle and repeat lifting and lowering the hook several times to check the effect. You can repeat the above steps until the hook is stable.

The improvement of the capacity of lifting machinery in hoisting operations has reduced people's labor intensity, but it has also increased operational risks and some new problems. Among them, the rotation of the crane's hook during hoisting operations is a problem that affects safety and progress.

1. Hook rotation phenomenon

Hook rotation often occurs without any warning during equipment hoisting operations. When the hoisting machine lifts a heavy object, the hook rotates and the wire rope threaded between the hook and the pulley group at the top of the boom becomes tangled together (as shown in Figure 1). The lifted heavy object also rotates with the hook. At this time, it is no longer possible to continue to lift or put down the lifted heavy object. The rotation of the hook will affect the normal progress of the hoisting operation and seriously threaten the safety of workers and equipment, so it must be avoided.

Hook rotation is related to the following factors:

　(1) The larger the crane, the higher the lifting height, that is, the longer the wire rope between the boom top pulley group and the hook, the greater the possibility of the hook rotating;

　(2) It is easier for the hook to rotate when the hook wire rope is wound into an odd-numbered match than an even-numbered match, and the smaller the number of wire ropes that are wound, the greater the possibility of the hook rotating;

　(3) The greater the weight a single wire rope bears, the greater the possibility of the hook rotating;

　(4) The smaller the overall dimensions of the hook assembly and the size of its pulley, the greater the possibility of the hook rotating;

(5) The speed of operating the crane lifting hook is unstable, especially when the heavy object is lifted off the ground, the possibility of the hook rotating increases.

2. Reasons for hook rotation

The causes of hook rotation include internal and external factors of the crane.

The internal cause of hook rotation is also the fundamental reason for its occurrence.

Regardless of the model, specification, or grade of the wire rope used in the crane, it will generate torque when it is stressed. Torque is caused by the way the wire rope is made, first the wires are twisted together helically to form strands, and then several strands are twisted together helically to form the rope. When force is applied, the steel wire and strands will be straightened, but the end of the wire rope is fixed during hoisting operations, so a torque is formed in 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 generates torque without being stressed. The existence of torque makes the hook assembly tend to rotate.

On the other hand, there are many external factors that directly cause the hook to rotate. For example, external forces such as manpower or wind during the hoisting process push the hook to rotate. The driver's unstable operation causes the hook and the weight to swing, causing the hook to rotate. The way the hook is wound causes the hook to be unbalanced and cause the hook to rotate.

3. Prevention and avoidance measures of hook rotation

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

　(1) When using a hook with multiple pulleys, try to use the outer pulley together with the pulley on the boom;

　(2) When the crane has multiple hooks, the pulley with a larger diameter should be used as much as possible;

(3) Try to use an even number of wire ropes; when conditions permit, try to use more wire ropes to reduce the stress on a single wire;

　(4) When threading and winding the wire rope, do not stagger too much between the pulley of the boom top section and the pulley of the hook, so as to reduce the horizontal rotational force generated by the wire rope on the hook when lifting the hook (Figure 2);

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

　(6) When hoisting, use a slide rope to control the hoisted object. If the lifting height is relatively high and the hook does not need to rotate when it is in place, the hook can be locked;

(7) When hoisting, the driver should operate smoothly, and the lifting hook and slewing movements should not be performed at the same time;

　(8) When purchasing a wire rope, try to choose a "non-rotating" wire rope if other conditions are met;

(9) After the crane's wire rope has been used for a period of time, it must be re-threaded or the fixed end must be untied to release the torque in the rope.

4. What to do after the hook rotates When the hook rotates, the wire ropes on the hook are kinked together. At this time, the lifting hook can no longer be operated, otherwise one of the wire ropes may be damaged due to excessive stress. The following methods can be used to deal with it:

　(1) When the weight is not high from the ground and the crane performance allows, you can use the luffing method to lower the weight and then straighten the hook. (2) If the heavy object has been lifted very high from the ground, you can only find a way to get closer to the surrounding buildings, or use other cranes to lift the cage to straighten the hook.

(3) After the hook rotates, the torque in the wire rope must be released. The specific method is: put the hook on the ground, untie the fixed end of the wire rope, multiply the number of turns m of the hook by the matching number n of the wire rope as the base k (it can be increased or decreased depending on the actual situation), rotate the end of the wire rope in the opposite direction of the twisting direction of the wire rope strands to release the torque, and then install the fixed end (as shown in Figure 3). Raise the boom to the maximum elevation angle and repeat lifting and lowering the hook several times to check the effect. You can repeat the above steps until the hook is stable.