What are the common problems of tower crane hoisting wire rope? [answered]

Tower crane has become an indispensable equipment for building high-rise buildings. The operating mechanism of tower crane usually includes lifting mechanism (winch), luffing mechanism, slewing mechanism, jacking mechanism and walking mechanism. Among them, the lifting mechanism is very important among major institutions because of its largest workload, the most frequent movement and the highest power.

1 technical background

In order to make the lifting height of the tower crane meet the height requirements of the building, designers often require that the steel wire rope drum of the tower crane lifting mechanism has sufficient rope capacity when designing the tower crane. No matter what type of steel wire rope drum is used, it is generally necessary to make the steel wire rope drum of the tower crane lifting mechanism accommodate multi-layer steel wire ropes to meet the needs of the tower crane, and the steel wire ropes on the drum shall be arranged neatly and correctly when the tower crane works, The winding is smooth, otherwise it may lead to safety accidents. However, the rope arrangement of most tower crane hoisting mechanisms (hoists) in the market is sometimes difficult to achieve, especially when the tower crane is newly installed or the tower crane is newly replaced with steel wire rope, the steel wire rope of the steel wire rope drum begins to collapse after 2 ~ 3 weeks of operation - local flattening of the steel wire rope, extrusion of rope strand or rope core, cage distortion and other phenomena, resulting in plastic deformation of the steel wire rope.

2 causes and hazards of wire rope crushing

2.1 causes of wire rope crushing the main causes of wire rope crushing are as follows: ① the included angle between the connecting line between the midpoint of tower top pulley and drum axis and the center line of wire rope is too large (it has been well designed and properly solved); ② The stress of multi-layer steel wire rope wound on the drum is uneven.

In order to meet the needs of the current construction of high-rise buildings, multi-layer steel wire ropes must be wound on the steel wire rope drum, whether the long drum is used to wind the steel wire rope or the popular short drum is used to wind the steel wire rope. However, the first winding of the steel wire rope (newly installed steel wire rope) is wound on the steel wire rope drum under no load. In this way, the rope diameter of the steel wire rope and the gap between the rope and the rope are formed under the natural state of no load of the steel wire rope. The rope diameter of the steel wire rope and the gap between the steel wire rope and the steel wire rope are larger than those under load. When the tower crane enters the working state, under the load, the steel wire rope will be elongated axially, the rope diameter will become smaller, the force of the steel wire rope acting on the vertical steel wire rope drum surface will increase, and the lower steel wire rope will be tightly pressed against the steel wire rope drum. In this way, each circle of the lower steel wire rope will produce a small margin larger than the circumference of the steel wire drum; When the small surplus of multiple coils of wire rope is accumulated to a certain amount in turn, it will overflow the wire rope of this layer and squeeze into the rope arrangement space of the upper wire rope, so as to be crushed and deformed by the loaded wire rope of the upper layer. At the same time, the diameter of the loaded steel wire rope on the upper layer becomes smaller, and it is easy to be embedded in the gap between the lower steel wire rope and the steel wire rope (this layer of steel wire rope is arranged without load).

After repeated extrusion, the lower steel wire rope is easy to form local flattening, rope strand or rope core extrusion, cage distortion and other crushing phenomena. Therefore, the main reason why the steel wire rope is crushed is that the bottom steel wire rope row is not preloaded when the steel wire rope is replaced (installed).

2.2 possible hazards caused by steel wire rope crushing. The crushed steel wire rope is easy to break without signs, resulting in accidents. As we all know, the steel wire of steel wire rope is made of high carbon steel. After plastic deformation, the steel wire rope is easy to break suddenly at the deformation (especially under the action of alternating stress). In addition, when the upper steel wire rope is pressed into the lower steel wire rope, the tower crane will pull the steel wire rope pressed by the upper layer out of the lower steel wire rope during operation. At the moment when the loaded steel wire rope is pulled out, the steel wire rope of the tower crane will lose weight temporarily, resulting in strong jumping. The impact load generated by the jumping wire rope will greatly increase the fracture risk of the damaged (crushed) wire rope. Once the hoisting wire rope of the tower crane breaks suddenly in the load state, it will produce huge impact load, which will also cause equipment damage in light cases and serious casualty accidents in heavy cases.

Therefore, the safety technical specification of tower crane requires that the steel wire rope with plastic deformation must be replaced immediately and it is strictly prohibited to continue to use.

3 solution

In order to avoid the collapse of the steel wire rope, when replacing (installing) the lifting steel wire rope of the tower crane, the steel wire rope at the bottom of the steel wire rope drum shall be arranged under load. Therefore, the author designed a simple device (Fig. 1) to overcome the above disadvantages of replacing (installing) steel wire rope arrangement of tower crane. The device is composed of a support, a pulley, a braking device, a braking force adjusting handle, a braking drum, etc. When the tower crane is replaced with a new steel wire rope, the steel wire rope shall be wound around the pulley through the pulley, and then fixed to the steel wire rope drum of the tower crane hoist. The other end shall be manually tensioned with awesome, and the brake force adjustment handle shall be adjusted to generate an appropriate braking force for the braking device. The winch of the tower crane shall be started at low gear to start rope arrangement, so as to realize the load rope arrangement of the steel wire rope. When more than two layers of wire ropes are arranged on the wire rope drum, the brake force adjustment handle of the rope guide can be loosened and the remaining wire ropes can be quickly discharged according to the conventional method. In this way, each layer of the arranged steel wire rope will be very close, and even if the upper steel wire rope is loaded, it will not squeeze into the gap between the lower steel wire ropes, so as to avoid the crushing deformation of the steel wire rope.

4 Conclusion

The author has been engaged in tower crane leasing for many years. After the new steel wire rope of the tower crane was replaced, the steel wire rope was often crushed in 2 ~ 3 weeks of normal operation. Since the use of this set of equipment, the new steel wire rope has never been crushed and deformed, and the effect is very ideal. This kind of equipment can also be shared by multiple tower cranes. When the tower crane needs to replace the steel wire rope, it can be fixed in the appropriate position for use. It can be removed and taken back to the warehouse after use, which is convenient and practical. chart